Interface Reflection Research Articles

Microwave absorption and bandwidth study of Y2Co17 rare earth soft magnetic alloy with easy-plane anisotropy

The easy-plane anisotropy of the Y2Co17 rare earth soft magnetic alloy has high saturation magnetization and operating frequency, and good impedance matching. Therefore, it is expected to become a kind of high-performance microwave absorbing material. In this paper, Y2Co17 alloy was prepared by a reduction-diffusion method, and its micropowder was prepared as polyurethane (PU) based composite absorbing materials (Y2Co17/PU composites). The microwave properties of composites with different volume fractions were calculated. The composites showed outstanding absorption characteristics in the range of 20–30 vol%, and the minimum reflection loss (RL) was less than −50 dB. When the volume fraction was 25%, the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm, and the Ku-band at a thickness of 1.08 mm. The absorption mechanism was analyzed by the interface reflection model. The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses. The effective absorption bandwidth values were in good agreement with the theoretical expectation.

Correlation between Scattering Matrix, Return Loss and Interface Reflection Loss in Nicolson Rose Wear Approximation

The phenomenon behind the absorption of electromagnetic waves by absorbingmaterials is resonance phenomenon. When there is a similarity between the value of theimpedance of electromagnetic waves in the air and the impedance of the material, theabsorption of energy by the material is maximized. The phenomenon is measured using anauxiliary instrument, namely the Vector Network Analyzer. This instrument is very effective forcalculating the absorption value of electromagnetic waves. However, the Vector NetworkAnalyzer instrument which is mostly available in Indonesian research institutions cannot directlydisplay the reflection loss of the electromagnetic wave absorbing material. An effective methodthat is effective for calculating the absorption in electromagnetic wave absorbing material isNicolson Rose Wear method. In this article, we design a computational tool based on NicolsonRose Wear approximation to calculate the reflection loss values from scattering matrix andcomparing it with return loss, which is often mistook as reflection loss.

Analysis of the effects of interface reflections on FTIR transmission spectra of thin layer samples

The natural existence of optical reflectance on both sides of sample interfaces in FTIR absorption spectra of very thin samples can cause substantial distortions of the true spectra. This document illustrates this, by selected simulated examples, how this distortion depends on the thickness of the sample. For the present purpose, radiation is restricted to collimated and samples are restricted to homogeneous and isotropic. Implications for histopathology are also considered.

The construction and destruction of gold nanoparticle assembly at liquid-liquid interface for Cd2+ sensing

The analyte-induced aggregation of plasmonic nanoparticles (NPs) in the bulk solution have been widely employed in optical sensors. However, in trace detection, the slow diffusion kinetics of NPs and the ultralow concentration of analytes significantly limit the binding opportunity of the analytes, thus impose penalties on the sensitivity, reproducibility and response time of the sensors. Herein, we propose a novel sensing method with two working modes that based on the construction/destruction of NP arrays at the liquid-liquid interface (LLI). For the turning-on mode, the emulsion state of the two immiscible liquid phases and specific binding between Cd2+ and cysteine (Cys) assemble NPs into a liquid plasmonic mirror at the LLI whose reflectance has a positive relationship with the concentration of Cd2+. For the turning-off mode, the assembled NP arrays are intentionally destructed with the introduction of Cd2+ which aggregates neighboring NPs, reduces the interfacial reflectance. Compared with the conventional bulk aggregation method in a single phase, the NPs here that scavenge Cd2+ in the aqueous phase are condensed onto the LLI, boosting the local NP concentration and the diffusion kinetics for several orders. The prototypes achieve the limit of detection as 29.3 ± 0.03 μg L−1, and are applicable in real-life samples.

Automatic asphalt layer interface detection and thickness determination from ground-penetrating radar data

Ground-penetrating radar (GPR) has been widely used in asphalt pavement layer thickness measurement. It requires the detection of pavement layer interfaces, which could be accomplished via manual inspection. This may be subjective and cause inaccurate thickness measurements due to the field data noise. Existing layer interface detection methods for thickness determination usually require customized programming and/or manual inputs for execution, which could hinder real-time applications. This article proposes an automatic method for asphalt pavement layer interface detection and thickness determination using GPR. The effects of in-situ noise levels on thickness measurement accuracy were discussed. The Canny edge detector was used to estimate the two-way travel time (TWTT) range. The wavelet transform was used for noise cancellation. Layer interface reflections were identified using the matched filter method for thickness determination. Vibration effect during the continuous GPR survey was mitigated using the empirical mode decomposition (EMD) method. A simulation study was conducted. The proposed method provided more accurate measurements than manual inspection for thickness values from 10.16 cm (4 in.) to 2.54 cm (1 in.). GPR field test was performed, and results were compared to field core thickness measurements. Results show that GPR-measured thickness errors are 6.5 % and 1.6 % using manual inspection and the proposed method, respectively. The proposed method is automatic and can be implemented using existing programming functions, which may enable real-time asphalt pavement thickness determination during GPR surveys.

Dynamic strength, reinforcing mechanism and damage of ceramic metal composites

• We fully study the shock responses of ceramic metal composites via NEMD . • The interaction of shock-wave with the interface affects dislocation strengthening. • An abnormal softening effect is captured under shock loading . • The interface possesses negative effect on damage for composites. Shock tolerance is desirable for ceramic particles-reinforced metal matrix composites in many applications, where the dislocation dynamics evolution under the extreme load is the key but still elusive. Herein, we have investigated the dislocation motion and interaction under shock loading of SiC/Al nanocomposites using molecular dynamics simulations. We have demonstrated that the plastic deformation occurs at an impact velocity (0.5 km/s) lower than the Hugoniot elastic limit of aluminum due to the reflected shear wave effect. The Al/SiC interfaces act as a dislocation emitter to control dislocation multiplication density and slip direction, opening a new pathway to achieve ultrahigh-strength via shock loading. When the impact velocity (1.0 or 1.5 km/s) exceeds the Hugoniot elastic limit, the effect of nanoparticles on dislocation structure has changed from multiplying to retarding dislocations. The spall strength of composites improves due to dislocations pile-up at interface. Instead, the damage in the matrix is exacerbated, owing to the enhanced residual peak stress and interface reflection waves. In addition, the effect of abnormal shock softening determined by atomic velocity is revealed, which could be suppressed by increasing impact energy dissipation. Meanwhile, dynamic compressive strength depends on pressure and dislocation structures evolution. Our atomistic insights might be helpful in designing advanced shock-tolerant materials.

Unique interface reflection phenomena tailored by nanoscale electromagnetic boundary conditions.

Local interface response effects are neglected based on the traditional electromagnetic boundary conditions (EMBCs) in an abrupt interface model. In this study, generalized nanoscale EMBCs are derived with interface response functions (IRFs) representing field inhomogeneity across the interface based on integral Maxwell's equations. They are rewritten in two different forms that correspond to the equivalent abrupt interface models with interface-induced dipoles or charges and currents. Interesting behaviors of Brewster angle shifting, non-extinction at Brewster angle, and unique absorption or gain effects are revealed based on the advanced Fresnel formula. IRFs-controlled GH-shift and angular GH-shift of a Gaussian beam near the Brewster angles are generated by the gradient interface. These unique phenomena provide some guidance for measuring the IRFs and expanding interface photonics at the nanoscale.

Battery state-of-charge estimation using machine learning analysis of ultrasonic signatures

The potential of acoustic signatures to be used for State-of-Charge (SoC) estimation is demonstrated using artificial neural network regression models. This approach represents a streamlined method of processing the entire acoustic waveform instead of performing manual, and often arbitrary, waveform peak selection. For applications where computational economy is prioritised, simple metrics of statistical significance are used to formally identify the most informative waveform features. These alone can be exploited for SoC inference. It is further shown that signal portions representing both early and late interfacial reflections can correlate highly with the SoC and be of predictive value, challenging the more common peak selection methods which focus on the latter. Although later echoes represent greater through-thickness coverage, and are intuitively more information-rich, their presence is not guaranteed. Holistic waveform treatment offers a more robust approach to correlating acoustic signatures to electrochemical states. It is further demonstrated that transformation into the frequency domain can reduce the dimensionality of the problem significantly, while also improving the estimation accuracy. Most importantly, it is shown that acoustic signatures can be used as sole model inputs to produce highly accurate SoC estimates, without any complementary voltage information. This makes the method suitable for applications where redundancy and diversification of SoC estimation approaches is needed. Data is obtained experimentally from a 210 mAh LiCoO2/graphite pouch cell. Mean estimation errors as low as 0.75% are achieved on a SoC scale of 0–100%.

Bilayer-film-decorated microsphere with suppressed interface reflection for enhanced nano-imaging.

Microspheres as special optical lenses have extensive applications due to their super-focusing ability and outstanding resolving power on imaging. The interface reflection between the microsphere and sample surface significantly affects nano-imaging as exhibited in the form of the Newton's rings pattern in virtual images. In this work, a new scheme of decorating the microsphere with a dielectric bilayer thin film is proposed to suppress the interface reflection and thus enhance the imaging performance. The particle swarm optimization algorithm is performed with a full-wave simulation to refine the bilayer thin film decorated microsphere design, which is successfully realized via a novel fabrication strategy. Experimental imaging results demonstrate that the Newton's rings pattern in virtual images is substantially diminished. Both the imaging contrast and effective field-of-view of the microsphere nano-imaging are improved via this effective light manipulation scheme, which is also applicable to promoting the performance of the microsphere in other optical applications.

Revisiting Multiple-Scattering Principles in a Crustal Waveguide: Equipartition, Depolarization and Coda Normalization

Seismic waves radiated by small crustal earthquakes are prone to multiple mode conversions caused by reflection and transmission at interfaces, and scattering by small-scale heterogeneities in the bulk of the medium. The goal of this study is to clarify the complex interplay between volume scattering and interface reflections in crustal waveguides and how it will impact the crustal energy propagation. To carry out this task, we have incorporated a rigorous description of wave polarization in the context of Monte–Carlo simulations of the multiple-scattering process by introducing a five-dimensional Stokes vector. To shed light on the wave content of the regional short-period seismic wavefield, we investigate the asymptotic partitioning of seismic energy onto P, SV and SH polarizations in the coda, as well as the angular distribution of energy flux in the waveguide. In full elastic space, equipartition theory predicts that (1) the energy ratio between P- and S-wave energies tends to $$\beta ^3/(2\alpha ^3)$$ , (2) an equal distribution of energy among SV- and SH-waves and (3) that energy fluxes are isotropic. In the presence of interfaces, we find that the isotropy of the wavefield is systematically broken and that energy ratios are shifted to the detriment of P-waves and in favor of SV-waves in a non-absorbing medium. This implies that a residual polarization is preserved in the waveguide. Through an extensive parametric study, we illustrate in detail how the anisotropy of the wavefield, the partitioning ratios and the shear wave polarization depend on the crustal attenuation parameters. The role of the initial polarization at the source has also been examined. In the case of an explosion and a shear dislocation with equal magnitude, we find that the energy level in the coda can differ by more than one order of magnitude when the effect of crustal scattering becomes very weak compared to reflections or transmissions at interfaces. When comparing different shear dislocation mechanisms, we find that the energy level in the coda can differ by up to 60%. While equipartition, depolarization and coda normalization remain fundamental guides to our understanding of the coda, their application requires a good a priori knowledge of the attenuation properties of the crust.

Development of temperature-responsive transmission switch film (TRTSF) using phase change material for self-adaptive radiative cooling

To overcome the problem of unable automatic turn on and off response to the ambient temperature of current static radiative cooling systems, we prepared a series of temperature-responsive transmission switch film (TRTSF) samples using n-octadecane as phase change material (PCM) and polydimethylsiloxane (PDMS) as carrier material. The phase change cycle permeability analysis showed that the TRTSF samples with PCM content above 30.0 w.t.% exhibit a serious leakage problem due to a large number of holes on surface. The TRTSF samples with 10.0–30.0 w.t.% PCM content were further analysed by Differential scanning calorimetry (DSC) and Thermogravimetry (TG), and compared with the theoretical PCM contents, which verified the reliability of the curing results of PCM in TRTSF from various aspects. The ultraviolet–visible light-near-infrared (UV–VIS-NIR) and mid-infrared (MIR) transmittance characterization of TRTSF revealed that the switching effect was obvious during solid–liquid phase change process. TRTSF microstructure analysis revealed that the particle size distribution of PCM microspheres was between 1 μm and 6 μm. The UV–VIS-NIR band (wavelength at 0.25–1.1 μm) transmittance of PCM decreased to less than 3.7% after solidification due to the interfacial reflectance of solid PCM particles increased to more than 66.8% even in monolayer, thus the solid PCM particles would produce Mie scattering and isolate the internal and external radiation heat transfer. However, the TRTSF can be used as the radiative cooling emission layer since its optical properties were similar to the PDMS when the PCM is in liquid phase. Overall, the TRTSF film prepared in this study successfully adapted the temperature switching properties, also, is expected to be further used for the development of self-adaptive radiative cooling systems.

Tunable bilayer dielectric metasurface via stacking magnetic mirrors.

Functional tunability, environmental adaptability, and easy fabrication are highly desired properties in metasurfaces. Here we provide a tunable bilayer metasurface composed of two stacked identical dielectric magnetic mirrors. The magnetic mirrors are excited by the interaction between the interference of multipoles of each cylinder and the lattice resonance of the periodic array, which exhibits nonlocal electric field enhancement near the interface and high reflection. We achieve the reversible conversion between high reflection and high transmission by manipulating the interlayer coupling near the interface between the two magnetic mirrors. Controlling the interlayer spacing leads to the controllable interlayer coupling and scattering of meta-atom. The magnetic mirror effect boosts the interlayer coupling when the interlayer spacing is small. Furthermore, the high transmission of the bilayer metasurface has good robustness due to the meta-atom with interlayer coupling can maintain scattering suppression against positional perturbation. This work provides a straightforward method to design tunable metasurface and sheds new light on high-performance optical switches applied in communication and sensing.

1300 nm Semiconductor Optical Amplifier Compatible With an InP Monolithic Active/Passive Integration Technology

In monolithic photonic integrated circuits (PICs), an optimized active/passive integration is needed to provide efficient coupling and low amount of interface reflections between amplifiers and passive components. A 1300 nm semiconductor optical amplifier (SOA) on InP substrate and optimized for butt-joint reflections is investigated. Material performance were assessed from measurements of broad area lasers. Room temperature operation reveals 1.2 W single facet output power with threshold current around 100 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> per well. Characteristic temperatures of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 75 K and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 294 K were obtained. A compact model description of the SOA, suitable for the design of PICs and rate equation analysis, was applied to parametrize the unsaturated gain measurements. Current injection efficiency of 0.65, transparency carrier density of 0.57 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , and free carrier absorption losses up to 15 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> were extracted from fitting the data. The model is verified with measurements of optical gain saturation. A modal gain of 15 dB for a 600 μm long narrow ridge SOA leads to output saturation power higher than 30 mW at 7 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This building block contributes to the development of an InP monolithic integration technology in the 1300 nm range, which can enable the use of photonic integrated circuits in many kind of applications.

Electromagnetic wave absorbing properties of coconut shell-derived nanocomposite

Lightweight and low-cost carbon material have recently been considered as a promising microwave absorbing material (MAM), especially, biomass-derived carbon with diverse porous structures has attracted a lot of attention, because they are sustainable and easily modifiable. The excellent electrical conductivity of carbon material facilitates the attenuation of microwaves. At the same time, the application of a single carbon material can lead to a dramatic increase in interfacial reflection of microwave. Therefore, the carbon materials need to be modified or assembled into specific structures. Here, the coconut shell, a common biomass from agricultural by-product, is combined with magnetic material to form a high-quality microwave-absorbing nanocomposite. The coconut shell-derived nanocomposite possesses a hierarchical structure, in which the carbon matrix is laminated in sheets, with square magnetic Fe/Fe3C cubes evenly distributed on the surface of the carbon matrix. The minimum reflection loss (RLmin) of the nanocomposite reaches −48.87 dB at 2 mm in 16.40 GHz, and the widest effective absorption bandwidth (EAB) could be up to 7.94 GHz (from 10.06 to 18.00 GHz). The superior microwave absorption of the nanocomposite is stemmed from the synergy of dielectric-magnetic effect and enhanced interfacial polarization. This novel carbon-based composite is expected to hold great promise for practical applications in microwave absorption.

Terahertz Multiple Echoes Correction and Non-Destructive Testing Based on Improved Wavelet Multi-Scale Analysis

During terahertz (THz) non-destructive testing (NDT), multiple echoes from the sample interface reflection signals are mixed with the detection signals, resulting in signal distortion and affecting the accuracy of the THz NDT results. Combined with the frequency property of multiple echoes, an improved wavelet multi-scale analysis is put forth in this paper to correct multiple echoes, allowing the maximum retention of detailed signal information in contrast with the existing echo correction methods. The results showed that the improved wavelet multi-scale analysis enhanced the continuity and smoothness of the image at least twice in testing adhesive layer thickness, prevented missing judgments and misjudgments in identifying characteristic defects, and ensured accurate detection results. Hence, it is of great significance for evaluating the THz NDT results.

Controllable thermal treatment of reduced graphene oxide for tunable electromagnetic wave absorption performance

The complex process of reduced graphene oxide (RGO) preparation hindered its merits of lightweight, high surface area, and notable dielectric loss in electromagnetic (EM) wave absorption performance. This work introduced a controllable ethanol-assisted hydrothermal and annealing treatment to simplify the preparation of RGO with improved agglomeration and achieved tunable EM wave absorption performance. Among series of RGO materials fabricated with different annealing temperatures, the optimized RGO achieves a strong reflection loss of −49.9 dB with a thickness of 3.9 mm, and a broad effective absorption bandwidth of 7.65 GHz with a thickness of 3.1 mm based on a 2 wt% filler content in the matrix. The vacancy defect density and C/O ratio of RGO were demonstrated to be correlated to the behavior of conductive loss and polarization relaxation for RGO and the interface reflection of EM wave. This controllable thermal treatment successfully enabled the simple preparation of RGO with reduced agglomeration and tunable EM wave absorption and effectively contributed to fabricating other carbon-based dielectric/magnetic materials as high-efficiency electromagnetic absorbers in future.

Switchable distributed Bragg reflector using GST phase change material.

We demonstrate the design, fabrication, and measurement of a switchable distributed Bragg reflector (DBR) that can be thermally switched from a close-to-zero reflective OFF state to a more than 70% reflection in its ON state. This is accomplished using a multilayer thin film stack using germanium (Ge) and the phase change material (PCM) Ge2Sb2Te5 (GST). The refractive indexes of Ge and GST in the amorphous state are closely matched, resulting in a nearly zero interface reflection. With appropriate antireflection coatings at the cavity ends, the overall reflection can be designed to be close to zero. When the GST is switched to the crystalline state, the refractive index contrast between the Ge and GST layers will increase dramatically contributing to the DBR reflection. Using this unique feature, we were able to design and experimentally demonstrate more than 70% reflection in the ON state and close to zero reflection in the OFF state at a wavelength of 2 µm.

Synergistic effect of niobium oxide and cobalt on electromagnetic properties of dodecahedron-carbon composites

Here, we report niobium pentoxide/niobium dioxide/cobalt/porous carbon (Nb2O5/NbO2/Co/C) nanocomposites synthesized through carbonization of zeolitic imidazolate framework-67/niobium pentoxide (ZIF-67/Nb2O5) precursor. It was showed that Nb2O5 was partially reduced to NbO2 during the carbonization process. With increasing content of Nb2O5, the surface roughness of the composite increased and the magnetic effect decreased. Specifically, the sample with 0.37 ​mmol Nb2O5 exhibited a minimum reflection loss of −64.68 ​dB at 11.76 ​GHz at 2.00 ​mm. The effective absorption bandwidth (RL ​< ​−10dB) of this sample was 4.0 ​GHz (9.44–13.44 ​GHz), covering most of the X-band and part of the Ku-band. This can be attributed to the incorporation of enhanced multiple interface reflections and increased interface capacitive structure, due to the difference in conductivity between the niobium oxides. Furthermore, the presence of the niobium oxides with low permittivity improved the impedance matching of the composites and hence increased the microwave absorption efficiency. The synergic effect of the low permittivity niobium oxides and the magnetic cobalt was responsible for the great enhancement in electromagnetic wave absorption of the composites. This work provides a new method to develop high-performance electromagnetic wave absorbing materials.

Enhanced microwave absorption performance of nitrogen-doped porous carbon dodecahedrons composite embedded with ceric dioxide

CeO2/Co/C dodecahedrons composites with excellent microwave absorption performance were synthesized by using a hydrothermal method. ZIF-67/CeO2 was first prepared by introducing CeO2 into the precursor of ZIF-67 and then CeO2/Co/C composite was obtained after heat treatment. Impedance matching of the samples could be well adjusted by controlling the content of CeO2. Unique dodecahedral structure for more interfacial reflection and cerium dioxide oxygen vacancies enhance microwave absorption performance. Specifically, the CeO2/Co/C exhibited a minimum reflection loss of −68.83 dB is observed at 5.92 GHz, while the thickness was 3.69 mm. The introduction of CeO2 effectively enhanced the impedance matching of the materials and improved the microwave absorption performance. Therefore, this CeO2/Co/C composite is a promising microwave absorber material with high performance.

λ/4–λ/4 Double-Layer Broadband Antireflective Coatings with Constant High Transmittance

Antireflective (AR) coatings can suppress the undesired interfacial Fresnel reflections, and they are widely used in optical devices and energy-related instruments. Conventional single-layer AR coatings, which only work at a single wavelength, encounter serious limitations in some practical applications because of their inherent properties. In this paper, λ/4–λ/4 double-layer antireflective (AR) coatings with constant high transmittance in a pre-determined wavelength range was prepared by the sol–gel method via acid-catalyzed and base-catalyzed SiO2 thin films. A double-layer antireflective coating with an almost constant transmittance value of 99.8% in the range of 550–700 nm was obtained, and the transmittance of this coating was higher than 99% in a wider range of 450–850 nm with a fluctuation of less than 1%. The coatings had good environmental stability and maintained constant high transmittance after two weeks of exposure in 50% humidity. The broadband AR coatings may have important applications in fields such as electroluminescent display.