Shen-Yun Wang

Novel triple-band polarization-insensitive wide-angle ultra-thin microwave metamaterial absorber

We report the design, analysis, fabrication, and measurement of a novel microwave triple-band metamaterial absorber that obtains three distinct high absorption peaks. The absorber is constructed of a periodic array of new resonant structure printed on a dielectric material with the thickness of λ/67 at the lowest fundamental resonant frequency. By manipulating the periodic patterned structures, significantly high absorption can be obtained at three specific resonance frequencies. This kind of triple-band absorber is polarization insensitive, and the absorption peaks remain high with large angles of incidence for both transverse electric and transverse magnetic polarizations, which provide more efficient absorptions for non-polarized or oblique incident electromagnetic wave. The experimental results show excellent absorption rates and the characteristic of polarization-insensitive for a wide range of incidence angles in the desired frequencies, which are in good correspondence with the simulated results.

Low-loss metamaterial electromagnetically induced transparency based on electric toroidal dipolar response

In this paper, a low-loss and high transmission analogy of electromagnetically induced transparency based on electric toroidal dipolar response is numerically and experimentally demonstrated. It is obtained by the excitation of the low-loss electric toroidal dipolar response, which confines the magnetic field inside a dielectric substrate with toroidal geometry. The metamaterial electromagnetically induced transparency (EIT) structure is composed of the cut wire and asymmetric split-ring resonators. The transmission level is as high as 0.88, and the radiation loss is greatly suppressed, which can be proved by the surface currents distributions, the magnetic field distributions, and the imaginary parts of the effective permeability and permittivity. It offers an effective way to produce low-loss and high transmission metamaterial EIT.

Electromagnetically induced transparency with large delay-bandwidth product induced by magnetic resonance near field coupling to electric resonance

In this paper, we numerically and experimentally demonstrate electromagnetically induced transparency (EIT)-like spectral response with magnetic resonance near field coupling to electric resonance. Six split-ring resonators and a cut wire are chosen as the bright and dark resonator, respectively. An EIT-like transmission peak located between two dips can be observed with incident magnetic field excitation. A large delay bandwidth product (0.39) is obtained, which has potential application in quantum optics and communications. The experimental results are in good agreement with simulated results.

Cylindrical optimized nonmagnetic concentrator with minimized scattering

By using optimized transformation function, we research on a minimized scattering nonmagnetic concentrator, which can realize impedance matching at the inner and the outer boundaries. It has been demonstrated that the optimized transformation function method can improve the concentrating performance remarkably. The cylindrical anisotropic shell can be mimicked by radial symmetrical sectors which alternate in composition between two profiles of isotropic dielectrics, and the permittivity in each sector can be properly determined by the effective medium theory. The nonmagnetic concentrator has been validated by full-wave finite element simulations. We can believe that this work will improve the flexibilities for the EM concentrator design.

A Hexagonal Focused Array for Microwave Hyperthermia: Optimal Design and Experiment

Hexagonal focused arrays operating at 433 MHz for microwave hyperthermia have been designed for the first time by optimizing the power transmission efficiency of the system consisting of the transmitting hexagonal array, a receiving antenna introduced in the target area, with an equivalent phantom representative of human body in between. The excitations of the arrays are obtained by solving an eigenvalue equation from the scattering parameters of the total hyperthermia system, including the transmitting array, body-mimicking phantom, matching layer and a virtual receiving antenna located in the prescribed region. Simulation and experimental results have demonstrated a good focusing capability of the arrays, and such a design has the virtues of rapid implementation and adjustable focusing positions.

A linear polarization converter with near unity efficiency in microwave regime

In this paper, we present a linear polarization converter in the reflective mode with near unity conversion efficiency. The converter is designed in an array form on the basis of a pair of orthogonally arranged three-dimensional split-loop resonators sharing a common terminal coaxial port and a continuous metallic ground slab. It converts the linearly polarized incident electromagnetic wave at resonance to its orthogonal counterpart upon the reflection mode. The conversion mechanism is explained by an equivalent circuit model, and the conversion efficiency can be tuned by changing the impedance of the terminal port. Such a scheme of the linear polarization converter has potential applications in microwave communications, remote sensing, and imaging.

Tailoring electromagnetically induced transparency with different coupling mechanisms.

Tailoring electromagnetically induced transparency with two different coupling mechanisms has been numerically demonstrated. The results show that EIT based on simultaneous electric resonance and magnetic resonance has relatively larger coupling distance compared with that based on electric resonance near field coupling to magnetic resonance. The relatively large coupling distance is due to the relatively small susceptibility change. For EIT based on simultaneous electric resonance and magnetic resonance, not only incident electric field but also the incident magnetic field pays a role on the susceptibility of system. The influence of the incident magnetic field leads to relatively smaller susceptibility change compared with that based on electric resonance near field coupling to magnetic resonance.

Optimization for nonmagnetic concentrator with minimized scattering

Based on the generalized transformation for a nonmagnetic cylindrical concentrator, we present nonlinear coordinate transformations to realize excellent concentrating performance with minimized scattering. By matching the impedance at both the inner and outer boundaries and utilizing nonlinear optimization techniques, the best parameters of the nonlinear transformation can be determined. Results show that the concentrating power is sensitive to the impedance at the inner interface. In addition, an alternating layered system consisting of nonmagnetic isotropic materials is applied to experimentally mimic the concentrator, and excellent concentrating performances have been observed.

Split-loop resonator array for microwave energy harvesting

In this paper, we propose a three-dimensional split-loop resonator composed of a bended wire, a metallic ground slab, and a coaxial line loaded with a lumped matching resistor to mimic the input impedance of a rectifier. An ensemble of such resonators can function as an efficient energy harvester. The energy capture mechanism is explained by an equivalent circuit model. A 20 × 20 resonator array is fabricated to resonate around 2.45 GHz. The simulated and measured results indicate that the proposed resonator array has nearly unity energy conversion efficiency at the resonant frequency and is quite promising as an energy harvester in the microwave wireless power transmission system.

A novel high-selective bandpass frequency selective surface with multiple transmission zeros

The design, analysis, and measurement of a novel frequency selective surface (FSS) are proposed, which works with high selectivity in X-band and wide out of band rejection in C-band and Ku-band. The proposed FSS is achieved by cascading two-layer periodic arrays of unit cells based on square loop structure. Multiple transmission zeros are obtained for broadening the stopband on the both sides of the passband. The presented double-layer FSS is insensitive to the variation of incident angle and polarization of a striking plane electromagnetic wave. By studying the electric fields and currents excited in the proposed structure, it explains the passband characteristics and the multiple transmission zeros in the two stopbands. Experimental verifications are carried out, which are consistent with the simulated results.