Polarization Of Incident Wave Research Articles

Wide-band microwave absorber with polarization insensitivity and incident angular stability using resistive ink for stealth application

A wide-band microwave absorber using five layers of resistive ink patterns is designed with a periodicity of 0.15λL, where λL denotes the wavelength at the lowest operating frequency. Symmetrically shaped resonators are patterned on five layers of FR4 substrates with air spacers between them. The fractional bandwidth of the absorber is 140% with absorption greater than 90% attained in the operating frequency range from 3.38 GHz to 19.5 GHz. Cross-polarized absorption of the structure is found to be less than 0.1%. Absorption is stable for a wide range of incident angles up to 40∘. Absorption behavior is found to be stable for both TE and TM polarized incident waves under normal incidence. Further, the mono-static radar cross-section is analyzed and found to be reduced below -40 db in the entire operating frequency.

Mueller Matrix Polarizing Power

The transformation of the states of polarization of electromagnetic waves through their interaction with polarimetrically linear media can be represented by the associated Mueller matrices. A global measure of the ability of a linear medium to modify the states of polarization of incident waves, due to any combination of enpolarizing, depolarizing and retarding properties, is introduced as the distance from the Mueller matrix to the identity matrix. This new descriptor, called the polarizing power, is applicable to any Mueller matrix and can be expressed as a function of the degree of polarimetric purity and the trace of the Mueller matrix. The graphical representation of the feasible values of the polarizing power provides a general view of its main peculiarities and features. The values of the polarizing power for several typical devices are analyzed.

Tunable multifunctional terahertz metasurface based on an indium antimonide medium

Active adjustable terahertz multifunctional devices are crucial for the application of terahertz technology. In this paper, we propose a composite metasurface structure based on an indium antimonide metal octagonal pattern, which achieves different functional switching by controlling the phase state of indium antimonide material under different ambient temperatures. When indium antimonide exhibits in the dielectric state, by stacking and encoding the unit cell, the designed metasurface has the functions of two-beam splitting beam superposition, vortex beam and quarter beam superposition, and dual vortex beam superposition for circularly polarized and linearly polarized wave incidence. When indium antimonide appears in the metallic state, the encoding metasurface alters the modulation function of incident circularly polarized and linearly polarized terahertz waves. This terahertz metasurface provides a new approach for the design of multifunctional devices that can flexibly regulate terahertz wave metasurfaces.

A broadband reconfigurable rasorber radome based on AFSR for RCS reduction

AbstractIn this paper, a broadband reconfigurable active frequency selective rasorber is proposed, which can be used as a radome for antenna radar cross section (RCS) reduction. By tuning the active components, the radome can achieve in‐band RCS reduction and reconfigurable absorptive/transmissive states. In the absorptive state, the max bandwidth with an absorption rate greater than 90% spanning from 1.62 to 5.37 GHz; in the absorptive/transmissive state, 2.2 GHz is the transmissive frequency with the insertion loss of 93% while absorbing in 0.94–2.06 GHz and 2.63–6.5 GHz, which demonstrate impressive characteristics of broadband and a high absorption rate. Additionally, the radome can maintain performance at ±35° angular incidence and is insensitive to incident wave polarization. Furthermore, it features a lightweight and low‐profile design, with a cell electrical size of just 0.078λ × 0.078λ × 0.066λ. The prototype test shows a noteworthy correlation with simulation. This study has wider applications in the electromagnetic stealth of communication antennas and aircraft, as well as in the control of electromagnetic pollution signals in space.

Design and analysis of a highly uniform five-band terahertz filter based on frequency selective surface

In this paper, a highly uniform five-band terahertz filter is presented, achieved by deforming two nested square ring structures. The metal pattern layer of the filter comprises a nested square ring structure with an inner and outer opening, and a metal strip connecting the inner and outer rings. Symmetrical openings divide nested square rings, breaking the current path and generating multiple metal bars of different lengths to excite dipole oscillations. Using metal strips to connect the inner and outer rings, the inner and outer resonant structures are integrated. Compared to a single resonant particle, the coupling of different single resonant particles amplifies the resonance of the combined structure, resulting in a wider stopband width and enhanced isolation between multiple passbands. A metal strip is also added to both ends of the outer ring opening to increase the equivalent capacitance of the outer ring, enhance the resonance, and improve out-of-band suppression. The transmission spectrum has five uniform passbands in the range of 1.3807–1.9917 THz, and the maximum passband ratio (MPR) of 3 dB bandwidth is about 1.16, and the ratio of 10 dB is about 1.17. The transmission coefficient of transmission zero is about 0.1, and the peak transmission coefficient of transmission peak is close to 1. The polarization of TE and TM incident waves is stable, and the filtering characteristics are good. Besides, the rectangular coefficients of the five passbands are all less than 1.33, showing excellent band selectivity. The resonance mechanism is explained by the Q value and electric field current distribution. The influence of structural parameter changes on filtering characteristics is also analyzed, and the main control parameters are found by using correlation analysis tools. From the changes in the MPR curve, it is verified that the structure parameters of the designed filter are in good condition. The multi-passband filter designed in this paper has uniform filtering characteristics, which is helpful to the development of terahertz multi-channel communication.

Strong chirality and asymmetric transmission effect in twisted bilayer α-MoO3 in terahertz band

Chirality and asymmetric transmission have wide-ranging applications in fields such as optics, chemical synthesis, pharmaceutical research, biological analysis, materials science and communication technology. In this work, we have demonstrated a terahertz (THz) device with strong chirality and asymmetric transmission effect based on a twisted bilayer α-MoO3. The unique optical response can be realized by adjusting structural parameters such as the thicknesses of the layers as well as the angle of relative rotation. It is found that the proposed structure achieves a giant circular dichroism (CD) value of 0.81 at 9.8 THz, which originates from the symmetry breaking of the structure. The phenomenon has been approved by the polarization conversion and the distributions of the electric field. In addition, the device exhibits the asymmetric transmission effect for circularly polarized wave incidence. The results show that the forward and backward transmissivity of circularly polarized waves with different handedness exhibit a significant difference of up to 0.55 at 9.2 THz. This work simultaneously achieves chirality and asymmetric transmission effect in the terahertz band, which paves the way for developing terahertz devices capable of chirality manipulation and optical isolation.

Polarization-independent full mode-converting elastic metasurfaces

This investigation proposes a novel elastic metasurface tailored to convert a longitudinal wave into a transverse wave and vice versa at an arbitrary refraction angle with full (100 %) conversion efficiency. The previous mode-converting elastic metasurface based on Snell's critical angle can convert a longitudinal wave into a transverse wave, but the refraction angle of the transverse wave cannot be smaller than the critical angle. In addition, the previous metasurface cannot convert a transverse wave into a longitudinal wave without generating a parasitic transverse wave. Here, we propose an elastic metasurface that enables full mode-converting transmission at an arbitrary refraction angle, regardless of whether the incident wave's polarization is longitudinal or transverse. To this end, we present a novel strategy to design unit cells that yield total mode-conversion efficiency as well as the desired phase shifts covering the entire 2π range. Shape optimization and geometry-flipping strategies were employed to design the unit cells constituting the metasurface. The concept of the unit cell's effective length was useful for the unit cell design. The designed metasurfaces were then used for various applications, such as longitudinal-to-transverse and transverse-to-longitudinal wave steering, splitting, and focusing. The performance of our metasurface was verified by ultrasonic experiments performed on an aluminum plate with the designed metasurface embedded. The realized full mode-converting transmission applicable for an arbitrary angle is expected to be critically valuable for nondestructive testing and medical ultrasounds requiring a specific elastic wave mode of the desired arbitrary beam pattern.

Influence of a Horizontally Polarized Wave Incidence on DOA Estimation by a Dipole Array Antenna in a Borehole

Influence of a Horizontally Polarized Wave Incidence on DOA Estimation by a Dipole Array Antenna in a Borehole

Low-RCS electromagnetic metasurface antenna based on shared-aperture technique

In this paper, a novel shared-aperture method of electromagnetic metasurface and antenna is proposed to obtain low radar-cross-section (RCS) performance. This method first designs low-RCS metasurface and conventional antenna independently, and then obtains novel low-RCS antenna by combining this metasurface with conventional antenna based on shared-aperture technique. Besides, current analysis and consequent local structure modification are also conducted to guarantee the antenna’s good radiation performance and broadband RCS reduction in the meantime. Using this method, a dual-layer polarization rotation unit cell is first proposed and its broadband working principle is investigated by both theoretical analysis and numerical comparison. Based on this unit cell, a broadband low-RCS metasurface is constructed. Then an initial shared-aperture metasurface antenna is obtained by substituting the middle cells in the metasurface with conventional patch antenna directly. Through careful analysis of surface current in radiation mode, the gain decrease of this metasurface antenna is revealed. On this basis, a limited removing strategy is put forward and some metasurface cells in the antenna is removed with the aid of current analysis. Consequently, an improved shared-aperture metasurface antenna is proposed. (The design flow of this metasurface antenna is displayed in the following Fig. 1) This improved antenna works from 6.3 GHz to 7.48 GHz, which is a bit wider than conventional patch antenna. Its gain is also higher than conventional antenna with the maximum improvement of 1 dB. Meanwhile, apparent RCS reduction is obtained from 6 GHz to 16 GHz for any polarized incident wave, and the reduction peak is larger than 20 dB. Fabrications and measurements are finally conducted. The good agreements of measured results and numerical calculations are achieved. The well-behaved radiation performance and broadband low-RCS property of this metasurface antenna verify the effectiveness of the proposed method. Different from most reported design method of low-RCS antenna directly from conventional antenna, the proposed method adopts a reverse thinking and converts the scattering optimization to radiation optimization, realizing the integration of metasurface and antenna, and making the design of low-RCS antenna easier and faster.

Holographic silver nanograting formation driven by TE0, TE1, and TE2 mode propagation in an AgCl slab Waveguide: Optical properties and analysis

Holographic silver nanogratings on the surface and within the volume, which have significant potential for data storage applications, are generated in silver chloride (AgCl) waveguides using a single laser beam exposure. This formation process leverages the interference between the polarized incident wave and the TEm modes propagating inside the AgCl waveguide. These plasmonic nanogratings are anisotropic nanostructures, demonstrating intriguing optical traits such as wavelength-specific linear dichroism and birefringence. The observed linear dichroism and birefringence in the holographic silver nanograting can modify the optical rotation and ellipticity of a probe beam traversing this anisotropic medium. Notably, volume holographic nanogratings function as complex nanogratings with a periodicity exceeding that of the incident wavelength. As a result, upon exposure, these complex nanogratings exhibit discernible light diffraction, while the surface holographic nanogratings do not show any diffraction pattern. Additionally, as the AgCl film thickness is increased and more complex nanogratings are formed within the AgCl waveguides, there is a noted reduction in the resulting birefringence.

Ultra-low radar cross-section realized by metasurface with nonuniform elements

A novel checkerboard metasurface is proposed to realize broadband ultra-low radar cross-section reduction (RCSR). The metasurface element is a non-uniform array which contains two uniform subarrays composed of 3 × 6 metallic patches. The reflection phases of the two subarrays can be compensated each other. Based on this characteristic, the non-uniform element reflects two orthogonally polarized waves with a phase difference shrinking to 180 ± 20° in a wideband from 11.2 to 23.0 GHz. When the non-uniform elements are arranged into a checkerboard structure, two co-polarized reflective waves with phase difference of 180 ± 20° are then generated for arbitrary polarized incident waves, resulting in an ultra-low RCS reduction. Simulation results show that the proposed checkerboard metasurface achieves at least 15 dB RCS reduction from 11.2 to 23 GHz (69%) for normal incident waves. The experimental results are good agreement with the simulations.

Synthesis of Polarization-Independent Perfect Anomalous Reflectors via Modulated Metasurfaces and an Analytical Design Model

A systematic approach to the synthesis of polarization-independent metasurfaces for anomalous reflection is presented. A fast analytical procedure is laid out to analyze the electromagnetic (EM) behavior of an impedance-modulated metasurface for arbitrary angles of incidence and reflection, subsequently serving as a means to provide the necessary impedance profile for reflection toward a specific direction, while capturing all propagation mechanisms, including surface waves (SWs) and nonlocal effects. We apply this procedure to design a metasurface for reflecting a normal incident wave to a different reflection angle, where the synthesized impedance is approximated by a discrete design, based on orthogonal metallic patches. This is done to provide control of both cases of incident wave polarization, while the unit cell analysis and extraction of equivalent impedance is easily performed by a full-wave computational eigenmode analysis of the unit cell. The unit cell design is performed by a simple fine-tuning process with minimal geometric modifications, and the actual discrete metasurface design is proven to agree well with the continuous model. The validity of the synthesis approach is perfectly demonstrated by the fabrication and experimental verification of a model design.

Controlling Plasmon Resonance of Gold and Silver Nanoparticle Arrays with Help of Liquid Crystal

The tunability of plasmonic resonances in gold and silver nanosphere arrays on a glass substrate, embedded in a liquid crystal matrix, was explored. The calculations involving the finite element method revealed that the optical properties of these arrays can be modulated by reorienting the liquid crystal. When the liquid crystal director was reoriented between planar and homeotropic configurations in the plane containing the incident wave polarization vector, the plasmonic resonance wavelength shifted within an approximately 100 nm range. A reduced shift of about 40 nm was observed when the reorientation occurred in the plane perpendicular to the polarization. Both metal nanosphere arrays showed notable near-field amplification. Gold achieved up to 18 times the amplification of the incident wave electric field, while silver reached 16 times but showed a remarkable 40 times amplification at the inter-band transition resonance wavelength. This research underscores the potential of using liquid crystal reorientation for controlling the plasmonic lattice resonance in metal nanosphere arrays, opening up new possibilities for adaptable plasmonic devices.

Dual channel transformation of scalar and vector terahertz beams along the optical path based on dielectric metasurface

Abstract The research on terahertz wave manipulation based on metasurfaces has gradually deepened, and the number of functions or electromagnetic control dimensions in a single device is constantly increasing. For the spatial dimension of terahertz field regulation, its design degrees of freedom have been expanded from a single transverse plane to the propagation path. In this paper, we propose a novel circularly polarization multiplexed metasurface for dual channel terahertz wave transmission control. Based on the spatial integration of two heterogeneous meta-atoms, which are spin-decoupled and isotropic, respectively, there are four phase channels that can be used at the same time, thus achieving different switching between vector and scalar beams in different circularly polarization channels along the optical path. For linearly polarized wave incidence, the device exhibits conversion between different vector beams longitudinally. To control more electric field components, we combine focused wavefront design with vector or scalar fields and utilize the focusing induced spin–orbit coupling effect, then complex amplitude switching of longitudinal electric field components is obtained. This article extends the manipulation of terahertz waves along the propagation trajectory based on metasurface from single to dual channel for the first time, providing a reference for the design of multifunctional meta-device in terahertz band.

Investigating Polarization-Sensitive Transmission and Reflection Metasurfaces for Advanced Wavefront Manipulation

This paper presents the design and optimization of a dual-band polarization-dependent metasurface capable of dynamically switching transmission and reflection characteristics. The metasurface is composed of three metallic patterns, with the bottom layer governing the reflection and transmission phase for both TE-polarization and TM-polarization states. The middle and top layers are strategically employed to ensure optimal transmission and reflection performance. The results confirm that the metasurface enables the transformation of the transmission band into a complete reflection band, and vice versa, through variations in the incident wave polarization. Remarkable transmission and reflection characteristics are achieved within the frequency ranges of 6.1–6.55 GHz and 8.9–9.3 GHz, respectively. The proposed metasurface offers promising applications in advanced communication systems and radar technology, enabling dynamic manipulation of electromagnetic waves.

A Low-RCS Circularly Polarized Reflectarray Antenna With a Linearly Polarized Feed

A low-radar cross section (RCS) circularly polarized (CP) reflectarray antenna with a linearly polarized (LP) feed is designed. The out-of-band RCS of the reflectarray for both the TE and TM polarized incident waves is reduced by replacing its ground with an absorptive frequency selective reflector (AFSR). A systematic methodology based on synthesis of the equivalent circuit model (ECM) is presented to expedite the design of the AFSR. The unit phasing element of the reflectarray is designed in such a way that it exhibits minimum coupling between the two orthogonal reflected LP-field components. Moreover, during the reflectarray construction, a novel phase synthesis is used which takes into account possible lowest of the existing mutual coupling while providing quadrature phase difference between the orthogonal LP components with minimum phase error. The proposed design is fabricated using 14×14 phasing elements to experimentally validate the numerically simulated results. The performance of the reflectarray is compared with a conventional reflectarray without the AFSR. It is observed that when the reflectarray is integrated with the AFSR, its gain is reduced only by 1.16 dB. However, its out-of-band RCS is reduced significantly. The 8-dB RCS reduction bandwidth can be observed from 3.55-7.2 GHz (67.9%) and from 11.85-14.21 GHz (18.11%). Moreover, it provides peak co-pol CP gain of 21.62 dBi, aperture efficiency of 41%, and 1-dB gain-bandwidth from 8.68-8.95 GHz, respectively.

Scattering Properties of Non-Gaussian Ocean Surface with the SSA Model Applied to GNSS-R

Global Navigation Satellite System Reflectometry (GNSS-R) is an emerging earth observation method for remote sensing of feature parameters using reflected signals from navigation satellites, and is a purely specular bistatic forward scattering observation means with special right-handed circular polarization incident wave. In this paper, the small-slope approximation model of non-Gaussian sea surface is used as the basis to construct the scattering model for the observation geometry of GNSS-R as well as the L-band characteristics, and the fully-polarization normalized bistatic radar scattering cross section (NBRCS) are simulated by the method of polarization synthesis to analyze the scattering characteristics under different wind speeds and directions on the ocean surface, which highlights the variation of NBRCS with wind direction, and the scattering modeling accuracy is improved by comparing with the data of CYGNSS. In addition, we adopt the observation geometry deviating from purely specular geometry, discuss the scattering azimuth angle, scattering influence, and the relative relationship between different polarizations of the scattering angle under the non-specular geometry.

Flexible Control of Phase and Polarization based on All‐Dielectric Metamaterials

AbstractA metasurface is a planar structure that can flexibly control the polarization, phase, and amplitude of incident electromagnetic waves. An all‐dielectric hexagonal cell structure to reduce the interaction between cells and achieve efficient parametric regulation of electromagnetic waves is proposed. The single resonant transmission phase and the geometric phase are superimposed to realize the composite phase unit structure and construct a multifunctional flat metasurface device. The designed metasurface can flexibly tune the phase and polarization of incident electromagnetic waves and enable multifunctional integration phenomena, such as polarization separation, light intensity convergence, and vector light generation, on a single metasurface.

Polarization-insensitive composite gradient-index metasurface array for microwave power reception

A composite gradient-index metasurface (C-GM) array for microwave power reception (MPR) operating at 5.8 GHz center frequency was introduced. The array is insensitive to the polarization of incident plane waves and possesses cosine gradient modulation characteristics, which can convert the incident plane waves into surface waves focused at the center of the array. The focused surface wave energy is then collected by an omnidirectional antenna and fed back to a single rectifier for radio frequency (RF) to direct current (DC) conversion, resulting in DC output. Simulation results show that the array can fully excite surface waves under different polarized plane wave excitations, and the omnidirectional antenna has good matching characteristics with the array, achieving an energy collection efficiency of 66.52%. The array was fabricated and measured, achieving an energy reception efficiency of 59.91% and an RF-DC conversion efficiency of 34.83%, which is consistent with the simulation results. The proposed C-GM array can capture higher electromagnetic power by simply increasing its size, without the need for additional rectifiers or complex matching networks, making it a flexible and efficient MPR solution for different application scenarios.

Ultra-broadband absorber based on multilayered graphene

We propose an absorber with ultra-broadband and independent polarization. The bandwidth of the absorber is widened by increasing the number of layers of patterned graphene and also decreased the sensitivity of structure on incident wave polarization. Full wave simulation is demonstrated from 5 GHz to 197 GHz (extraordinary relative bandwidth 190%) the absorption is obtained above 90%. The equivalent circuit model is used for obtaining the input admittance of the proposed absorber. By adjusting the input admittance in a wide frequency range, matching is obtained. The destructive interference and multiple resonances approach is used in designing the absorber. The polarization effect of incident waves on absorption and bandwidth is studied. The parametric study is accomplished by analyzing the absorber’s performance and optimizing the structure.