Time-domain Technique Research Articles

Numerical Analysis of a Highly Sensitive Surface Plasmon Resonance Sensor for SARS-CoV-2 Detection.

In this paper, we propose a surface plasmon resonance (SPR) structure based on Kretschmann configuration incorporating layers of silicon and BaTiO3 on top of Ag for real-time detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using thiol-tethered DNA as a ligand. Extensive numerical analysis based on transfer matrix theory as well as finite-difference time-domain (FDTD) technique has been performed to characterize the sensor response considering sensitivity, full width at half maxima, and minimum reflection. About 7.6 times enhanced sensitivity has been obtained using the proposed architecture for SARS-CoV-2 detection, compared to the basic Kretschmann configuration. Notably, the structure provides consistent enhancement over other competitive SPR structures for both angular and wavelength interrogations with a figure-of-merit of 692.28. Additionally, we repeated simulations for various ligate–ligand pairs to assess the range of applicability and robust performance improvement has been observed. As a result, the proposed sensor design provides a suitable configuration for highly sensitive, rapid, noninvasive biosensing which can be useful if adopted in experimental sensing protocols.

Phenomenology of automotive radar interference

Mutual interference in automotive radar is expected to become a major issue owing to the rapid increase in the number of vehicles on the road equipped with radar. The phenomenology of interference in frequency modulated continuous wave radar is presented. Interference is empirically analysed at every signal processing stage in the victim radar by means of experimentally verified simulation modelling. Knowledge of how interference manifests in different domains provides a useful tool to develop algorithms for interference detection, mitigation and/or avoidance. The receiver's filter response is analysed to minimise the interference duration and increase the effectiveness of time-domain mitigation techniques. A innovative method of interference parameter extraction by using spectrograms is also introduced.

Group Based Dual Mode Key Management Scheme for Secure Communication in Vehicular Ad Hoc Networks

Vehicular ad hoc networks (VANETs) provide similar services at various service points, so selecting the efficient service among the available services is a crucial task. Similarly, accessing services to exchange time-critical messages demands secure schemes. In this work, an efficient group-based dual mode key management (G-DMKM) scheme is proposed to select efficient service and the secure route to access the service. In G-DMKM for each session, the base stations are grouped according to localization in a time window manner which restricts the key and group lifetime. The time-domain randomization technique is used to generate a group key for each group and is shared between all stations and vehicles. Vehicles are authenticated for communication based on group and private keys. The private key is generated by the base station under which the vehicle is located. In G-DMKM, the multi-attribute location selection approach (MALSA) computes the multi-attribute service fitness (MASF) for each service to select the optimal service from the available services. Furthermore, Secure Transmission Support (STS) estimates the STS value for each route identified towards the service point, and the route with the highest STS support is selected for secure access to the service and data transmission. Simulation results show that the inclusion of an STS-supported route improves G-DMKM efficiency in all aspects compared to the conditional privacy-preserving authentication (CPAS), Proxy Based Authentication Scheme (PBAS), and Secure Privacy-Preserving Authentication Scheme with Cuckoo Filter (SPACF).

Deep convolution neural network for damage identifications based on time-domain PZT impedance technique

Recently, Intelligence-based structural health monitoring (SHM) methods have investigated widely. Most of these methods are for detecting and classifying different structural damages by the means of features extraction from the structural responses signals, for instance different back propagation artificial neural networks SHM based methods. However, automatic features extraction, that eliminates the need for expertise and performing visual inspection to evaluate structures status is still a big challenge. In this study, therefore, a novel convolution neural network-based algorithm along with a hybrid training method has been proposed to detect, quantify and localize structural damage. The proposed method has been evaluated experimentally, many damaged and undamaged structural conditions have been conducted, acquiring samples of time-domain PZT impedance response signals from a beam. As the results show that, the method obtained a significant execution on damage detection, damage size evaluation and damage location recognition with high accuracy and reliability.

Micro/Nano profile measurement by structured illumination microscopy utilizing time-domain phase-shift technique

Aiming at the technical difficulties in the rapid detection and reconstruction of three-dimensional micro-nano devices that are difficult to achieve both high precision and high speed, this paper proposes a structured light detection method based on time-domain phase shift technology. The measured light is modulated by a spatial light modulator, and the time-domain phase shift technology is further employed to realize the detection and reconstruction of three-dimensional micro-nano devices. Compared with the traditional structured light detection method, this technology uses the spatial light modulator to measure the phase shift while the sample is scanned axially, so as to ensure the measurement accuracy and improve the measurement efficiency. By analyzing the measurement data, this method can quickly realize three-dimensional shape detection and reconstruction, and the measurement accuracy can be better than 10 nm.

Efficient and de-noising calculation for extracting impulse response function in time-domain

ABSTRACT Impulse response function (IRF) and frequency response function (FRF) are the bases and preconditions for acquiring the parameters of a dynamic system and accurately obtaining the dynamic response of the system both in time and frequency domains. In the test of dynamic characteristics of a structural system, for some cases, it is not suitable to use the average power spectrum and cross-spectrum methods to obtain the FRF of the system. This paper studies the methods of extracting the IRF in the time domain, where the measured input and output signals contain white Gaussian noise. According to Duhamel’s integral and the time-domain averaging technique, an efficient average recursive (AR) algorithm with anti-noise performance is proposed to obtain the impulse response function. In the AR method, it is assumed that the input and output data of the system are composed of white Gaussian noise with a mean value of zero. The proposed AR algorithm avoids the inversion of a larger matrix and improves the efficiency of calculation. Simulation and experimental results show that it has apparent advantages in computing efficiency and de-noising.

A Novel Time-Domain Passive Islanding Detection Technique for Grid-Connected Hybrid Distributed Generation System

In this paper, a time-domain passive islanding detection technique for a grid-connected hybrid distributed generating system has been developed using modified empirical mode decomposition (MOEMD). With the help of the MOEMD, the point of common coupling voltage is decomposed into several oscillatory components called intrinsic mode functions. The islanding will be detected if the magnitude of the islanding detection waveform exceeds the threshold over a predefined delay time. The proposed technique can identify all kinds of islanding cases even for zero power mismatches nearly at 0.3 s of the predefined delay time. The effectiveness of the proposed scheme is tested for different operating conditions that include various non-islanding events. Moreover, the proposed method is faster than the discrete wavelet transform technique, and it has low computational time. The advantages of the proposed method are independent of the system parameters, zero non-detection zone, no classifier requirement, and its performance is independent of the capacity and nature of D.G. connected to the grid.

A High-Efficient Wireless Power Receiver for Hybrid Energy-Harvesting Sources

This article presents a power-efficient hybrid energy-harvesting system that scavenges energy from solar, vibration, and radio frequency (RF) energy sources and converts into regulated output dc voltage courtesy buck–boost dc–dc converter. The proposed architecture incorporates tetra-paths for maintaining high power conversion efficiency (PCE) over extended input power range (−10 to 30 dBm). A time-domain maximum power point tracking technique is proposed for solar energy harvester. A high-efficiency full wave rectifier is designed for triboelectric rectifier. A 5.8-GHz RF-dc converter with adaptive matching is proposed to increase dynamic range of the input power. The chip is implemented in 0.18-µm bipolar-CMOS-DMOS process. The die area of the chip is 2.8 mm × 5.0 mm, including the pads. The solar and triboelectric energy harvesters achieve a measured peak efficiencies of 75.4% and 92.3%, respectively. The high-power 5.8-GHz RF-dc converter achieves measured PCE of 76% at 30 dBm input power. The low-power dual-band RF-dc converter operating at 900 MHz and 2.4 GHz obtains measured peak efficiencies of 73% and 71.9% at 0 dBm input, respectively. The buck–boost dc–dc converter employed in the proposed hybrid energy harvesting system achieves a measured peak PCE of 94.5%.

Characterization of topographic effects on sonic boom reflection by resolution of the Euler equations.

The influence of topography on sonic boom propagation is investigated. The full two-dimensional Euler equations in curvilinear coordinates are solved using high-order finite-difference time-domain techniques. Simple ground profiles, corresponding to a terrain depression, a hill, and a sinusoidal terrain, are examined for two sonic boom waves: a classical N-wave and a low-boom. Ground reflection of the sonic boom is affected by elevation variations: a concave ground profile induces compression, which tends to increase the peak pressure in particular, while the opposite is true for convex elevation variations, which lead to expansion and a reduction in peak pressure. The reflected boom is then strongly altered. Furthermore, a sufficiently concave topography can cause focal zones, which generate extra contributions at ground level in the form of U-waves in addition to the reflected wave. This mechanism has the largest effect on waveforms at ground level. The variations of standard metrics are of a few dBs compared to a flat ground for both sonic boom waves, and they are notably greater for the terrain depression than for the hill. Finally, in the case of a sinusoidal terrain, the pressure waveforms are composed of multiple arrivals due to successive focal zones.

Sonic boom reflection over irregular terrain

An overview of recent studies on sonic boom reflection over irregular terrain is presented. Numerical simulations based on the two-dimensional Euler equations are performed using high-order finite-difference time-domain techniques, allowing for an accurate prediction of diffraction. Studies are done for two sonic boom waves: a conventional N-wave and a low-boom wave. First, ground elevation effects on sonic boom are examined. An academic ground profile, corresponding to a terrain depression, is considered to highlight mechanisms at play. In particular, caustics due to ground elevation variations induce another contribution at the ground level, in the form of a U-wave. Results for real ground profiles are then presented and cumulative effects, due to the succession of terrain irregularities, are shown. Second, propagation of sonic boom over an urban profile is investigated. Possible resonance effects inside street canyons are discussed. For all cases, statistics of noise metrics are examined. [This work was performed within the framework of the LabexCeLyA of the University of Lyon, within the program ‘‘Investissements d’Avenir” (ANR-10-LABX-0060/ANR-16-IDEX-0005) operated by the French National Research Agency and has received funding from the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 769896 (RUMBLE).]

Terahertz tunable three band narrowband perfect absorber based on Dirac semimetal

A tunable terahertz (THz) narrowband absorber in view of bulk Dirac semimetal (BDS) is designed in this paper. The tunable terahertz absorber's basic unit comprises BDS, intermediate medium, and metal substrate. The BDS has good surface conductivity and the Fermi energy of that is flexible tunable, and the good surface conductivity might make controlled by Fermi energy. The absorption characteristics of the designed absorber are simulated by the finite integral time domain technique. The calculation results show that the designed absorber achieves ideal absorption in 139.97 μm, 163.52 μm, 247.76 μm bands, and the absorption rate is more than 0.96, which realizes ideal narrowband absorption and dynamic tuning. We find that the absorption peaks are flexible and adjustable by changing the Fermi energy of BDS, and the frequency adjustability of the absorber is analyzed. In addition, the effects of different structural parameters on the absorption efficiency and the absorption performance at different incident angles are studied. These results show that, compared with traditional metamaterials, Dirac semimetallic absorbing materials can tune the resonant frequency more effectively, even without reconstructing the structure, which has great application value in many fields, and provide a new reference for future research.

Performance analysis of optimized plasmonic half-adder circuit using Mach-Zehnder interferometer for high-speed switching applications

Metal-insulator-metal (MIM, Plasmonic) waveguide has an exceptional quality of propagating the surface plasmon beyond the diffraction of light into a deep sub-wavelength scale. In this paper, the basic structure for a half-adder circuit is proposed by inducing nonlinear Kerr-material to the Mach-Zehnder interferometers (MZIs). The half-adder circuit design is optimized by using MIM plasmonic waveguide-based MZIs in the footprint of 85 μm ​× ​10 μm. Some parameters like extinction ratio, transmission efficiency, and insertion loss are calculated and found as 16.53 ​dB, 74% and 0.338 ​dB, respectively. The proposed device is concentrated in optical communication with transverse electric (TE) polarization at an operating wavelength of 1550 ​nm. This design is simulated by using the finite-difference time-domain (FDTD) technique and verified by using MATLAB simulation.

Design of a hybrid mode and wavelength division (de)multiplexer based on contra-directional grating assisted couplers on the SOI platform

This paper presents a hybrid mode and wavelength division (de)multiplexer (MDM-WDM), based on the silicon-on-insulator platform using the grating assisted contra-directional coupling principle. The proposed hybrid MDM-WDM is able to (de)multiplex six channels with two wavelengths and three modes. The proposed device is designed by cascading three grating assisted coupler sections. Each coupler section is dedicated to reflecting a specific mode at two wavelengths. The operation of the proposed design is simulated by the 2.5D finite-difference time-domain technique. The analysis shows that the proposed device structure exhibits an insertion loss of < 0.55 d B , return loss of > --> 12.81 d B , extinction ratio of > --> 15.49 d B , and crosstalk of < − 12.74 d B . A fabrication tolerance study for the MDM-WDM device is also performed by changing the inter waveguide distance between the respective multimode bus waveguide and the single-mode waveguide.

New Results for the 1968 Belice, South Italy, Seismic Sequence: Solving the Long-Lasting Ambiguity on Causative Source

AbstractWe present the first estimates of moment tensor solutions and probabilistic nonlinear hypocenter locations for the 1968 Belice earthquake sequence, which is the most relevant seismic activity occurred in western Sicily in historical times. This seismic phase, including six earthquakes with magnitude between 5 and 6.4, produced severe damages and fatalities in a sector of the Nubia–Eurasia plate margin, previously considered aseismic. Poorly constrained and often controversial hypocenter locations and focal mechanism solutions available from the literature have led to a long-lasting ambiguity on the possible causative source of the sequence, also having primary effects on the regional seismotectonic modeling and seismic hazard evaluations. The two main fault models proposed in the literature alternatively assigned a primary role to the north-northwest-trending Nubia–Eurasia plate convergence, causing thrust faulting on about east-trending structures or to the differential foreland retreat driving dextral strike-slip movements on about north–south-oriented faults. By focusing on the starting and the most energetic phase of the 1968 sequence, we computed the moment tensor solutions for three of the strongest earthquakes using digitized waveforms and a time-domain waveform inversion technique. Then, we also analyzed, by means of a Bayesian hypocenter location technique, the spatial distribution of the 1968 earthquakes. All the results indicate that the 1968 Belice sequence was characterized by predominant reverse faulting occurring on about east-to-northeast-trending structures, thus solving the dualism between models previously proposed in the literature. Our findings well agree both with the geodynamic framework governed by the Nubia–Eurasia north-northwest-trending convergence and with the geological reconstructions of the regional thrust front in the western Sicily area. The results of moment tensor estimations and nonlinear hypocenter locations furnishing an improved knowledge of the most relevant seismic activity of western Sicily also concur to better constraint the seismotectonic modeling of the region.

Numerical design of high-performance WS2/metal/WS2/graphene heterostructure based surface plasmon resonance refractive index sensor

The development of a high-performance bio-sensor utilizing the surface plasmon resonance (SPR) phenomenon has attracted great attention recently as a promising and precise sensing technology. Here, we proposed a WS2/metal/WS2/graphene heterostructure based SPR sensor with improved performances. The finite-difference time-domain (FDTD) technique was employed to model and develop the prospective sensor. The effects of integrating different layers, the analyte thickness on the performance of the sensor, and the electric field distribution were investigated systematically. We found that the optimized structure of the developed sensor exhibits the highest sensitivity of 208 deg/RIU with a detection accuracy of 1.12 and a quality factor of 223.66 RIU−1, which is superior to existing two-dimensional material based SPR sensors. The enhancement of light-material interaction caused by the coating of a monolayer WS2 on both sides of the metal improved the sensor performance significantly. These findings demonstrate a new way of performance enhancement in the composite layer sensor, aimed at further improving the identification of specific biomolecules such as glucose, blood disease, environmental monitoring, and agricultural applications.

Two-dimensional viscoelastic imaging using an enhanced FDTD-AHI approach

Ultrasound viscoelastography is a quantitative and convenient imaging model that images soft tissues based on shear waves’ propagation. Thanks to the interaction between ultrasonic waves and shear waves, the physical features of soft tissues (elasticity, viscosity) are expressed by complex shear modulus (CSM) parameters, useful information for diagnosing tissue medical states. Therefore, this paper presented a new efficient approach to estimate CSM and reconstruct the viscoelastic images. This paper develops a two-dimensional shear wave propagation model applying finite difference time domain (FDTD) technique and then employing a proposed bandpass filter to reduce measured particle velocity noise of shear wave; finally, algebraic Helmholtz inversion (AHI) is utilized to estimate the CSM directly. As already known, excitation frequency for ultrasound viscoelastography system is a single one. In the previous research, the low pass filter is used to reduce frequency vibrations and measurement noise as well as fluctuations at low frequency; however, it is unable to completely eliminate noise since the measured particle velocity is affected by high-frequency noise and fluctuations in low frequency. Therefore, the enhanced FDTD-AHI algorithm applies a bandpass filter, which retains only the frequency band containing the excitation frequency, promising to eliminate low- and high-frequency noise. Moreover, we proposed to cut the transient part of the filtered signal to avoid affecting AHI step and thus to improve the CSM estimation. The simulation scenarios have proved the effectiveness of the enhanced FDTD-AHI algorithm. The proposed method’s normalized error is significantly reduced compared to the traditional manner using a low pass filter. We reconstructed two-dimensional images of elasticity and viscosity in the area of interest. The estimated quality near the excitation source is quite good. Still, far away from the excitation source, it is of low quality, and there are many large fluctuations due to the reduced shear wave and being much affected by noise. Another limitation of our proposed method is that it can reduce the additive noise in the lower and higher frequencies of the exciting one except the noise around this frequency. The shear wave propagation model using FDTD method provides high accuracy and low complexity compared to the finite element method (FEM). The absence of optimal or adapted filters in our approach can reduce the imaging system’s computational complexity.

Correlation between mechanical and optical properties of ZnO nanowire

Understanding mechanical and optical responses is significantly important for the development and application of nanowire devices. Hence, special structures are required to provide a level of performance that is adequate for the given application. With this breakthrough, in this work, a model is proposed by combining finite element modeling (FEM) software package ABAQUS and three-dimensional (3D) finite-difference time-domain (FDTD) techniques to measure the strain dependence on the optical behaviors of ZnO nanowire with and without embedding ZnS nanowire and also by the effects of various diameter sizes for the first time. The effects that bending strain have on the optical properties of the material such as electric field intensity and magnetic field intensity have been investigated. The obtained results indicate that the optical characteristics are strongly dependent on the applied strain. In addition, the novel method introduced, is able to furnish a powerful tool for quick comparison between theoretical models and experimental setups for the different properties of nanomaterial, and also should be useful to future predictions for other complex structures. Furthermore, the insights acquired in this study may provide valuable information on the development of robust ZnO nanowire based nanodevices.

Implementation of Passive and Active Circuit Elements in Cylindrical Finite-Difference Time-Domain Formulation

The implementation of passive and active linear circuit elements in cylindrical finite-difference time-domain technique (CFDTD) is developed. The updating equations for active element such as a voltage sources and passive elements such as resistors, capacitors and inductors are represented for elements located along one of the cylindrical coordinate’s independent parameters. The analytical solutions for simple circuit configurations are computed and used as a reference to verify and confirm the accuracy of the developed CFDTD formulation and numerical results.

Terahertz generation by means of ZnGeP2 large aperture photoconductive antenna

The generation of terahertz (THz) radiation using a ZnGeP2 (ZGP) large-aperture photoconductive antenna (PCA) was demonstrated. The semiconductors were excited above and below the bandgap (400 and 800 nm) by a femtosecond Ti:sapphire laser. The THz pulse waveform generated by the ZGP antenna was measured using a time-domain spectroscopy technique. The antenna’s THz pulse energy dependence on the optical pump energy was measured, and saturation fluence and carrier mobility were estimated. The ZGP and a chemical vapor deposited ZnSe-based PCA were compared.

ECG signal analysis using CWT, spectrogram and autoregressive technique

The cardiovascular system is a combination of the heart, blood and blood vessels. Cardiovascular diseases (CVD) are a key factor behind casualties worldwide among both women and men. About 9.4 million deaths occur due to high Blood Pressure (BP) only, out of which 51% deaths are due to strokes and 45% deaths are due to coronary heart diseases. The Electrocardiogram (ECG) represents the heart health condition of the subject, (patient) since it is acquired through electrical conduction, which appears in terms of P-QRS-T waves. But analysis of these waves is very tedious due to the existence of different noises/artifacts. Computer Aided Diagnosis (CAD) system is required in practical medical scenario for better and automated ECG signal analysis and to compensate for human errors. In general, implementation of a CAD system for ECG signal analysis requires; preprocessing, feature extraction and classification. In the existing literature, some authors have used time domain techniques which yield good performance for cleaned ECG signals i.e., without noise/artifact. Some authors have used frequency domain techniques later, but they suffer from the problem of spectral leakage making them unsuitable for real time/pathological datasets. The existing techniques from both these domains are not able to effectively analyze nonlinear behavior of ECG signals. These limitations have motivated this work where Continuous Wavelet Transform (CWT), Spectrogram and Autoregressive (AR) technique are used collectively for interpreting nonlinear and non-stationary features of the ECG signals. In this paper, both Massachusetts Institute of Technology-Beth Israel Hospital Arrhythmia database (MB Ar DB) and Real-time database (RT DB) have been used. Performance of the proposed method is compared with that of the previous studies on the basis of sensitivity (SE) and detection rate (D.R). The proposed technique yields SE of 99.90%, D.R of 99.81% & SE of 99.77%, D.R of 99.87% for MB Ar DB and RT DB, respectively. Therefore, the proposed technique showcases the possibility of an encouraging diagnostic tool for further improving the present situation of health informatics in cardiology labs/hospitals.