Split Ring Resonator
Encyclopedia
A split-ring resonator (SRR) is a component of a Negative index metamaterial (NIM), also known as Double negative metamaterials (DNG) or Left-handed medium (LHM). It also component of other types of metamaterial
such as Single Negative metamaterial (SNG). SRRs are also used for research in Terahertz metamaterials
, Acoustic metamaterials
, and Metamaterial antennas
. A single cell SRR has a pair of enclosed loops with splits in them at opposite ends. The loops are made of nonmagnetic metal like copper
and have a small gap between them. The loops can be concentric, or square, and gapped as needed.
penetrating the metal rings will induce rotating currents
in the rings, which produce their own flux to enhance or oppose the incident field
(depending on the SRRs resonant properties). This field pattern is dipolar
. Due to splits in the rings the structure can support resonant wavelength
s much larger than the diameter
of the rings. This would not happen in closed rings. The small gaps between the rings produces large capacitance
values which lower the resonating frequency
, as the time constant
is large. The dimensions of the structure are small compared to the resonant wavelength. This results in low radiative losses
, and very high quality factors.
At frequencies below the resonant frequency, the real part of the magnetic permeability of the SRR becomes large (positive), and at frequencies higher than resonance it will become negative. This negative permeability
can be used with the negative dielectric
constant of another structure to produce negative refractive index materials.
. In a straightforward manner he stated that ε (permittivity)
as a dielectric constant and µ (magnetic permeability) "are the fundamental characteristic quantities which determine the propagation of electromagnetic waves in matter." Furthermore, these quantities determine the index of refraction "n". He realized, that materials with simultaneous negative values for ε and µ can exist within the laws of physics, and that these substances have some properties different from materials with positive values for ε and µ. Veselago described the unusual consequences of such a left-handed substance; a refraction that is reversed, an inversion of the Doppler and Cerenkov effects, the vectors E, H, and k occur as a left-handed set, a sign change of the group
velocity, bi-concave and bi-convex lenses change roles, and the reversal of radiation pressure to radiation tension. In other words, dramatically different propagation
characteristics.
Thirty years later physicist
s would agree when practical structures that exhibit negative values for ε,µ, and n were fabricated and demonstrated in the year 2000. These are called electromagnetic metamaterials, and the first of these used a nested split ring resonator design and are still in use today for research. (see illustration at the beginning of this article). However, the research has gone from negative values for ε,µ, and n in the microwave - gigahertz range up to terahertz and infrared
frequencies.
at times, and homogeneous material
, at other times. The view of homogeneous or composite depends on the discussion underway. The composite description is employed when discussing the individual components of the medium, above the atomic level. The original purpose of defining permittivity, ε, and permeability, µ was to support a homogeneous view of an electromagnetic medium
. In this view, the contents of the cell (split-ring resonator and conducting wire) will define the system wide response of ε, and µ. The electromagnetic wave will not detect an internal structure smaller than the wavelength, and the micro-structure is then described by effective permittivity ( ε-eff) and effective permeability (µ-eff), which are electromagnetic constituents of a homogeneous material.
To date (December 2009) the capability for desired results in visible spectrum
has not been achieved. However, in 2005, it was noted that, physically, a nested
circular split-ring resonator must have an inner radii of 30 to 40 nanometers for success in the mid-range of the visible spectrum.
Microfabrication
and nanofabrication techniques utilize direct laser beam writing or electron beam lithography
, and this depends on the desired resolution.
At first a single SRR looked like a ring with small segment removed which results in a "C" shape, on fiberglass, printed circuit board
material. In this type of configuration it is actually two concentric
bands of non-magnetic conductor
material. There is one gap in each band placed 180° relative to each other. The gap in each band gives it the distinctive "C" shape, rather than a totally circular or square shape. Then multiple cells of this double band configuration are fabricated onto circuit board material by an etching technique and lined with copper wire strip arrays are added. After processing, the boards are cut and assembled into an interlocking unit. It is constructed into a periodic array with a large number of SRRs.
There are now a number of different configurations that use the SRR nomenclature.
array of SRRs was used for the first actual demonstration of a negative index of refraction. For this demonstration, square shaped SRRs, with the lined wire configurations, were fabricated into a periodic, arrayed, cell structure. This is the substance of the metamaterial. Then a metamaterial prism
was cut from this material. The prism experiment demonstrated a negative index of refraction for the first time in the year 2000; the paper about the demonstration was submitted to the journal Science
on January 8, 2001, accepted on February 22, 2001 and published on April 6, 2001.
Just before this prism experiment, Pendry
et al. was able to demonstrate that a three-dimensional array of intersecting thin wires could be used to create negative values of ε. In a later demonstration, a periodic array of copper split-ring resonators could produce an effective negative μ. In 2000 Smith et al. were the first to successfully combine the two arrays and produce a LHM which had negative values of ε and μ for a band of frequencies in the GHz range.
SRRs were first used to fabricate left-handed metamaterials for the microwave
range, and several years later for the terahertz range. By 2007, experimental demonstration of this structure at microwave frequencies has been achieved by many groups. In addition, SRRs have been used for research in acoustic metamaterials. The arrayed SRRs and wires of the first Left-handed metamaterial were melded into alternating layers. This concept and methodology was then applied to (dielectric) materials with optical resonances
producing negative effective permittivity for certain frequency intervals resulting in "photonic bandgap frequencies". Another analysis showed Left Handed Material to be fabricated from inhomogeneous constituents, which yet results in a macroscopically homogeneous
material. SRRs had been used to focus a signal from a point source, increasing the transmission distance for near field
waves. Furthermore, another analysis showed SRRs with a negative index of refraction capable of high-frequency magnetic response
, which created an artificial magnetic device composed of non-magnetic materials (dielectric circuit board).
The resonance phenomena that occurs in this system is essential to achieving the desired effects.
SRRs also exhibit resonant electric response in addition to their resonant magnetic response. The response, when combined with an array of identical wires is averaged over the whole composite structure which results in effective values, including the refractive index. The original logic behind SRRs specifically, and metamaterials generally was to create a structure, which imitates an arrayed atomic structure only on a much larger scale.
There is the 1-D Split-Ring Structure with two square
rings, one inside the other. One set of cited "unit cell
" dimension
s would be an outer square
of 2.62 mm and an inner square of 0.25 mm. 1-D structures such as this are easier to fabricate compared with constructing a rigid 2-D structure.
The Symmetrical-Ring Structure is another classic example. Described by the nomenclature these are two rectangular square D type configurations, exactly the same size, laying flat, side by side, in the unit cell
. Also these are not concentric
. One set of cited dimensions are 2 mm on the shorter side, and 3.12 mm on the longer side. The gaps in each ring face each other, in the unit cell.
The Omega
Structure, as the nomenclature describes, has an Ω-shaped ring structure. There are two of these, standing vertical, side by side, instead of laying flat, in the unit cell. In 2005 these were considered to be a new type of metamaterial. One set of cited dimensions are annular parameters of R = 1.4 mm and r = 1 mm, and the straight edge is 3.33 mm.
Another new metamaterial
in 2005 was a coupled “S” shaped structure. There are two vertical "S" shaped structures, side by side, in a unit cell. There is no gap as in the ring structure, however there is a space between the top and middle parts of the S and space between the middle part and bottom part of the S. Furthermore, it still has the properties of having an electric plasma frequency and a magnetic resonant frequency.
Other types of split-ring resonators are the spiral resonator with 8 loops. broadside coupled
split-ring resonator (BC-SRR). Two-layer multi spiral resonator (TL-MSR), the broad-side coupled spiral resonator with four turns, the open split-ring resonator (OSRR), and the open
complementary split-ring resonator (OCSRR). Transmission line configurations include SRR-based CRLH (composite right-left-handed) transmission line and its equivalent compliment.
region.
The splits in the ring allow the SRR unit to achieve resonance at wavelengths much larger than the diameter of the ring. The unit is designed to generate a large capacitance, lower the resonant frequency, and concentrate the electric field. Combining units creates a design as a periodic medium. Furthermore, the multiple unit structure has strong magnetic coupling with low radiative losses.
Metamaterial
Metamaterials are artificial materials engineered to have properties that may not be found in nature. Metamaterials usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior....
such as Single Negative metamaterial (SNG). SRRs are also used for research in Terahertz metamaterials
Terahertz metamaterials
Terahertz metamaterials are a new class of composite, artificial materials which interact at terahertz frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz...
, Acoustic metamaterials
Acoustic metamaterials
Acoustic metamaterials are artificially fabricated materials designed to control, direct, and manipulate sound in the form of sonic, infrasonic, or ultrasonic waves, as these might occur in gases, liquids, and solids. The hereditary line into acoustic metamaterials follows from theory and research...
, and Metamaterial antennas
Metamaterial antennas
Metamaterial antennas are a class of antennas which use metamaterials to increase performance of miniaturized antenna systems. Their purpose, as with any electromagnetic antenna, is to launch energy into free space...
. A single cell SRR has a pair of enclosed loops with splits in them at opposite ends. The loops are made of nonmagnetic metal like copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and have a small gap between them. The loops can be concentric, or square, and gapped as needed.
Overview
A magnetic fluxMagnetic flux
Magnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
penetrating the metal rings will induce rotating currents
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
in the rings, which produce their own flux to enhance or oppose the incident field
Surface normal
A surface normal, or simply normal, to a flat surface is a vector that is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a...
(depending on the SRRs resonant properties). This field pattern is dipolar
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
. Due to splits in the rings the structure can support resonant 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...
s much larger than the diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
of the rings. This would not happen in closed rings. The small gaps between the rings produces large capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
values which lower the resonating 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...
, as the time constant
Time constant
In physics and engineering, the time constant, usually denoted by the Greek letter \tau , is the risetime characterizing the response to a time-varying input of a first-order, linear time-invariant system.Concretely, a first-order LTI system is a system that can be modeled by a single first order...
is large. The dimensions of the structure are small compared to the resonant wavelength. This results in low radiative losses
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...
, and very high quality factors.
At frequencies below the resonant frequency, the real part of the magnetic permeability of the SRR becomes large (positive), and at frequencies higher than resonance it will become negative. This negative permeability
Permeability (electromagnetism)
In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. In other words, it is the degree of magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability is typically...
can be used with the negative 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...
constant of another structure to produce negative refractive index materials.
Background
In 1967 a paper was published that was written by Victor G. VeselagoVictor Veselago
Victor Georgievich Veselago is a Russian physicist. In 1967, he was the first to publish a theoretical analysis of materials with negative permittivity, ε, and permeability μ....
. In a straightforward manner he stated that ε (permittivity)
Permittivity
In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how...
as a dielectric constant and µ (magnetic permeability) "are the fundamental characteristic quantities which determine the propagation of electromagnetic waves in matter." Furthermore, these quantities determine the index of refraction "n". He realized, that materials with simultaneous negative values for ε and µ can exist within the laws of physics, and that these substances have some properties different from materials with positive values for ε and µ. Veselago described the unusual consequences of such a left-handed substance; a refraction that is reversed, an inversion of the Doppler and Cerenkov effects, the vectors E, H, and k occur as a left-handed set, a sign change of the group
velocity, bi-concave and bi-convex lenses change roles, and the reversal of radiation pressure to radiation tension. In other words, dramatically different propagation
Wave propagation
Wave propagation is any of the ways in which waves travel.With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves....
characteristics.
Thirty years later physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
s would agree when practical structures that exhibit negative values for ε,µ, and n were fabricated and demonstrated in the year 2000. These are called electromagnetic metamaterials, and the first of these used a nested split ring resonator design and are still in use today for research. (see illustration at the beginning of this article). However, the research has gone from negative values for ε,µ, and n in the microwave - gigahertz range up to terahertz and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
frequencies.
Composite and homogeneous
Periodic configurations of the split-ring resonator is described as a compositeComposite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
at times, and homogeneous material
Homogeneity (physics)
In general, homogeneity is defined as the quality or state of being homogeneous . For instance, a uniform electric field would be compatible with homogeneity...
, at other times. The view of homogeneous or composite depends on the discussion underway. The composite description is employed when discussing the individual components of the medium, above the atomic level. The original purpose of defining permittivity, ε, and permeability, µ was to support a homogeneous view of an electromagnetic medium
Transmission medium
A transmission medium is a material substance that can propagate energy waves...
. In this view, the contents of the cell (split-ring resonator and conducting wire) will define the system wide response of ε, and µ. The electromagnetic wave will not detect an internal structure smaller than the wavelength, and the micro-structure is then described by effective permittivity ( ε-eff) and effective permeability (µ-eff), which are electromagnetic constituents of a homogeneous material.
Characteristics
The SRR is designed to mimic the magnetic response of atoms, only on a much larger scale. Also, as part of periodic composite structure these are designed to have a stronger magnetic coupling than is found in nature. The larger scale allows for more control over the magnetic response, while each unit is smaller than the radiated electromagnetic wave. SRRs are much more active than ferromagentic material found in nature. The pronounced magnetic response in such lightweight materials demonstrates an advantage over heavier, naturally occurring materials. Each unit can be designed to have its own magnetic response. The response can be enhanced or lessened as desired. In addition, the overall effect reduces power requirements.Various configurations
There is a variety of split-ring resonators - rod-split-rings, nested split-rings, single split rings, deformed split-rings, spiral split-rings, and extended S-structures. The variations of split ring resonators have achieved different results, including smaller and higher frequency structures. The research which involves some of these types are discussed throughout the article.To date (December 2009) the capability for desired results in visible spectrum
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
has not been achieved. However, in 2005, it was noted that, physically, a nested
circular split-ring resonator must have an inner radii of 30 to 40 nanometers for success in the mid-range of the visible spectrum.
Microfabrication
Microfabrication
Microfabrication is the term that describes processes of fabrication of miniature structures, of micrometre sizes and smaller. Historically the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" or "semiconductor device...
and nanofabrication techniques utilize direct laser beam writing or electron beam lithography
Electron beam lithography
Electron beam lithography is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film , and of selectively removing either exposed or non-exposed regions of the resist...
, and this depends on the desired resolution.
SRR configuration
Split-ring resonators (SRR) are one of the most common elements used to fabricate metamaterials. Split-ring resonators are non-magnetic materials, which are usually fabricated from circuit board material to create metamaterials.At first a single SRR looked like a ring with small segment removed which results in a "C" shape, on fiberglass, printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
material. In this type of configuration it is actually two concentric
Concentric
Concentric 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...
bands of non-magnetic conductor
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...
material. There is one gap in each band placed 180° relative to each other. The gap in each band gives it the distinctive "C" shape, rather than a totally circular or square shape. Then multiple cells of this double band configuration are fabricated onto circuit board material by an etching technique and lined with copper wire strip arrays are added. After processing, the boards are cut and assembled into an interlocking unit. It is constructed into a periodic array with a large number of SRRs.
There are now a number of different configurations that use the SRR nomenclature.
Demonstrations
A periodicPeriodic function
In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...
array of SRRs was used for the first actual demonstration of a negative index of refraction. For this demonstration, square shaped SRRs, with the lined wire configurations, were fabricated into a periodic, arrayed, cell structure. This is the substance of the metamaterial. Then a metamaterial prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
was cut from this material. The prism experiment demonstrated a negative index of refraction for the first time in the year 2000; the paper about the demonstration was submitted to the journal Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
on January 8, 2001, accepted on February 22, 2001 and published on April 6, 2001.
Just before this prism experiment, Pendry
Pendry
Pendry is the surname of :*Professor John Pendry, English theoretical physicist*Tom Pendry, Baron Pendry, English politician*Jan-Simon Pendry, the original creator of the Berkeley Automounter...
et al. was able to demonstrate that a three-dimensional array of intersecting thin wires could be used to create negative values of ε. In a later demonstration, a periodic array of copper split-ring resonators could produce an effective negative μ. In 2000 Smith et al. were the first to successfully combine the two arrays and produce a LHM which had negative values of ε and μ for a band of frequencies in the GHz range.
SRRs were first used to fabricate left-handed metamaterials for the microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
range, and several years later for the terahertz range. By 2007, experimental demonstration of this structure at microwave frequencies has been achieved by many groups. In addition, SRRs have been used for research in acoustic metamaterials. The arrayed SRRs and wires of the first Left-handed metamaterial were melded into alternating layers. This concept and methodology was then applied to (dielectric) materials with optical resonances
Optical cavity
An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric...
producing negative effective permittivity for certain frequency intervals resulting in "photonic bandgap frequencies". Another analysis showed Left Handed Material to be fabricated from inhomogeneous constituents, which yet results in a macroscopically homogeneous
Homogeneity (physics)
In general, homogeneity is defined as the quality or state of being homogeneous . For instance, a uniform electric field would be compatible with homogeneity...
material. SRRs had been used to focus a signal from a point source, increasing the transmission distance for near field
Near 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...
waves. Furthermore, another analysis showed SRRs with a negative index of refraction capable of high-frequency magnetic response
Magnetic susceptibility
In electromagnetism, the magnetic susceptibility \chi_m is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field...
, which created an artificial magnetic device composed of non-magnetic materials (dielectric circuit board).
The resonance phenomena that occurs in this system is essential to achieving the desired effects.
SRRs also exhibit resonant electric response in addition to their resonant magnetic response. The response, when combined with an array of identical wires is averaged over the whole composite structure which results in effective values, including the refractive index. The original logic behind SRRs specifically, and metamaterials generally was to create a structure, which imitates an arrayed atomic structure only on a much larger scale.
Several types of SRR
In research based in metamaterials, and specifically negative refractive index, there are different types of split-ring resonators. Of the examples mentioned below most all of them have a gap in each ring. In other words, with a double ring structure, each ring has a gap.There is the 1-D Split-Ring Structure with two square
Square (geometry)
In geometry, a square is a regular quadrilateral. This means that it has four equal sides and four equal angles...
rings, one inside the other. One set of cited "unit cell
Cell (geometry)
In geometry, a cell is a three-dimensional element that is part of a higher-dimensional object.- In polytopes :A cell is a three-dimensional polyhedron element that is part of the boundary of a higher-dimensional polytope, such as a polychoron or honeycomb For example, a cubic honeycomb is made...
" dimension
Dimension
In physics and mathematics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it...
s would be an outer square
Square (geometry)
In geometry, a square is a regular quadrilateral. This means that it has four equal sides and four equal angles...
of 2.62 mm and an inner square of 0.25 mm. 1-D structures such as this are easier to fabricate compared with constructing a rigid 2-D structure.
The Symmetrical-Ring Structure is another classic example. Described by the nomenclature these are two rectangular square D type configurations, exactly the same size, laying flat, side by side, in the unit cell
Cell (geometry)
In geometry, a cell is a three-dimensional element that is part of a higher-dimensional object.- In polytopes :A cell is a three-dimensional polyhedron element that is part of the boundary of a higher-dimensional polytope, such as a polychoron or honeycomb For example, a cubic honeycomb is made...
. Also these are not concentric
Concentric
Concentric 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...
. One set of cited dimensions are 2 mm on the shorter side, and 3.12 mm on the longer side. The gaps in each ring face each other, in the unit cell.
The Omega
Omega
Omega is the 24th and last letter of the Greek alphabet. In the Greek numeric system, it has a value of 800. The word literally means "great O" , as opposed to omicron, which means "little O"...
Structure, as the nomenclature describes, has an Ω-shaped ring structure. There are two of these, standing vertical, side by side, instead of laying flat, in the unit cell. In 2005 these were considered to be a new type of metamaterial. One set of cited dimensions are annular parameters of R = 1.4 mm and r = 1 mm, and the straight edge is 3.33 mm.
Another new metamaterial
Metamaterial
Metamaterials are artificial materials engineered to have properties that may not be found in nature. Metamaterials usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior....
in 2005 was a coupled “S” shaped structure. There are two vertical "S" shaped structures, side by side, in a unit cell. There is no gap as in the ring structure, however there is a space between the top and middle parts of the S and space between the middle part and bottom part of the S. Furthermore, it still has the properties of having an electric plasma frequency and a magnetic resonant frequency.
Other types of split-ring resonators are the spiral resonator with 8 loops. broadside coupled
split-ring resonator (BC-SRR). Two-layer multi spiral resonator (TL-MSR), the broad-side coupled spiral resonator with four turns, the open split-ring resonator (OSRR), and the open
complementary split-ring resonator (OCSRR). Transmission line configurations include SRR-based CRLH (composite right-left-handed) transmission line and its equivalent compliment.
First demonstrations with the SRR
On May 1, 2000 it was reported that an array of split ring resonators was combined with an array of conducting wires to achieve negative propagation of electromagnetic waves in the microwaveMicrowave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
region.
The splits in the ring allow the SRR unit to achieve resonance at wavelengths much larger than the diameter of the ring. The unit is designed to generate a large capacitance, lower the resonant frequency, and concentrate the electric field. Combining units creates a design as a periodic medium. Furthermore, the multiple unit structure has strong magnetic coupling with low radiative losses.
Magnetic resonances for different SRR parameters and designs
Depending on the number of splits and the number of rings resonant frequency will vary. Also as capacitors are added across the splits, this also affects the resonant frequency. The addition of capacitors can create a tunable medium. The geometry of the SRRs is also studied to note its relationship to the resonant frequency. These variations, along with testing veractors, also help to determine the nonlinear response in some cases.Towards 3D electromagnetic metamaterials in the THz range
Towards 3D electromagnetic metamaterials in the THz range.Nanoscale cut-wire pairs
Negative index materials can be fabricated using other configurations such as periodic metallic crosses, or a swiss rollSwiss roll
A Swiss roll or jelly roll is a type of sponge cake roll. The thin cake is made of eggs, flour and sugar and baked in a very shallow rectangular baking tray, called a sheet pan. The cake is removed from the pan and spread with jam or buttercream, rolled up, and served in circular slices.The...
Negative permeability material for red light
Permeability for one wavelength of the visible spectrum at 780 nm.Controllable permeability across visible spectrum
Magnetic resonance across the visible spectrum (nanostripts)See also
- Acoustic metamaterialsAcoustic metamaterialsAcoustic metamaterials are artificially fabricated materials designed to control, direct, and manipulate sound in the form of sonic, infrasonic, or ultrasonic waves, as these might occur in gases, liquids, and solids. The hereditary line into acoustic metamaterials follows from theory and research...
- MetamaterialMetamaterialMetamaterials are artificial materials engineered to have properties that may not be found in nature. Metamaterials usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior....
- Metamaterial absorberMetamaterial absorberA metamaterial absorber manipulates the loss components of the complex effective parameters, permittivity and magnetic permeability of metamaterials, to create a material with particularly high absorption...
- Metamaterial cloakingMetamaterial cloakingMetamaterial cloaking is the scientific application of metamaterials in order to achieve invisibility-cloaking. This is accomplished by manipulating the paths traversed by light through a novel optical material....
- Metamaterial antennasMetamaterial antennasMetamaterial antennas are a class of antennas which use metamaterials to increase performance of miniaturized antenna systems. Their purpose, as with any electromagnetic antenna, is to launch energy into free space...
- Negative index metamaterialsNegative index metamaterialsNegative index metamaterials or negative index materials are artificial structures where the refractive index has a negative value over some frequency range. This does not occur in any known natural materials, and thus is only achievable with engineered structures known as metamaterials...
- Nonlinear metamaterialsNonlinear metamaterialsA nonlinear metamaterial is an artificially constructed material that can exhibit properties not found in nature. Its response to electromagnetic radiation can be characterized by its permittivity and material permeability. The product of the permittivity and permeability results in the refractive...
- Photonic metamaterialsPhotonic metamaterialsPhotonic metamaterials, also known as Optical metamaterials, are a type of electromagnetic metamaterial, which are designed to interact with optical frequencies which are terahertz , infrared , and eventually, visible wavelengths. As a type of metamaterial, the periodic structures are made up of...
- Photonic crystalPhotonic crystalPhotonic crystals are periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons...
- Seismic metamaterialsSeismic metamaterialsSeismic metamaterials, are metamaterials which are designed to counteract the adverse effects of seismic waves on artificial structures, which exist on or near the surface of the earth...
- SuperlensSuperlensA superlens, super lens or perfect lens is a lens which uses metamaterials to go beyond the diffraction limit. The diffraction limit is an inherent limitation in conventional optical devices or lenses. In 2000, a type of lens was proposed, consisting of a metamaterial that compensates for wave...
- Terahertz metamaterialsTerahertz metamaterialsTerahertz metamaterials are a new class of composite, artificial materials which interact at terahertz frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz...
- Tunable metamaterialsTunable metamaterialsA tunable metamaterial is a metamaterial with a variable response to an incident electromagnetic wave. This includes remotely controlling how an incident electromagnetic wave interacts with a metamaterial. This means the capablitity to determine whether the EM wave is transmitted, reflected, or...
External links
- Google scholar List of Papers by JB Pendry
- Imperial College, Department of Physics, Condensed Matter Theory Group
- Personal Profile of John Pendry at Imperial college
- Video: John Pendry lecture: The science of invisibility April 2009, SlowTV
- Shepard, K. W. et al. Split-ring resonator for the Argonne Superconducting Heavy Ion Booster. IEEE Transactions on Nuclear Science, VoL. NS-24, N0.3, JUN 1977