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J B Pendry

Publications and source records attributed to J B Pendry.

14 recordsLinked to original sources
PubMed2006

Metamaterial electromagnetic cloak at microwave frequencies.

A recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We describe here the first practical realization of such a cloak; in our demonstration, a copper cylinder was "hidden" inside a cloak constructed according to the previous theoretical prescription. The cloak was constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreased scattering from the hidden object while at the same time reducing its shadow, so that the cloak and object combined began to resemble empty space.

Journal Article↗
PubMed2006

Controlling electromagnetic fields.

Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

Journal Article↗
PubMed2005

Saturation of the magnetic response of split-ring resonators at optical frequencies.

We investigate numerically the limits of the resonant magnetic response with a negative effective permeability mu(eff) for single-ring multicut split-ring resonator (SRR) designs up to optical frequencies. We find the breakdown of linear scaling due to the free electron kinetic energy for frequencies above approximately 100 THz. Above the linear scaling regime, the resonance frequency saturates, while the amplitude of the resonant permeability decreases, ultimately ceasing to reach negative value. The highest resonance frequency at which mu(eff) < 0 increases with the number of cuts in the SRR. A LC circuit model provides explanation of the numerical data.

Journal Article↗
PubMed2005

Perfect corner reflector.

We numerically investigate the electromagnetic field radiated by a line source within a perfect lens [Phys. Rev. Lett. 85, 3966 (2000)] consisting of two orthogonal planes delimiting positive and negative index media. Use of a coordinate transformation [J. Phys. Condens Matter 15, 6345 (2003)] together with a well-adapted transfer-matrix method permits rigorous calculation of the vector field. We find that two negative corners combine to make a cavity that traps light along closed trajectories. Finally, we numerically show that the field presents some spatial oscillations with a period that is proportional to absorption sigma inside the negative materials as 1/ln sigma and that it is associated with an infinite density of states when sigma tends toward 0.

Journal Article↗
PubMed2005

Generating Bessel beams by use of localized modes.

We propose a novel method for generating both propagating and evanescent Bessel beams. To generate propagating Bessel beams we propose using a pair of distributed Bragg reflectors (DBRs) with a resonant point source on one side of the system. Those modes that couple with the localized modes supported by the DBR system will be selectively transmitted. This is used to produce a single narrow band of transmission in kappa space that, combined with the circular symmetry of the system, yields a propagating Bessel beam. We present numerical simulations showing that a propagating Bessel beam with central spot size of approximately 0.5lambda0 can be maintained for a distance in excess of 3000lambda0. To generate evanescent Bessel beams we propose using transmission of a resonant point source through a thin film. A transmission resonance is produced as a result of the multiple scattering occurring between the interfaces. This narrow resonance combined with the circular symmetry of the system corresponds to an evanescent Bessel beam. Because propagating modes are also transmitted, although the evanescent transmission resonance is many orders of magnitude greater than the transmission for the propagating modes, within a certain distance the propagating modes swamp the exponentially decaying evanescent ones. Thus there is only a certain regime in which evanescent Bessel beams dominate. However, within this regime the central spot size of the beam can be made significantly smaller than the wavelength of light used. Thus evanescent Bessel beams may have technical application, in high-density recording for example. We present numerical simulations showing that with a simple glass thin film an evanescent Bessel beam with central spot size of approximately 0.34lambda0 can be maintained for a distance of 0.14lambda0. By choice of different material parameters, the central spot size can be made smaller still.

Journal Article↗
PubMed2004

A chiral route to negative refraction.

Negative refraction is currently achieved by driving the magnetic permeability and electrical permittivity simultaneously negative, thus requiring two separate resonances in the refracting material. The introduction of a single chiral resonance leads to negative refraction of one polarization, resulting in improved and simplified designs of negatively refracting materials and opening previously unknown avenues of investigation in this fast-growing subject.

Journal Article↗
PubMed2004

Metamaterials and negative refractive index.

Recently, artificially constructed metamaterials have become of considerable interest, because these materials can exhibit electromagnetic characteristics unlike those of any conventional materials. Artificial magnetism and negative refractive index are two specific types of behavior that have been demonstrated over the past few years, illustrating the new physics and new applications possible when we expand our view as to what constitutes a material. In this review, we describe recent advances in metamaterials research and discuss the potential that these materials may hold for realizing new and seemingly exotic electromagnetic phenomena.

Journal Article↗
PubMed2004

Mimicking surface plasmons with structured surfaces.

Metals such as silver support surface plasmons: electromagnetic surface excitations localized near the surface that originate from the free electrons of the metal. Surface modes are also observed on highly conducting surfaces perforated by holes. We establish a close connection between the two, showing that electromagnetic waves in both materials are governed by an effective permittivity of the same plasma form. The size and spacing of holes can readily be controlled on all relevant length scales, which allows the creation of designer surface plasmons with almost arbitrary dispersion in frequency and in space, opening new vistas in surface plasmon optics.

Journal Article↗
PubMed2004

Terahertz magnetic response from artificial materials.

We show that magnetic response at terahertz frequencies can be achieved in a planar structure composed of nonmagnetic conductive resonant elements. The effect is realized over a large bandwidth and can be tuned throughout the terahertz frequency regime by scaling the dimensions of the structure. We suggest that artificial magnetic structures, or hybrid structures that combine natural and artificial magnetic materials, can play a key role in terahertz devices.

Journal Article↗
PubMed2001

Theory of extraordinary optical transmission through subwavelength hole arrays.

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface. Different regimes of tunneling (resonant through a "surface plasmon molecule," or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.

Journal Article↗
PubMed2001

Microstructured magnetic materials for RF flux guides in magnetic resonance imaging.

Magnetic resonance imaging and spectroscopy systems use coils, either singly or as arrays, to intercept radio-frequency (RF) magnetic flux from regions of interest, often deep within the body. Here, we show that a new magnetic material offers novel possibilities for guiding RF flux to the receiver coil, permitting a clear image to be obtained where none might otherwise be detectable. The new material contains microstructure designed according to concepts taken from the field of photonic band gap materials. In the RF range, it has a magnetic permeability that can be produced to specification while exhibiting negligible direct-current magnetism. The latter property is vital to avoid perturbing the static and audio-frequency magnetic fields needed to obtain image and spectral data. The concept offers a new paradigm for the manipulation of RF flux in all nuclear magnetic resonance systems.

Humans↗
PubMed1983

X-ray absorption near edge structure (XANES) for CO, CN and deoxyhaemoglobin: geometrical information.

We use the recently developed multiple scattering theory to give a quantitative analysis of the X-ray absorption near edge structure (XANES) of haemoglobin and some of its substituents. We demonstrate that the XANES may contain information not provided by the extended X-ray absorption fine structure (EXAFS) part of the spectrum about the coordination geometry around the Fe atom, and in particular discuss the sensitivity of the XANES to the orientation of the CN group in HbCN. The anisotropy of the system leads to a strong dependence of the calculated spectrum on the polarisation of the X-rays. We show how this effect can be exploited in further XANES structural studies.

Carboxyhemoglobin↗