Reflective Layer Research Articles

Inclined bending seismic reflection layer in the crust illuminated by distributed fibre-optic-sensing measurements in western Japan

Distributed acoustic sensing (DAS), which enables a single fibre-optic cable to function as multiple sensors, is a technique to measure the strain rate distributed along the cable. This technique is applied to record ground motions in western Japan via a 50 km-long fibre-optic cable beneath a national road. The measured values are strain changes along the cable every 5 m, corresponding to 9788 sensor deployments. This high-density measurement along the long cable successfully recorded the 2021 M2.8 and M3.2 earthquakes that occurred in the crust within the distance of the cable in southern Kyoto. The direct S waves were followed by seismic waves approximately 8–14 s later, which were reflected by lower crustal structures. These waveforms were previously reported by observing many earthquakes via multiple seismometers, but the DAS observations clearly illuminate reflected wavefields from single earthquake observations for the first time. The numerical simulation of the strain-rate wavefields of these earthquakes reveals the existence of a north-dipping thin layer with a slow seismic velocity in the lower crust, which becomes steeper in the shallower part. This layer might represent the path of slab-derived fluid to the shallow fault zone.

Highly Enhanced Light Recycling in Quantum Dot Displays by Sidewall Reflectors

AbstractQuantum dot (QD) color conversion‐based displays have emerged as one of the most promising next‐generation devices due to their superior emission properties in terms of color expression. To date, however, existing QD color conversion layer (QD‐CCL) technologies have suffered from low luminance and power efficiency, mainly due to significant light absorption by the bank structure. Here, the color conversion efficiency of QD‐CCL has been significantly enhanced by fabricating a highly reflective metal layer on the side surface of the bank structure. Using a high‐aspect‐ratio silver reflector fabricated through a secondary sputtering lithographic technique involving argon ion bombardment, the fabricated QD‐CCL is combined with a blue organic light‐emitting diode (OLED) serving as a light source. As a result, light recycling from the reflector significantly enhances color conversion efficiency and luminance by up to 4.60‐fold and 4.29‐fold, respectively. Optical simulation reveals that higher pixel resolution provides greater reflection probabilities during extraction. This photomask‐free approach is not only simple but also highly compatible with existing semiconductor fabrication processes, making it a viable commercial alternative for all color‐converting structures that utilize light‐emitting materials with omnidirectional emission characteristics.

Tunable mid-infrared absorber based on Dirac metamaterials

Abstract In this paper, a tunable metamaterial absorber based on Dirac semimetal is proposed, which consists of three different structures, from top to bottom, namely a double semicircular Dirac semimetal resonator, a silicon dioxide (SiO2) substrate, and a continuous vanadium dioxide (VO2) reflector layer. When the Fermi energy level of the Dirac semimetal is 10\ meV, the absorber absorbs more than 90% in the 39.06-84.76\ THz range. Firstly, taking advantage of the tunability of the conductivity of the Dirac semimetal, the dynamic tuning of the absorption frequency can be achieved by changing the Fermi energy level of the Dirac semimetal without the need to optimise the geometry and remanufacture the structure. Secondly, the structure has been improved by the addition of the phase change material VO2, resulting in a much higher absorption performance of the absorber. Since vanadium dioxide is a temperature-sensitive metal oxide with an insulating phase below the phase transition temperature (about 68℃) and a metallic phase above the phase transition temperature, this paper also analyses the effect of vanadium dioxide on the absorptive performance at different temperatures, with the aim of further improving the absorber performance.

Reduction of TCF effect in FBAR devices using DC bias

This study investigates the effect of applied DC bias on the resonant and antiresonant frequency of FBAR devices. In our model, we introduce linear electrostrictive coefficients and compare the theoretical results with experimental data. The FBAR structure utilizes an air cavity as the acoustic reflector layer, with Mo and AlN as the materials for the top/bottom electrodes and the piezoelectric layer, respectively. The resonant and antiresonant frequencies of the FBAR are designed at 2313.1 and 2374.7 MHz, respectively. Under an applied DC bias ranging from −10 to +10 V, the frequency shifts for the resonant and antiresonant frequencies are 37.7 and 27.7 ppm/V, respectively. The theoretical results, incorporating linear electrostrictive coefficients N=−7×1010 and G=−5×109, show excellent agreement with the measured results of the FBAR device. Finally, we compensated for the frequency drift by applying a 20 V DC bias at high temperatures to the FBAR device. These findings have significant implications for improving the performance of RF communication systems in varying temperature environments.

Study the impact of spacer at thermal degradation process of MLI-based insulation in fire condition

To reduce CO2 emissions, energy carriers such as hydrogen are considered to be a solution. Consumption of hydrogen as a fuel meets several limitations such as its low volumetric energy density in gas phase. To tackle this problem, storage as well as transportation in liquified phase is recommended. To be able to handle this component in liquid phase, an efficient thermal insulation e.g., MLI insulation is required. Different studies have been addressed the vulnerability of such insulation against high thermal loads e.g., in an accident engaging fire. Some of research works have highlighted the importance of considering the MLI thermal degradation focusing on its reflective layer. However, limited number of studies addressed the thermal degradation of spacer material and its effect on the overall heat flux.In this study, through systematic experimental measurements, the effect of thermal loads on glass fleece, glass paper as well as polyester spacers are investigated. The results are reported in various temperature and heat flux profiles. Interpreting the temperature profiles revealed that, as the number of spacers in the medium increases, the peak temperature detectable by the temperature sensor on the measurement plate decreases. Each individual spacer contributes to mitigating the radiative energy received by the measurement plate. Stacks of 20–50 spacers (this is the number of layers in commercial MLI systems applied for liquid hydrogen applications) can potentially reduce the thermal radiation by 1–2 orders of magnitude.An empirical correlation to predict a heat flux attenuation factor is proposed, which is useful for further numerical and analytical studies in the temperature range from ambient to 300 °C.

Enhanced performance of GaN-based thin-film flip-chip LEDs with reflective current blocking layers

Enhanced performance of GaN-based thin-film flip-chip LEDs with reflective current blocking layers

Multivariate gradient structure design of flexible thermoplastic polyurethane based composite foam for enhanced electromagnetic interference shielding performance

Flexible and efficient electromagnetic interference (EMI) shielding polymer composite foams are rapidly developing, but it is difficult to avoid the deterioration of shielding properties after foaming. To solve the issue, in this work, composite foams with multivariate gradient structure of thermoplastic polyurethane (TPU) mixed with multiwalled carbon nanotubes (MWCNTs) were constructed by combining the soft-hard domains proportional gradient of TPU with filler content gradient. Gradient-structured TPU/MWCNTs foams with impedance matching layer and high reflector layer were obtained and impedance matching layer with large cells significantly reduced the density while high reflector layer with a few cells maintained relatively perfect conductive network, whose shielding efficiency was 38.2 % higher than that of unfoamed sample. Furthermore, TPU/MWCNTs composite foams presented great stability even after 1000 times bending. This special multivariate gradient structure shows potential applications in microelectronic devices and aerospace fields and is critical to the development of high-performance EMI shielding polymer foams.

A tunable chiral metasurface useable in terahertz imaging and wavefront shaping

We proposed a tunable chiral metasurface comprising a reflective bottom layer of gold, a dielectric layer of polyimide, and a structural top layer of gold-graphene. Its main properties were studied via numerical simulations conducted using CST Studio Suite. The results indicate that, based on the chiral metasurface, we achieved dual-band circular dichroism of −0.5 and 0.77 at 0.9 THz and 1.06 THz, respectively, and complementary near-field imaging applications were realized by tuning the Fermi level (E f ) of graphene. Subsequently, exploiting the exceptional selective characteristics of circularly polarized waves using a chiral metasurface, eight chiral phase-gradient metasurfaces were constructed by rotating the chiral structure. Moreover, based on the Pancharatnam-Berry phase principle, tunable wavefront shaping applications were further realized, including anomalous reflection, vortex beams, and focusing. In anomalous reflection, the reflection angles for left-circularly polarized (LCP) and right-circularly polarized (RCP) incidences are opposite when adjusting the E f of graphene. For example, when the graphene E f is 0 eV and the LCP wave is incident at 0°, the reflection angle is −18°. Conversely, when the graphene E f is 1 eV and the RCP wave is incident at 0°, the reflection angle is 18°. In the application of vortex beams, by adjusting the E f of graphene, we achieved vortex beams with opposite topological charges under different circularly polarized incidences. In the focusing application, the incident LCP and RCP can achieve focusing and defocusing, respectively. And the graphene E f can dynamically control the focusing efficiency at the incident LCP, increasing it from 13.63% to 44.84%.

Multi-scale structural design of multilayer magnetic composite materials for ultra-wideband microwave absorption

Broadband microwave absorbing (MA) materials have important applications in reducing electromagnetic radiation pollution and realizing low scattering characteristics. However, current MA materials with single-layer structure generally cannot meet this requirement due to the difficulty in achieving good impedance matching. Here, we design a multilayer-structured MA material, which consists of a wave transmitting layer, a carbon-magnetic material composite absorbing layer, a strong magnetic absorbing layer and a reflector layer. Hollow Co/CoFe@C composite particles prepared using CoCoPBA as templates are used as fillers to design carbon-magnetic material composite absorbing layer. The Co/CoFe bimagnetic phases enhance permeability while the hollow structure optimizes permittivity, which endows this absorbing layer with strong microwave absorption ability with a reflection loss of −47.18 dB. The introduction of a strong magnetic absorbing layer that combines FeSiAl with high permeability and SmFeB with high coercivity further significantly improves the overall impedance matching of the material. Benefitting from the multi-scale structural design, the obtained multilayer MA material achieves strong microwave absorption in both low and high frequency ranges, and the effective absorption bandwidth reaches 12.85 GHz, far superior to the traditional single-layer MA material.

Sapphire optical fiber with (BN/SiBCN)n coating prepared by chemical vapor deposition for high-temperature sensing applications

To enhance the load-bearing capacity of sapphire optical fiber (SOF) in extreme environments, this study prepared SOF/(BN/SiBCN)n by optimizing the nanostructure through increased deposition temperature of BN using alternating chemical vapor deposition. Simulation results indicated an inverse correlation between the leakage loss of SOF/BN/SiBCN and BN thickness; at room temperature, the tendency for coating cracking along the radial direction of SOF/BN/SiBCN is positively correlated with BN thickness, whereas this trend reverses at 1500 °C. Mechanical testing revealed that the tensile strength of SOF/BN/SiBCN is inversely correlated with the tendency for interlayer cracking, aligning with the findings from residual stress simulations; under an air environment at 1500 °C, SOF/(BN/SiBCN)2 exhibited the highest tensile strength, indicating that the layered matrix design effectively mitigates the risk of BN oxidation by creating barrier layers. Optical test demonstrated that the BN coating functions as a total reflection layer to suppress the scattering of optical signals on the sapphire optical fiber surface. In conclusion, the coating design of SOF/(BN/SiBCN)n could meet the material requirements for sapphire optical fiber sensors in extreme environments.

Two-step scattering theory method for designing metamaterials

Abstract A two-step method for designing an acoustic metamaterial with desired properties is proposed. At the first step, the scattering matrices of its elements are calculated using the Lippmann-Schwinger type equation. For scatterers of small wave size, the problem is reduced to determining the phases of several scattering coefficients. At the second step, the particular design of metamaterial elements is determined. This problem can be considered an inverse scattering problem or a problem of optimizing the geometric parameters of a metamaterial element. The second approach turns out to be more practically applicable. As an example, a metamaterial in the form of a reflective layer with a narrow waveguide channel is considered, and the design of its elements is determined with the proposed method.

Investigating the effect of annealing on structural and optical properties of TiO2 and SiO2 broadband reflective layers coated by the plasma sputtering method

Investigating the effect of annealing on structural and optical properties of TiO2 and SiO2 broadband reflective layers coated by the plasma sputtering method

An Opto-electrophysiology Neural Probe with Photoelectric Artifact-Free for Advanced Single-Neuron Analysis.

Opto-electrophysiology neural probes targeting single-cell levels offer an important avenue for elucidating the intrinsic mechanisms of the nervous system using different physical quantities, representing a significant future direction for brain-computer interface (BCI) devices. However, the highly integrated structure poses significant challenges to fabrication processes and the presence of photoelectric artifacts complicates the extraction and analysis of target signals. Here, we propose a highly miniaturized and integrated opto-electrophysiology neural probe for electrical recording and optical stimulation at the single-cell/subcellular level. The design of a total internal reflection layer addresses the photoelectric artifacts that are more pronounced in single-cell devices compared to conventional implantable BCI devices. Finite element simulations and electrical signal tests demonstrate that the opto-electrophysiology neural probe eliminates the photoelectric artifacts in the time domain, which represents a significant breakthrough for optoelectrical integrated BCI devices. Our proposed opto-electrophysiology neural probe holds substantial potential for promoting the development of in vivo BCI devices and developing advanced therapeutic strategies for neurological disorders.

Electric-magnetic dual-gradient structure design of thin MXene/Fe3O4 films for absorption-dominated electromagnetic interference shielding

The challenge of achieving high-performance electromagnetic interference (EMI) shielding films, which focuses on electromagnetic waves absorption while maintaining thin thickness, is a crucial endeavor in contemporary electronic device advancement. In this study, we have successfully engineered hybrid films based on MXene nanosheets and Fe3O4 nanoparticles, featuring intricate electric–magnetic dual-gradient structures. Through the collaborative influence of a unique dual-gradient structure equipped with transition and reflection layers, these hybrid films demonstrate favorable impedance matching, abundant loss mechanisms (Ohmic loss, interfacial polarization and magnetic loss), and an “absorb-reflect-reabsorb” process to achieve absorption-dominated EMI shielding capability. Compared with the single conductive gradient structure, the dual-gradient structure effectively enhances the absorption intensity per unit thickness, and thus reduces the thickness of the film. The optimized film demonstrates a remarkable EMI shielding effectiveness (SE) of 49.98 dB alongside an enhanced absorption coefficient (A) of 0.51 with a thickness of only 180 μm. The thin films with a dual-gradient structure hold promise for crafting absorption-dominated electromagnetic shielding materials, highlighting the potential for advanced electromagnetic protection solutions.

Theoretical investigation of enhanced terahertz metamaterial absorber integrated with blocked-impurity-band detector

Blocked-impurity-band (BIB) device becomes a prevalent terahertz detection technology, but its overall optical performance, such as quantum efficiency, is constrained by the thickness of the absorption layer. Metamaterial absorbers can effectively concentrate and absorb terahertz waves at a subwavelength scale, and their ultra-thin thickness facilitates device integration. A multi-band metamaterial absorber is developed and simulated tailored for the working band of Ge-doped BIB detectors. The design is founded on a three-layer structure with Ti rectangular resonator, Ge dielectric layer, and Ti reflective layer. This configuration achieves two absorption peaks at 74.16 μm and 92.09 μm, with optical absorption reaching 95.66% and 97.29%, respectively. The operating wavelength can be regulated by altering the geometric parameters of the rectangular resonator, and it exhibits angle-insensitive properties under small-angle incidence. These findings enhance the application of BIB detectors in terahertz detection technology, potentially improving their performance in deep space exploration.

Pattern reconfigurable UHF RFID universal reader antenna array

In response to the rising demand for adaptable and versatile RFID reader antenna, this paper presents an integrated reader system featuring an array of four antennas. The primary objective is to design four identical, circularly polarized, high-gain, wide-band antennas that cover the 860–960 MHz UHF RFID band. Each antenna consists of three layers, the radiator and director layers, designed as patch antennas with trimmed edges and a central slot, while the reflector layer is constructed from a copper material. These layers are assembled with four Teflon spacers, and a coaxial connector is utilized for feeding the antenna. An open-circuit stub is used to improve impedance matching. CST Microwave Studio was employed for design optimization. The four sector antennas achieve a 150 MHz bandwidth (833–983 MHz) and a maximum gain of 8.4 dBi. When combined with a four-port RFID reader (ThingMagic M6E), the antenna system generates four electronically switchable beams in the azimuth plane. The proposed antenna exhibits left-hand circular polarization (LHCP) within the RFID ISM band, maintaining an axial ratio (AR) between 1 dB and 3 dB. The antenna array, including the reader and control unit, measures 255 × 255 × 210 mm. Simulation and measurement results confirm the system's performance and functionality.

(Dielectric Science and Technology Division Poster Award, 3rd Place) Radical Oxidation for Enhancing Polishing-Rate and Improving Slurry Stability in Ag-Film Chemical–Mechanical-Planarization

Recently, Ag-film has been utilized as a reflective layer in organic-light-emitting- diode on silicion(OLEDoS). The formation of a reflective Ag-film layer was conducted by Ag-film deposition and following Ag-film chemical-mechanical planarization (CMP). The Ag-film has ductility property (i.e., hardness of 0.3 GPa) so that a reletively soft CMP pad should be used to minimize the generation of the CMP induced scratches. However, using a soft CMP pad, it is notably difficult to achieve a high Ag-film polishing-rate (i.e., 300 nm/min). Thus, to enhance Ag-film polishing-rate, a Fenton reaction between ferric ions and H2O2 has been applied. Although, a Fenton reaction enhancing dissolved oxygen concentration can increase remarkably the Ag-film polishing-rate, the CMP slurry using Fenton reaction has produced a detrimental slurry stability after mixing with H2O2 (i.e., extremely low H2O2 pot life time. In this study, as a solution, the Ag-film CMP slurry was designed via radical oxidation on the Ag-film surface during CMP, without using Fenton reaction (i.e., mixing ferric ions with H2O2). The radical oxidation was achived by using halide oxidant (i.e., H5IO6), which radical oxidation degree principally depended on halide oxidant concentration and slurry pH, showing a notable high Ag-film polishing-rate (i.e., 400 nm/min) without the precence of corrosion. Without using Fenton reaction, the secondary diameter of colloidal abrasives in the designed Ag-film CMP slurry was not changed for several months. In our presentation, we will prove the mechanism of the radical oxidation on the polished Ag-film surface. In addition, we will present the dependencies of the chemical dominant polishing properties (i.e., OH radical, chemical oxidation degree of the Ag-film surfcae, chemical composition of chemical oxidation, slurry adsortion degree, and corrosion potential and current) as well as the mechanical dominant polishing properties (i.e., electrostatic force between abrasives and Ag-film surface) on the halid oxidant concentration.

Metasurface-Embedded Contact Lenses for Holographic Light Projection.

Contact lenses have been instrumental in vision correction and are expected to be utilized in augmented reality (AR) displays through the integration of electronic and optical components. In optics, metasurfaces, an array of sub-wavelength nanostructures, have offered optical multifunctionality in an ultra-compact form factor, facilitating integration into various imaging, and display systems. However, transferring metasurfaces onto contact lenses remains challenging due to the non-biocompatible materials of extant imprinting methods and the structural instability caused by the swelling and shrinking of the wetted surface. Here, a biocompatible method is presented to transfer metasurfaces onto contact lenses using hyaluronic acid (HA) as a soft mold and to allow for holographic light projection. A high-efficiency metahologram is obtained with an all-metallic 3D meta-atom enhanced by the anisotropy of a rectangular structure, and a reflective background metal layer. A corrugated metal layer on the HA mold is supported with a SiO2 capping layer, to avoid unwanted wrinkles and to ensure structural stability when transferred to the surface of pliable and wettable contact lenses. Biocompatible method of transferring metasurfaces onto contact lenses promises the integration of diverse optical components, including holograms, lenses, gratings and more, to advance the visual experience for AR displays and human-computer interfaces.

Dynamic multicolor electrochromic skin in high-brightness flexible WO3/Au asymmetric Fabry–Perot nanocavity fabricated on Nylon 66 porous substrate

Recently, the Fabry–Perot (F–P) cavity electrochromic devices, which are constructed by combining nano-size inorganic electrochromic material WO3 and reflective metal layers, have attracted considerable attention due to their potentials in the fields of dynamic multicolor displays and active camouflage. However, in the few studies that have been reported, the peak reflectance of flexible F–P cavity multicolor electrochromic devices in the visible wavelength band is generally lower than 30 %, which limits their reflective display and camouflage effects in high-brightness environments. Thus, we have combined multicolor reflective electrochromic electrodes in WO3/Au asymmetric F–P nanocavity constructed by magnetron sputtering on a Nylon 66 porous substrate with a highly transparent UV-cured gel electrolyte and a PET plastic sealing procedure. As a result, a flexible and dynamic multicolor electrochromic skin with high reflectance (Rmax＞50 %) and excellent flexibility (bending radius of 4 mm) has been fabricated. The WO3 electrochromic layer at the top works as the dynamic dielectric layer in the broadband absorption Fabry–Perot cavity, and the inert metal Au layer at the bottom works as the reflective layer. The WO3/Au asymmetric F–P cavity can acutely capture the variation in optical constants of WO3 due to the thickness change and electric-driven effects. This cavity facilitates the selective reflection and absorption of the energy distribution of the spectrum after the induced interferometric resonance. As a result, the cavity exhibits a rich array of structural colors, including ocher, taupe, yellow, orange, green, and violet. The electrochromic skin exhibits a fast switching time and maintains 99.43 % of the optical modulation amplitude (ΔR) after 110 coloring/bleaching cycles. It provides a potential option in the field of flexible high-brightness reflective displays and dynamic camouflage in the future.

Wide-angle non-reciprocal thermal radiator based on a periodic toroidal array structure

Non-reciprocal thermal radiation is crucial for energy transfer and storage applications. However, the range of angles of incidence limits the development of non-reciprocal thermal radiation. To address this problem, we have proposed and developed a non-reciprocal thermal radiation device with wide-angle characteristics, which operates in the mid-infrared spectral range. The radiator consists of a silicon-based periodic toroidal array, a Weyl semimetal (WSM), and a metal reflective layer Ag. A strong nonreciprocity of 0.88 is observed at 9.36 μm wavelength and 41.8° angle, while a nonreciprocity of 0.87 can be sustained within the range of 36°–74°. In addition, the nonreciprocity can be maintained above 0.8 in the spectral range of 9.3 μm ∼9.4 μm. Compared with the previous single working angle, our work has dramatically broadened the angle of energy absorption, and the non-reciprocal intensity can be maintained at a high level. Through a detailed analysis of the magnetic field modulus and impedance characteristics at non-reciprocal wavelengths, we reveal that cavity resonance excitation is the core physical process of mid-infrared wide-angle non-reciprocal radiation. In addition, changing the axial vector of the WSM can lead to a redshift of the non-reciprocal wave peaks. The proposed two-dimensional mid-infrared non-reciprocal emitter can realize wide-angle domain emission at specific wavelengths, which is promising for applications in energy storage and conversion systems such as solar cells and thermophotovoltaic cells.