Incident Wave Research Articles

Ground vibration isolation using mass scatters: A comparative study with trench barriers and wave‐impeding blocks

AbstractTraffic‐induced ground vibrations cause significant problems for residents and nearby structures. Reducing the effect of these vibrations on the neighboring environment is a key challenge, particularly in urban areas. This study presents both numerical and experimental investigations of the performance of mass scatters for screening ground vibrations. A three‐dimensional numerical model is validated and extended to conduct a comparative study on the efficiency of three geotechnical methods of isolation. These methods include trench barriers, wave‐impeding blocks (WIBs), and mass scatters. The results showed that mass scatters represent an efficient way of scattering ground vibrations, and their efficiency is mainly related to the weights of mass scatters and their natural frequency, which control the dynamic soil response in the frequency domain. Rigid trench barriers are less effective than soft ones, and their efficiency is more pronounced regarding the WIB. Soft barriers with a depth of an order of half of the wavelength can decrease the vibration levels by up to 50%, which is comparable to the performance of enormous mass scatters. The dimensions of WIBs must be chosen according to the wavelength of incident waves and the cutoff frequency of the topsoil layer. Considering the significant wavelength of traffic‐induced vibration, the use of trench barriers or WIBs becomes impractical and expensive; therefore, mass scatters appear to be an efficient and practical solution.

Frequency distribution of different joint slopes containing ceramic soil under seismic wave action

The dynamic response characteristics of high and steep slopes under the action of earthquakes and blasting was focused on, especially the frequency distribution and propagation laws, which are crucial for slope stability assessment. Using stress wave theory as the theoretical basis and advanced FLAC3D numerical simulation technology, we systematically analyze the frequency response of slope under different joint conditions under seismic waves. The nonlinear characteristics of reflected P-wave coefficient and the significant sensitivity of joint to incident wave frequency are revealed when the Angle of incident P-wave changes. The results show that with the increase of the incidence Angle of the incident P-wave, the reflection coefficient of the reflected P-wave decreases slowly at first and then increases sharply to 1.0. The reflection coefficient of the wave at the joint is more sensitive to the frequency of the incident wave. In a biplanar rock mass, multiple reflections of waves between structural planes produce transmitted waves with different time differences.

Flexible substrate based wideband polarization converter with extremely high polarization conversion ratio

In this article an anticipated reflection-mode cross-polarization converters (CPCs) are designed on a polydimethylsiloxane (PDMS) based flexible substrate operating in the GHz region. The proposed CPC metasurface comprises three layers where a flexible substrate is endwise between the resonating layer and ground layers. The converter can convert linear to circular and circular to cross-polarized waves at the frequency range of 5–8 GHz, as evidenced by the identical amplitude of Rxx and Ryx and a phase difference of 90°. More than 99 % of the polarization conversion ratio (PCR) was performed between the 6.75 and 9.07 GHz frequency range, while more than 80 % of the PCR was performed between the 6.0 and 10.73 GHz frequency range. The highest PCR values show nearly flawless energy conversion from an x-polarized incident wave to a y-polarized reflected wave. The PCR ratio of 80 % is achieved by this ultra-wideband linear-to-cross- and circular-to-cross-polarization converter. The anticipated converter's spectrum for all incidence angles between 0◦ and 60°. The PCR remained higher than 99 % over a wide incidence angle range to 60° without much performance degradation. The bending stability of the PDMS-based flexible substrate is also investigated up to 60°. The structure is fabricated on a flexible substrate, and the measured performance is compared with simulated results. Radar, antenna, and communications systems, as well as other cross-polarization converters, can utilize the transmitted wave's very high polarization purity result.

Effect of graphene on absorption spectrum of Si/SiO2 multilayer

In recent decades, photonic crystals have emerged as a key technology in several fields, including light management, photovoltaics, detection, and lasing. This success can be attributed to the ability to regulate electromagnetic waves, which can be achieved by, through a variety of techniques, disruption the periodicity of crystals. In this study, the introduction of graphene as a material defect in a one-dimensional photonic crystal consisting of six Si/SiO2 patterns is subjected to investigation. The calculations are performed using the transfer matrix method, with the experimental data serving as the input, following a protocol that involves exploring the variation of the absorption spectra as a function of the parameters of the material system and the incident electromagnetic wave. The findings illustrate that the absorption peak exhibits a pronounced dependency on the positioning of the material defect, the graphene layer thickness, and the incident angle. This paves the way for a more detailed inquiry into its potential utility in the domain of detection.

Gradient metasurface covered with water-based channels for reconfigurable RCS reduction

A gradient metasurface covered with water-based channels (GMWC) is proposed for RCS (radar cross section) reduction reconfiguration. The amplitude and phase response of the metasurface unit covered by the water-based channel (WC) is altered, which results in a change in the monostatic scattering of the GMWC. Under the normal incidence of X-polarized plane waves, the RCS reduction of GMWC shows different levels when different water channels are activated. The simulated results show that the average RCS reduction of GMWC increases from 5 dB to 20 dB in 5 dB steps in the 6 GHz to 8.2 GHz frequency band under four different reconstruction states (10000;01000;00100;00001). Besides, GMWC has an average RCS reduction of 10 dB within UWB (4–18 GHz) under state 10000. Finally, GMWC is fabricated and measured, and the measured results are in agreement with the simulated results. The RCS reduction reconfiguration characteristic of GMWC has potential application in target camouflage.

A novel multifunctional chiral metasurface with asymmetric transmission

The multiband, multifunctional chiral metasurface with asymmetric transmission exhibits significant potential for diverse applications in modern communication systems, ranging from enhanced signal modulation and polarization control to advanced beam steering and compact antenna design. This research presents a versatile and advanced chiral metasurface operating at multiple bands with diverse functionalities, including asymmetric transmission. The proposed metasurface effectively transforms an incoming Linearly Polarized (LP) wave into a Circularly Polarized (CP) wave. Additionally, it functions as a 90° polarization rotator for the incident LP wave. The design starts with an element of a 2 × 2 supercell comprising a Square Split Ring Resonator (SSRR) and an I-shaped resonator. The right diagonal elements of a supercell undergo scaling down, giving rise to a rotational asymmetry. Chirality is introduced into the design, and cross polarization conversion is enhanced by rotating all four elements by 90° relative to each other. On the back side of the substrate, each element undergoes a 90° rotation compared to its counterpart on the front side, realizing the asymmetric transmission feature. The incorporation of multiband and multifunctional features within a single supercell equips the subject chiral metasurface to be utilized in various engineering applications.

Effects of internal intervention in tubes on shock wave attenuation, formation and propagation of flame during high-pressure hydrogen release

Experiments on the impacts of the combination of fin structure and expansion chamber on shock wave attenuation, hydrogen ignition, and flame characteristics during high-pressure hydrogen release were carried out. The fin is a four-edged platform hollowed out on all sides. The inflated upper and lower tube walls are located 85, 95, and 105 mm away from the nickel burst disk. With the incident shock wave traveling through the fin, the reflected shock and the superposition of multiple reflected shock waves appear, and the reflected shock wave intensity can equal that of the release pressure. The decrease of the incident shock wave intensity behind the fin leads to the decrease of the non-uniformity of the mixed layer temperature, further causing the decrease of the flame propagation velocity. The presence of fins increases the probability of ignition in the fin region and the critical release pressure for ignition is significantly lower than that in the barrier free tube, mainly because the fin inside intensifies the hydrogen/air mixture, resulting in a lower minimum ignition energy required for self-ignition. Furthermore, the decrease of flame propagation velocity leads to the increase of hydrogen consumption inside the tube and the decrease of shock overpressure outside.

Three-dimensional mesoscopic investigation on the dynamic compressive behavior of coral sand concrete with reinforced granite coarse aggregate (GCA)

In the construction of island and reef engineering, coral concrete shows a good application prospect due to its abundant raw materials. However, the porous and fragile mechanical characteristics of coral reefs limit their use as coarse aggregate in the preparation of coral concrete materials. This study utilized hard and dense granite as the coarse aggregate and regarded coral sand concrete as a two-phase composite material consisting of spherical granite coarse aggregate (GCA) and coral mortar. It investigated the enhancement effect of granite on coral concrete from a microscopic perspective. Five 3D mesoscopic models with different GCA contents and randomly distributed aggregates were established to reveal the variation patterns and failure mechanisms of coral sand concrete under impact loading with GCA. The findings demonstrate that the K&C model can effectively simulate the dynamic compression behavior of coral mortar and granite materials. Under the action of a half-sine incident wave, the dynamic compressive strength of the samples increases with the increase in GCA, demonstrating that the addition of GCA can effectively enhance the impact resistance of coral sand concrete. As the content of GCA increases, the sensitivity of the samples to the loading wave amplitude also increases accordingly.

Advanced terahertz refractive index sensor in all-dielectric metasurface utilizing second order toroidal quasi-BIC modes for biochemical environments

We present a novel design for an all-dielectric metasurface ultra-sensitive refractive index (RI) sensor, characterized by a high-quality factor (Qf) and figure of merit (FOM). This design incorporates two high-order toroidal modes, including electric toroidal quadrupole (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{e}$$\\end{document}​) and magnetic toroidal quadrupole (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{m}$$\\end{document}​) based on quasi‑bound states in the continuum (q-BIC) resonances. Our findings demonstrate the feasibility of switching between \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{e}$$\\end{document} and \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{m}$$\\end{document}​ through various symmetry-breaking mechanisms. To excite these high-order toroidal modes, we explored several symmetry-breaking strategies, including complex structural designs, symmetry disruption, and variations in the incident wave angle. Symmetry breaking in the structure induces new modes in the transmission spectrum, which are highly advantageous for sensing applications due to the presence of dark modes. The designed metasurface exhibits the capability to sense a broad range of RI in diverse environments, particularly in biochemical fields. Sensitivity (S) is significantly enhanced by the excitation of new resonance modes and adjustments in the incidence angle, increasing from 217 GHz/RIU in a symmetrical structure to 512.3 GHz/RIU for \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{e}$$\\end{document}​. The FOM improves from 197 RIU 1 to 8538 RIU− 1 for \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{e}$$\\end{document}​ and 152,395 RIU− 1 for \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{m}$$\\end{document}​. Additionally, the Qf rises from 872 to 17,983 and 921,351 for \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{e}$$\\end{document}​ and \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:{Q}_{T}^{m}$$\\end{document}​, respectively.

Failure characteristics and stress wave propagation of red sandstone under explosion with varying gas energies

AbstractThis study designs a blasting loading device capable of changing the utilization of explosive gas by modifying the constraint conditions. The propagation of crack and stress waves in red sandstone under different explosive gases is recorded using digital image correlation technology and ultra‐dynamic strain gauges. Both methods are effectively validated against each other. The results showed that as the utilization of explosive gas increases, the explosive stress wave induces layer cracking at the specimen's far end and tensile failure at its near end. In addition, the larger the stress wave's amplitude, the greater the spatial attenuation coefficients of the compression and tension waves. The study ultimately deduces the propagation process of the incident wave and analyzes the influence of stress wave propagation on the specimen's failure characteristics.

Non-radiating sources in elastodynamics and their applications in the exterior cloaking

In this work, we develop a mathematical framework on constructed general non-radiating sources of elastic waves governed by the Navier equation via the approach of Helmholtz decomposition and potential theory in elastodynamics. Our study offers a rather comprehensive analysis. We first provide a rigorous justification of the general non-radiating sources. Based on the complete destructive interference of external elastic fields generated by specific radiating sources, a general non-radiating elastic source is derived and shown to possess a hidden interior wave field. For an incident wave, targets remain invisible within non-radiating source regions, and the geometry and boundary conditions of obstacles can be very general, which holds significant practical implications. Moreover, we introduce an effective novel method for designing such generalized non-radiating sources. To avoid the complex structure, we propose to use radiating source overlay construction on specific nodes at the boundary of non-radiating regions construction and derive sharp error estimates to evaluate the cloaking performance. The proposed scheme is capable of nearly cloaking arbitrary obstacles with a high accuracy. Numerical verifications validate the precision of our analytical findings.

Terahertz Sensing with Extraordinary Optical Transmission Hole Arrays

Purpose: The purpose of this paper is to substantiate the enhanced performance of hyperbolic anisotropic (HA) meta-surfaces at anomalous extraordinary optical transmission (EOT) resonances. These resonances exhibit distinct transmission peaks highly sensitive to environmental changes, making them particularly valuable for sensing applications. By demonstrating improved transmission efficiency and sensitivity, this study aims to contribute to developing advanced sensing technologies that leverage the unique properties of HA meta-surfaces in detecting minute variations in their surroundings. Methodology: To verify the enhanced sensing performance of anomalous EOT resonances, this study employs a well-established experimental method involving depositing a thin analyte layer of varying thicknesses onto the meta-surface. The study aims to determine which resonance condition provides optimal sensitivity by comparing the performance between regular and anomalous EOT resonances. It explores the improved performance of HA meta-surfaces at anomalous EOT resonances, which occur under certain non-standard conditions, offering potentially superior sensing capabilities compared to regular EOT. Findings: The results indicate that when the analyte is applied to the non-patterned side of the metasurface, the anomalous EOT resonance achieves superior sensing performance. This enhanced sensitivity can be attributed to the unique interaction dynamics between the incident THz waves and the meta-surface structure under abnormal conditions. Unique Contribution to Theory, Policy and Practice: This phenomenon is beneficial in the terahertz (THz) range, making HA meta-surfaces ideal for thin-film label-free sensing applications. The EOT resonance occurs due to the interaction between incident light and the periodic structure of the holes, leading to enhanced light transmission at specific wavelengths. The findings highlight the potential of using anomalous EOT resonances in HA meta-surfaces to develop highly sensitive and efficient sensors for detecting changes in thin films, paving the way for advanced sensing technologies in various scientific and industrial applications.

Hyperspectral Analysis of Silicon Nanowires Manufactured Through Metal-Assisted Chemical Etching

Abstract This study used hyperspectral imaging to analyze localized near-field interactions between incident electromagnetic waves and silicon nanowire (SiNW) arrays manufactured through catalytic etching of Si wafers for different durations. The results revealed that the unetched upper surface area on Si wafers and reflection of incident light decreased with increasing etching time. A light reflection band peaking at approximately 880 nm was generated from arrays etched for more than 1 h. We used six separate hyperspectral images to analyze the wavelength-dependent spatial optical responses of the fabricated SiNW arrays. The images revealed hot spots of light reflection from unetched Si surfaces in the wavelength range of 470–750 nm and a resonant peak at 880 nm for a photonic crystal derived from a random SiNW array. Accordingly, hyperspectral imaging enables the assessment of localized optical responses of SiNW arrays, which can then be optimized to cater to various applications.

A Study of Free Surface Agitation in a Shipyard Using Numerical Modeling

In recent years, the Port of Topolobampo, Sinaloa, Mexico, has experienced unusual free sea surface elevations, particularly during the months of November and December, affecting the shipyard areas, service docks, and berthing locations. This study focuses on analyzing the oscillatory behavior of free surface elevations in shipyard regions. A hydrodynamic model was employed to simulate the circulation and sea surface agitation, aiming to quantify the elevation magnitudes based on oceanographic and meteorological data from November of the preceding year. A 30-day numerical simulation was conducted, revealing the velocity fields associated with coastal currents and tides during November, as well as the interaction between incident waves and wave transformations due to protective structures. The results demonstrated accurate behavior in 95% of the simulation period, while anomalous elevations exceeding those specified in the design and operational guidelines of the Port of Topolobampo were observed during the final five days of the simulation. An ANOVA test was performed between the surface elevation and vertically integrated velocity to assess whether the deviations in the last five days were statistically significant compared to the rest of the simulation period. With a P-value of less than 0.05, the null hypothesis of no difference was rejected, confirming a significant variation. These findings suggest that the extreme values recorded should be considered for the potential redesign of shipyard infrastructure.

Study on the Design Method of High-Resolution Volume-Phase Holographic Gratings.

Volume-phase holographic gratings are suitable for use in greenhouse gas detection imaging spectrometers, enabling the detection instruments to achieve high spectral resolution, high signal-to-noise ratios, and high operational efficiency. However, when utilized in the infrared wavelength band with high dispersion requirements, gratings struggle to meet the demands for low polarization sensitivity due to changes in diffraction performance caused by phase delays in the incidence of light waves with distinct polarization states, and current methods for designing bulk-phase holographic gratings require a large number of calculations that complicate the balance of diffraction properties. To overcome this problem, a design method for transmissive bulk-phase holographic gratings is proposed in this study. The proposed method combines two diffraction theories (namely, Kogelnik coupled-wave theory and rigorous coupled-wave theory) and establishes a parameter optimization sequence based on the influence of design parameters on diffraction characteristics. Kogelnik coupled-wave theory is employed to establish the initial Bragg angle range, ensuring that the diffraction efficiency and phase delay of the grating thickness curve meet the requirements for incident light waves in various polarization states. Utilizing rigorous coupled-wave theory, we optimize grating settings based on criteria such as a center wavelength diffraction efficiency greater than 95%, polarization sensitivity less than 10%, maximum bandwidth, and spectral diffraction efficiency exceeding 80%. The ideal grating parameters are ultimately determined, and the manufacturing tolerances for various grating parameters are analyzed. The design results show that the grating stripe frequency is 1067 lines per millimeter, and the diffraction efficiencies of TE and TM waves are 96% and 99.89%, respectively. The diffraction efficiency of unpolarized light is more than 88% over the whole spectral range with an average efficiency of 94.49%, an effective bandwidth of 32 nm, and a polarization sensitivity of less than 7%. These characteristics meet the performance requirements for dispersive elements based on greenhouse gas detection, the spectral resolution of the detection instrument is up to 0.1 nm, and the signal-to-noise ratio and working efficiency are improved by increasing the transmittance of the instrument.

Generation of bessel-like beam by a binary ultrasonic lens

Bessel beams have already been used in acoustic tweezers, ultrasonic medical imaging, and Doppler velocity estimation due to their non-diffractive and self-healing properties. We proposed a binary ultrasonic lens, with ultra-thin planar periodic structures for efficient conversion of the plane wave into a Bessel-like beam. The effectiveness of long-axis focusing has been demonstrated through simulations and experiments with FWHM of 8.5 mm and 9.5 mm around 10 mm. By varying the operating frequency of the incident wave from 1.9 MHz to 2.2 MHz, the position of the long-axis focusing point can be adjusted experimentally from 23.05 mm to 28.95 mm. Additionally, the beam generated by the binary ultrasonic lens can form a focused sound field when passing through multi-layered tissues and the self-healing capability of the Bessel-like beam has been numerically validated, showing strong robustness. This binary ultrasonic lens for a Bessel-like beam would conform better to ergonomic and miniaturization requirements, and expand versatile applications in clinical diagnosis and therapy.

Influence of the shock wave-turbulence interaction on the swirl distortion in hypersonic inlet

This study uses the Large Eddy Simulation (LES) technique to conduct an exhaustive analysis of the flow characteristics within the Rectangular-to-Elliptical shape Transition (REST) inlet under Mach 6 conditions. It mainly focuses on investigating the influence of the shock wave-turbulence interaction on the swirl distortion at the inlet exit. At the design condition, characterized by 0° Attack and 0° Sideslip, the incident shock wave at the inlet lip undergoes multiple reflections within the boundary layer of the domain wall, culminating in the formation of turbulent structures. The first reflected shock wave has the highest energy, exerting a significant impact on the boundary layer and the exit swirl distortion. On the contrary, the energy of the incident shock wave is progressively reduced due to repeated reflections, which results in reducing the exit swirl distortion. Under off-design conditions, characterized by 6° Attack and 0° Sideslip as well as 6° Attack with 6° Sideslip, variations in the incoming flow make the incident shock wave move inward, decreasing the frequency of shock wave reflections and even significantly reducing the reflected shock waves under conditions of 6° Attack and 6° Sideslip. However, this results in significantly increasing the exit swirl angle and distortion intensity. The obtained results demonstrate that changes in the incoming flow conditions significantly affect the level of exit swirl distortion by modulating the shock wave-turbulence interaction, especially in terms of the positioning of the incident shock wave and the quantity of reflected shock waves. In addition, this paper studies the wall heat transfer coefficient of the inlet. The obtained results show that the interaction between shock waves and the boundary layer significantly affects the heat transfer coefficient. This study provides a foundation for the comprehension and prediction of the performance of hypersonic inlets across a spectrum of flight conditions, and for the guidance of the design and optimization of such inlets.

Second harmonic generation based on graphene hyperstructure for higher resolution and performance on top of achieving fundamental wave detection in theory

In this paper, an innovative one-dimensional graphene hyperstructure (GHS) is proposed, allowing for the concurrent detection of multiple physical parameters in both the fundamental and second harmonic generation. The sensing characteristics of GHS pertaining to magnetic field strength (B), incident electromagnetic wave angle (θ), and graphene thickness (dgt) are systematically investigated. Moreover, through the incorporation of second harmonic generation alongside fundamental detection, higher resolution and performance are achieved. The findings indicate an expansion of the measurement range for B, θ, and dgt, from 0.3∼0.5 T, 35∼55°, and 1∼6 layers to 0.3∼1 T, 35∼65°, and 1∼10 layers, providing increased flexibility and adjustability. Additionally, by leveraging nonlinear effects and widening the Fabry-Perot cavity width, this structure effectively enhances the quality factor (Q) from 2.94 × 102 to 1.95 × 105, resulting in a substantial improvement in sensing performance. This development holds tremendous promise in surpassing the diffraction limit and addressing high-Q value sensing requirements. In comparison to conventional detectors, the GHS not only enhances detection efficiency but also harbors the potential for multiple physical quantities detection. This forward-looking research is pivotal in its successful resolution of detector performance limitations, ushering in novel possibilities across diverse domains.

Far field operator splitting and completion in inverse medium scattering

Abstract We study scattering of time-harmonic plane waves by compactly supported inhomogeneous objects in a homogeneous background medium. The far field operator associated to a fixed scatterer describes multi-static remote observations of scattered fields corresponding to arbitrary superpositions of plane wave incident fields at a single frequency. In this work we consider far field operators for systems of two well-separated scattering objects, and we discuss the nonlinear inverse problem to recover the far field operators associated to each of these two scatterers individually. This is closely related to the question whether the two components of the scatterer can be distinguished by means of inverse medium scattering in a stable way. We also study the restoration of missing or inaccurate components of an observed far field operator and comment on the benefits of far field operator splitting in this context. Both problems are ill-posed without further assumptions, but we give sufficient conditions on the diameter of the supports of the scatterers, the distance between them, and the size of the missing or corrupted data component to guarantee stable recovery whenever sufficient a priori information on the location of the unknown scatterers is available. We provide algorithms, error estimates, a stability analysis, and we demonstrate our theoretical predictions by numerical examples.

Radio absorption in structures like artificial magnetic conductors at large angles of incidence of TM-polarized waves

The frequency-angular characteristics of the reflection of TM-polarized waves from thin (thickness up to 1/200 wavelength) artificial magnetic conductor (AMC) and radio absorber (RA) based on band-reflecting and band-passing gratings are presented. It is shown that the operating frequency bands of the AMC and RA expand tens of times when the angle of incidence changes from 0 to 89 degrees. In this case, the value of the ratio (is the difference in wavelengths at the edges of the absorption band and is the thickness of the RA) increases to 30.