Peiheng Zhou

Ultra-Thin Reflective Metamaterial Polarization Rotator Based on Multiple Plasmon Resonances

We propose the design, simulation, and measurement of a broadband reflective metamaterial polarization rotator in the microwave region based on multiple plasmon resonances. An utra-thin wideband polarization conversion composing of arrays of oval ring pattern, a dielectric layer and a continuous metallic layer is further demonstrated both numerically and experimentally. Two plasmon resonances are generated by magnetic and electric resonances, leading to bandwidth expansion of cross-polarization reflection. The simulated results show that the polarization conversion ratio (PCR) is greater than 68.6% in 8.0-18.0 GHz with incidence angle up to 30° for both y-and x-polarized waves and the maximum conversion efficiency is nearly 100% at the two plasmon resonance frequencies. Experimental results under normal and oblique incidence agree well with simulated ones. The proposed rotator has applications in the area of polarization control.

Resistance Selection of High Impedance Surface Absorbers for Perfect and Broadband Absorption

High impedance surface absorbers comprising of lossless dielectric substrate and resistive pattern were studied based on equivalent circuit method. Resonant conditions in terms of potential resonant frequencies and corresponding equivalent resistance were deduced. Theoretical calculation, numerical simulation and experiment showed that expected absorption was obtained by matching the capacitance, inductance and the resistance. We demonstrated that the optimal resistance of frequency-dispersive was between 0 and 377 Ω. For square, dipole and square ring pattern, a mean resistance value was required to achieve broadband absorption. It offered a way to create broadband and perfect absorbers by controlling the surface resistance of sub-wavelength structures.

A Broadband Radar Absorber Based on Perforated Magnetic Polymer Composites Embedded With FSS

This paper presents a design method of broadband radar absorber (RA) combining together the features of frequency selective surfaces (FSSs), subwavelength hole array, and magnetic absorbing sheets. The absorber is constructed of a periodic array of square conducting patches embedded into a magnetic absorbing substrate perforated with circular hole arrays and backed by a metal ground. The absorption characteristics of the magnetic absorbing substrate are tuned and improved by means of perforating holes and embedding FSSs. After optimizing the dimensions of the holes and FSSs, the RA with a thickness of 2.4 mm achieves a reflection coefficient less than -10 dB from 6.3 to 17.3 GHz, which is nearly 3.6 times the bandwidth of the magnetic absorbing substrate. Meanwhile, the weight of the RA decreases by 15% due to the hole perforation, and the reflection coefficient is insensitive to incident angle from 0° to 30° for both TE and TM polarizations.

Realization of broadband reflective polarization converter using asymmetric cross-shaped resonator

Cross-shaped resonator (CSR) in metamaterial usually corresponds to adjust resonant characteristics. In this report, a simple and broadband reflective polarization converter is realized at GHz frequencies by breaking the symmetry of the CSR. The experimental results demonstrate that the polarization conversion ratio (PCR) over 0.8 is achieved from 8.3 GHz to 14.3 GHz for linearly polarized (LP) incident waves under normal incidence. The high polarization conversion efficiency can be sustained when the incident angle increases to 60 degrees. By taking advantage of surface current distribution and the interference theory, the physical mechanisms are elucidated in detail. Finally, the broadband polarization conversion can also be achieved by decreasing the geometrical parameters of the converter in the mid-infrared frequency range.

A Study on the Effective Permittivity of Carbon/PI Honeycomb Composites for Radar Absorbing Design

Radar absorbing honeycomb composites with different coating thicknesses are prepared by impregnation of aramid paper frame with solutions containing conductive carbon blacks (non-magnetic) and PI (polyimide). Expressions for the effective permittivity of the composites are studied and validated both in theory and experiment. It is found that a theoretical equivalent panel with given permittivity can be obtained to represent the honeycomb structure in the quasistatic approximation, which provides a feasible way to optimize the design of radar absorbing honeycomb structure by connecting the effective electromagnetic parameters with the unit cell dimensions. The effective permittivity is measured by a network analyzer system in the frequency range of 8-12 GHz and compared with the theoretical result.

Adjustable wideband reflective converter based on cut-wire metasurface

We present the design, analysis, and measurement of a broadband reflective converter using a cut-wire (CW) metasurface. Based on the characteristics of LC resonances, the proposed reflective converter can rotate a linearly polarized (LP) wave into its cross-polarized wave at three resonance frequencies, or convert the LP wave to a circularly polarized (CP) wave at two other resonance frequencies. Furthermore, the broad-band properties of the polarization conversion can be sustained when the incident wave is a CP wave. The polarization states can be adjusted easily by changing the length and width of the CW. The measured results show that a polarization conversion ratio (PCR) over 85% can be achieved from 6.16 GHz to 16.56 GHz for both LP and CP incident waves. The origin of the polarization conversion is interpreted by the theory of microwave antennas, with equivalent impedance and electromagnetic (EM) field distributions. With its simple geometry and multiple broad frequency bands, the proposed converter has potential applications in the area of selective polarization control.

Ultrabroadband Design for Linear Polarization Conversion and Asymmetric Transmission Crossing X- and K- Band

In this work, a high-efficiency and broadband reflective converter using ultrathin planar metamaterial (MM) composed of single-layered SRR is firstly realized. Numerical and experimental results demonstrate that the cross-polarization conversion reflectance above 0.84 is achieved from 8.6 to 18.6 GHz for linearly polarized (LP) incident waves under normal incidence. Subsequently, a multi-layered MM based on SRR enables a dramatic improvement of the recently demonstrated asymmetric transmission (AT) effect. Theoretical and measured results present that strong one-way transmission of two orthogonally polarized waves crossing C- and K- band has been observed. These two separated AT pass-bands have a function of selective polarization filter, which can be switched on/off by changing the polarization state of incident waves. The physical mechanisms are elucidated by taking advantage of electric fields and current distributions. Considering the broad bandwidth and the dual band, we believe that these two structures will be beneficial for designing polarization-controlled and selective transmission converter.

Prediction of Microwave Absorption Behavior of Grading Honeycomb Composites Based on Effective Permittivity Formulas

Microwave absorbing honeycomb composites with grading coating thickness are prepared by impregnation of aramid paper frame within water solutions of conductive carbon blacks. Based on effective medium method, grading impedance in the composites can be theoretically expressed by a linear approximation of the inversely tapered effective permittivity at wave propagation direction, which provides a feasible way to optimize the design of microwave absorbing honeycomb structures. The consistent result of calculations and experimental measurements for positive impedance grading design confirms the broadband absorption effect in high frequencies.

Spin wave mode transition induced by surface anisotropy and characteristic length in magnetic nanoparticles

In magnetic nanoparticles with cylindrical symmetry of the magnetization configurations, spin wave mode transition (SWMT) is predicted for the case of a surface anisotropy parallel to the uniform magnetization. Theoretical investigation has shown that a characteristic length can be determined to evaluate the spatial influence of the spin wave mode excited by surface anisotropy. This knowledge implies SWMT occurs as the particle size exceeds the corresponding characteristic length. An indirect experimental observation of the SWMT is also provided. These results can be utilized for ferromagneticresonances control in magnetic devices.

Modes Coupling Analysis of Surface Plasmon Polaritons Based Resonance Manipulation in Infrared Metamaterial Absorber

Surface plasmon polaritons (SPPs) and standing wave modes provide interesting and exotic properties for infrared metamaterial absorbers. Coupling of these modes promises further development in this field but restricted by the complexity of modes analysis. In this work, we investigate the general phenomenon of modes coupling supported by a metal (with grating)-dielectric-metal sandwich structure based on rigorous coupled-wave analysis (RCWA) method and experiment results. Through the analysis of fundamental modes, a new approach based on the boundary conditions is introduced to reveal the coupling mechanism and the corresponding resonance shifting phenomenon with simple but rigorous derivations. The strong coupling between SPPs excited on the dielectric-metal interfaces and rigorous modes of standing waves in the dielectric layer can be manipulated to improve the detection sensitivity of sensors and emissivity efficiency of infrared emitters.