arXiv subjects
Publications and source records attributed to A. D. Boardman.
In this letter, we present the first experimental study of a new chiral metamaterial consisting of toroidal wire windings. We show that the metamaterial exhibits three bands of circular dichroism in the GHz range. We discuss the response of the structure in terms of multipole moments, including the (magnetic) toroidal dipole moment.
It is shown that a new type of metamaterial, a 3D-array of toroidal solenoids, displays a significant toroidal response that can be readily measured. This is in sharp contrast to materials that exist in nature, where the toroidal component is weak and hardly measurable. The existence of an optimal configuration, maximizing the interaction with an external electromagnetic field, is demonstrated. In addition, it is found that a characteristic feature of the magnetic toroidal response is its strong dependence on the background dielectric permittivity of the host material, which suggests possible applications. Negative refraction and backward waves exist in a composite toroidal metamaterial, consisting of an array of wires and an array of toroidal solenoids.
The perfect lens property of a dispersive and lossy left-handed metamaterial (LHM) disk is exploited to superimpose a source of electromagnetic radiation onto its mirror image, formed as a result of reflection from a perfect electric conductor (PEC) or a perfect magnetic conductor (PMC). The superposition of a vertical wire-dipole antenna with its PEC-image results in an increase of the radiation resistance of the antenna compared to that of an antenna emitting in free space. On the other hand, if the same antenna is coupled to a PMC-image it is shown that the result is the formation of a non-radiating configuration. The finite-difference time-domain (FDTD) analysis is performed and this allows a detailed characterization of the systems. It is shown that the non-radiating system allows relatively large amounts of electromagnetic energy to be stored in the LHM-disk and that is indicative of strong electromagnetic fields inside the material. This property is employed in a second-harmonic generation (SHG) process and the potential of a non-radiating configuration as an efficient nonlinear device is demonstrated.
An expression for the electromagnetic field energy density in a dispersive, lossy, left-handed metamaterial, consisting of an array of split-ring resonators and an array of wires is derived. An electromagnetic field with general time-dependence is considered. The outcome is compared with previously published results. In the absence of losses, agreement with the general result for the energy density in a dispersive material is obtained. The formulae are verified using the finite-difference time-domain (FDTD) numerical method. The applicability of two commonly used permeability models to the problem of calculating the energy stored in an array of split-ring resonators is discussed.
The influence of an externally applied magnetic field upon classic cubic quintic dissipative solitons is investigated using both exact simulations and a Lagrangian technique. The basic approach is to use a spatially inhomogeneous magnetic field and to consider two important geometries, namely the Voigt and the Faraday effects. A layered structure is selected for the Voigt case with the principal aim being to demonstrate non-reciprocal behaviour for various classes of spatial solitons that are known to exist as solutions of the complex Ginzburg-Landau cubic-quintic envelope equation under dissipative conditions. The system is viewed as dynamical and an opportunity is taken to display the behaviour patterns of the spatial solitons in terms of two-dimensional dynamical plots involving the total energy and the peak amplitude of the spatial solitons. This action this leads to limit cycle plots that beautifully reveal the behaviour of the solitons solutions at all points along the propagation axis. The closed contour that exists in the absence of a magnetic field is opened up and a limit point is exposed. The onset of chaos is revealed in a dramatic way and it is clear that detailed control by the external magnetic field can be exercised. The Lagrangian approach is adjusted to deal with dissipative systems and through the choice of particular trial functions, aspects of the dynamic behaviour of the spatial are predicted by this approach. Finally, some vortex dynamics in the Faraday configuration are investigated.
It is shown that a pair of identical emitters (e.g. wire dipole antennas) in the focal points of a disc, made of left-handed metamaterial (a "perfect" lens), form a non-radiating electromagnetic configuration. The emitters are fed with voltages of equal magnitude and pi-out-of-phase. Detailed finite-difference time-domain (FDTD) modeling shows that there are non-propagating electromagnetic fields generated - fields that remain confined within the region between the emitters and the lens. The energy balance of the system shows that the radiation resistance of the system is very low. This means that the input power is converted to heat in the volume of the lens and only a small fraction of it is radiated. The system performance shows that disturbing the configuration of the non-propagating electromagnetic fields with the presence of an externally introduced object stimulates radiation. This suggests possible detector applications. In-phase feeding voltages are also studied with the consequence that the radiation resistance of the antennae is increased.
A finite-difference time-domain (FDTD) numerical analysis is used to demonstrate that a toroidal solenoid, coaxial with an electric dipole, is a remarkable non-radiating configuration. It can be used to measure the dielectric permittivity of any ambient matter. It becomes a directional radiator at an interface between two dielectric media, depositing energy in the material with the highest polarizability.
Some basic properties of nonradiating systems are considered. A simple connection is established between the existence of residual electromagnetic potentials and the current density spectrum of the system. The properties of specific configurations based on toroidal and supertoroidal currents are modeled with the finite-difference time-domain method. Possible applications are discussed. A design of a new type of nonradiating system, based on a left-handed metamaterial is proposed and the system performance is modeled numerically.