Bae-Ian Wu

A Study of Using Metamaterials as Antenna Substrate to Enhance Gain

Using a commercial software, simulations are done on the radiation of a dipole antenna embedded in metamaterial substrates. Metamaterials under consideration are composed of a periodic collection of rods, or of both rods and rings. The S-parameters of these metamaterials in a waveguide are analyzed and compared with their equivalent plasma or resonant structure. Farfield radiation is optimized by analytic method and is simulated numerically. The metamaterial is shown to improve the directivity.

Guided modes with imaginary transverse wave number in a slab waveguide with negative permittivity and permeability

The guidance conditions of modes with both real and imaginary transverse wave numbers inside a dielectric slab with negative permittivity and permeability are solved. We show that for real transverse wave numbers, cutoffs exist for all modes, unlike in conventional media where the first even mode is always propagating. In addition, we also show that guided modes exist for imaginary transverse wave numbers, with the power concentrated at the interfaces instead of having maxima inside the slab. A graphical method of determining the imaginary transverse wave numbers of the guided modes is introduced which clearly identifies the different conditions of propagation depending on the properties of the slab. In particular, propagation of guided waves inside less dense negative media is shown to be possible.

Planar focusing antenna design by using coordinate transformation technology

The coordinate transformation by using form-invariant transformations of Maxwell equations has led to an approach for designing devices with anisotropic metamaterial. In this paper, we present the design methodology for a low profile planar focusing antenna based on the transformation of a parabolic antenna. The electromagnetic behavior of the planar antenna is simulated by a two-dimensional finite element method and the results show that the planar antenna has the same performances as the parabolic antenna. The coordinate transformation technology provides an alternative design method to the conventional antennas.

Lateral displacement of a Gaussian beam reflected from a grounded slab with negative permittivity and permeability

A unique negative lateral shift is demonstrated in this letter for a Gaussian beam reflected from a grounded slab with both negative permittivity and permeability, which is distinctly different from a shift caused by a regular grounded slab. The incident beam is modeled as a tapered wave with a Gaussian spectrum. The waves inside and outside the slab are solved analytically from Maxwell’s equations by matching the boundary conditions at the interfaces. It is shown that the field values in all regions can be unambiguously determined. Numerical simulations are presented and the field values as well as the power densities are computed for all regions, and a dramatic negative lateral shift is observed when both e and μ are negative.

Extraordinary surface voltage effect in the invisibility cloak with an active device inside.

The electromagnetic field solution for a spherical invisibility cloak with an active device inside is established. Extraordinary electric and magnetic surface voltages are induced at the inner boundary of a spherical cloak, which prevent electromagnetic waves from going out. The phase and handness of polarized waves obliquely incident on such boundaries are kept in the reflected waves. The surface voltages due to an electric dipole inside the concealed region are found equal to the auxiliary scalar potentials at the inner boundary, which consequently gain physical counterparts in this case.

Čerenkov radiation in materials with negative permittivity and permeability

The mathematical solution for Cerenkov radiation in a novel medium, left-handed medium (LH medium), which has both negative permittivity and permeability, is introduced in this paper. It is shown that the particle motion in the LH medium generates power that propagates backward. In this paper, both dispersion and dissipation are considered for the LH medium. The results show that in such a material, both forward power and backward power exist. In addition, we show that the losses will affect the Cerenkov angle. The idea of building a Cerenkov detector using LH medium is introduced, which could be useful in particle physics to identify charged particles of various velocities.

Controllable left-handed metamaterial and its application to a steerable antenna

A controllable left-handed metamaterial based on a varactor-loaded S-shaped resonator structure is presented to realize an active radome. By controlling the phase properties of the radome, the antenna exhibits continuous scanning capability in a range of ±40°, which is confirmed by theoretical analysis.

Research Progress in Reversed Cherenkov Radiation in Double-Negative Metamaterials

We review the research progress in reversed Cherenkov radiation in double-negative metamaterials (DNMs) starting from the first experimental verification of the DNMs reported in 2001, including theories, numerical computation and simulation and experiments. We also discuss the potential applications to particle detectors and highpower microwave or millimeter-wave devices, including the oscillators and amplifiers, and the formidable challenges needed to be resolved before the benefits of using such artificial materials can be harvested. Corresponding author: Z. Y. Duan (zhyduan@uestc.edu.cn).

Lateral shift makes a ground-plane cloak detectable.

We examine the effectiveness of the ground-plane invisibility cloak generated from quasiconformal mapping of electromagnetic space. This cloak without anisotropy will generally lead to a lateral shift of the scattered wave, whose value is comparable to the height of the cloaked object, making the object detectable. This can be explained by the fact that the corresponding virtual space is thinner and wider than it should be. Ray tracing on a concrete model shows that, for a bump with a maximum height of 0.2 units to be hidden, the lateral shift of a ray with 45° incidence is around 0.15 units.

Application of coordinate transformation in bent waveguides

We apply coordinate transformations in the design of waveguides with bent geometry to reduce reflection at the incident port. It was found that in the case of metallic waveguides, by applying the transformation to the medium inside a right-angle bent waveguide, low reflection can be obtained. For the case of dielectric waveguides, this can also be done by applying the same transformation to the bent region containing both the dielectric core and its claddings. Our proposed technique provides an alternative method for designing bent waveguides with low insertion loss.