Finite Integration Technique Research Articles

Design and experimental investigation of an origami inspired X-band accordion waveguide

This paper presents design, numerical analysis and experimental investigation of an origami inspired X-band accordion waveguide that is aimed to create a flexible and adaptive solutions. The design process is conducted in a Finite Integration Technique (FIT) based microwave simulation software to model and simulate the proposed waveguide, and that shows structural benefits of origami technique based paper folding. Proposed waveguide model is numerically analyzed under both X and Y bending with 30˚, 60˚, 90˚ and 120˚ bending angle to provide its flexibility. Besides, the electric and magnetic field distributions were also obtained and explained in details to provide working mechanism of the proposed accordion waveguide. The S21 transmission characteristics between ports exhibits a decrease of 0.015 dB in numerical results, which is negligible and acceptable in applications. The experimental results demonstrate that the proposed waveguide has effective transmission characteristics within the 8–12 GHz X-band frequency range, with a satisfactory S21 transmission parameter. The numerical and experimental results show that proposed origami inspired accordion waveguide has a huge potential for application in dynamic microwave and satellite components.

Microstrip Patch Antenna Design for 5G and Beyond Wireless Communication Systems

This paper gives a theoretical evaluation on how feeder lengths are appropriate for distinct conductor materials using rectangular microstrip patch antenna shape with the help of finite integration techniques (FIT). In this study, the ground surface width is 5.6mm and the ground surface length is 4.65 mm for the rectangular microstrip patch antenna. The length of the patch is 3.44 mm while the patch width is 4.40 mm. The substrate thickness is at 0.20 mm, the patch thickness is 0.035 mm the additional inner feed length is 1.05 mm and the microstrip line feed width is 0.6 mm. Antenna of rectangular microstrip patch type has been designed to work in the 20 – 36 frequency band and working frequency of the proposed antenna is 28 GHz. Compared to the use of a single conductor on the surface of the designed patch antenna, three different conductor materials-copper, gold, and aluminum-were applied to the patch surface of the antenna. The return loss (S11), voltage standing wave ratio (VSWR), bandwidth (BW), directivity and gain of the microstrip antenna parameters are studied using finite integration method Computer Simulation Technology (CST) based on nine different feed lengths in microstrip antenna design. When analyzing the feature of the simulation, the optimal S11 can be observed at the 28 resonant frequencies in the copper conductor. According to the analysis results, for copper conductor the best S11 was obtained at a resonant frequency of 28.03 GHz. The value of S11 is -31.19 dB and the BW value is 968 MHz. For the gold conductor the high return loss is achieved using the at the resonated frequency of 28.01 GHz. S11 value is -32 dB and the BW value is 972 MHz Aluminum conductor has the highest value of S11 with a resonant frequency of 28.01 GHz as shown in -33.29 dB and BW value is 976 MHz. Unsurprisingly, the characterization of the conductor deposition on each structure shows that aluminum conductor yielded the best S11 among all the conductor types. The VSWR is equal to 1.05 for copper conductor at resonant frequency of 28.03 GHz, 1.05 at gold conductor at a resonant frequency of 28.01 and 1.04 for aluminum conductor at a resonant frequency of 28.01 GHz. The maximum directivity values that have been attained in the three-dimensional (3D) representation of the copper conductor, gold and aluminum conductor antennas are nearly 6.99 dBi, respectively. The maximum values of the gain are obtained for the 3D representation of copper, gold and aluminum conductor antennas are 6.61, 6.60 and 6.58 dBi, respectively.

Compact Ultra-Wide Band Two Element Vivaldi Non-uniform Slot MIMO Antenna for Body-Centric Applications

This work presents a novel compact two-port Vivaldi Non-uniform Slot MIMO Antenna (VNSMA) to overcome the challenges of traditional ultra-wideband (UWB) antennas, such as large size, limited bandwidth (BW), high mutual coupling, and suboptimal performance in wearable devices. Designed based on Vivaldi non-uniform slot profile antenna (VNSPA) theory, this antenna offers superior performance metrics and significantly advances wearable antenna technology. The novelty of this work is investigating different positions for the two compact UWB VNSA to get better performance with smaller sizes, wider impedance matching BW, and lower mutual coupling (MC) where side by side at an angle of 180ᵒ is determined to be the best configuration. Detailed parametric studies were performed on this configuration for better performance, where the MC was further reduced by etching the ground plane with a vertical slot between the two antennas and L slots around the Microstrip to Slot (M/S) transition, respectively. Furthermore, BW and gain enhancements were obtained by etching exponential tapered and triangular slots at its two edges. Using the Finite Integration Technique (FIT), Computer Simulation Technology (CST) software is used for the simulations in this work. The VNSMA is tested on a CST Gustav human phantom and gives excellent results with low specific absorption rate (SAR) values at several UWB frequencies. The proposed VNSMA provides good, measured outcomes of S11 < -11.08 dB with wide BW of 12.5 GHz (2.33–14.83 GHz) covering high isolation of -23 dB (for most of frequency band), moderate-high gain of 5.89 dBi, radiation efficiency of 66-90%, low Envelope Correlation Coefficient (ECC) of 0.002 and high diversity gain (DG) of 9.99 dBi, stable radiation patterns, and average group delay of 1.2 ns. This innovative design, which optimizes antenna positioning and incorporates ground plane modifications, achieves remarkable improvements in BW, which covers multiple bands, including WLAN (2.4–2.485 GHz), X-band (8-12 GHz), and part of Ku band (12-18 GHz). The findings demonstrate the antenna's potential for various high-resolution microwave imaging applications, particularly in medical diagnostics like breast and brain cancer detection, showcasing its impact in wearable technology and healthcare.

The leakage field characteristics of a large hybrid electromagnetic pulse simulator.

The leakage field of a hybrid electromagnetic pulse simulator with horizontal polarization is simulated and experimentally investigated based on the finite integration technique in this paper. The field distribution characteristics and far-field radiation pattern of the simulator are given. The attenuation characteristics of the electric field at specific directions in the z = 2m plane are also predicted by numerical data fitting. Finally, according to the ICNIRP guidelines, the safe distances that satisfy the occupational and public exposure limits are obtained, and the safety regions lower than the reference levels are given. Results show that the electric field in the α = 0° direction is mainly contributed by the main polarization component (Ey), while the total electric field in the α = 90° direction also requires consideration of the vertical component (Ez). The dominant radiation direction in the z = 2m plane lies between α = 0° and 30°, which poses the highest demand for the safe distance around the simulator. In addition, impedance mismatch and ground reflection are the main factors affecting the waveforms of the radiated electric field.

Numerical Modeling of Hybrid Solar/Thermal Conversion Efficiency Enhanced by Metamaterial Light Scattering for Ultrathin PbS QDs-STPV Cell

Ultrathin cells are gaining popularity due to their lower weight, reduced cost, and enhanced flexibility. However, compared to bulk cells, light absorption in ultrathin cells is generally much lower. This study presents a numerical simulation of a metamaterial light management structure made of ultrathin lead sulfide colloidal quantum dots (PbS CQDs) sandwiched between a top ITO grating and a tungsten backing to develop an efficient hybrid solar/thermophotovoltaic cell (HSTPVC). The optical properties were computed using both the finite integration technique (FIT) and the finite element method (FEM). The absorptance enhancement was attributed to the excitations of magnetic polaritons (MP), surface plasmon polaritons (SPP), and lossy mode resonance (LMR). The HSTPVC with the metamaterial optical light management structure was assessed for short-circuit current density, open-circuit voltage, and conversion efficiency. The results show a conversion efficiency of 18.02% under AM 1.5 solar illumination and a maximum thermophotovoltaic conversion efficiency of 12.96% at TB = 1600 K. The HSTPVC can operate in a hybrid solar/thermal conversion state when the ITO grating is included by combining the advantages of QDs and metamaterials. This work highlights the potential for developing a new generation of hybrid STPV cells through theoretical modeling and numerical simulations.

Numerical analysis of the effects of pores on propagating guided waves

The present numerical study aims to analyze the effect of pores on propagating guided waves while outlining the relevance of pore formation and its significance to structural properties. The primary focus of this study was on the pores present in planar carbon fiber-reinforced polymer (CFRP) parts. The wavefield data were generated by applying the elastodynamic finite integration technique (EFIT) solver AE3D, allowing for a systematic analysis based on fully controllable configurations and noise-free data. An isotropic material model was used to simplify the modeling of the anisotropic CFRP by assuming the averaged quasi-isotropic properties of the CFRP in all directions. More than 220 specimens containing single pores or four basic configurations of pore accumulations were modeled and analyzed in terms of their effect on the out-of-plane component of the propagating guided waves. Analysis of the guided wavefield data focused on the direction-dependent maximum amplitude differences and deviations in the wavefield energy. Mode- and wavenumber-specific amplitude loss along the centerline was analyzed using a matrix pencil algorithm. Finally, principal component analysis (PCA) was conducted to examine deviations caused by the presence of pores. Analysis of the wavefield effects of the pores for each specific configuration showed good differentiation between the considered pore volume groups. At the same time, the effects of the pores were shown to be significantly dependent on the pore configuration in terms of orientation and morphological properties. Associated with this, the intersecting outcome ranges for different pore volume groups were evident when all the pore configurations were considered simultaneously.

Application of multi-objective optimization genetic algorithm to design terahertz metamaterials with fano resonances

In the prosperous development of terahertz (THz) metamaterials, Fano resonances have gained attention due to their potential applications in ultrasensitive systems. The performance of Fano resonance is directly influenced by the geometrical parameters of the element structure. However, the traditional design rules for Fano resonances in metamaterials rely on an empirical trial-and-error strategy, necessitating significant effort to achieve optimal results. To address this issue, we propose a design method in this study that utilizes the finite integration technique in time domain (FITD) along with a multi-objective optimization genetic algorithm for the intelligent design of metamaterial structures exhibiting the Fano resonance phenomenon. The FITD method is primarily used to calculate the Fano resonance with different metamaterial geometric structure parameters, while the genetic algorithm efficiently selects the optimal solution. Our method, characterized by high efficiency and complete independence from prior knowledge, could offer a new design technique for metamaterials with specific functions, thereby contributing to the development of THz applications.

Left-handed metamaterial based on circular split ring (CSRR) resonator for microwave sensing Application

This paper presents a new metamaterial structure specifically designed to operate in the L, S, and C frequency bands. It is characterized by a small unit cell size of 15mm × 15 mm. The metamaterial's electromagnetic properties are thoroughly examined, utilizing FR-4 substrate material and copper circular split ring resonators (CSRRs). The Computer Simulation Technology (CST) software uses the finite integration technique (FIT) to precisely model the effective parameters over a frequency range of 0–6 GHz. In simulations and experiments, the structure demonstrates negative refractive index, effective permittivity, and effective permeability. The electric and magnetic field distributions within the unit cell are accurately characterized using vector fields. In addition, the equivalent circuit is simulated and depicted using ADS software, with comparisons drawn between the measured data and the simulated data. The experimental validation, conducted using six varying thicknesses of FR4 materials, verifies the resemblance between the simulated and the measured transmission coefficients. Moreover, the effective medium ratio (EMR) of the metamaterial is calculated to be 12.74, indicating its promising capabilities for microwave sensing applications. The examination of the sensor model uncovers such metrics as quality factors, frequency detection resolution (FDR) values, and sensitivities, all of which enhance our comprehension of the material's performance. This discovery has the potential to advance the development of sensing metamaterials, which could significantly impact various applications and enhance research in the field.

Advancing electromagnetic field modeling in axially anisotropic media with conformal method in 3D cylindrical coordinate systems

A conformal methodology for solving electromagnetic fields in axially anisotropic media in 3D cylindrical coordinate systems is proposed for the investigation of high-power microwave devices filled with such media. This method leverages the material properties of axially anisotropic media and employs the finite integral technique for solution. A simplified conformal algorithm is utilized for the boundaries of the computational region, extending the traditional conformal method for axially anisotropic media in 3D cylindrical coordinates. The proposed methodology is validated through simulations of TM01 and TE01 mode propagation in a circular waveguide filled with the medium. Subsequently, the method is integrated into particle-in-cell simulations, and an X-band relativistic backward wave oscillator filled with an axially anisotropic medium exhibiting azimuthal conductivity is numerically modeled. The results demonstrate that the medium with azimuthal conductivity effectively mitigates asymmetric modes in the relativistic backward wave oscillator, aligning with published literature. This study offers technical insights for research on high-power microwave devices incorporating axially anisotropic media, potentially facilitating the development of innovative microwave devices with enhanced performance characteristics.

Design of Concrete Mock-Ups with Complex Defect Scenarios Using Numerical Simulations

The major objective when applying non-destructive testing (NDT) in civil engineering is the detection of defects such as honeycombs. Defects can impair the service life of structures and could lead in the worst case to fatal failures. All structures such as bridges, tunnels, locks etc. are unique objects with variation in geometry, dimensions, materials, environmental condition, load scenarios etc. Thus, the interpretation of NDT data is challenging and the validation of the NDT method, the training of inspectors and the reliability analysis of NDT rely on mock-ups with known defect situations mimicking the type of defect as realistic as possible. The considered defect sizes inside the mock-ups should cover the transition zone between detectable and non-detectable to properly evaluate the capability of the inspection system. However, knowledge about the limits of an inspection system is mostly non-existent. To overcome this limitation, this study applies realistic numerical simulations for ultrasonic testing in reinforced concrete performed with the elastodynamic finite integration technique (EFIT) to identify this transition zone. First, the study shows the development and the validation of a numerical representation of concrete considering the implementation of a qualitatively realistic noise level. Additionally, the accurate representation of the sources during ultrasonic testing is confirmed by an investigation of the radiation characteristic for dry point contact ultrasonic transducers. The simulation outcome enabled the design of a mock-up, which explores the detection limits for honeycombs during ultrasonic testing under different boundary conditions. A case study demonstrates the applicability of the design scheme based on numerical simulation. In the real specimen designed with the assistance of numerical simulations, 68%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$68\\mathrm{\\%}$$\\end{document} of the implemented defects are detectable, proving the effectiveness of the design methodology.

Total variation regularization analysis for inverse volatility option pricing problem

We investigate in this paper an inverse problem of recovering the space-dependent volatility in option pricing. To enhance precision across the domain, we transform the original problem into an inverse source problem of a bounded degenerate parabolic equation, utilizing linearization and variable substitution. Unlike classical methods, we apply a total variation regularization combined with a novel generalized finite integration technique. This approach accommodates volatility jumps in an overnight rate scenario. Leveraging an optimal control framework, we demonstrate that the inverse problem can be reformulated as an optimal control problem whose existence, necessary conditions, local uniqueness and stability for the minimizer of control functional are obtained. For numerical verification, we derive the Euler equation and design a discretization algorithm with generalized finite integration technique. Numerical examples showcase the robustness of our approach, highlighting advantages in accuracy and effectiveness over other strategies.

Tuneable double negative (DNG) Tri-Hexagonal split ring resonator metamaterial for 5G application

This paper introduces a compact tuneable metamaterial (MTM) unit cell featuring a tri-hexagon and tri-square split ring resonator (THTSSSR) structure designed for 5G communication applications. Metamaterials are employed to achieve unique electromagnetic properties not found in natural materials. The design process involves the arrangement of three square rings and three hexagon rings as metallic patches on a Rogers substrate (RT 5880), measuring 7 x 7 mm2 with a thickness of 1.575 mm. The proposed design exhibits double negative (DNG) properties, with resonances in the transmission coefficient (S21) at 3.493 GHz and a bandwidth of −10 dB covering frequencies between 3.057 and 3.711 GHz. Numerical simulations conducted using finite-integration techniques (FIT) in CST Microwave Studio validate the design's effectiveness, with confirmation through the Advanced Design System (ADS). The MTM unit cell demonstrates tuneable attributes, including negative permittivity ranging from 3.39 to 5 GHz and negative permeability from 3.39 to 3.86 GHz. These findings highlight the compactness and tunability of the proposed design, making it promising for 5G communication applications.

Efficient testing of weld seam models with radii of curvature in the millimeter range using laser ultrasound

Laser ultrasound is a widely used tool for industrial quality assurance when a contactless and fast method is required. In this work, we used a laboratory setup based on a confocal Fabry–Perot interferometer to examine weld seam models. The focus was placed on small samples with curved surfaces (small in the sense that the radius of curvature is comparable to the largest ultrasonic wavelength) and on efficient ways to detect the presence and volume of process pores, with the goal to transfer this method to industrial applications. In addition to this experimental method for investigating welds, a numerical method that models the experimental setup was implemented in MATLAB. For this purpose, first the thermal effects of the excitation process were taken into account by solving the thermal diffusion equation with an explicit scheme. Then, the elastodynamic equations were solved using the Elastodynamic Finite Integration Technique, taking into account the stresses induced by the excitation process. The B-Scans generated with this numerical model were compared with experimental B-Scans for simple test cases and good agreement was found. In a next step, the additional structures in the B-Scans resulting from air inclusions were identified and investigated with both methods using flat test specimens at first. Besides the direct echoes, structures from skimming surface waves and multiple reflections were visible. These additional structures are unwanted in defect reconstruction methods like the Synthetic Aperture Focusing Technique (SAFT) as they would lead to artifacts. In samples much larger than the largest ultrasound wavelength, however, these unwanted structures are still negligible in amplitude or can be well separated temporally, but for small samples this is no longer the case. As a result, reconstruction methods based on direct echoes like SAFT are difficult to apply. For many industrial applications, the reconstruction is not decisive at all, but only the knowledge of the total volume of process pores (TVPP). It is shown with both experimental and numerical methods, that this TVPP can be estimated from the variation in the B-Scans from various small weld seam models.

Periodic stub implementation with plasmonic waveguide as a slow-wave coupled cavity for optical refractive index sensing

Optical biosensors based on plasmonic nanostructures have attracted great interest due to their ability to detect small refractive index changes with high sensitivity. In this work, a novel plasmonic coupled cavity waveguide is proposed for refractive index sensing applications. The structure consists of a metal–insulator–metal waveguide side coupled to an array of asymmetric H-shape element, designed to provide dual-band resonances. The sharp transmission dips and large field enhancements associated with dual-band resonances can enable sensitive detection of material under test. The resonator array creates a slow light effect to improve light-matter interactions. The structure was simulated using the finite integration technique as the full-wave technique, and the sensitivity and figure of merit were extracted for different ambient refractive indices. The maximum sensitivity of 1774 nm/RIU and high figure of merit of 2 × 104 RIU−1 for the basic model and 1.15 × 105 RIU−1 for the modified model were achieved, demonstrating the potential for high-performance sensing. The unique transmission characteristics also allow for combined spectral shaping and detection over a broad bandwidth. The simple, compact geometry makes the design suitable for on-chip integration. This work demonstrates a promising refractive index sensor based on coupled dual-band resonators in a plasmonic waveguide.

Polarization Insensitive and Thin Metamaterial Absorber Performed in High-Frequency 5G Bands

A variety of fascinating applications, including 5G communication devices, high-speed data transfer, and large-scale Internet of Things (IoT), make life easier with 5G technology. Despite the 5G’s superior features, the percentage of electromagnetic (EM) waves in the environment execute a significant increase, unpleasantly. Broadband metamaterial absorbers are an appealing alternative to gather these unwanted signals. This study aims to numerically investigate a broadband metamaterial absorber (MMA) in the 5G high-frequency spectral range with the metasurface formed with coupled resistors. In addition, the 24.25-27.5GHz frequency range, one of the high-frequency 5G bands used by selected countries such as the European Union and China, was preferred. The minor aim of this study is that the usage of coupled elements as resistors may have the ability to increase the absorption bandwidth and magnitude. Comprehensive simulations were performed using the finite integration technique (FIT) utilized by the CST Microwave Studio program to investigate the absorber performance and other relevant parameters. The unit cell design is created metal-substrate-metal structures as asymmetric, single-layer, and easy to implement. The absorption responses are investigated according to the oblique incidence angle, polarization angle for TE &amp;amp;TM modes. The suggested MMA provided an absorbency response above 87.6% in the frequency range 24.20-27.30GHz under normal incidence. Moreover, to comprehend the physical mechanism on absorption, the top and bottom surfaces of the absorber's electric field and surface current distributions are assessed. The designed MMA resulting in relatively high performance and polarization insensitive is helpful for electromagnetic interference (EMI) shielding of 5G signals in the FR2/mmWave frequency regime.

Magnetic characterization of steel strips using transient field measurements: global sensitivity analysis and regression from a machine-learning perspective

In this contribution, the magnetic characterization of steel strips is studied using synthetic data of field-gradient transients, which have been produced via the finite integration technique. The material law is described and parameterized using the Jiles–Atherton model. The sensitivity of relevant magnetic indicators with respect to the material parameters is then analyzed using two global methods: Sobol’ indices and δ-sensitivity indices. In order to accelerate the evaluation of these quantities, a fast metamodel is built using machine learning techniques from a simulated dataset. The solution of the inverse problem based on a tailored learning framework is tested for the different proposed identifiers, and their suitability for the magnetic characterization of the material in question is finally discussed.

Wideband close perfect meta surface absorber for solar photovoltaic and optical spectrum applications

The leading research challenge is to develop a meta-surface absorber design for optimal performance across ultraviolet, visible, and near-infrared wavelengths. In ongoing research, a meta-surface absorber is being introduced, designed to achieve near-perfect absorption of 99% across the 250–2500 nm UV–Vis-NIR spectrum for both Transverse electric (TE) and Transverse magnetic (TM) polarized waves. The aimed design features a symmetrical resonator pattern, resulting in a polarization-insensitive absorption response. Additionally, the absorption response demonstrates robustness when altering the geometric parameters of the meta-surface unit cell. Precise simulation and modelling of the proposed meta-surface absorber are achieved by Employing a Finite Difference Frequency Domain (FDFD) solver, coupled with the Finite Integration Technique (FIT) and a tetrahedral mesh component. Verification of absorption characteristics is conducted through three frameworks: impedance matching, interference, and an equivalent circuit model. The suggested meta-structure design exhibits a uniform absorption response, as determined through considerations of impedance matching, interference theory, and the equivalent circuit theory. The PCR value is significantly lower than recent studies, reinforcing that the proposed meta-surface primarily serves as an absorber, not a polarization converter. The absorption response of the suggested meta-structure design remains consistent across the range of electromagnetic wave polarization angles from 0 to 90 for both TE and TM waves. Furthermore, the absorption response of the proposed design demonstrates stability up to an incident angle of 70 for electromagnetic waves. The distribution of electric and magnetic fields, along with surface current density on the proposed design, validates the existence of localized, propagating, and cavity surface plasmon resonance. These collectively create anti-parallel current flow, leading to the absorption of incident EM waves. Furthermore, the suggested design achieves a solar energy thermal conversion efficiency of 99% across the operational spectrum at a working temperature of 573 K, substantiating its potential for use as a solar absorber. Thus, this study presents a meta-structure unit cell that addresses the challenge with near-perfect absorption, polarization independence, and angle robustness. Applications include photodetection, thermal mapping, solar harvesting, and photo-trapping.

Wide-angle and polarization-insensitive perfect metamaterial absorber

We propose a cross-shaped resonator design of a metamaterial (MTM) absorber that shows a 98% average absorbance in the range of 400–1100[Formula: see text]nm. This design consists of three layers: a tungsten-based cross-shaped on the top, silicon dioxide (SiO2) in the middle layer, and a tungsten layer at the bottom. The finite integration technique (FIT) method is used to simulate the metamaterial absorber’s performance. We have observed the absorber’s performance on the different thicknesses of a dielectric layer. We have presented the absorption spectrum for transverse electric (TE) and transverse magnetic (TM) modes for different polarization angles (0°–90°) and incident angles (0°–60°). Additionally, we have investigated the short-circuit current density for different dielectric layer thicknesses and different incidence angles. This is theoretically analogous to parametric studies. The universal AM 1.5 solar spectrum properties have been used to investigate the feasibility of the proposed MTM absorber as a solar cell. The proposed MTM has many potential uses, including for solar cells.

A new large area MCP-PMT for high energy detection

20-inch Large area photomultiplier tube based on microchannel plate (MCP-PMT) is newly developed in China. It is widely used in high energy detection experiments such as Jiangmen Underground Neutrino Observatory (JUNO), China JinPing underground Laboratory (CJPL) and Large High Altitude Air Shower Observatory (LHAASO). To overcome the poor time performance of the existing MCP-PMT, a new design of large area MCP-PMT is proposed in this paper. Three-dimensional models are developed in CST Studio Suite to validate its feasibility. Effects of the size and bias voltage of the focusing electrodes and MCP configuration on the collection efficiency (CE) and time performance are studied in detail using the finite integral technique and Monte Carlo method. Based on the simulation results, the optimized operating and geometry parameters are chosen. Results show that the mean ratio of photoelectrons landing on the MCP active area is 97.5%. The acceptance fraction of the impinging photoelectrons is close to 100% due to the emission of multiple secondary electrons when hitting the MCP top surface. The mean transit time spread (TTS) of the photoelectrons from the photocathode is 1.48 ns.

A multiscale 3D hotspot-rich nanostructured substrate for biomolecular detection of SARS-CoV-2

The current fabrication methods of surface-enhanced Raman scattering (SERS) chips used for biological detection mostly require antibodies conjugated on nanostructured metals or additionally connected to a reporter, which leads to complicated fabrication processes and increases the cost of these chips. More importantly, only a single-layer (2D) signal source is generated on the substrate of the chip, resulting in poor sensitivity. Herein, we constructed a single-component, multiscale, three-dimensional SERS (M3D-SERS) substrate from silver nanowires (AgNWs) packing. According to our results, the Raman enhancement effect of the M3D-SERS substrate was related to the degree of AgNWs stacking along the z axis. In addition, the light source-dependent plasmonic partition and hotspot formation of the M3D-SERS substrate were evaluated by the finite integration technique to prove that M3D-SERS offers advantages, with isotropic localized surface plasmon resonance as well as homogeneous hotspot distribution, for SERS over its 1D and 2D counterparts. Experimentally, the optimal construction of the M3D-SERS chip was explored and established based on the Raman signal enhancement of bovine serum albumin, and consequently, the efficiency of the M3D-SERS chip in detecting SARS-CoV-2-related biomolecules was investigated based on the detection superiority to biomolecules. This study demonstrates a simple, label-free, pre-treatment-free potential biosensor technology that can be used in healthcare units. Furthermore, in combination with a suitable laser light source, this technology can be applied for efficient detection in point-of-care tests with a handheld spectrometer.