Effect Of Multiple Reflections Research Articles

Doping Evolution of the Superconducting Order Parameter of Na(Fe, Co)As Alkali-Metal Pnictides

Using incoherent multiple Andreev reflection effect spectroscopy, we have studied the multiple-gap superconducting state of underdoped and overdoped Na(Fe, Co)As single crystals. We directly determined the magnitudes of the microscopic superconducting order parameters, their temperature dependences, and characteristic ratios 2Δ(0)/kBTc. The obtained large data statistics unambiguously proves a significant decrease in the degree of the large superconducting gap possible anisotropy in the overdoped compositions away from the antiferromagnetic and nematic regions of the doping phase diagram.

Analysis of Wave Propagation Across Layered Rock Masses Considering Multiple Reflection Effects

Analysis of Wave Propagation Across Layered Rock Masses Considering Multiple Reflection Effects

Enhanced electromagnetic wave absorption of magnetite-spinach derived carbon composite

The high density, high cost, and environmental pollution hinder the application of iron-based electromagnetic wave-absorbing materials. Although bio-carbon is a green and lightweight dielectric wave-absorbing material, the wave-absorbing performance of bio-carbon is still limited. This work successfully combined magnetite Fe3O4 with porous carbon derived from spinach stem using hydrothermal and calcination methods. This process optimizes the matching of the dielectric constant and magnetoconductivity of the as prepared composite material, resulting in a significant improvement in electromagnetic microwave absorption capacity. XRD, SEM, TEM, XPS, VSM and EMW absorption network analyzer are used to detect and characterize the samples. The composite material shows a excellent minimum reflection loss value of −48.81 dB and an efficacious absorption bandwidth of 4.73 GHz at the optimal raw material ratio. The tests also show the porous structure of the sample with the coercivity and saturation magnetization of 29.36 Oe and 10.75 emu/g, respectively. The test results indicate that the excellent electromagnetic wave absorption is due to the synergistic effect of multiple reflection, Debye relaxation, and interfacial polarization. This Fe3O4-bio-carbon composite is cheap and simple to prepare, and it also has excellent wave absorption performance. Therefore, it shows great application potential in civilian and military electromagnetic wave absorption fields.

Low-frequency and dual-band microwave absorption properties of novel VB-group disulphides (3R–TaS2) nanosheets

As electromagnetic technology advances and demand for electronic devices grows, concerns about electromagnetic pollution intensify. This has spurred focused research on innovative electromagnetic absorbers, particularly chalcogenides, noted for their superior absorption capabilities. In this study, we successfully synthesize 3R–TaS2 nanosheets using a straightforward calcination method for the first time. These nanosheets exhibit significant absorption capabilities in both the C-band (4–8 ​GHz) and Ku-band (12–18 ​GHz) frequency ranges. By optimizing the calcination process, the complex permittivity of TaS2 is enhanced, specifically for those synthesized at 1000 ​°C for 24 ​h. The nanosheets possess dual-band absorption properties, with a notable minimum reflection loss (RLmin) of −41.4 ​dB in the C-band, and an average absorption intensity exceeding 10 ​dB in C- and Ku-bands, in the absorbers with a thickness of 5.6 ​mm. Additionally, the 3R–TaS2 nanosheets are demonstrated to have an effective absorption bandwidth of 5.04 ​GHz (3.84–8.88 ​GHz) in the absorbers with thicknesses of 3.5–5.5 ​mm. The results highlight the multiple reflection effects in 3R–TaS2 as caused by their stacked structures, which could be promising low-frequency absorbers.

Vat photopolymerization 3D printing SiBCN ceramic metamaterials with strong electromagnetic wave absorption

Starting from the simulation prediction, SiBCN polymer-derived-ceramic metamaterials, integrating both structure and function in a single component, were obtained using vat photopolymerization technology starting from a preceramic polymer. The low-density gyroid triply periodic minimal surface (TPMS) structures used in this study increases the multiple reflection loss of electromagnetic wave (EMW) in the macro-interpenetrating channel structure, generates surface characteristics (stair-stepping effect) structure interface polarization, and improves microwave absorption characteristics. The possible multiple reflection effects of a gyroid structure on electromagnetic waves are discussed by Computer Simulation Technology simulation. At the same time, the precipitated phases in polymer derived ceramics (PDCs) were adjusted by controlling the pyrolysis temperature. The results show that the crystal phases (such as β-SiC and C) precipitated in the gyroid structure sample pyrolyzed at 1200°C enrich the heterogeneous interface polarization in the material. In addition, C forms a (semi-)conductive network, which increases the conductivity loss. The effective absorption bandwidth (EAB, RL<-10 dB) of the samples pyrolyzed at 1200°C was 3.09 GHz (thickness of 2.21 mm) and the minimum reflection loss (RLmin) was −70.6 dB (thickness of 2.31 mm), indicating that the samples have favorable EMW absorption properties and great potential for applications, providing a foundation for the preparation of high-performance lightweight structural ceramics.

Rational construction of ZnFe2O4 decorated hollow carbon cloth towards effective electromagnetic wave absorption

As typical magnetic materials, ferrites and their composites play dominant roles in the design of high-performance electromagnetic wave (EW) absorber. Solvent thermal method is the most popular route for synthesizing ferrites, while systematical comparison research about the influence of reaction solvents of solvent thermal process on ferrite based material's EW absorption performance has rarely been carried out. Thus in this work, we adopted cotton fabric as raw material, and synthesized two kinds of zinc ferrite decorated hollow carbon cloth (CC@ZnFe2O4) composites through solvent thermal reaction where deionized water and ethylene glycol was adopted as reaction solvents, respectively. After comprehensive and detailed comparison of the structures and performances of these two ferrite composites, the CC@ZnFe2O4 synthesized in deionized water phase possesses an ideal optimal absorption efficiency for EW, that is the minimum reflection loss (RL min) of −46 dB, while the effective absorption bandwidth of CC@ZnFe2O4 composites synthesized in ethylene glycol phase is wider (4.9 GHz). The synergistic effect of impedance matching, interface polarization, magnetic resonance, and multiple reflections co-determined the ideal EW absorption performances of these two samples. The research can not only provide new guidance for the secondary utilization of waste textiles, but also become an important reference for the preparation of ferrite based high-performance EW absorbers through solvent thermal method.

Simultaneous Measurement of Local Pulse Wave Velocities in Radial Arteries Using a Soft Sensor Based on the Fiber Bragg Grating Technique.

Arterial stiffness has been proved to be an important parameter in the evaluation of cardiovascular diseases, and Pulse Wave Velocity (PWV) is a strong indicator of arterial stiffness. Compared to regional PWV (PWV among different arteries), local PWV (PWV within a single artery) outstands in providing higher precision in indicating arterial properties, as regional PWVs are highly affected by multiple parameters, e.g., variations in blood vessel lengths due to individual differences, and multiple reflection effects on the pulse waveform. However, local PWV is less-developed due to its high dependency on the temporal resolution in synchronized signals with usually low signal-to-noise ratios. This paper presents a method for the noninvasive simultaneous measurement of two local PWVs in both left and right radial arteries based on the Fiber Bragg Grating (FBG) technique via correlation analysis of the pulse pairs at the fossa cubitalis and at the wrist. Based on the measurements of five male volunteers at the ages of 19 to 21 years old, the average left radial PWV ranged from 9.44 m/s to 12.35 m/s and the average right radial PWV ranged from 11.50 m/s to 14.83 m/s. What is worth mentioning is that a stable difference between the left and right radial PWVs was observed for each volunteer, ranging from 2.27 m/s to 3.04 m/s. This method enables the dynamic analysis of local PWVs and analysis of their features among different arteries, which will benefit the diagnosis of early-stage arterial stiffening and may bring more insights into the diagnosis of cardiovascular diseases.

Cyanuric Acid-Assisted Synthesis of Hierarchical Amorphous Carbon Nitride Assembled by Ultrathin Oxygen-Doped Nanosheets for Excellent Photocatalytic Hydrogen Generation.

Amorphous carbon nitride with typical short-range order arrangement as an effective photocatalyst is worth exploring but remains a great challenge because its disordered structure induces severe recombination of photogenerated charge carriers. Herein, for the first time, we demonstrate that a hierarchical amorphous carbon nitride (HACN) with structural oxygen incorporation can be synthesized via a cyanuric acid-assisted melem hydrothermal process, accompanied by freeze-drying and pyrolysis. The complex composed of melem and cyanuric acid exhibiting a unique 3D self-supporting skeleton and significant phase transformation is responsible for the formation of an interconnected hierarchical framework and amorphous structure for HACN. These features are beneficial to enhance its visible light harvesting by the multiple-reflection effect within the architecture consisting of more exposed porous nanosheets and introducing a long band tail absorption. The well-designed morphology, band tail state, and oxygen doping effectively inhibit rapid band-to-band recombination of the photogenerated electrons and holes and facilitate subsequent separation. Accordingly, the HACN catalyst exhibits exceptional visible light (λ > 420 nm)-driven photoreduction for hydrogen production with a rate of 82.4 μmol h-1, which is 21.7 and 9.5 times higher than those of melem-derived carbon nitride and crystalline nanotube carbon nitride counterparts, respectively, and significantly surpasses those of most reported amorphous carbon nitrides. Our controlling of rearrangement of the in situ supramolecular self-assembly of melem oligomer using cyanuric acid directly instructs the development of highly efficient amorphous photocatalysts for converting solar energy into hydrogen fuel.

MOF derived α-Fe2O3/Ti3C2Tx magnetic-dielectric composites for microwave absorption

The design and development of microwave-absorbing materials with excellent performance hold significant importance in both civil and military fields. The combination of magnetic loss materials and dielectric loss materials can achieve complementary performance effects and regulate impedance matching. In this paper, spindle-like α-Fe2O3 was synthesized using MIL-88A as a template, which was then composited with Ti3C2Tx phase possessing excellent electrical conductivity to obtain Fe2O3/Ti3C2Tx composites. Ti3C2Tx can provide good conductance loss and dipole polarization relaxation, while the incorporation of Fe2O3 between the layers of Ti3C2Tx not only triggers the interfacial polarization effect but also increases layer spacing, thereby enhancing multiple reflection effects. Furthermore, the magnetic-dielectric synergies further optimize the impedance matching. Through the combined action of multiple mechanisms, the Fe2O3/Ti3C2Tx composites (with a mass ratio of 1:3 for Fe2O3 and Ti3C2Tx) exhibit a minimum reflection loss of −34 dB and an effective absorption bandwidth of 1.53 GHz at a thickness of 3 mm, as well as an effective absorption bandwidth of 2.805 GHz at a thickness of 1.5 mm. This paper presents a reference strategy for constructing highly efficient microwave absorbers derived from Metal-organic frameworks (MOFs) and MXene based on their outstanding properties.

Upper Critical Field and Tunneling Spectroscopy of Underdoped Na(Fe,Co)As Single Crystals.

A comprehensive study of superconducting properties of underdoped NaFe0.979Co0.021As single crystals by a combination of upper critical field measurements and incoherent multiple Andreev reflection effect (IMARE) spectroscopy is presented. The Hc2(T) temperature dependences are measured at magnetic fields up to 16 T with in-plane and out-of-plane field directions and considered within single-band and two-band models in order to estimate the Hc2(0) value. In IMARE spectroscopy probes, the magnitude, characteristic ratio, and temperature dependence of the superconducting order parameters (ΔL,S(T)) are determined locally and directly. A possible k-space anisotropy of the large superconducting gap is demonstrated. We show that usage of a quadruple of λij0 coupling constants obtained in the IMARE experiment can significantly reduce the number of free parameters required to fit the Hc2(T) dependence within a two-band approach (from six to two).

Synergetic dielectric and magnetic losses of melamine sponge-loaded puffed-rice biomass carbon and Ni3ZnC0.7 for optimal effective microwave absorption

Multi-dimensional design and the combination of multiple phases can effectively enhance the dielectric loss properties and multiple reflection effects of absorbers. Herein, a novel multi-dimensional microporous nanostructured composite, melamine sponge (MS) loaded puffed-rice biomass carbon (C) together with bimetallic carbide material Ni3ZnC0.7 (Ni3ZnC0.7-MS/C) was synthesized by simple vacuum filtration and hydrothermal calcination. The result indicates that small Ni3ZnC0.7 particles with little Ni doping uniformly decorated on the surfaces of the three-dimensional (3D) melamine sponge and puffed rice carbons. The Ni3ZnC0.7-MS/C composite mixed with paraffin (weight ratio of 1:2) exhibited the best electromagnetic wave (EMW) absorption performance, and the minimum reflection loss (RLmin) value of the Ni3ZnC0.7-MS/C composite reaches −107.7 dB with a matching thickness of 2.78 mm and the maximum effective absorption bandwidth for RL below −10 dB (EABmax) is adjusted to 9.2 GHz at a matching thickness of 4.0 mm. The dipole polarization effect of the N doping and the different interfaces provided by the 3D structure of the MS carbon enhance the conduction loss and interface polarization, while the positive effects of eddy current and resonance caused by Ni3ZnC0.7 effectively improve the microwave absorption performances. This melamine sponge–loaded bimetallic carbon composite exhibited a magnetic/dielectric loss combination, resulting in a high-performance absorber with lightweight, cost-effective and efficient properties.

Honeycomb-like bamboo powders-derived porous carbon with low filler loading, high-performance microwave absorption

Nowadays, the problem posed by electromagnetic wave pollution to electronic devices and biological systems is of serious concern. To create a microwave absorber, component and structural modulation is crucial. Biomass-derived porous carbon is a potential material for microwave absorption applications due to the characteristics of lightweight, high specific surface area, and significant dielectric loss. In this study, by examining the impact of various KOH concentrations on the pore structure, bamboo powders with an 80-mesh size were used as a raw material to create honeycomb-like bamboo powders-derived porous carbon (BPDPC) materials. The activation mechanism of the BPDPC material is also explained. Based on the electromagnetic parameters, the sample BPDPC-4 impregnated with 4 mol/L KOH has a maximum effective absorption bandwidth (RL ≤ −10 dB) of 4.76 GHz at a matching thickness of 2.0 mm, covering 11.54–16.30 GHz and a minimum reflection loss (RLmin) of −40.99 dB at a matching thickness of 2.2 mm at 5 wt% ultra-low filler loading. Due to polarization loss, conduction loss, and the mutually beneficial effects of multiple electromagnetic wave reflection and scattering, the superior wave absorption performance is explained. This work also serves as a reference for investigating porous carbon generated from biomass.

Modelling the influences of powder layer depth and particle morphology on powder bed fusion using a coupled DEM-CFD approach

Optimising the quality of metal parts produced by additive manufacturing requires an understanding of how the powder characteristics impact both layer spreading and the subsequent powder melting. Here we present a simulation study which couples models of powder spreading (by the Discrete Element Method) and powder bed fusion by laser beam (by CFD). Previous simulations of these processes have mostly assumed idealised smooth surfaces, spherical particles and a single laser track. Here we seek a more realistic description by spreading over a previously-melted (rough) surface and by melting a number of tracks laid side-by-side to mimic the crosshatched scans typically used during part production. The effects of powder morphology (via a range of particle shapes including spheres, disks, ellipsoids and cuboids) and layer depth on spreading and subsequent melting have been investigated. We find that the fraction of laser energy transferred to the part and the melt pool volume both increase rapidly with the volume of powder deposited, due to the combined effects of multiple laser reflections and the insulating nature of the powder layer. In contrast, particle shape has very little effect on the overall melting behaviour of the powder, with the volume deposited and uniformity of coverage being the key determining factors. These observations suggest that the use of cheaper non-spherical powders is feasible provided that a sufficiently uniform coverage can be achieved at small layer depths.

On the radiative and multiple reflection corrections of the van der Waals force between two particles/atoms: dipolar contribution

We present a theoretical formalism based on fluctuational electrodynamics and the Maxwell-stress tensor for describing the impact of radiative and multiple reflections corrections on the van der Waals force between two nanoscale spherical particles and a pair of atoms in the dipolar approximation. Particularly, we examine the van der Waals forces for two metallic particles whose dielectric constant is represented by the Drude model, for two dielectric particles in which their material response has phononic resonances, and for two atoms with dynamic polarizabilities containing a single resonant frequency. For the metallic particles, in relation to the case in which the aforementioned effects are omitted, the van der Waals force is unchanged by the radiative corrections of the polarizabilities, whereas the mechanism of multiple reflections perturbs force about a few percentage points when the spheres nearly touch each other. In contrast to the the metallic case, the radiative corrections of the polarizabilities of the dielectric particles modify peculiarly the van der Waals force in comparison to the case where such corrections are neglected; there is a critical interparticle separation that divides two regimes: when the interparticle separation is smaller (larger) than this critical distance the force with radiative corrections is smaller (greater) than that without these corrections. Moreover, the van der Waals force is practically unchanged when effect of multiple reflections is taken into account. For the atomic case, the deviation of the van der Waals force due to multiple reflections is about a few percentage points when the interatomic separation corresponds to twice the van der Waals radius, and this deviation can reach about seventeen percent at a separation of 2.5 times the atomic radius. This work might have implications concerning the fine-tuning between theoretical and experimental outcomes of the van der Waals forces.

Self-powered photoelectrochemical immunosensor with triple enhanced photoelectric response for sensitive detection of cTnI

A self-powered photoelectrochemical (PEC) immunosensor triple enhanced photoelectric response was proposed for the sensitive cardiac troponin (cTnI) detection. The self-powered PEC platform was constructed by sulfur indium copper hollow nanocage as a photocathode and hollow nanometer sphere heterojunction (In2S3 @CdIn2S4) as a photoanode, where the coulomb force of distinct photoelectrodes as the driving force effectively improves the photoelectric response without redox-mediator or external potential. In addition, the reverse transfer of photo-generated charge carriers increases the photoelectric response capacity due to the internal electric field effect in type II heterojunction. What is more exciting is that carefully designed hollow materials playing energy conversion function possess compelling properties. Given the advantages of multiple reflection effects in the cavity, thin-shell configuration and large surface, the designed hollow materials possessed a higher photon capture rate, a shorter-range transfer for photon-generated charges, and more active site points for the associated redox reactions, which facilitated the entire photoelectric response process. Based on the above strategies, the proposed PEC immunosensor achieved triple enhanced photoelectric response to present high sensitivity for detecting cTnI. The present study has gone some way to design nanomaterials with superior photoelectric activity, which paves a way for detecting other disease markers in high sensitivity.

On Increasing Efficiency of UV Germicidal Recirculation for Air Sanitation

Enclosed germicidal irradiators, known as recirculators, have become widely used for air sanitation over the last years. The article presents the studies of the most common design of the device in terms of implementation of its target functionality. In the course of practical work, the role of shape and UV - C optical properties of material of the irradiation chamber walls for formation of efficient germicidal radiant flux inside it was studied. The significant effect of multiple reflections on the target functionality of the device was substantiated by calculations and confirmed by the test results. The article proposes the design of the irradiator and the analytical expressions for calculation of the irradiating chamber reflecting surface profile shape providing beneficial conditions for formation of an increased efficient germicidal flux inside it by means of multiple reflections.

Non-line-of-sight multiple reflection underwater wireless optical communications channel model based on a capillary waves rough sea surface.

In a non-line-of sight reflective underwater wireless optical communications (UWOC) link, the transmitted beam relies on reflections from the sea surface to propagate to the underwater receiver. Most previous research on reflective channels has sufficiently considered single reflections from a smooth or rough surface, while ignoring the effect of multiple reflections. In fact, a rough sea surface may cause the reflected photons to hit the sea surface again, which is referred as a multiple reflection process. To make up for deficiencies in the existing literature, we first construct a capillary waves rough sea surface model, and then present a multiple reflection channel model with the help of the Monte Carlo ray tracing approach. The path loss and channel impulse response (CIR) were further evaluated based on the model for different communications scenarios. Numerical results suggest that multiple reflections increase the path loss by more than about 5dB, and reduce the CIR amplitude to less than one-third compared to a single reflection. The work done in this paper aims to provide theoretical support for UWOC system design.

Three-dimensional inhomogeneous temperature tomography of confined-space flame coupled with wall radiation effect by instantaneous light field

Optical tomography has been demonstrated to be a powerful tool for the three-dimensional (3D) measurement of the dynamic characteristics of turbulent flame. Many practical visualizations of reaction flows require imaging through optical windows on the combustor, which have complex interactions with wall temperature, reflection characteristics, and limited optical access, which may seriously influence the imaging quality. Previous work focused on unconfined flame imaging, and lacked the study of the multiple reflection effects of the wall and the tomographic reconstruction within a wide temperature range. To solve these problems, the effect of chamber wall radiation on the photothermal information is analyzed in the forward problem, and the flame temperature with wall radiation is reconstructed in the inverse problem. In the forward problem, the light field acquisition model of spontaneous emission of the confined flame is developed through the backward Monte Carlo method based on the radiation distribution factor, which can comprehensively consider the essential effects such as radiative attenuation, wall reflection, medium scattering interference, and limited optical access. The recorded light field signals indicate that the reflection pattern and transfer mechanism of the wall material could affect the contribution of radiative source terms in different discrete domains to the detected energy. A novel tomography algorithm, namely, the adaptive threshold segmentation iterative regularization (ATSIR) method, has been proposed to extend the temperature range of tomography. The key of this method is to carry out a two-step reconstruction of the high and low-temperature regions through the temperature threshold, and introduce the prior smoothing information to alleviate the ill-posedness of tomography. The visualization results show that the well-established algorithms (e.g., least-square QR-factorization and regularization) have lower reconstruction quality for the combustion field within a wide temperature range, even if the regularization term is added. However, the proposed ATSIR method has the advantages of better suppression of fluctuations, smaller reconstruction error, and stronger anti-noise ability. The detailed analysis of the radiative transfer mode and 3D temperature visualization of the combustion field in a confined space can provide a valuable guideline for the safety design of the engine combustion chamber and fuel utilization.

Ultrawideband Compact Lightweight Biconical Antenna With Capability of Various Polarizations Reception for Modern UAV Applications

This article presents the results of numerical modeling, optimization, fabrication and performance measurements of a new biconical antenna for modern unmanned aerial vehicle (UAV) applications. The developed antenna effectively combines a set of fundamental constructive and electromagnetic requirements, which include compact structure and small total dimensions, lightweight, and ultrawideband operating frequency range with the capability of receiving or transmitting both circular, horizontal, vertical, and one of slant linear polarizations. For the first time, an effect of multiple resonance reflections in the structure of biconical antenna with a polarizer and deterioration of antenna’s matching and gain characteristics at a series of frequencies was detected by measurements. Theoretical analysis of the observed resonances has been carried out in this article. Possible ways to exclude resonances are given. In the most part of operating frequency range 2–18 GHz, the developed antenna provides voltage standing wave ratio (VSWR) less than 2 and gain higher than 3 dBi for the -45° slant polarization, while the +45° slant polarization is discriminated by more than 15 dB.

Customizing the structure and chemical composition of ultralight carbon foams for superior microwave absorption performance

Developing biomass-derived three-dimensional porous carbon materials (porous carbon foam, PCF) has become a common strategy to obtain lightweight and efficient electromagnetic microwave-absorbing materials. Without the introduction of a template and subsequent activation process, several ultra-lightweight honeycomb PCF samples were successfully prepared from dried ballonflower/yamakurage (DB) by simple calcination. In addition, the calcination temperature plays a decisive role in regulating the pore size, composition and microwave absorption properties of PCF samples. Furthermore, it is worth noting that different cutting directions also influenced the hole size of the PCF sample and the microwave absorption performances. Under the combined effects of multiple reflections and scattering of PCF porous structure, dipole polarization of abundant heterogeneous atoms and good conductive loss of carbon material, the vertical cutting sample PCF-900V exhibits optimal microwave absorption performances with the minimal reflection loss (RLmin) value of −46.95 dB at 1.46 mm thickness and the effective absorption bandwidth (EAB) value of 5.52 GHz at 1.72 mm matching thickness respectively, indicating its great potential for application as a promising lightweight and efficient microwave absorbing material.