Time-domain Algorithm Research Articles

Multizone active noise control for impulsive scattered sound of a rigid cylinder

Active noise control (ANC) can be applied to attenuate the scattered sound from an object, rendering it invisible to incident waves. This study proposes two secondary loudspeaker placement optimization methods for multizone ANC of impulsive scattered sound from a rigid cylinder. The first method is frequency-domain weighted least absolute shrinkage and selection operator (LASSO) algorithm, and the second method is a time-domain iterative algorithm. Based on the two methods, a broadband feedforward ANC system is presented to suppress impulsive forward-scattered and backward-scattered sound. The experimental results show that compared with the configuration of uniformly placed loudspeakers and traditional LASSO algorithms, the proposed weighted LASSO algorithm and iterative algorithm achieve better control performance in the target and observing areas with less power when controlling 500 Hz–1000 Hz impulsive scattered sound.

Approximating Constant-Q Seismic Wave Propagations in Acoustic and Elastic Media Using a Cole–Cole Model

ABSTRACT Seismic wave propagation in the Earth’s interior inevitably encounters attenuation and dispersion effects, which usually can be represented by a constant-Q model. However, solving the constant-Q wave equations formulated by fractional Laplacians is computationally intensive. Alternatively, the Cole–Cole model provides an optimal description of seismic attenuation. Because of the fractional time derivatives of both stress and strain in the expression, this method exhibits good adaptability and flexibility. In this article, we investigate the performance of the Cole–Cole model to approximate constant-Q behaviors with different fractional orders in acoustic and elastic media. The phase velocity and quality factor are compared to determine an optimal fractional order. After that the Cole–Cole model can be easily represented by the other three parameters (i.e., relaxed modulus, minimum angular frequency, and minimum quality factor), which are similar to the constant-Q theory (reference modulus, reference angular frequency, and frequency-independent quality factor). The first-order viscoacoustic and viscoelastic wave equations are derived to implement seismic wavefield simulations by combining conservation equation and stress–displacement relation. Furthermore, a time-domain algorithm is developed to solve the wave equations based on the Grunwald–Letnikov approximation and finite-difference scheme. Numerical modeling results calculated by our proposed method have good consistencies with the reference solutions from the constant-Q theory, suggesting that a small fractional order can well approximate the constant-Q outputs in a broad frequency band.

Symmetrical Coupling Multi-Cavity Bandpass Filter for CMOS Compatible Fluorescence Detection

Integration of functional components such as excitation light source, micro-fluidic chip, optical filters, and complementary metal–oxide–semiconductor (CMOS) sensors on a single photonics chip for fluorescence detection by advanced semiconductor process, is a future technology for rapid responding, high accuracy, and handheld point-of-care diagnosis protocol in field application of daily life. We designed a CMOS compatible bandpass filter on a glass substrate based on symmetrical coupling multi-cavity (SCMC) SiN/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film stacker aimed at detection of 5-carboxylfluorescein (5-FAM), a commonly used fluorescence probe in biotechnology and medicine diagnosis. The calculation based on transfer matrix method (TMM) and 2D finite difference time domain (FDTD) algorithm, revealed that there was an optimized number of cavities in the SCMC stacker, for the transmittance in the pass band decreasing with the increment of the number of cavities while the optical density in the stop band improving with it. For a SCMC stacker with 10 resonant cavities, both the TMM and 2D FDTD calculation, figured out that the fluorescence emission and the remained excitation source should be directed to incident on the SCMC stacker with an angle less than 18° for a good passing of fluorescence emission centered at 520 nm and blocking of excitation light of a wavelength of 488 nm. It provided new insights for future design and fabrication of micro-lens array and micro-apertures array for the highly integrated photonics chip aimed at detection of fluorescence on a single chip.

A new method for solving arcs of pantograph network based on Newton’s iterative method

It has been verified that the discharge pulse generated by the pantograph-catenary system has the biggest impact on the high-speed EMU as the electromagnetic interference source. But the spectrum obtained from the existing pantograph discharge model does not contain high frequencies and is far from the measurement results. In this paper, a novel scheme based on Newton’s method and finite difference time domain (FDTD) algorithm was presented to solve this problem. Firstly, Newton’s method was utilized to solve the Habedank model, and the dynamic conductance of the arc was obtained. Then, the equivalent distributed parameter circuit model of the traction power supply system was established, which was solved by the FDTD and state variable method to obtain the time-domain waveform of the arc voltage. The significant features of this scheme are that it can realize the synchronous calculations of the arc dynamic conductance and the voltage responses along the catenary. Through this scheme, a stable arc voltage time domain waveform can be obtained, and the arc voltage spectrum is highly consistent with the test results.

Simulation study of alleviating the communication blackout using high-power microwave irradiating plasma sheaths

During hypersonic vehicle flight at high speed, plasma sheath on the vehicle surface will attenuate or even interrupt the communication signal, leading to the “communication blackout” problem. The vehicle probably moves a long distance during the communication blackout due to its high speed, which is a serious threat to the safety of the vehicle. This paper proposes a method to solve the communication blackout problem using high-power microwave (HPM) irradiation. The multicomponent compressible model, finite difference time domain algorithm, and multi-fluid model are used to simulate the interaction between HPM and plasma sheath. The results show that after HPM irradiation, the electromagnetic (EM) wave transmissivity of the plasma sheath will change, and the electric field (E-field) amplitude and irradiation time of HPM significantly influence the change of transmissivity. Thereafter, analyses of the changes of the collision and plasma frequencies of the plasma sheath after HPM irradiation showed the transmissivity of the plasma sheath to low-frequency EM waves is improved by optimizing E-field amplitude and irradiation time of HPM. Therefore, HPM irradiation can be performed to enhance the transmissivity of the plasma sheath to the communication signal, thus alleviating the communication blackout problem.

An improved NExT method for modal identification with tests validation

The Natural Excitation Technique (NExT) is widely used in structural modal parameter identification. However, the cross-correlation function is susceptible to the mode shape of each order, which is obtained by the traditional NExT method combined with other modal identification methods between the two measuring points, resulting in large errors of the identified frequency and damping ratio of various modes. Therefore, in this study, to obtain the modal responses of the target order correctly and eliminate interaction of various modes, a new combined NExT method with improved Empirical Mode Decomposition (EMD) method is developed. The improved NExT method is introduced firstly, then, the structural modal parameters are identified by five different methods, which are Ibrahim Time Domain Technique, Sparse Time Domain Algorithm, Autoregressive Moving Average timing method, Least Square Complex Exponential and Eigensystem Realization Algorithm respectively. The correction and improvement of the new method are verified through a simple-supported beam experiment and a shaking table test of a 12-story benchmark tall building at Tongji University. The structural modal parameters are identified and compared through adopting traditional NExT method and the proposed new NExT algorithm. Results illustrate that the improved NExT algorithm in this paper has a higher accuracy and effectiveness than the traditional one in structural modal parameter identification.

Performance analysis of various fundamental frequency estimation algorithms in the context of pathological speech.

Reliable fundamental frequency (f0) extraction algorithms are crucial in many fields of speech research. The current bulk of studies testing the robustness of different algorithms have focused on healthy speech and/or measurements of sustained vowels. Few studies have tested f0 estimations in the context of pathological speech, and even fewer on continuous speech. The present study evaluated 12 available pitch detection algorithms on a corpus of read speech by 24 speakers (8 healthy speakers, 8 speakers with Parkinson's disease, and 8 with head and neck cancer). Two fusion methods' algorithms have been tested: one based on the median of algorithms and one based on the fusion between the best algorithm for voicing detection and the algorithm that generates the most accurate f0 estimations on voiced parts. Our results show that time-domain algorithms, like REAPER, are best for voicing detection while deep neural network algorithms, like FCN- f0, yield better accuracy for the f0 values on voiced parts. The combination of REAPER and FCN- f0 yields the best ratio performance/implementation complexity, since it generates less than 4% errors on voicing detection and less than 5% of gross errors in the estimation of the f0 values for all speaker groups.

A time domain anti-jamming processing algorithm for GNSS ranging receiver

Traditional anti-jamming algorithms lead to a deviation of the Global Navigation Satellite System receiver’s ranging value, which has become the main obstacle to the improvement of the accuracy of the high-precision ranging receiver. Traditional time-domain anti-jamming (TDAJ) algorithms can cause signal distortion, resulting in ranging bias. This study aims to solve this problem by proposing a design method for adding preprocessing filters in time-domain anti-jamming navigation receivers. In this method, an optimal order filter for adaptively correcting signal distortion is designed according to the time-domain anti-jamming filter coefficients. The experimental results show that the algorithm proposed in this paper can effectively solve the problem of ranging bias caused by the traditional time-domain anti-jamming algorithm. The algorithm can be widely used in dedicated satellite missions that require high positioning accuracy, such as navigation signal monitoring receivers, satellite payload receivers, and precision approach and landing systems for carrier-based aircraft.

A hybrid FDTD/MoM algorithm with a non-uniform grid for MRI RF coil design

In ultra-high-field (UHF) magnetic resonance imaging (MRI) applications, the design and analysis of high-frequency radio frequency (RF) coils requires full-wave electromagnetic (EM) methods that can handle complex field-tissue interactions. Using a Huygens' equivalent surface, the Method of Moments (MoM) and the Finite-Difference Time-Domain (FDTD) algorithm can be combined to accurately model the high-frequency RF coils. In previous research, a uniform FDTD mesh structure was considered, providing a compromised solution for coil-tissue interactions. This paper proposes a hybrid FDTD/MoM algorithm with non-uniform meshes. The fine mesh domain is set at the Huygens' surface, and the other domain uses coarse meshes. The proposed algorithms are strictly validated, and their computational performance is compared against conventional methods. Results show that the new algorithm can improve the calculation efficiency without losing accuracy. Specifically, compared with the uniform FDTD method, the numerical difference between both hybrid methods remains at 3.2%. Still, the calculation time of the non-uniform grid algorithm is reduced by 64.2%, demonstrating the effectiveness of the new algorithm for modeling RF coils for UHF-MRI applications.

Characteristic Model and Efficient FDTD-SPM Algorithm for Fishnet Metasurfaces Analysis

Intelligent metasurfaces to create smart electromagnetic environments have attracted a surge of interest. The multiscale property of metasurfaces results in a huge computational challenge, further hindering their engineering development. Our previous paper has developed a fast finite difference time domain (FDTD) algorithm for patchlike metasurfaces analysis using the surface susceptibility model (SSM). This study extends that to efficient fishnetlike metasurfaces analysis using the surface porosity model (SPM), a useful complement to SSM. We introduce the SPM to FDTD, replacing brute force simulations, to accelerate fishnetlike metasurfaces analysis. At last, we conduct a series of numerical experiments, demonstrating that the proposed FDTD-SPM algorithm greatly reduces the number of computational meshing lattices and the consumed time.

Analysis on Uncertainty of Field-to-Wire Coupling Model in Time Domain

This paper presents an approach for the time domain statistical simulation of field-to-wire coupling model with uncertain wire position in traverse direction. The parameters of governing equations of field-to-wire coupling model about the wire position are expanded to the augmented governing equations by using the generalized polynomial chaos technique with normalized orthogonal basis functions. And the coefficients of the polynomial chaos expansions are solved by combining with the stochastic Galerkin method. However, the solution of augmented governing equations is a complex problem. Therefore, a new finite-difference time-domain (FDTD) algorithm based on the implicit Wendroff difference format is proposed to solve the governing equations, and the general iterative equations are given in this paper. The proposed methods are verified by a field-to-wire coupling model. The effectiveness and advantages of the new FDTD algorithm and the uncertainty analysis method based on generalized polynomial chaos technique are verified, which are achieved by comparing with the conventional leapfrog fashion FDTD algorithm and the Monte Carlo technique, respectively.

Internal fault probability-based time domain differential protection applied to transmission lines connecting battery energy storage stations

Battery energy storage station (BESS) presents disparate fault current characteristics in charge and discharge states. Classic and recently proposed differential protection algorithms, including phasor-based and time-domain algorithms, are heavily influenced by operating state of BESS. Problems such as low sensitivity and ineffectiveness may arise, especially in charge state. In response to this issue, this paper applies Bayes' Theorem to calculate the probability of internal fault occurrence, named as internal fault probability. In this article, fault current characteristics of BESS under different operating states are described, and then the causes of performance problems of classic and recently proposed differential protection algorithms are analyzed. Subsequently, virtual operating current vector is developed, and the difference of virtual operating current vector in time-domain waveform under various conditions is described. On this basis, internal fault probability-based differential protection (IFP-DP) is presented. Besides, its operating performances under internal and external faults are analyzed. The advantageous performance of IFP-DP is fully validated by changing fault location, type, resistance, operating state and considering outliers, current transformer (CT) saturation, and loss of data. Proposed IFP-DP exhibits gratifying performance in operating time, sensitivity and security in the presence of BESS.

Magnetic-Core-Shell-Satellite Fe3O4-Au@Ag@(Au@Ag) Nanocomposites for Determination of Trace Bisphenol A Based on Surface-Enhanced Resonance Raman Scattering (SERRS).

As a typical representative of endocrine-disrupting chemicals (EDCs), bisphenol A (BPA) is a common persistent organic pollutant in the environment that can induce various diseases even at low concentrations. Herein, the magnetic Fe3O4-Au@Ag@(Au@Ag) nanocomposites (CSSN NCs) have been prepared by self-assembly method and applied for ultra-sensitive surface-enhanced resonance Raman scattering (SERRS) detection of BPA. A simple and rapid coupling reaction of Pauly’s reagents and BPA not only solved the problem of poor affinity between BPA and noble metals, but also provided the SERRS activity of BPA azo products. The distribution of hot spots and the influence of incremental introduction of noble metals on the performance of SERRS were analyzed by a finite-difference time-domain (FDTD) algorithm. The abundance of hot spots generated by core–shell–satellite structure and outstanding SERRS performance of Au@Ag nanocrystals were responsible for excellent SERRS sensitivity of CSSN NCs in the results. The limit of detection (LOD) of CSSN NCs for BPA azo products was as low as 10−10 M. In addition, the saturation magnetization (Ms) value of CSSN NCs was 53.6 emu·g−1, which could be rapidly enriched and collected under the condition of external magnetic field. These magnetic core–shell–satellite NCs provide inspiration idea for the tailored design of ultra-sensitive SERRS substrates, and thus exhibit limitless application prospects in terms of pollutant detection, environmental monitoring, and food safety.

Simulation of Light-Trapping Characteristics of Self-Assembled Nano-Ridges in Ternary Organic Film

The presence of self-assembled nano-ridged (SANR) structures in PTB7-Th:PC70BM:PC60BM ternary organic blend film with the specific component ratio was experimentally clarified, and the light-trapping effect of the SANR structures was demonstrated. On this basis, the light-trapping characteristics of the PTB7-Th:PC70BM:PC60BM ternary blend film with the SANR structures were investigated by using the finite-difference time-domain (FDTD) algorithm. The results showed that the SANR structures have a light-trapping effect, which can effectively reduce the transmittance and reflectance of the incident photons at the specific wavelengths and thus exhibit stronger photon absorption, especially for the photons in the wavelength range of 550–650 nm. The light-trapping effect of the SANR structures does not depend on the direction of photon incidence, and the active layer traps the photons incident from both its top and bottom. The dimensional variation of the SANR has a significant effect on the light-trapping characteristics of the active layer, and the effect caused by the height variation is overwhelmingly superior compared with that of the width variation. In addition, the higher the density of the SANR, the more significant the light-trapping effect of the active layer. This work provides a theoretical basis for the further experimental enhancement of the photon absorption capacity of the PTB7-Th:PC70BM:PC60BM active layer with SANR structures.

AC compensation of 3D magnetic diagnostic signals in DIII-D and National Spherical Torus Experiment-Upgrade (NSTX-U) for real-time application.

A time domain algorithm has been developed to remove the vacuum pickup generated by both coil current (DC) and induced vessel current (AC) in real time from three dimensional (3D) magnetic diagnostic signals in the National Spherical Torus Experiment-Upgrade (NSTX-U) and DIII-D tokamaks. The possibility of detecting 3D plasma perturbations in real time is essential in modern and future tokamaks to avoid and control MHD instabilities. The presence of vacuum field pickup, due to toroidally asymmetric (3D) coils or to misalignment between sensors and axisymmetric (2D) coils, pollutes the measured plasma 3D field, making the detection of the magnetic field produced by the plasma challenging. Although the DC coupling between coils and sensors can be easily calculated and removed, the AC part is more difficult. An algorithm based on a layered low-pass filter approach for the AC compensation and its application for DIII-D and NSTX-U data is presented, showing that this method reduces the vacuum pickup to the noise level. Comparison of plasma response measurements with and without vacuum compensation shows that accurate mode locking detection and plasma response identification require precise AC and DC compensations.

Design of Portable Wireless Fall Monitoring and Warning System

Aiming at preventing the old man falling down in the field of study, this article studies the status quo, focusing on sitting down research and analyze the behavior characteristic, this paper proposes a portable wireless fall monitoring and alarm system scheme design and manufacture, the conventional time-domain motion data multilevel threshold detection algorithm combined with combined with frequency domain characteristics of machine learning classification has realized the real-time identification of fall behavior. The time domain data used rectangular window filter to preserve the critical time series of behavior occurrence, fully considering the time characteristics of data changes, and completed the detection of lying posture and falling and the exclusion of daily low-intensity activities of the elderly. In the frequency domain, Discrete Fourier Transform (DFT) was applied to the combined acceleration data of sitting posture fall and moderate intensity activity, and the Support Vector Machine (SVM) classifier model was established by using frequency domain features. Complete the recognition and detection of sitting posture fall, and complement the detection of lying posture fall. After the decision of falling is made, the information of falling will be sent to the guardian of the elderly in time through wireless communication module, and the on-site alarm will be made at the same time, so that the elderly can get help from others in time when there are people nearby.

A novel time-domain fitting method for estimating Fricke-Morse model parameters based on single-frequency sinusoidal complete response measurements

Fricke-Morse model is a widely-used 2R-1C equivalent circuit for electrical bioimpedance (EBI) analysis, whose model parameters are usually fitted in multi-frequency (MF) EBI measurements. This paper proposes a novel time-domain fitting method on estimation of the model parameters in single-frequency (SF) sinusoidal complete response (SCR) (the combination of initial transient and steady-state response) measurements. The analytical expressions of the model parameters are firstly deduced based on SCR analysis. Then a time-domain least square iterative optimization algorithm is developed to fit the model parameters, in which the analytical model expressions are calculated as the iterative initial values. Experimental measurements conducted on a 2R-1C circuit and the biceps brachii of a healthy volunteer in SF-SCR measurements show the mean difference less than 1% and 5%, respectively, compared to the results estimated using a commercial EBI device in reference MF-EBI measurements. The proposed SF-SCR method provides an alternative to EBI analysis, which could greatly simplify the hardware design and thus significantly reduce the equipment cost compared to the traditional MF-EBI method.

Multifunctional magnetic Fe3O4/Cu2O-Ag nanocomposites with high sensitivity for SERS detection and efficient visible light-driven photocatalytic degradation of polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) with carcinogenic, teratogenic and mutagenic properties are persistent organic pollutants in the environment. Herein, the novel multifunctional Fe3O4/Cu2O-Ag nanocomposites (NCs) have been established for ultra-sensitive surface-enhanced Raman scattering (SERS) detection and visible light-driven photocatalytic degradation of PAHs. Fe3O4/Cu2O-Ag NCs with different amounts of Ag nanocrystals were synthesized, and the effect of Ag contents on SERS performance was studied by finite-difference time-domain (FDTD) algorithm. The synergistic interplay of electromagnetic and chemical enhancement was responsible for excellent SERS sensitivity of Fe3O4/Cu2O-Ag NCs. The limit of detection (LOD) of optimal SERS substrates (FCA-2 NCs) for Nap, BaP, Pyr and Ant was as low as 10-9, 10-9, 10-9 and 10-10 M, respectively. The SERS detection of PAHs in actual soil environment was also studied. Moreover, a simple SERS method was used to monitor the photocatalytic process of PAHs. The recovery and reuse of Fe3O4/Cu2O-Ag NCs were achieved through magnetic field, and the outstanding SERS and photocatalytic performance were still maintained even after eight cycles. This magnetic multifunctional NCs provide a unique idea for the integration of ultra-sensitive SERS detection and efficient photocatalytic degradation of PAHs, and thus will have more hopeful prospects in the field of environmental protection.

Effect of state-dependent time delay on dynamics of trimming of thin-walled structures

Trimming of cantilever thin-walled structures is commonly seen in aerospace industry, including trimming of blades. Trimming with helix angle tools can cause the vibration of the thin-walled workpiece along the tool-axis, which may disturb the time delay between cutting by the current and previous teeth. The time delay dependent on the vibration state makes the stability analysis of trimming process challenging. This paper is the first attempt to uncover the effect of state-dependent time delay of the trimming process caused by workpiece vibration on chatter stability. Modeling of the cutter-workpiece interactions, state-dependent time delay and the dynamic chip generation mechanism are presented. A time-domain numerical algorithm with an improved stability metrics is constructed to analyze the trimming stability behaviors. We found that the two dominant states can occur, namely, period-n instabilities with time-varying time delay and stability with constant time delay. A focused experimental study was carried out to calibrate this new finding. This study reveals the way the workpiece vibration affects the time delay and stability in the trimming process.

Time-Domain Coupling Model for Nonparallel Frequency-Dependent Overhead Multiconductor Transmission Lines Above Lossy Ground

Expansion of power grids has resulted in the construction of multiple transmission lines within constrained spaces inevitably making them nonuniform in nature. Existing transmission line models available in electromagnetic transient (EMT) simulators are based on classical multiconductor transmission line (MTL) theory with the assumption that the transmission lines are infinitely long and have uniform cross-sectional dimensions. This paper develops a time-domain model, namely dispersive scattered field transmission line (DSFTL) model, for multiconductor dispersive nonuniform overhead transmission lines above lossy, frequency-dependent ground. The proposed model which consists of closed-form equations in the time-domain has been implemented using a modified finite-difference time-domain (MFDTD) algorithm and integrated into an EMT simulator (PSCAD/EMTDC). Results have been compared with and verified by those obtained using a full-wave approach and measured data available in the literature. Simulations of nonuniform structures that include nonlinear components (such as breakers) have also been carried out under fault conditions.