Hengyi Sun

Broadband and Broad-angle Polarization-independent Metasurface for Radar Cross Section Reduction

In this work, a broadband and broad-angle polarization-independent random coding metasurface structure is proposed for radar cross section (RCS) reduction. An efficient genetic algorithm is utilized to obtain the optimal layout of the unit cells of the metasurface to get a uniform backscattering under normal incidence. Excellent agreement between the simulation and experimental results show that the proposed metasurface structure can significantly reduce the radar cross section more than 10 dB from 17 GHz to 42 GHz when the angle of incident waves varies from 10° to 50°. The proposed coding metasurface provides an efficient scheme to reduce the scattering of the electromagnetic waves.

Ultra-Low-Loss High-Contrast Gratings Based Spoof Surface Plasmonic Waveguide

Large metallic losses and short propagation lengths associated with surface plasmons (SPs) have long been considered as the obstacles which severely limit the practical applications of surface plasmonic waveguides. In this paper, we introduce the concept of dielectric spoof SPs (SSPs) and show that subwavelength high-contrast gratings (HCGs) offer a route to effectively suppress the losses and hence dramatically increase the propagation length of surface electromagnetic waves. We experimentally realized a wideband ultra-low-loss high-confinement plasmonic waveguide constructed by a high refractive-index dielectric array with deep-subwavelength periodicity on a metal substrate. Simulation and measurement results on the near-field distributions and S-parameters at microwave frequencies provide explicit evidences of strong field localization and show excellent transmission efficiency of HCGs-based SSPs across a broad frequency band. More importantly, the propagation length of the HCGs-based SSPs is proved to be at least more than one order of magnitude larger than that of metallic gratings-based SSPs at the same or even higher level of field confinement. Thus, the SSPs as experimentally realized in this paper hold great promise for numerous practical applications in ultra-low-loss and long-range transmission SP devices and circuits and may open up new vistas in SP optics.

Ultra-wideband and broad-angle linear polarization conversion metasurface

In this work, a metasurface acting as a linear polarization rotator, that can efficiently convert linearly polarized electromagnetic waves to cross polarized waves within an ultra wide frequency band and with a broad incident angle, is proposed. Based on the electric and magnetic resonant features of the unit cell, composed by a double-head arrow, a cut-wire, and two short V-shaped wire structures, three resonances, which lead to the bandwidth expansion of cross-polarization reflections, are generated. The simulation results show that an average polarization conversion ratio of 90% from 17.3 GHz to 42.2 GHz can be achieved. Furthermore, the designed metasurface exhibits polarization insensitivity within a broad incident angle, from 0° to 50°. The experiments conducted on the fabricated metasurface are in good agreement with the simulations. The proposed metasurface can find potential applications in reflector antennas, imaging systems, and remote sensors operating at microwave frequencies.

Non-concentric textured closed surface for huge local field enhancement

It has been demonstrated that textured closed surfaces are good platforms to support spoof localized surface plasmons with great field confinement and enhancement. Here, we propose a non-concentric textured closed structure to significantly increase the level of field confinement and enhancement. By properly texturing the closed surface with gradient-depth grooves, we show that the incoming electromagnetic waves can be highly confined and focused at the deepest groove on the closed surface. Moreover, we find that the field enhancement factor of this structure is quite sensitive to the polarization angle of the incident wave, which can find potential applications in polarization sensors and energy harvesting devices at microwave and terahertz frequencies.

Enhancing the Number of Modes in Metasurfaced Reverberation Chambers for Field Uniformity Improvement

The use of metasurfaces to increase the number of modes, lower the operating frequency, and improve the field uniformity in reverberation chambers (RCs) is investigated in this paper. The method used to improve the field uniformity and decrease the resonance frequencies is based on increasing the number of modes by using the concept of subwavelength cavities. The resonance frequencies of a RC with metasurface wall are derived and expressed analytically in terms of macroscopic characteristics. Simulation of the reflection phase of the unit cell is then given as a guideline to choose the required microscopic parameters of the designed metasurface. The mode density in such subwavelength RCs is then obtained using a numerical eigenmode solver. Compared to traditional RCs, a much higher modal density is obtained at low frequencies. The standard deviation of the field uniformity in the test volume of the RC corresponding to different types of metasurface walls is finally compared. It is shown that by increasing the number of modes in the RC at the lower band, the operating frequency decreases and the field uniformity of the RC is improved.

Tunable Spoof Surface Plasmons Bulleye Antenna

A tunable spoof surface plasmons antenna using sinusoidally modulated corrugated reactance surface based on a bulleye structure is proposed in this paper. The designed antenna is made of concentric metallic grooves etched on a metal plate, the depth of which is of sinusoidal periodic variation in the radial direction. This makes it possible that highly confined spoof surface plasmons along corrugated surface can be converted to radiation modes. The proposed bulleye antenna can work from 25.8 to 33 GHz and a bandwidth of 7.2 GHz and its main lobe can be directed at 30∘ from the vertical direction at 30 GHz. This antenna has a maximum gain of 15 dB and its main lobe can scan from 14∘ to 58∘ by tuning the frequency from 28 to 32 GHz.

Electromagnetic performance of surface-mounted permanent magnet machines with third harmonic injected rotor and overlapping winding

This paper compares the electromagnetic performance of three phase 24-slot/8-pole surface-mounted permanent magnet (SPM) machines with various permanent magnet shapes, in which the overlapping winding is employed. The permanent magnets (PM) on the rotor are designated as conventional one, sine shape, and sine shape with third harmonic injection. It is found that compared with machines with Sine-shaped PMs, the average torque of machines with Sine+3rd-shaped PMs can be improved by>9% but the cogging torque increases. The increased cogging torque can be reduced by optimizing the configurations of machines such as the width of slots, yoke and teeth. The third harmonic in the airgap flux density is introduced by the PM rotor of sine shape with third harmonic injection, and thus the iron losses are also compared among the machines with different PM shapes.

Influence of magnetization on performance of SPM machine with 3rd harmonic injected rotor

The influence of magnetization on the electromagnetic performance in the surface-mounted permanent magnet (SPM) machine with sinusoidal+3rd harmonic shaped rotor is investigated in this paper. The flux density, cogging torque, phase back-EMF, torque and loss are analyzed by finite element (FE) method. The differences of electromagnetic performance between the machines with parallel and radial magnetization manners are illustrated. It is found that the machine with parallel magnetization can produce high torque but also accompanied by high torque ripple compared to that with radial magnetization.

Adaptively generating the multiple-scattering characteristic basis functions

The order of the characteristic basis functions (CBFs) has an important influence on efficiency and accuracy of the multiple-scattering (MS) characteristic basis functions method (CBFM). When the object under analysis is divided into many blocks, two or three order CBFs may be enough to obtain accurate results. However, if the number of blocks is small, more high order of the CBFs may be required. In this paper, an adaptive method for generating MS CBFs is proposed. It can adaptively decide the order of CBFs. Thus, users can select the appropriate order without depending on their experience.

Realization of high-efficiency anomalous reflection using phase gradient metasurface at UHF

In this paper, a phase-gradient metasurface which consists of 7 arcuate cross-shaped metal-medium-metal units with different geometries is designed to realize anomalous reflection at 3GHz with 99% reflection efficiency of both x-polarized and y-polarized waves. The simulation results on near electric field distributions show excellent agreement of the anomalous reflection angle with theoretical analysis. This metasurface can be easily scaled to other frequency bands and find potential applications in optical communications.