Artificial dielectrics
Encyclopedia
Artificial dielectrics are artificial electromagnetic
materials consisting of array
ed, synthetic substances. The arrays themselves, and the distances between synthetic substances are usually evenly spaced on, or within, a substrate. Hence, the arrays of inclusions are in a periodic or lattice
structure. The lattice spacing is smaller than the impinging electromagnetic wavelength
of interest. These were first conceptualized, constructed and deployed for interaction in the microwave
frequency range in the 1940s and 1950s. The constructed medium, the artificial dielectric, has an effective permittivity
and effective permeability
, as intended.
In addition, some artificial dielectrics may consist of irregular lattices, random mixtures, or a non-uniform concentration of particles.
Artificial dielectrics came into use with the radar microwave technologies developed between the 1940s and 1970s. The term "artificial dielectrics" came into use because these are macroscopic
analogues of naturally occurring dielectrics. The difference between the natural and artificial substance is that the atoms or molecules are artificially (human) constructed materials. Artificial dielectrics were proposed because of the need for lightweight structures and components for various microwave delivery devices.
Artificial dielectrics are a direct historical link to metamaterials
.
in 1948 when he was employed by Bell Laboratories. It described materials of practical dimensions that imitated the electromagnetic response of natural dielectric solids. The artificial dielectrics were borne out of a need for lightweight low loss materials for large and otherwise heavy devices.
is part of its description.
A lattice structure, with some degree of spatial ordering is present. Also, the applied field is longer in wavelength than the lattice spacing. This then allows for a macroscopic description expressed as electric permittivity and magnetic permeability.
In order to manufacture an artificial permittivity and permeability there must be a capability to access the atoms themselves. This degree of precision is impractical. However, in the late 1940s - in the domain of long wavelengths - it became possible to manufacture larger scale, and more accessible scatterers that mimic the local response of natural materials - along with a synthesized macroscopic response. In the radio frequency and microwave regions such artificial crystal lattice structures were assembled. The scatters responded to an electromagnetic field like atoms and molecules in natural materials, and the media behaved much like dielectrics with an effective media response.
The scattering elements are designed to scatter the electromagnetic field in a prescribed manner. The geometric shape of the elements—spheres, disks, conducting strips, etc. -- contribute to the design paramaters.
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
materials consisting of array
Array
In computer science, an array data structure or simply array is a data structure consisting of a collection of elements , each identified by at least one index...
ed, synthetic substances. The arrays themselves, and the distances between synthetic substances are usually evenly spaced on, or within, a substrate. Hence, the arrays of inclusions are in a periodic or lattice
Lattice model (physics)
In physics, a lattice model is a physical model that is defined on a lattice, as opposed to the continuum of space or spacetime. Lattice models originally occurred in the context of condensed matter physics, where the atoms of a crystal automatically form a lattice. Currently, lattice models are...
structure. The lattice spacing is smaller than the impinging electromagnetic 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 interest. These were first conceptualized, constructed and deployed for interaction in 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...
frequency range in the 1940s and 1950s. The constructed medium, the artificial dielectric, has an effective 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...
and effective 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...
, as intended.
In addition, some artificial dielectrics may consist of irregular lattices, random mixtures, or a non-uniform concentration of particles.
Artificial dielectrics came into use with the radar microwave technologies developed between the 1940s and 1970s. The term "artificial dielectrics" came into use because these are macroscopic
Macroscopic
The macroscopic scale is the length scale on which objects or processes are of a size which is measurable and observable by the naked eye.When applied to phenomena and abstract objects, the macroscopic scale describes existence in the world as we perceive it, often in contrast to experiences or...
analogues of naturally occurring dielectrics. The difference between the natural and artificial substance is that the atoms or molecules are artificially (human) constructed materials. Artificial dielectrics were proposed because of the need for lightweight structures and components for various microwave delivery devices.
Artificial dielectrics are a direct historical link to metamaterials
NIM
The Nuclear Instrumentation Module standard defines mechanical and electrical specifications for electronics modules used in experimental particle and nuclear physics...
.
Seminal work
The term artificial dielectric was originated by Winston E. KockWinston E. Kock
Winston Kock was the first Director of NASA Electronics Research Center in Cambridge, Massachusetts from September 1, 1964 to October 1, 1966...
in 1948 when he was employed by Bell Laboratories. It described materials of practical dimensions that imitated the electromagnetic response of natural dielectric solids. The artificial dielectrics were borne out of a need for lightweight low loss materials for large and otherwise heavy devices.
Dielectric analog
Natural dielectrics, or natural materials, are a model for artificial dielectrics. When an electromagnetic field is applied to a natural dielectric local responses and scattering occur on the atomic or molecular level. The macroscopic response of the material is then described as electric permittivity and magnetic permeability. However, for this macroscopic response to be valid a type of spatial ordering must be present between the scatterers. In addition, a certain relation to the wavelengthWavelength
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...
is part of its description.
A lattice structure, with some degree of spatial ordering is present. Also, the applied field is longer in wavelength than the lattice spacing. This then allows for a macroscopic description expressed as electric permittivity and magnetic permeability.
In order to manufacture an artificial permittivity and permeability there must be a capability to access the atoms themselves. This degree of precision is impractical. However, in the late 1940s - in the domain of long wavelengths - it became possible to manufacture larger scale, and more accessible scatterers that mimic the local response of natural materials - along with a synthesized macroscopic response. In the radio frequency and microwave regions such artificial crystal lattice structures were assembled. The scatters responded to an electromagnetic field like atoms and molecules in natural materials, and the media behaved much like dielectrics with an effective media response.
The scattering elements are designed to scatter the electromagnetic field in a prescribed manner. The geometric shape of the elements—spheres, disks, conducting strips, etc. -- contribute to the design paramaters.
Rodded medium
The rodded medium (plasma medium) is also known as the wire mesh, and wire grid. It is a square lattice of thin parallel wires The initial research pertaining to this medium was conducted by J. Brown, K.E. Golden, and W. Rotman.External links
- A Luneburg Lens for the SKA Summary of the MNRF research project into the manufacture of a low-cost microwave refracting spherical lens for radioastronomy, proposes the use of artificial dielectrics.
- A lens constructed of uniform spherical shells seems feasible.