Wen Xuan Tang

Convolution Operations on Coding Metasurface to Reach Flexible and Continuous Controls of Terahertz Beams

The concept of coding metasurface makes a link between physically metamaterial particles and digital codes, and hence it is possible to perform digital signal processing on the coding metasurface to realize unusual physical phenomena. Here, this study presents to perform Fourier operations on coding metasurfaces and proposes a principle called as scattering‐pattern shift using the convolution theorem, which allows steering of the scattering pattern to an arbitrarily predesigned direction. Owing to the constant reflection amplitude of coding particles, the required coding pattern can be simply achieved by the modulus of two coding matrices. This study demonstrates that the scattering patterns that are directly calculated from the coding pattern using the Fourier transform have excellent agreements to the numerical simulations based on realistic coding structures, providing an efficient method in optimizing coding patterns to achieve predesigned scattering beams. The most important advantage of this approach over the previous schemes in producing anomalous single‐beam scattering is its flexible and continuous controls to arbitrary directions. This work opens a new route to study metamaterial from a fully digital perspective, predicting the possibility of combining conventional theorems in digital signal processing with the coding metasurface to realize more powerful manipulations of electromagnetic waves.

A Broadband Bessel Beam Launcher Using Metamaterial Lens

An approach of generating broadband Bessel beams is presented. The broadband Bessel beams are produced by a gradient index (GRIN) metamaterial lens illuminated by broadband waveguide antenna. The metamaterial lens is constructed with multi-layered structure and each layer is composed of GRIN metamaterials. The metamaterials are designed as dielectric plates printed with metallic patterns in the center region and drilled by air holes near the edge, which operate in wide band. The metamaterial lens serves as a convertor which transforms the spherical beams emitted from feed into conical beams. The conical beams form quasi-Bessel beams in the near-field region. The aperture diameter of the GRIN lens is much larger than the operating wavelength to guarantee the transformation. In principle, this kind of metamaterial lens can produce Bessel beams at arbitrary distance by designing the refractive-index distribution. To verify the approach, we have designed, fabricated and tested a metamaterial lens. Full-wave simulation and experiment results have proved that the generated Bessel beams can be maintained in distance larger than 1 meter within a ranging from 12 GHz to 18 GHz.

Negative Index Material Composed of Meander Line and Srrs

A compact meander-line resonator is proposed in this paper, which could provide negative permittivity with a small unit-towavelength ratio. The meander-line structure is simple to be designed and is convenient to be controlled. Negative index materials (NIM) are realized using units composed of meander lines and split-ring resonators (SRRs), which have simultaneously negative permittivity and permeability in a specified pass band with relatively low loss. Simulation results show the identified properties of the meander-line resonator and NIM.

Tailoring Radiation Patterns in Broadband With Controllable Aperture Field Using Metamaterials

Metamaterials (MTMs) have advantages to control electromagnetic (EM) waves with high flexibility. However, the application of MTMs in antennas has mainly focused on controlling the phases of EM waves (e.g., to transform spherical waves into planar waves in flat lens and Luneburg lens). In this work, we experimentally demonstrate a method to control the radiation patterns in broadband using MTMs. By controlling the inhomogeneous refractive-index distribution of MTMs, both amplitudes and phases of EM waves on the antenna aperture are designed as required. We present an example to produce a new MTM lens antenna to possess high gain and low sidelobes simultaneously. Experimental results show excellent performance of the antenna in a broad band from 12 GHz to 18 GHz.

Suppressing Side-Lobe Radiations of Horn Antenna by Loading Metamaterial Lens

We propose a new approach to control the amplitude and phase distributions of electromagnetic fields over the aperture of a horn antenna. By loading a metamaterial lens inside the horn antenna, a tapered amplitude distribution of the aperture field is achieved, which can suppress the side-lobe radiations of the antenna. The metamaterial is further manipulated to achieve a flat phase distribution on the horn aperture to avoid the gain reduction that usually suffers in the conventional low-sidelobe antenna designs. A prototype of the metamaterial-loaded horn antenna is designed and fabricated. Both numerical simulations and measured results demonstrate the tapered aperture-field distribution and significant reduction of side-lobe and back-lobe radiations in the operating frequency band.

Electric and magnetic responses from metamaterial unit cells at terahertz

Metamaterials are artificial media with novel electromagnetic properties. We study the metamaterial unit cells at terahertz frequencies, investigate their electric and magnetic responses to the incident wave, and retrieve their effective material parameters. Simulation results reveal the origins of the effective permittivity and permeability and prove the predicted responses persuasively. In addition, we prove that symmetric resonant structures exhibit purer resonance properties than the asymmetric ones.

Realization of broadband acoustic metamaterial lens with quasi-conformal mapping

Recently, transformation acoustics has been widely recognized for its ability to convert the acoustic pressure field into desired spatial patterns, resulting in numerous functionalities with unique functionalities. Here, we propose and realize a two-dimensional flattened Luneburg lens using quasi-conformal mapping in the acoustic regime, allowing geometries with curved shapes to be converted into flat systems while the broadband and low-loss properties are preserved. Importantly, such an acoustic metamaterial lens is composed of purely isotropic materials that are easy to obtain via artificial structures. Our results may give rise to various applications, such as medical treatments and novel imaging systems.

A single metamaterial plate as bandpass filter, transparent wall, and polarization converter controlled by polarizations

We propose an anisotropic homogeneous metamaterial flat plate having multiple functionalities under different polarizations of incident waves. From the theoretical analysis based on Maxwells equations, we demonstrate that a single one-dimensional anisotropic metamaterial slab with the tailored constitutive parameters serves as a bandpass filter, a transparent wall, and a polarization converter under illuminations of differently polarized waves. We present a special structural unit to realize the tailored constitutive parameter tensors of the anisotropic metamaterial from which a three-dimensional metamaterial flat plate is designed and fabricated. The measured results agree very well to theoretical calculations and full-wave simulations, demonstrating the excellent performance of the polarization-controlled multiple functionalities of the single metamaterial plate.

Ultra-wideband filtering of spoof surface plasmon polaritons using deep subwavelength planar structures

Novel ultra-wideband filtering of spoof surface plasmon polaritons (SPPs) is proposed in the microwave frequency using deep subwavelength planar structures printed on thin and flexible dielectric substrate. The proposed planar SPPs waveguide is composed of two mirror-oriented metallic corrugated strips, which are further decorated with parallel-arranged slots in the main corrugated strips. This compound structure provides deep subwavelength field confinement as well as flexible parameters when employed as a plasmonic waveguide, which is potential to construct miniaturization. Using momentum and impedance matching technology, we achieve a smooth conversion between the proposed SPPs waveguide and the conventional transmission line. To verify the validity of the design, we fabricate a spoof SPPs filter, and the measured results illustrate excellent performance, in which the reflection coefficient is less than −10 dB within the −3 dB passband from 1.21 GHz to 7.21 GHz with the smallest insertion loss of 1.23 dB at 2.21 GHz, having very good agreements with numerical simulations. The ultra-wideband filter with low insertion loss and high transmission efficiency possesses great potential in modern communication systems.

Three-Dimensional Anisotropic Zero-Index Lenses

We propose, design, and experimentally demonstrate three-dimensional 3-D anisotropic zero-index lenses, which can improve the directivity of traditional antennas. We show that a 3-D anisotropic zero-index lens with εu → 0 is efficient to transverse magnetic (TM) modes and can decrease the beam width of the main lobe in the E-plane; while a 3-D anisotropic zero-index lens with μu → 0 is efficient to transverse electric (TE) modes and can reduce the beam width of the main lobe in the H-plane, in which u represents the propagating direction. If such two lenses are packed together, the directivity of both E- and H-planes is significantly improved. To verify this unique property, we design and fabricate four 3-D anisotropic zero-index lenses using metamaterials in the microwave frequency and perform the experiments in the anechoic chamber. Experimental results demonstrate that the beam widths of both E- and H-plane gain patterns are greatly reduced, which have good agreements to the full-wave simulations.