Abstract: A new 2-D ultra-thin transmissive phase gradient metasurface (TPGM) with polarization-independent property is proposed based on the generalized Snell’s law of refraction. The super unit cell of the tri-layer TPGM consists of $6 \times 6$ suitably selected elements with $- {60}^\circ $ phase gradient at $x $ -direction and 60° phase gradient at $y $ -direction, respectively. The characterizations and working mechanisms of the TPGM are investigated in depth through theoretical calculation, comparative analysis, and eletromagnetic (EM) simulation. Four types of TPGMs with different functionalities are proposed based on the derived four-step design method. Numerical results show that the TPGMs are capable of manipulating the differently polarized wave independently. For demonstration and potential applications, an ultra-thin polarization beam splitter (PBS) working at X-band is implemented by a specially designed 2-D TPGM and is launched by a wideband horn antenna from the perspective of high integration, simple structure, and low cost. Numerical and experimental results coincide well, indicating that the PBS advances in many aspects such as separating and controlling the orthogonally polarized waves with a polarized splitting ratio better than 18 dB, obtaining a comparable bandwidth of more than 600 MHz, gaining a high transmission efficiency and also adopting a simple fabrication process based on the convenient print circuit board (PCB) technology.

Abstract: Microwave absorbing materials (MAMs) have numerous important applications in electronic communications, signal protection, radar dodging, etc. Although it has been proposed as a promising MAM, BaTiO3 has a high reflection coefficient at the interface with air, causing a large reflection. Thus, its efficiency of microwave absorption is not satisfactory. Here, we report that hydrogenation has largely improved the microwave absorption of BaTiO3 nanoparticles. Hydrogenation is performed on BaTiO3 nanoparticles by treating pristine BaTiO3 nanoparticles at 700 °C for 4 hours in a pure H2 environment. The enhanced microwave absorption efficiency with a reflection loss value (−36.9 dB) is attributed to the increased resonance of polar rotations with the incident electromagnetic field which is amplified by the increased interfacial polarization caused by the built-in electrical field along the boundaries between different grains created within these nanoparticles.

Abstract: The current study deals with the oblique wave trapping by bottom-standing and surface-piercing porous structures of finite width placed at a finite distance from a vertical rigid wall Using the Sollitt and Cross model for wave motion within the porous structure, the problems are analyzed based on the small-amplitude water wave theory in water of finite depth The solutions of the associated boundary value problems are obtained analytically using the eigenfunction expansion method and numerically using a multidomain boundary-element method In the boundary-element method, the boundary value problems are converted into integral equations over the physical boundaries The physical boundaries are discretized into a finite number of elements to obtain a system of linear algebraic equations Various aspects of structural configurations, in trapping surface gravity waves, are analyzed from the computed results on the reflection coefficients and the hydrodynamic forces Suitable arrangements of the rigid

Abstract: Expanding bandwidths and arbitrary control of technology remain key issues in the field of electromagnetic waves, especially in terahertz (THz) wave. In this paper, we propose a novel method to achieve broadband low-scattering THz characteristics with wide-angle and polarization independence by a 2-bit flexible and nonabsorptive coding metasurface. The coding metasurface is composed of four digital elements based on double cross metallic line for “00”, “01”, “10”, and “11.” The reflection phase difference of neighboring elements is about 90° over a broad THz frequency band and wide incident angles. The low scattering coefficients below –10 dB were achieved over a wide frequency band from 0.8 THz to 1.5 THz when the incident angle is less than 50° by coding the four elements sequences. This superior property is maintained when the flexible coding metasurface is wrapped around a metallic cylinder with different dimensions. These results present a novel method to control THz waves freely and demonstrate significant scientific value in practical applications.

Abstract: A low-loss and low-crosstalk surface-wave transmission line (T-line) is demonstrated at sub-THz in CMOS. By introducing periodical sub-wavelength structures onto the metal transmission line, surface plasmon polaritons (SPP) are excited and propagate signals via a strongly localized surface wave. Two coupled SPP T-lines and two quasi-TEM T-lines are both fabricated on-chip, each with a separation distance of 2.4 μm using standard 65 nm CMOS technology. Measurement results show that the SPP T-lines achieve wideband reflection coefficient lower than -14 dB and crosstalk ratio better than -24 dB, which is 19 dB lower on average than the traditional T-lines from 220 GHz to 325 GHz. The demonstrated compact and wideband SPP T-lines have shown great potential for future realization of highly dense on-chip sub-THz communications in CMOS.

Abstract: A wideband microstrip-fed open-slot antenna with dual-band circular polarization (CP) has been presented. A bent feeding structure and three slots, including a T-shaped and two inverted-L topologies etched in the ground plane, are designed to excite two orthogonal $E$ vectors with equal amplitude and 90 $^\circ $ phase difference (PD) for a radiating right-hand circularly polarized (RHCP) wave at 1.57 GHz and left-hand circularly polarized (LHCP) wave at 2.33 GHz. The two bands are the operated bandwidth of the global positioning system (GPS) and satellite digital audio radio (SDAR) service system. To improve the impedance bandwidth at the low-frequency band, a parasitic rectangular patch is added on the top plane of the substrate. Several resonances are merged, and thus, a wide impedance bandwidth is obtained. The measured impedance bandwidth of a reflection coefficient $ ranges from 1.45 to 3.93 GHz, and thus covers most of the commercial wireless communication systems, such as GPS, DCS, PCS, IMT-2000, WLAN, LTE, and WiMAX. The axial-ratio bandwidths are 65 MHz at the lower band (1.57 GHz) and 107 MHz at the upper band (2.33 GHz).

Abstract: In this paper, the composites of polyvinylidene fluoride (PVDF)/nickel (Ni) prepared through simple blending and hot-molding process have been investigated for dielectric, electromagnetic shielding, and radar absorbing properties In order to study complex permittivity of the composites in 40 Hz–20 MHz frequency range, impedance spectroscopy (IS) technique is used Besides, the complex permittivity and permeability in addition to shielding effectiveness (SE), reflection coefficient (backed by air), and loss factor are calculated using scattering parameters measured in X-band (82–124 GHz) by waveguide method Further, in X-band, a theoretical analysis of single layer absorbing structure backed by perfect electrical conductor is then performed A flanged coaxial holder has also been designed, fabricated, calibrated, and tested for electromagnetic interference SE measurement in the broad frequency range (50 MHz–18 GHz) The IS results indicate large enhancement in dielectric constant as a function of Ni lo

Abstract: This paper presents the results from several experiments aimed at determining the effectiveness of combined caissons with an internal rubble mound to dissipate incident sea wave energy. Techniques for assessing the reflection coefficient from wave tank data are discussed via a comparison between the established two- and three-probe methods and a new method using four probes. It is shown that obtaining reliable results for the incident and reflected waves requires the determinant of the linear system derived from the Fourier transform to be sufficiently greater than zero. This requirement was always satisfied for the three- and four-probe methods, but it was not always satisfied for the two-probe method. The experiments showed that the calculated reflection coefficient decreased when the ratio of the water depth, D, to the wavelength, L, increased. Increasing the caisson chamber width b and the upper frontal opening h also substantially decreased the reflection coefficient. Plotting the reflection ...

Abstract: Soliton transport in tubelike networks is studied by solving the nonlinear Schr\"odinger equation (NLSE) on finite thickness (``fat'') graphs. The dependence of the solution and of the reflection at vertices on the graph thickness and on the angle between its bonds is studied and related to a special case considered in our previous work, in the limit when the thickness of the graph goes to zero. It is found that both the wave function and reflection coefficient reproduce the regime of reflectionless vertex transmission studied in our previous work.

Abstract: We propose an effective microwave method for reference-plane-invariant and thickness-independent constitutive parameters measurement of thin materials. A function depending only on the interface reflection coefficient to facilitate fast computations of constitutive parameters is derived. In addition to the extraction of sample thickness, the method can also be applied to unique retrieval of constitutive parameters whose electromagnetic properties are yet unknown. We have performed an uncertainty analysis to examine how the accuracy of the method can be improved. Finally, we have compared the proposed method with other similar methods in the literature using measurements of distilled water and a thinner Plexiglas sample (1 mm). From the comparison, we note that the accuracy of our proposed method is not affected by any inaccurate knowledge of reference-plane positions and the sample length (or both) while those of compared methods are seriously decreased.

Abstract: We determined that the electromagnetic vertical transverse isotropic response in a layered earth can be obtained by solving two equivalent scalar equations, which were for the vertical electric field and for the vertical magnetic field, involving only a scalar global reflection coefficient. Besides the complete derivation of the full electromagnetic response, we also developed the corresponding computer code called EMmod, which models the full electromagnetic fields including internal multiples in the frequency-wavenumber domain and obtains the frequency-space domain solutions through a Hankel transformation by computing the Hankel integral using a 61-point Gauss-Kronrod integration routine. The code is able to model the 3D electromagnetic field in a 1D earth for diffusive methods such as controlled source electromagnetics as well as for wave methods such as ground penetrating radar. The user has complete freedom to place the source and the receivers in any layer. The modeling is illustrated with three examples, which aim to present the different capabilities of EMmod, while assessing its correctness.

Abstract: The sensor configuration of a magnetostrictive guided-wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work, we develop the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveforms measured using the magnetostrictive sensor, and estimate the time–frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. The reflection coefficients are calculated using the modal energies of the separated modes. Experimental results on a carbon steel pipe are presented, which show that the accurate and quantitative defect characterization could be enabled using the proposed technique.

Abstract: Global expressions are proposed for end-correction coefficients in micro perforated plates (MPPs) using non-dimensional parameters. MPPs are sound absorbers with small perforation diameters such that the Stokes boundary layers fill up almost the entire perforation. Sound absorption does not only occur within the perforation, but also takes place just outside of it. The latter contribution plus the outside inertia effect on the transfer impedance of the MPP are referred to as end-corrections. In order to determine them, an analytical solution employing the very thin Stokes layer assumption has been derived. However, this assumption requires empirical coefficients in the end-corrections for accurate results. To explore the effects of various parameters a numerical model is used. This model is verified with open-end reflection coefficient measurements. The most prominent result from this study is that compared to plate thickness, the ratio of perforation diameter to Stokes layer thickness (Shear number) and edge geometry affect the end-correction coefficients more significantly. The effect of plate thickness can be neglected for practical purposes, therefore, expressions for the end-corrections in terms of Shear number and edge geometry are provided. The relative error of these expressions is <3% compared to the numerical results.

Abstract: In this paper, a simple microstrip antenna for the radio frequency identification (RFID) applications and wireless local area network (WLAN) is presented. The antenna has two operating bands at 2.45 and 5.8 GHz, which are reserved for RFID applications and WLAN applications. The studied antenna design, analysis and characterization have been performed using CST electromagnetic simulation software. The antenna was analyzed with FR4 substrate. Reflection coefficient, VSWR and directivity results were simulated, presented and discussed. The designed antenna was fabricated on ArlonAD320 dielectric with relative permittivity of 3.2. SMA female connector is used for feeding with characteristic impedance of 50 Ω. The measured reflection coefficient of the proposed antenna is compared with the simulated one, good agreement is observed. The proposed antenna is simple in design and compact in size, providing broadband impedance matching, consistent omnidirectional radiation patterns and appropriate gain characteristics (>1.5 dBi) in the RFID frequencies regions.

Abstract: A linear chirp reflectometry with chirp stretching processing is used to detect and to locate low-voltage control and instrumentation cable splices and fault. Time delay information in the reflected signal is transformed to the instantaneous beat angular frequency by stretching process and the instantaneous beat angular frequency is estimated by Kalman smoother in order to obtain the high resolution time-frequency spectrum of the nonstationary signal. Based on the estimated instantaneous beat angular frequency, the magnitude and phase difference of the reflection coefficient are estimated by Kalman filtering. To verify the performance of the proposed method, comparative experiments are conducted to detect and to locate the splice under different conditions in comparison with traditional time-domain reflectometry method and the proposed method. In addition, to demonstrate the efficacy of the proposed method, the experiments are carried out for the assessment of state of the shunt and serial faults on cable under test. The location and reflection coefficient of a nominal, water submerged, an opened splice, shunt fault and serial fault ( $10~\Omega , 30 ~\Omega , 50~\Omega , 70 ~\Omega , 90 ~\Omega , 1 ~\text{k}\Omega $ ) are estimated by the proposed method. The proposed method exhibits advantages in that it uses the pulse compression to improve the range resolution and SNR of reflectometer simultaneously, and the proposed technique can accurately assess the state of the fault, which is closed to short fault or open fault.

Abstract: i»?The following contribution aims to test two synthetic aperture radar (SAR)-image-based techniques to obtain geometry and constitutive parameter information about low-permittivity lossless dielectric materials. While characterization of high-permittivity dielectrics is relatively affordable in SAR images, the low amount of power reflected back by lowpermittivity bodies makes their characterization a challenging task. The first proposed technique combines two illumination angles (normal and 45) to overcome the permittivity-geometry uncertainty appearing on each independent case. The second method makes use of the relationship between reflection coefficient amplitudes between two media, which can be directly extracted from the SAR image to provide an estimation of the dielectric object permittivity. Uncertainty of both techniques can be reduced by properly combining them. We validate these methods using a simulation-based application example in the form of a millimeter-wave portal-based system for concealed-object detection.

Abstract: Acoustic impedance inversion involves conversion of seismic traces to a reflection coefficient time series and then into acoustic impedance. The usual assumption for the transformation of poststack seismic data into impedance is that seismic traces can be modeled using the simple convolutional model. According to the convolutional model, a seismic trace is a normal-incidence record, which is an assumption that is strictly true only if the earth structure is composed of horizontal layers. In the presence of dipping layers, such an assumption is violated, which introduces bias in the result of impedance inversion. I implemented impedance inversion in the stratigraphic coordinate system, in which the vertical direction is normal to the reflectors and seismic traces represent normal-incidence seismograms. Tests on field data produced more accurate and detailed impedance results from inversion in the stratigraphic coordinate system, compared to impedance results using the conventional Cartesian coordin...

Abstract: In this paper, a rigorous method to analyze the electromagnetic scattering of an elliptically polarized plane wave by two concentric spheres buried in a dielectric stratified medium is presented. The interaction of the electromagnetic radiation with the stratified material is taken into account by means of the transfer matrix approach, in this way we can consider the stratified medium as an effective single interface. All the electromagnetic fields are expanded in series of spherical vector harmonics. The transmitted field through the stratified medium is obtained by means of the effective transmission coefficient. This field is scattered by the two concentric spheres, and the scattered field interacts again with the stratified material. The scattered-reflected and scattered-transmitted fields by the layered medium are computed by exploiting the plane-wave spectrum of the scattered field, considering the reflection and transmission of each elementary plane wave by the effective interface. The boundary conditions imposition on the spheres' surfaces leads to a linear system that returns the unknown coefficients of the problem. A numerical code has been implemented to compute the field over all the space. In order to compute the scattered fields, a truncation criterion has been proposed for the numerical evaluation of the series. Finally, to validate the presented method, comparisons between the results of the proposed code and the results of simulations with a software based on the finite element method have been implemented, showing very good agreement.

Abstract: We investigated the appearance of Chern-Simons terms in electrodynamics at the surface or interface of materials. The requirement of locality, gauge invariance, and renormalizability in this model is imposed. Scattering and reflection of electromagnetic waves in three different homogeneous layers of media is determined. Snell's law is preserved. However, the transmission and reflection coefficient depend on the strength of the Chern-Simons interaction (connected with Hall conductance), and parallel and perpendicular components are mixed.

Abstract: In this paper, an equivalent circuit model for a frequency-selective surface (FSS) embedded in a thick plasma layer is introduced. The plasma layer is a lossy and dispersive medium, and therefore, the equivalent model is not purely imaginary and consists of resistive elements as well as inductance and capacitance elements. First, a square patch FSS is simulated in a wide frequency range from 1 to 25 GHz by a full-wave electromagnetic software, and then all the circuit elements are calculated by genetic algorithm optimization to achieve reflection coefficient similar to the one obtained by simulation. It is shown that this model can mimic the simulated behavior with good approximation. Then values of different elements of the model through practical variations of cold plasma parameters are plotted, and the effects of electron density and collision frequency are investigated on circuit elements.

Abstract: An extended formulation of the intersection approach (IA) algorithm is presented to synthesize matrices of complex reflection coefficients for dual-polarized reflectarrays. The synthesis of complex reflection coefficients allows to impose copolar as well as cross-polar specifications, since these coefficients fully characterize the behavior of the unit cell. The implementation of the algorithm is based on the use of the fast Fourier transform (FFT) in both the forward and backward projectors of the IA, allowing for a highly efficient and fast synthesis process of dual-polarized reflectarrays. Although arbitrary restrictions can be enforced in the reflection coefficients, they might not be feasible for passive antennas. Hence, the unit cell is analyzed as a lossless and lossy passive two-port network and the restriction equations are derived for both cases involving amplitudes and phases of the reflection coefficients. The lossless constraints proved to be too restrictive so lossy restrictions should be applied to achieve feasible reflection coefficients for passive array design. Test cases are provided, which confirm that the algorithm is able to synthesize with success radiation patterns with copolar and cross-polar requirements with restrictions applied to the reflection coefficients.

Abstract: The travel time and amplitude of ground-penetrating radar (GPR) waves are closely related to medium parameters such as water content, porosity, and dielectric permittivity. However, conventional estimation methods, which are mostly based on wave velocity, are not suitable for real complex media because of limited resolution. Impedance inversion uses the reflection coefficient of radar waves to directly calculate GPR impedance and other parameters of subsurface media. We construct a 3D multiscale stochastic medium model and use the mixed Gaussian and exponential autocorrelation function to describe the distribution of parameters in real subsurface media. We introduce an elliptical Gaussian function to describe local random anomalies. The tapering function is also introduced to reduce calculation errors caused by the numerical simulation of discrete grids. We derive the impedance inversion workflow and test the calculation precision in complex media. Finally, we use impedance inversion to process GPR field data in a polluted site in Mongolia. The inversion results were constrained using borehole data and validated by resistivity data.

Abstract: The seabed reflection loss (shortly “bottom loss”) is an important quantity for predicting transmission loss in the ocean. A recent passive technique for estimating the bottom loss as a function of frequency and grazing angle exploits marine ambient noise (originating at the surface from breaking waves, wind, and rain) as an acoustic source. Conventional beamforming of the noise field at a vertical line array of hydrophones is a fundamental step in this technique, and the beamformer resolution in grazing angle affects the quality of the estimated bottom loss. Implementation of this technique with short arrays can be hindered by their inherently poor angular resolution. This paper presents a derivation of the bottom reflection coefficient from the ambient-noise spatial coherence function, and a technique based on this derivation for obtaining higher angular resolution bottom-loss estimates. The technique, which exploits the (approximate) spatial stationarity of the ambient-noise spatial coherence function, is demonstrated on both simulated and experimental data.

Abstract: Radiometric systems may comprise a radiometer, an antenna and a processor communicatively coupled together. The processor may provide a contact-focused output based on filtering or other processing of a raw radiometric output signal. The contact-focused output may facilitate determination of whether contact has been achieved and/or assessment of contact. A miniaturized reflectometer may be configured to determine an amount of reflected power from the antenna. The processor may be configured to determine a reflection coefficient of the reflected power determined by the reflectometer and to identify tissue type based on the reflection coefficient. Systems and methods for facilitating deeper temperature measurements of a radiometer are described.