Wireless energy transfer
Encyclopedia
Wireless energy transfer or wireless power is the transmission of electrical energy from a power source
to an electrical load without artificial interconnecting conductor
s. Wireless transmission is useful in cases where interconnecting wires are inconvenient, hazardous, or impossible. The problem of wireless power transmission
differs from that of wireless telecommunications, such as radio
. In the latter, the proportion of energy
received becomes critical only if it is too low for the signal to be distinguished from the background noise. With wireless power, efficiency is the more significant parameter. A large part of the energy sent out by the generating plant must arrive at the receiver or receivers to make the system economical.
The most common form of wireless power transmission is carried out using direct induction
followed by resonant magnetic induction
. Other methods under consideration include electromagnetic radiation
in the form of microwaves or lasers
.
surrounding the conductor; magnetic field lines around the conductor and lines of electric force radially about the conductor.
In a direct current
circuit, if the current is continuous, the fields are constant; there is a condition of stress in the space surrounding the conductor, which represents stored electric and magnetic energy, just as a compressed spring or a moving mass represents stored energy. In an alternating current
circuit, the fields also alternate; that is, with every half wave of current and of voltage, the magnetic and the electric field start at the conductor and run outwards into space with the speed of light. Where these alternating fields impinge on another conductor a voltage and a current are induced.
Any change in the electrical conditions of the circuit, whether internal or external involves a readjustment of the stored magnetic and electric field energy of the circuit, that is, a so-called transient. A transient is of the general character of a condenser discharge through an inductive circuit. The phenomenon of the condenser discharge through an inductive circuit therefore is of the greatest importance to the engineer, as the foremost cause of high-voltage and high-frequency troubles in electric circuits.
Electromagnetic induction is proportional to the intensity of the current and voltage in the conductor which produces the fields and to the frequency
. The higher the frequency the more intense the induction effect. Energy is transferred from a conductor that produces the fields (the primary) to any conductor on which the fields impinge (the secondary). Part of the energy of the primary conductor passes inductively across space into secondary conductor and the energy decreases rapidly along the primary conductor. A high frequency current does not pass for long distances along a conductor but rapidly transfers its energy by induction to adjacent conductors. Higher induction resulting from the higher frequency is the explanation of the apparent difference in the propagation of high frequency disturbances from the propagation of the low frequency power of alternating current systems. The higher the frequency the more preponderant become the inductive effects that transfer energy from circuit to circuit across space. The more rapidly the energy decreases and the current dies out along the circuit, the more local is the phenomenon.
The flow of electric energy thus comprises phenomena inside of the conductor and phenomena in the space outside of the conductor—the electric field—which, in a continuous current circuit, is a condition of steady magnetic and dielectric stress, and in an alternating current circuit is alternating, that is, an electric wave launched by the conductor to become far-field electromagnetic radiation traveling through space with the speed of light.
In electric power transmission and distribution, the phenomena inside of the conductor are of main importance, and the electric field of the conductor is usually observed only incidentally. Inversely, in the use of electric power for radio telecommunications it is only the electric and magnetic fields outside of the conductor, that is electromagnetic radiation, which is of importance in transmitting the message. The phenomenon in the conductor, the current in the launching structure, is not used.
The electric charge displacement in the conductor produces a magnetic field and resultant lines of electric force. The magnetic field is a maximum in the direction concentric, or approximately so, to the conductor. That is, a ferromagnetic body tends to set itself in a direction at right angles to the conductor. The electric field has a maximum in a direction radial, or approximately so, to the conductor. The electric field component tends in a direction radial to the conductor and dielectric bodies may be attracted or repelled radially to the conductor.
The electric field of a circuit over which energy flows has three main axes at right angles with each other:
Where the electric circuit consists of several conductors, the electric fields of the conductors superimpose upon each other, and the resultant magnetic field lines and lines of electric force are not concentric and radial respectively, except approximately in the immediate neighborhood of the conductor. Between parallel conductors they are conjugate
of circles. Neither the power consumption in the conductor, nor the magnetic field, nor the electric field, are proportional to the flow of energy through the circuit. However, the product of the intensity of the magnetic field and the intensity of the electric field is proportional to the flow of energy or the power, and the power is therefore resolved into a product of the two components i and e, which are chosen proportional respectively to the intensity of the magnetic field and of the electric field. The component called the current is defined as that factor of the electric power which is proportional to the magnetic field, and the other component, called the voltage, is defined as that factor of the electric power which is proportional to the electric field.
In radio telecommunications the electric field of the transmit antenna propagates through space as a radio wave
and impinges upon the receive antenna where it is observed by its magnetic and electric effect. Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays and gamma rays are shown to be the same electromagnetic radiation
phenomenon, differing one from the other only in frequency of vibration.
over distances up to about one-sixth of the wavelength used. Near field energy itself is non-radiative but some radiative losses do occur. In addition there are usually resistive losses. With electrodynamic induction, electric current flowing through a primary coil creates a magnetic field
that acts on a secondary coil producing a current within it. Coupling must be tight in order to achieve high efficiency. As the distance from the primary is increased, more and more of the magnetic field misses the secondary. Even over a relatively short range the inductive coupling is grossly inefficient, wasting much of the transmitted energy.
This action of an electrical transformer
is the simplest form of wireless power transmission. The primary and secondary circuits of a transformer are not directly connected. Energy transfer takes place through a process known as mutual induction. Principal functions are stepping the primary voltage either up or down and electrical isolation. Mobile phone
and electric toothbrush
battery charger
s, and electrical power distribution transformer
s are examples of how this principle is used. Induction cooker
s use this method. The main drawback to this basic form of wireless transmission is short range. The receiver must be directly adjacent to the transmitter or induction unit in order to efficiently couple with it.
The application of resonance increases the transmission range somewhat. When resonant coupling is used, the transmitter and receiver inductors are tuned to the same natural frequency. Performance can be further improved by modifying the drive current from a sinusoidal to a nonsinusoidal transient waveform. Pulse power transfer occurs over multiple cycles. In this way significant power may be transmitted between two mutually-attuned LC circuits having a relatively low coefficient of coupling. Transmitting and receiving coils are usually single layer solenoids or flat spirals with series capacitor
s, which, in combination, allow the receiving element to be tuned to the transmitter frequency.
Common uses of resonance-enhanced electrodynamic induction are charging the batteries of portable devices such as laptop computers and cell phones, medical implants
and electric vehicles
. A localized charging technique selects the appropriate transmitting coil in a multilayer winding array structure. Resonance is used in both the wireless charging pad (the transmitter circuit) and the receiver module (embedded in the load) to maximize energy transfer efficiency. This approach is suitable for universal wireless charging pads for portable electronics such as mobile phones. It has been adopted as part of the Qi
wireless charging standard.
It is also used for powering devices having no batteries, such as RFID patches and contactless smartcards, and to couple electrical energy from the primary inductor to the helical resonator of Tesla coil wireless power transmitters.
Electrostatic or capacitive coupling
is the passage of electrical energy through a dielectric
. In practice it is an electric field gradient or differential capacitance
between two or more insulated terminals, plates, electrodes, or nodes that are elevated over a conducting ground plane. The electric field is created by charging the plates with a high potential, high frequency alternating current power supply. The capacitance between two elevated terminals and a powered device form a voltage divider.
The electric energy transmitted by means of electrostatic induction can be utilized by a receiving device, such as a wireless lamp. Tesla
demonstrated the illumination of wireless lamps by energy that was coupled to them through an alternating electric field.
The principle of electrostatic induction is applicable to the electrical conduction wireless transmission method.
methods achieve longer ranges, often multiple kilometer ranges, where the distance is much greater than the diameter of the device(s). The main reason for longer ranges with radio wave and optical devices is the fact that electromagnetic radiation in the far-field can be made to match the shape of the receiving area (using high directivity
antennas or well-collimated Laser Beam
) thereby delivering almost all emitted power at long ranges. The maximum directivity for antennas is physically limited by diffraction
.
to receiver
, the wavelength
and the Rayleigh criterion or diffraction
limit, used in standard radio frequency
antenna
design, which also applies to lasers. In addition to the Rayleigh criterion Airy's diffraction limit
is also frequently used to determine an approximate spot size at an arbitrary distance from the aperture
.
The Rayleigh criterion dictates that any radio wave, microwave or laser beam will spread and become weaker and diffuse
over distance; the larger the transmitter antenna or laser aperture compared to the wavelength
of radiation, the tighter the beam and the less it will spread as a function of distance (and vice versa). Smaller antennae also suffer from excessive losses due to side lobe
s. However, the concept of laser aperture considerably differs from an antenna. Typically, a laser aperture much larger than the wavelength induces multi-moded radiation and mostly collimators are used before emitted radiation couples into a fiber or into space.
Ultimately, beamwidth
is physically determined by diffraction due to the dish size in relation to the wavelength of the electromagnetic radiation used to make the beam. Microwave power beaming can be more efficient than lasers, and is less prone to atmospheric attenuation
caused by dust or water vapor
losing atmosphere to vaporize the water in contact.
Then the power levels are calculated by combining the above parameters together, and adding in the gains and losses
due to the antenna characteristics and the transparency and dispersion
of the medium through which the radiation passes. That process is known as calculating a link budget
.
Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range. A rectenna
may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft
leaving orbit has been considered.
Power beaming by microwaves has the difficulty that for most space applications the required aperture sizes are very large due to diffraction
limiting antenna directionality. For example, the 1978 NASA
Study of solar power satellites required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have difficulties with atmospheric absorption and beam blockage by rain or water droplets. Because of the "thinned array curse
," it is not possible to make a narrower beam by combining the beams of several smaller satellites.
For earthbound applications a large area 10 km diameter receiving array allows large total power levels to be used while operating at the low power density suggested for human electromagnetic exposure safety. A human safe power density of 1 mW/cm2 distributed across a 10 km diameter area corresponds to 750 megawatts total power level. This is the power level found in many modern electric power plants.
Following World War II
, which saw the development of high-power microwave emitters known as cavity magnetrons, the idea of using microwaves to transmit power was researched. By 1964 a miniature helicopter propelled by microwave power had been demonstrated.
Japanese researcher Hidetsugu Yagi
also investigated wireless energy transmission using a directional array antenna that he designed. In February 1926, Yagi and Uda published their first paper on the tuned high-gain directional array now known as the Yagi antenna
. While it did not prove to be particularly useful for power transmission, this beam antenna has been widely adopted throughout the broadcasting and wireless telecommunications industries due to its excellent performance characteristics.
Wireless high power transmission using microwaves is well proven. Experiments in the tens of kilowatts have been performed at Goldstone
in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island. These methods achieve distances on the order of a kilometer.
In the case of electromagnetic radiation closer to visible region of spectrum (10s of microns (um)
to 10s of nm
), power can be transmitted by converting electricity into a laser
beam that is then pointed at a solar cell
receiver.
This mechanism is generally known as "powerbeaming" because the power is beamed at a receiver that can convert it to usable electrical energy.
Advantages of laser
based energy transfer compared with other wireless methods are:
Its drawbacks are:
The laser "powerbeaming" technology has been mostly explored in military weapons
and aerospace
applications and is now being developed for commercial and consumer electronics
Low-Power applications. Wireless energy transfer system using laser for consumer space has to satisfy Laser safety
requirements standardized under IEC 60825.
To develop an understanding of the trade-offs of Laser ("a special type of light wave"-based system):
Geoffrey Landis
is one of the pioneers of solar power satellite and laser-based transfer of energy especially for space and lunar missions.
The continuously increasing demand for safe and frequent space missions has resulted in serious thoughts on a futuristic space elevator
that would be powered by lasers. NASA's space elevator would need wireless power to be beamed to it for it to climb a tether.
NASA's Dryden Flight Research Center has demonstrated flight of a lightweight unmanned model plane powered by a laser beam. This proof-of-concept demonstrates the feasibility of periodic recharging using the laser beam system and the lack of need to return to ground.
"Lasermotive" demonstrated laser powerbeaming at one kilometer during NASA's 2009 powerbeaming contest. Also "Lighthouse DEV" (a spin off of NASA Power Beaming Team) along with "University of Maryland" is developing an eye safe laser system to power a small UAV. Since 2006, "PowerBeam" which originally invented the eye-safe technology and holds all crucial patents in this technology space, is developing commercially ready units for various consumer and industrial electronic products.
electrical power transmission systems rely on current flowing through the earth plus a single wire insulated from the earth to complete the circuit. In emergencies high-voltage direct current power transmission systems can also operate in the 'single wire with earth return' mode. Elimination of the raised insulated wire, and transmission of high-potential, high-frequency alternating current through the earth with an atmospheric return circuit has been investigated as a method of wireless electrical power transmission. Transmission of electrical energy through the earth alone, eliminating the second conductor is also being investigated.
Low frequency alternating current can be transmitted through the inhomogeneous earth with low loss because the net resistance between earth antipodes is considerably less than 1 ohm. The electrical displacement takes place predominantly by electrical conduction through the oceans, and metallic ore bodies and similar subsurface structures. The electrical displacement is also by means of electrostatic induction through the more dielectric regions such as quartz deposits and other non-conducting minerals.
Alternating current can be transmitted through atmospheric strata having a barometric pressure of less than 135 millimeters of mercury. Current flows by means of electrostatic induction through the lower atmosphere up to about two or three miles above the plants (this is the middle part in a three-space model) and the flow of ions, that is to say, electrical conduction through the ionized region above three miles. Intense vertical beams of ultraviolet light may be used to ionize the atmospheric gasses directly above the two elevated terminals resulting in the formation of plasma high-voltage electrical transmission lines leading up to the conducting atmospheric strata. The end result is a flow electrical current between the two elevated terminals by a path up to and through the troposphere and back down to the other facility. Electrical conduction through atmospheric strata is made possible by the creation of capacitively coupled discharge plasma through the process of atmospheric ionization.
Tesla discovered that electrical energy can be transmitted through the earth and the atmosphere. In the course of his research he successfully lit lamps at moderate distances and was able to detect the transmitted energy at much greater distances. The Wardenclyffe Tower
project was a commercial venture for trans-Atlantic wireless telephony and proof-of-concept demonstrations of global wireless power transmission. The facility was not completed because of insufficient funding.
Earth is a naturally conducting body and forms one conductor of the system. A second path is established through the upper troposphere
and lower stratosphere
starting at an elevation of approximately 4.5 miles.
A global system for "the transmission of electrical energy without wires" called the World Wireless System
, dependent upon the high electrical conductivity of plasma
and the high electrical conductivity of the earth, was proposed as early as 1904.
The same transmitter used for the atmospheric conduction method is used for the terrestrial single-conductor earth resonance method.
The fundamental earth resonance frequency is claimed to be approximately 11.78 Hz. With the earth resonance method some harmonic of this fundamental frequency is used. "I would say that the frequency should be smaller than twenty thousand per second, through shorter waves might be practicable" and on the low end, "a frequency of nine hundred and twenty-five per second" is used, "when it is indispensable to operate motors of the ordinary kind."
Observations have been made that may be inconsistent
with a basic tenet of physics related to the scalar derivatives of the electromagnetic potentials that are presently considered to be nonphysical
.
Patents, Microwave powered aircraft, John E. Martin, et al. (1990)., Solid state solar to microwave energy converter system and apparatus, Kenneth W. Dudley, et al. (1976)., Microwave power receiving antenna, Carroll C. Dailey (1970)., Method of Utilizing Radiant Energy, Nikola Tesla (1901)., Apparatus for the Utilization of Radiant Energy, Nikola Tesla (1901).
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
to an electrical load without artificial interconnecting conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
s. Wireless transmission is useful in cases where interconnecting wires are inconvenient, hazardous, or impossible. The problem of wireless power transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
differs from that of wireless telecommunications, such as radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
. In the latter, the proportion of energy
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
received becomes critical only if it is too low for the signal to be distinguished from the background noise. With wireless power, efficiency is the more significant parameter. A large part of the energy sent out by the generating plant must arrive at the receiver or receivers to make the system economical.
The most common form of wireless power transmission is carried out using direct induction
Inductive coupling
In electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire through electromagnetic induction...
followed by resonant magnetic induction
Resonant inductive coupling
Resonant inductive coupling or electrodynamic induction is the near field wireless transmission of electrical energy between two coils that are highly resonant at the same frequency. The equipment to do this is sometimes called a resonant or resonance transformer. While many...
. Other methods under consideration include electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
in the form of microwaves or lasers
Beam-powered propulsion
Beam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
.
Electric energy transfer
An electric current flowing through a conductor carries electrical energy. When an electric current passes through a circuit there is an electric field in the dielectricDielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
surrounding the conductor; magnetic field lines around the conductor and lines of electric force radially about the conductor.
In a direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
circuit, if the current is continuous, the fields are constant; there is a condition of stress in the space surrounding the conductor, which represents stored electric and magnetic energy, just as a compressed spring or a moving mass represents stored energy. In an alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
circuit, the fields also alternate; that is, with every half wave of current and of voltage, the magnetic and the electric field start at the conductor and run outwards into space with the speed of light. Where these alternating fields impinge on another conductor a voltage and a current are induced.
Any change in the electrical conditions of the circuit, whether internal or external involves a readjustment of the stored magnetic and electric field energy of the circuit, that is, a so-called transient. A transient is of the general character of a condenser discharge through an inductive circuit. The phenomenon of the condenser discharge through an inductive circuit therefore is of the greatest importance to the engineer, as the foremost cause of high-voltage and high-frequency troubles in electric circuits.
Electromagnetic induction is proportional to the intensity of the current and voltage in the conductor which produces the fields and to the frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. The higher the frequency the more intense the induction effect. Energy is transferred from a conductor that produces the fields (the primary) to any conductor on which the fields impinge (the secondary). Part of the energy of the primary conductor passes inductively across space into secondary conductor and the energy decreases rapidly along the primary conductor. A high frequency current does not pass for long distances along a conductor but rapidly transfers its energy by induction to adjacent conductors. Higher induction resulting from the higher frequency is the explanation of the apparent difference in the propagation of high frequency disturbances from the propagation of the low frequency power of alternating current systems. The higher the frequency the more preponderant become the inductive effects that transfer energy from circuit to circuit across space. The more rapidly the energy decreases and the current dies out along the circuit, the more local is the phenomenon.
The flow of electric energy thus comprises phenomena inside of the conductor and phenomena in the space outside of the conductor—the electric field—which, in a continuous current circuit, is a condition of steady magnetic and dielectric stress, and in an alternating current circuit is alternating, that is, an electric wave launched by the conductor to become far-field electromagnetic radiation traveling through space with the speed of light.
In electric power transmission and distribution, the phenomena inside of the conductor are of main importance, and the electric field of the conductor is usually observed only incidentally. Inversely, in the use of electric power for radio telecommunications it is only the electric and magnetic fields outside of the conductor, that is electromagnetic radiation, which is of importance in transmitting the message. The phenomenon in the conductor, the current in the launching structure, is not used.
The electric charge displacement in the conductor produces a magnetic field and resultant lines of electric force. The magnetic field is a maximum in the direction concentric, or approximately so, to the conductor. That is, a ferromagnetic body tends to set itself in a direction at right angles to the conductor. The electric field has a maximum in a direction radial, or approximately so, to the conductor. The electric field component tends in a direction radial to the conductor and dielectric bodies may be attracted or repelled radially to the conductor.
The electric field of a circuit over which energy flows has three main axes at right angles with each other:
- The magnetic field, concentricConcentricConcentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...
with the conductor. - The lines of electric force, radial to the conductor.
- The power gradient, parallelParallel (geometry)Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
to the conductor.
Where the electric circuit consists of several conductors, the electric fields of the conductors superimpose upon each other, and the resultant magnetic field lines and lines of electric force are not concentric and radial respectively, except approximately in the immediate neighborhood of the conductor. Between parallel conductors they are conjugate
Conjugate element (field theory)
In mathematics, in particular field theory, the conjugate elements of an algebraic element α, over a field K, are the roots of the minimal polynomialof α over K.-Example:The cube roots of the number one are:...
of circles. Neither the power consumption in the conductor, nor the magnetic field, nor the electric field, are proportional to the flow of energy through the circuit. However, the product of the intensity of the magnetic field and the intensity of the electric field is proportional to the flow of energy or the power, and the power is therefore resolved into a product of the two components i and e, which are chosen proportional respectively to the intensity of the magnetic field and of the electric field. The component called the current is defined as that factor of the electric power which is proportional to the magnetic field, and the other component, called the voltage, is defined as that factor of the electric power which is proportional to the electric field.
In radio telecommunications the electric field of the transmit antenna propagates through space as a radio wave
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
and impinges upon the receive antenna where it is observed by its magnetic and electric effect. Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays and gamma rays are shown to be the same electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
phenomenon, differing one from the other only in frequency of vibration.
Electromagnetic induction
Energy transfer by electromagnetic induction is typically magnetic but capacitive coupling can also be achieved.Electrodynamic induction method
The electrodynamic induction wireless transmission technique is near fieldNear and far field
The near field and far field and the transition zone are regions of the electromagnetic radiation field that emanates from a transmitting antenna, or as a result of radiation scattering off an object...
over distances up to about one-sixth of the wavelength used. Near field energy itself is non-radiative but some radiative losses do occur. In addition there are usually resistive losses. With electrodynamic induction, electric current flowing through a primary coil creates a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
that acts on a secondary coil producing a current within it. Coupling must be tight in order to achieve high efficiency. As the distance from the primary is increased, more and more of the magnetic field misses the secondary. Even over a relatively short range the inductive coupling is grossly inefficient, wasting much of the transmitted energy.
This action of an electrical transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
is the simplest form of wireless power transmission. The primary and secondary circuits of a transformer are not directly connected. Energy transfer takes place through a process known as mutual induction. Principal functions are stepping the primary voltage either up or down and electrical isolation. Mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
and electric toothbrush
Electric toothbrush
An electric toothbrush is a toothbrush that uses electric power supplied usually by a battery to move the brush head rapidly, either oscillating side to side, or rotation-oscillation .- History :...
battery charger
Battery charger
A battery charger is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.The charge current depends upon the technology and capacity of the battery being charged...
s, and electrical power distribution transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s are examples of how this principle is used. Induction cooker
Induction cooker
An induction cooker uses induction heating for cooking. Unlike other forms of cooking, heat is generated directly in the pot or pan , as opposed to being generated in the stovetop by electrical coils or burning gas...
s use this method. The main drawback to this basic form of wireless transmission is short range. The receiver must be directly adjacent to the transmitter or induction unit in order to efficiently couple with it.
The application of resonance increases the transmission range somewhat. When resonant coupling is used, the transmitter and receiver inductors are tuned to the same natural frequency. Performance can be further improved by modifying the drive current from a sinusoidal to a nonsinusoidal transient waveform. Pulse power transfer occurs over multiple cycles. In this way significant power may be transmitted between two mutually-attuned LC circuits having a relatively low coefficient of coupling. Transmitting and receiving coils are usually single layer solenoids or flat spirals with series capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s, which, in combination, allow the receiving element to be tuned to the transmitter frequency.
Common uses of resonance-enhanced electrodynamic induction are charging the batteries of portable devices such as laptop computers and cell phones, medical implants
Implant (medicine)
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue...
and electric vehicles
Electric car
An electric car is an automobile which is propelled by electric motor, using electrical energy stored in batteries or another energy storage device. Electric cars were popular in the late-19th century and early 20th century, until advances in internal combustion engine technology and mass...
. A localized charging technique selects the appropriate transmitting coil in a multilayer winding array structure. Resonance is used in both the wireless charging pad (the transmitter circuit) and the receiver module (embedded in the load) to maximize energy transfer efficiency. This approach is suitable for universal wireless charging pads for portable electronics such as mobile phones. It has been adopted as part of the Qi
Wireless Power Consortium
The Wireless Power Consortium is a business alliance of more than 60 firms to develop open standards for inductive charging.-History:The organization was started in 2008 to create a universal wireless power charging standard so that electronic products and charging stations using the same standard...
wireless charging standard.
It is also used for powering devices having no batteries, such as RFID patches and contactless smartcards, and to couple electrical energy from the primary inductor to the helical resonator of Tesla coil wireless power transmitters.
Electrostatic induction method
Capacitive coupling
In electronics, capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. This coupling can have an intentional or accidental effect...
is the passage of electrical energy through a dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
. In practice it is an electric field gradient or differential capacitance
Differential capacitance
Differential capacitance in physics, electronics, and electrochemistry is a measure of the voltage-dependent capacitance of a nonlinear capacitor, such as an electrical double layer or a semiconductor diode...
between two or more insulated terminals, plates, electrodes, or nodes that are elevated over a conducting ground plane. The electric field is created by charging the plates with a high potential, high frequency alternating current power supply. The capacitance between two elevated terminals and a powered device form a voltage divider.
The electric energy transmitted by means of electrostatic induction can be utilized by a receiving device, such as a wireless lamp. Tesla
Nikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
demonstrated the illumination of wireless lamps by energy that was coupled to them through an alternating electric field.
The principle of electrostatic induction is applicable to the electrical conduction wireless transmission method.
Electromagnetic radiation
Far fieldNear and far field
The near field and far field and the transition zone are regions of the electromagnetic radiation field that emanates from a transmitting antenna, or as a result of radiation scattering off an object...
methods achieve longer ranges, often multiple kilometer ranges, where the distance is much greater than the diameter of the device(s). The main reason for longer ranges with radio wave and optical devices is the fact that electromagnetic radiation in the far-field can be made to match the shape of the receiving area (using high directivity
Directivity
In electromagnetics, directivity is a figure of merit for an antenna. It measures the power density the antenna radiates in the direction of its strongest emission, versus the power density radiated by an ideal isotropic radiator radiating the same total power.An antenna's directivity is a...
antennas or well-collimated Laser Beam
Light beam
A light beam or beam of light is a narrow projection of light energy radiating from a source into a beam. Sunlight is a natural example of a light beam when filtered through various mediums...
) thereby delivering almost all emitted power at long ranges. The maximum directivity for antennas is physically limited by diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
.
Beamed power, size, distance, and efficiency
The size of the components may be dictated by the distance from transmitterTransmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
to receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
and the Rayleigh criterion or diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
limit, used in standard radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
design, which also applies to lasers. In addition to the Rayleigh criterion Airy's diffraction limit
Airy disc
In optics, the Airy disk and Airy pattern are descriptions of the best focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light....
is also frequently used to determine an approximate spot size at an arbitrary distance from the aperture
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
.
The Rayleigh criterion dictates that any radio wave, microwave or laser beam will spread and become weaker and diffuse
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
over distance; the larger the transmitter antenna or laser aperture compared to the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of radiation, the tighter the beam and the less it will spread as a function of distance (and vice versa). Smaller antennae also suffer from excessive losses due to side lobe
Side lobe
In antenna engineering, side lobes or sidelobes are the lobes of the far field radiation pattern that are not the main lobe....
s. However, the concept of laser aperture considerably differs from an antenna. Typically, a laser aperture much larger than the wavelength induces multi-moded radiation and mostly collimators are used before emitted radiation couples into a fiber or into space.
Ultimately, beamwidth
Beamwidth
In telecommunication, the term beamwidth has the following meanings:1. In the radio regime, of an antenna pattern, the angle between the half-power points of the main lobe, when referenced to the peak effective radiated power of the main lobe....
is physically determined by diffraction due to the dish size in relation to the wavelength of the electromagnetic radiation used to make the beam. Microwave power beaming can be more efficient than lasers, and is less prone to atmospheric attenuation
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
caused by dust or water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
losing atmosphere to vaporize the water in contact.
Then the power levels are calculated by combining the above parameters together, and adding in the gains and losses
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
due to the antenna characteristics and the transparency and dispersion
Dispersion
Dispersion may refer to:In physics:*The dependence of wave velocity on frequency or wavelength:**Dispersion , for light waves**Dispersion **Acoustic dispersion, for sound waves...
of the medium through which the radiation passes. That process is known as calculating a link budget
Link budget
A link budget is the accounting of all of the gains and losses from the transmitter, through the medium to the receiver in a telecommunication system. It accounts for the attenuation of...
.
Microwave method
Rectenna
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional...
may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft
Beam-powered propulsion
Beam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
leaving orbit has been considered.
Power beaming by microwaves has the difficulty that for most space applications the required aperture sizes are very large due to diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
limiting antenna directionality. For example, the 1978 NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Study of solar power satellites required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have difficulties with atmospheric absorption and beam blockage by rain or water droplets. Because of the "thinned array curse
Thinned array curse
The thinned array curse is a theorem in electromagnetic theory of transmitters. It states that a transmitting aperture which is synthesized by a coherent phased array of smaller apertures that are spaced apart will have a smaller minimum beam spot size The thinned array curse (sometimes, sparse...
," it is not possible to make a narrower beam by combining the beams of several smaller satellites.
For earthbound applications a large area 10 km diameter receiving array allows large total power levels to be used while operating at the low power density suggested for human electromagnetic exposure safety. A human safe power density of 1 mW/cm2 distributed across a 10 km diameter area corresponds to 750 megawatts total power level. This is the power level found in many modern electric power plants.
Following World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, which saw the development of high-power microwave emitters known as cavity magnetrons, the idea of using microwaves to transmit power was researched. By 1964 a miniature helicopter propelled by microwave power had been demonstrated.
Japanese researcher Hidetsugu Yagi
Hidetsugu Yagi
Hidetsugu Yagi was a Japanese electrical engineer. When working at Tohoku University, he wrote several important articles that introduced a new antenna design by his colleague Shintaro Uda to the English-speaking world.The Yagi antenna, patented in 1926, allows directional communication using...
also investigated wireless energy transmission using a directional array antenna that he designed. In February 1926, Yagi and Uda published their first paper on the tuned high-gain directional array now known as the Yagi antenna
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
. While it did not prove to be particularly useful for power transmission, this beam antenna has been widely adopted throughout the broadcasting and wireless telecommunications industries due to its excellent performance characteristics.
Wireless high power transmission using microwaves is well proven. Experiments in the tens of kilowatts have been performed at Goldstone
Goldstone Deep Space Communications Complex
The Goldstone Deep Space Communications Complex — commonly called the Goldstone Observatory — is located in California's Mojave Desert. Operated by ITT Corporation for the Jet Propulsion Laboratory, its main purpose is to track and communicate with space missions. It includes the Pioneer...
in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island. These methods achieve distances on the order of a kilometer.
Laser method
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
to 10s of nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
), power can be transmitted by converting electricity into a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
beam that is then pointed at a solar cell
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
receiver.
This mechanism is generally known as "powerbeaming" because the power is beamed at a receiver that can convert it to usable electrical energy.
Advantages of laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
based energy transfer compared with other wireless methods are:
- collimated monochromatic wavefrontWavefrontIn physics, a wavefront is the locus of points having the same phase. Since infrared, optical, x-ray and gamma-ray frequencies are so high, the temporal component of electromagnetic waves is usually ignored at these wavelengths, and it is only the phase of the spatial oscillation that is described...
propagation allows narrow beam cross-section area for energy transmission over large ranges. - compact size of solid state lasers-photovoltaicsPhotovoltaicsPhotovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...
semiconductor diodes fit into small products. - no radio-frequency interference to existing radio communication such as Wi-fiWi-FiWi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
and cell phones. - control of access; only receivers illuminated by the laser receive power.
Its drawbacks are:
- Conversion to light, such as with a laser, is inefficient
- Conversion back into electricity is inefficient, with photovoltaic cells achieving 40%-50% efficiency. (Note that conversion efficiency is rather higher with monochromatic light than with insolation of solar panels).
- Atmospheric absorption causes losses.
- As with microwave beaming, this method requires a direct line of sight with the target.
The laser "powerbeaming" technology has been mostly explored in military weapons
Directed-energy weapon
A directed-energy weapon emits energy in an aimed direction without the means of a projectile. It transfers energy to a target for a desired effect. Intended effects may be non-lethal or lethal...
and aerospace
Laser propulsion
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass...
applications and is now being developed for commercial and consumer electronics
Consumer electronics
Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...
Low-Power applications. Wireless energy transfer system using laser for consumer space has to satisfy Laser safety
Laser safety
Laser safety is safe design, use and implementation of lasers to minimize the risk of laser accidents, especially those involving eye injuries. Since even relatively small amounts of laser light can lead to permanent eye injuries, the sale and usage of lasers is typically subject to government...
requirements standardized under IEC 60825.
To develop an understanding of the trade-offs of Laser ("a special type of light wave"-based system):
- Propagation of a laser beam (on how Laser beam propagation is much less affected by diffraction limits)
- Coherence and the range limitation problem (on how spatial and spectral coherence characteristics of Lasers allows better distance-to-power capabilities)
- Airy disk (on how wavelength fundamentally dictates the size of a disk with distance)
- Applications of laser diodes (on how the laser sources are utilized in various industries and their sizes are reducing for better integration)
Geoffrey Landis
Geoffrey A. Landis
Geoffrey A. Landis is an American scientist, working for the National Aeronautics and Space Administration on planetary exploration, interstellar propulsion, solar power and photovoltaics...
is one of the pioneers of solar power satellite and laser-based transfer of energy especially for space and lunar missions.
The continuously increasing demand for safe and frequent space missions has resulted in serious thoughts on a futuristic space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
that would be powered by lasers. NASA's space elevator would need wireless power to be beamed to it for it to climb a tether.
NASA's Dryden Flight Research Center has demonstrated flight of a lightweight unmanned model plane powered by a laser beam. This proof-of-concept demonstrates the feasibility of periodic recharging using the laser beam system and the lack of need to return to ground.
"Lasermotive" demonstrated laser powerbeaming at one kilometer during NASA's 2009 powerbeaming contest. Also "Lighthouse DEV" (a spin off of NASA Power Beaming Team) along with "University of Maryland" is developing an eye safe laser system to power a small UAV. Since 2006, "PowerBeam" which originally invented the eye-safe technology and holds all crucial patents in this technology space, is developing commercially ready units for various consumer and industrial electronic products.
Electrical conduction
Disturbed charge of ground and air method
Single wire with Earth returnSingle wire earth return
Single wire earth return or single wire ground return is a single-wire transmission line for supplying single-phase electrical power from an electrical grid to remote areas at low cost...
electrical power transmission systems rely on current flowing through the earth plus a single wire insulated from the earth to complete the circuit. In emergencies high-voltage direct current power transmission systems can also operate in the 'single wire with earth return' mode. Elimination of the raised insulated wire, and transmission of high-potential, high-frequency alternating current through the earth with an atmospheric return circuit has been investigated as a method of wireless electrical power transmission. Transmission of electrical energy through the earth alone, eliminating the second conductor is also being investigated.
Low frequency alternating current can be transmitted through the inhomogeneous earth with low loss because the net resistance between earth antipodes is considerably less than 1 ohm. The electrical displacement takes place predominantly by electrical conduction through the oceans, and metallic ore bodies and similar subsurface structures. The electrical displacement is also by means of electrostatic induction through the more dielectric regions such as quartz deposits and other non-conducting minerals.
Alternating current can be transmitted through atmospheric strata having a barometric pressure of less than 135 millimeters of mercury. Current flows by means of electrostatic induction through the lower atmosphere up to about two or three miles above the plants (this is the middle part in a three-space model) and the flow of ions, that is to say, electrical conduction through the ionized region above three miles. Intense vertical beams of ultraviolet light may be used to ionize the atmospheric gasses directly above the two elevated terminals resulting in the formation of plasma high-voltage electrical transmission lines leading up to the conducting atmospheric strata. The end result is a flow electrical current between the two elevated terminals by a path up to and through the troposphere and back down to the other facility. Electrical conduction through atmospheric strata is made possible by the creation of capacitively coupled discharge plasma through the process of atmospheric ionization.
Terrestrial transmission line with atmospheric return
Tesla discovered that electrical energy can be transmitted through the earth and the atmosphere. In the course of his research he successfully lit lamps at moderate distances and was able to detect the transmitted energy at much greater distances. The Wardenclyffe Tower
Wardenclyffe Tower
Wardenclyffe Tower also known as the Tesla Tower, was an early wireless telecommunications tower designed by Nikola Tesla and intended for commercial trans-Atlantic wireless telephony, broadcasting, and to demonstrate the transmission of power without interconnecting wires...
project was a commercial venture for trans-Atlantic wireless telephony and proof-of-concept demonstrations of global wireless power transmission. The facility was not completed because of insufficient funding.
Earth is a naturally conducting body and forms one conductor of the system. A second path is established through the upper troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
and lower stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
starting at an elevation of approximately 4.5 miles.
A global system for "the transmission of electrical energy without wires" called the World Wireless System
Wardenclyffe Tower
Wardenclyffe Tower also known as the Tesla Tower, was an early wireless telecommunications tower designed by Nikola Tesla and intended for commercial trans-Atlantic wireless telephony, broadcasting, and to demonstrate the transmission of power without interconnecting wires...
, dependent upon the high electrical conductivity of plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
and the high electrical conductivity of the earth, was proposed as early as 1904.
Terrestrial single-conductor surface wave transmission line
The same transmitter used for the atmospheric conduction method is used for the terrestrial single-conductor earth resonance method.
The fundamental earth resonance frequency is claimed to be approximately 11.78 Hz. With the earth resonance method some harmonic of this fundamental frequency is used. "I would say that the frequency should be smaller than twenty thousand per second, through shorter waves might be practicable" and on the low end, "a frequency of nine hundred and twenty-five per second" is used, "when it is indispensable to operate motors of the ordinary kind."
Observations have been made that may be inconsistent
Anomaly (physics)
In quantum physics an anomaly or quantum anomaly is the failure of a symmetry of a theory's classical action to be a symmetry of any regularization of the full quantum theory. In classical physics an anomaly is the failure of a symmetry to be restored in the limit in which the symmetry-breaking...
with a basic tenet of physics related to the scalar derivatives of the electromagnetic potentials that are presently considered to be nonphysical
Philosophy of mathematics
The philosophy of mathematics is the branch of philosophy that studies the philosophical assumptions, foundations, and implications of mathematics. The aim of the philosophy of mathematics is to provide an account of the nature and methodology of mathematics and to understand the place of...
.
Timeline of wireless power
- 1820: André-Marie AmpèreAndré-Marie AmpèreAndré-Marie Ampère was a French physicist and mathematician who is generally regarded as one of the main discoverers of electromagnetism. The SI unit of measurement of electric current, the ampere, is named after him....
develops Ampere’s law showing that electric current produces a magnetic field. - 1831: Michael FaradayMichael FaradayMichael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
develops Faraday’s law of induction describing the electromagnetic force induced in a conductor by a time-varying magnetic flux. - 1836: Nicholas CallanNicholas CallanFather Nicholas Joseph Callan was an Irish priest and scientist from Darver, Co. Louth, Ireland. He was Professor of Natural Philosophy in Maynooth College near Dublin from 1834, and is best known for his work on the induction coil....
invents the electrical transformer. - 1864: James Clerk MaxwellJames Clerk MaxwellJames Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
synthesizes the previous observations, experiments and equations of electricity, magnetism and optics into a consistent theory and mathematically modelsMaxwell's equationsMaxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. These fields in turn underlie modern electrical and communications technologies.Maxwell's equations...
the behavior of electromagnetic radiationElectromagnetic radiationElectromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
. - 1888: Heinrich Rudolf HertzHeinrich Rudolf HertzHeinrich Rudolf Hertz was a German physicist who clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell...
confirms the existence of electromagnetic radiation. Hertz’s "apparatus for generating electromagnetic waves" was a VHF or UHF "radio wave" spark gap transmitter. - 1891: TeslaNikola TeslaNikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
improves Hertz-wave wireless transmitter RF power supply or exciter in his patent No. 454,622, "System of Electric Lighting." - 1893: Tesla demonstrates the wireless illumination of phosphorescent lamps of his design at the World's Columbian ExpositionWorld's Columbian ExpositionThe World's Columbian Exposition was a World's Fair held in Chicago in 1893 to celebrate the 400th anniversary of Christopher Columbus's arrival in the New World in 1492. Chicago bested New York City; Washington, D.C.; and St...
in ChicagoChicagoChicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...
. - 1893: Tesla publicly demonstrates wireless power before a meeting of the National Electric Light AssociationNational Electric Light AssociationThe National Electric Light Association was a national United States trade association including the operators of central power generation stations and interested individuals. Founded in 1885 by G. S. Bowen Terry and Charles A. Brown, it represented the interests of various private companies...
in St. Louis. - 1894: Tesla lights incandescent lamps wirelessly at the 35 South Fifth AvenueFifth Avenue (Manhattan)Fifth Avenue is a major thoroughfare in the center of the borough of Manhattan in New York City, New York, United States. The section of Fifth Avenue that crosses Midtown Manhattan, especially that between 49th Street and 60th Street, is lined with prestigious shops and is consistently ranked among...
laboratory in New York City by means of "electro-dynamic induction" or resonant inductive coupling. - 1894: Hutin & LeBlanc, espouse long held view that inductive energy transfer should be possible, they received U.S. Patent # 527,857 describing a system for power transmission at 3 kHz.
- 1894: Jagdish Chandra BoseJagdish Chandra BoseAcharya Sir Jagadish Chandra Bose, CSI, CIE, FRS was a Bengali polymath: a physicist, biologist, botanist, archaeologist, as well as an early writer of science fiction...
ignites gunpowderGunpowderGunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...
and rings a bell at a distance using electromagneticElectromagnetic radiationElectromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
waves, showing that communications signals can be sent without using wires. - 1896: Tesla demonstrates wireless transmission over a distance of about 48 kilometres (29.8 mi).
- 1897: Tesla files his first patent application dealing specifically with wireless transmissionWirelessWireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
. - 1899: Tesla continues his wireless power transmission research in Colorado Springs and writes, "the inferiority of the induction method would appear immense as compared with the disturbed charge of ground and air method."
- 1902: Nikola Tesla vs. Reginald Fessenden - U.S. Patent Interference No. 21,701, System of Signaling (wireless); wireless power transmission, time and frequency domain spread spectrumSpread spectrumSpread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...
telecommunications, electronic logic gateLogic gateA logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
s in general. - 1904: At the St. Louis World's Fair, a prize is offered for a successful attempt to drive a 0.1 horsepowerHorsepowerHorsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
(75 WWattThe watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
) airship motorElectric motorAn electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
by energy transmitted through space at a distance of at least 100 feet (30.5 m). - 1916: Tesla states, "In my [disturbed charge of ground and air] system, you should free yourself of the idea that there is [electromagnetic] radiation, that energy is radiated. It is not radiated; it is conserved."
- 1917: Tesla's Wardenclyffe towerWardenclyffe TowerWardenclyffe Tower also known as the Tesla Tower, was an early wireless telecommunications tower designed by Nikola Tesla and intended for commercial trans-Atlantic wireless telephony, broadcasting, and to demonstrate the transmission of power without interconnecting wires...
is demolished. . . .
- 1926: Shintaro UdaShintaro UdaJapanese inventor. Assistant of professor Hidetsugu Yagi at Tohoku University, where they invented the Yagi-Uda antenna in 1926. In February 1926, Yagi and Uda published their first report on the wave projector antenna in a Japanese publication. Yagi applied for patents on the new antenna both in...
and Hidetsugu YagiHidetsugu YagiHidetsugu Yagi was a Japanese electrical engineer. When working at Tohoku University, he wrote several important articles that introduced a new antenna design by his colleague Shintaro Uda to the English-speaking world.The Yagi antenna, patented in 1926, allows directional communication using...
publish their first paper on Uda's "tuned high-gain directional array" better known as the Yagi antennaYagi antennaA Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
.
- 1961: William C. BrownWilliam C. BrownWilliam C. Brown was an American electrical engineer who helped to invent the crossed-field amplifier in the 1950s and also pioneered microwave power transmission in the 1960s....
publishes an article exploring possibilities of microwave power transmission. - 1964: Brown demonstrates on CBS NewsCBS NewsCBS News is the news division of American television and radio network CBS. The current chairman is Jeff Fager who is also the executive producer of 60 Minutes, while the current president of CBS News is David Rhodes. CBS News' flagship program is the CBS Evening News, hosted by the network's main...
with Walter CronkiteWalter CronkiteWalter Leland Cronkite, Jr. was an American broadcast journalist, best known as anchorman for the CBS Evening News for 19 years . During the heyday of CBS News in the 1960s and 1970s, he was often cited as "the most trusted man in America" after being so named in an opinion poll...
a model helicopter that receives all of the power needed for flight from a microwave beam. Between 1969 and 1975, Brown is technical director of a JPL RaytheonRaytheonRaytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in weapons and military and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...
program that beams 30 kW over a distance of 1600 meters (1 mile) at 84% efficiency. - 1968: Peter GlaserPeter GlaserPeter Edward Glaser is an American scientist and aerospace engineer. He served as Vice President, Advanced Technology , was employed at Arthur D. Little, Inc., Cambridge, MA ; subsequently he served as a consultant to the company . He was president of Power from Space Consultants...
proposes wirelessly transmitting solar energy captured in space using "Powerbeaming" technology. This is usually recognized as the first description of a solar power satellite. - 1971: Prof. Don Otto develops a small trolley powered by inductionInductive couplingIn electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire through electromagnetic induction...
at The University of Auckland, in New Zealand. - 1973: The world's first passive RFID system is demonstrated at Los-Alamos National Lab.
- 1975: Goldstone Deep Space Communications ComplexGoldstone Deep Space Communications ComplexThe Goldstone Deep Space Communications Complex — commonly called the Goldstone Observatory — is located in California's Mojave Desert. Operated by ITT Corporation for the Jet Propulsion Laboratory, its main purpose is to track and communicate with space missions. It includes the Pioneer...
does experiments in the tens of kilowatts. - 1988: A power electronics group led by Prof. John Boys at The University of Auckland in New Zealand, develops an inverter using novel engineering materials and power electronics and conclude that power transmission by means of electrodynamic induction should be achievable. A first prototype for a contact-less power supply is built. Auckland Uniservices, the commercial company of The University of Auckland, patents the technology.
- 1989: Daifuku, a Japanese company, engages Auckland Uniservices Ltd. to develop technology for car assembly plants and materials handling providing challenging technical requirements including multiplicity of vehicles.
- 1990: Prof. John Boys team develops novel technology enabling multiple vehicles to run on the same inductive power loop and provide independent control of each vehicle. Auckland UniServices Patents the technology.
- 1996: Auckland Uniservices develops an Electric Bus power system using electrodynamic induction to charge (30-60 kW) opportunistically commencing implementation in New Zealand. Prof John Boys Team commission 1st commercial IPT Bus in the world at Whakarewarewa, in New Zealand.
- 1998: RFID tags are powered by electrodynamic induction over a few feet.
- 1999: Dr. Herbert L. Becker powers a lamp and a hand held fan from a distance of 30 feet.
- 1999: Prof. Shu Yuen (Ron) Hui and Mr. S.C. Tang of the City University of Hong Kong file a patent on "Coreless Printed-Circuit-Board (PCB) transformers and operating techniques", which form the basis for future planar charging surface with "vertical flux" leaving the planar surface. The circuit uses resonant circuits for wireless power transfer. EP(GB)0935263B
- 2000: Prof. Shu Yuen (Ron) Hui invent a planar wireless charging pad using the "vertical flux" approach and resonant power transfer for charging portable consumer electronic products. A patent is filed on "Apparatus and method of an inductive battery charger,” PCT Patent PCT/AU03/00 721, 2000.
- 2000: Based on the coreless PCB transformer developed by Prof. Ron Hui, Prof. B. Choi and his team at Kyungpook National University publish a paper on “A new contactless battery charger for portable telecommunication/computing electronics,” in Proc. ICCE’00 Int. Conf. Consumer Electron., 2000, pp. 58–59. The coreless PCB transformer is used to wirelessly charge a mobile phone.
- 2001 Prof. Shu Yuen (Ron) Hui and Dr. S.C. Tang file a patent on "Planar Printed-Circuit-Board Transformers with Effective Electromagnetic Interference (EMI) Shielding". The EM shield consists of a thin layer of ferrite and a thin layer of copper sheet. It enables the underneath of the future wireless charging pads to be shielded with a thin EM shield structure with thickness of typically 0.7mm or less. Patent: US6,501,364.
- 2001: Prof. Ron Hui's team demonstrate that the coreless PCB transformer can transmit power close to 100W in ‘A low-profile low-power converter with coreless PCB isolation transformer, IEEE Transactions on Power Electronics, Volume: 16 Issue: 3 , May 2001. A team of Philips Research Center Aachen, led by Dr. Eberhard Waffenschmidt, use it to power an 100W lighting device in their paper "Size advantage of coreless transformers in the MHz range" in the European Power Electronics Conference in Graz.
- 2001: SplashpowerSplashpowerSplashpower Ltd. was a United Kingdom-based company founded in June 2001. It had been attempting to develop technology for wireless charging of portable devices such as mobile phones, personal digital assistants, mp3 players and cameras...
formed in the UK. Uses coupled resonant coils in a flat "pad" style to transfer tens of watts into a variety of consumer devices, including lamp, phone, PDA, iPod etc. - 2002: Prof. Shu Yuen (Ron) Hui extends the planar wireless charging pad concept using the vertical flux approach to incorporate free-positioning feature for multiple loads. This is achieved by using a multilayer planar winding array structure. Patent were granted as "Planar Inductive Battery Charger", GB2389720 and GB 2389767.
- 2004: Electrodynamic induction used by 90 percent of the US$1 billion clean room industry for materials handling equipment in semiconductor, LCD and plasma screen manufacture.
- 2005: Prof. Shu Yuen (Ron) Hui and Dr. W.C. Ho of City University of Hong Kong publish their work in the IEEE Transactions on a planar wireless charging platform with free-positioning feature. The planar wireless charging pad is able to charge several loads simultaneously on a flat surface.
- 2005: Prof Boys' team at The University of Auckland, refines 3-phase IPT Highway and pick-up systems allowing transmission of power to moving vehicles in the lab.
- 2007: A localized charging technique is reported by Dr. Xun Liu and Prof. Ron Hui for the wireless charging pad with free-positioning feature. With the aid of the double-layer EM shields enclosing the transmitter and receiver coils, the localized charging selects the right transmitter coil so as to minimize flux leakage and human exposure to radiation.
- 2007: Using electrodynamic induction a physics research group, led by Prof. Marin SoljacicMarin SoljacicMarin Soljačić is a Croatian physicist and electrical engineer known for wireless non-radiative energy transfer.-Biography:...
, at MIT, wirelessly power a 60W light bulb with 40% efficiency at a 2 metres (6.6 ft) distance with two 60 cm-diameter coils. - 2008: Bombardier offers a new wireless power transmission product PRIMOVE, a system for use on trams and light-rail vehicles.
- 2008: Industrial designer Thanh Tran, at Brunel University make a wireless lamp incorporating a high efficiency 3W LED.
- 2008: Intel reproduces Tesla's original 1894 implementation of electrodynamic induction and Prof. John Boys group's 1988 follow-up experiments by wirelessly powering a nearby light bulb with 75% efficiency.
- 2008: Greg Leyh and Mike Kennan of the Nevada Lightning Laboratory publish a paper on Tesla's disturbed charge of ground and air method of wireless power transmission with circuit simulations and test results showing an efficiency greater than can be obtained using the electrodynamic induction method.
- 2009: Palm (now a division HP) launches the Palm PrePalm PreThe Palm Pre is a multimedia smartphone designed and marketed by Palm with a multi-touch screen and a sliding keyboard. The smartphone was the first to use Palm's Linux based mobile operating system, webOS...
smartphone with the Palm Touchstone wireless charger. - 2009: A Consortium of interested companies called the Wireless Power ConsortiumWireless Power ConsortiumThe Wireless Power Consortium is a business alliance of more than 60 firms to develop open standards for inductive charging.-History:The organization was started in 2008 to create a universal wireless power charging standard so that electronic products and charging stations using the same standard...
announce they are nearing completion for a new industry standard for low-power (which is eventually published in August 2010). inductive chargingInductive chargingInductive charging uses an electromagnetic field to transfer energy between two objects. This is usually done with a charging station. Energy is sent through inductive coupling to an electrical device, which then can use that energy to charge batteries....
- 2009: An Ex approved Torch and Charger aimed at the offshore market is introduced. This product is developed by Wireless Power & Communication, a Norway based company.
- 2009: A simple analytical electrical model of electrodynamic induction power transmission is proposed and applied to a wireless power transfer system for implantable devices.
- 2009: LasermotiveLaserMotiveLaserMotive is a U.S. engineering firm developing technologies for efficiently transmitting power via lasers, a form of wireless energy transfer.-History:LaserMotive was founded in 2006 by physicists Tom Nugent and Jordin Kare.-Technology:...
uses diode laser to win $900k NASA prize in power beaming, breaking several world records in power and distance, by transmitting over a kilowatt more than several hundred meters. - 2009: Sony shows a wireless electrodynamic-induction powered TV set, 60 W over 50 cm
- 2010: Haier Group debuts “the world's first” completely wireless LCD television at CES 2010 based on Prof. Marin SoljacicMarin SoljacicMarin Soljačić is a Croatian physicist and electrical engineer known for wireless non-radiative energy transfer.-Biography:...
's follow-up research on Tesla's electrodynamic induction wireless energy transmission method and the Wireless Home Digital InterfaceWireless Home Digital InterfaceWireless Home Digital Interface is a consumer electronic standard for a wireless HDTV connectivity throughout the home. It is being driven by AMIMON, Hitachi Ltd., LG Electronics, Motorola, Samsung Group, Sharp Corporation and Sony....
(WHDI). - 2010: System On Chip (SoC) group in University of British Columbia develops an optimization tool for the design of highly efficient wireless power transmission systems using multiple coils. The design is optimized for implantable applications and power transfer efficiency of 82% is achieved.
See also
- Beam-powered propulsionBeam-powered propulsionBeam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
- Beam Power Challenge — one of the NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Centennial ChallengesCentennial ChallengesThe Centennial Challenges are NASA space competition prize contests for non-government-funded technological achievements by American teams.-Current Challenges:... - Distributed generationDistributed generationDistributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources....
- Electricity distributionElectricity distributionFile:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
- Electric power transmissionElectric power transmissionElectric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
- Transmission mediumTransmission mediumA transmission medium is a material substance that can propagate energy waves...
- Microwave power transmission
- Friis transmission equationFriis transmission equationThe Friis transmission equation is used in telecommunications engineering, and gives the power received by one antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. The formula was derived in 1945 by Danish-American radio engineer Harald T...
- Thinned array curseThinned array curseThe thinned array curse is a theorem in electromagnetic theory of transmitters. It states that a transmitting aperture which is synthesized by a coherent phased array of smaller apertures that are spaced apart will have a smaller minimum beam spot size The thinned array curse (sometimes, sparse...
- Resonant inductive couplingResonant inductive couplingResonant inductive coupling or electrodynamic induction is the near field wireless transmission of electrical energy between two coils that are highly resonant at the same frequency. The equipment to do this is sometimes called a resonant or resonance transformer. While many...
- Differential capacitanceDifferential capacitanceDifferential capacitance in physics, electronics, and electrochemistry is a measure of the voltage-dependent capacitance of a nonlinear capacitor, such as an electrical double layer or a semiconductor diode...
- Wardenclyffe TowerWardenclyffe TowerWardenclyffe Tower also known as the Tesla Tower, was an early wireless telecommunications tower designed by Nikola Tesla and intended for commercial trans-Atlantic wireless telephony, broadcasting, and to demonstrate the transmission of power without interconnecting wires...
- Electromagnetic compatibilityElectromagnetic compatibilityElectromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
Further reading
Books- Walker, J., Halliday, D., & Resnick, R. (2011). Fundamentals of physics. Hoboken, NJ: Wiley.
- Hu, A. P. (2009). Wireless/Contactless power supply: Inductively coupled resonant converter solutions. Saarbrücken, Germany: VDM Verlag Dr. Müller.
- Valone, T. (2002). Harnessing the wheelwork of nature: Tesla's science of energy. Kempton, Ill: Adventure Unlimited Press.
- General Electric Co. (1915). General Electric review, Volume 18. "Wireless Transmission of Energy" By Elihu Thomson. General Electric Company, Lynn. (ed. Lecture by Professor Thomson, National Electric Light Association, New York.)
- Steinmetz, C. P. (1914). Elementary lectures on electric discharges, waves and impulses, and other transients. New York: McGraw-Hill book co., inc.
- Louis Cohen (1913). Formulae and tables for the calculation of alternating current problems. McGraw-Hill.
- Kennelly, A. E. (1912). The application of hyperbolic functions to electrical engineering problems: Being the subject of a course of lectures delivered before the University of London in May and June 1911. London: University of London Press.
- Orlich, E. M. (1912). Die Theorie der Wechselströme.
- Fleming, J. A. (1911). Propagation of electric currents in telephone & telegraph conductors. New York: Van Nostrand.
- Franklin, W. S. (1909). Electric waves: An advanced treatise on alternating-current theory. New York: Macmillan Co.
Patents, Microwave powered aircraft, John E. Martin, et al. (1990)., Solid state solar to microwave energy converter system and apparatus, Kenneth W. Dudley, et al. (1976)., Microwave power receiving antenna, Carroll C. Dailey (1970)., Method of Utilizing Radiant Energy, Nikola Tesla (1901)., Apparatus for the Utilization of Radiant Energy, Nikola Tesla (1901).
- U.S. Patent 649,621, Apparatus for Transmission of Electrical Energy, Nikola Tesla (1900).
External links
- Howstuffworks "How Wireless Power Works" — describes near-range and mid-range wireless power transmission using induction and radiation techniques.
- Microwave Power Transmission, — its history before 1980.
- The Stationary High Altitude Relay Platform (SHARP), — microwave beam powered.
- Marin Soljačić's MIT WiTricity — wireless power transmission pages.
- Anticipating MIT WiTricity — Tesla demonstrated resonant magnetic induction over 110 years ago.