Variation Of Propagation Velocity Research Articles

Robust, high-resolution, indexed 3D slowness surfaces for Rayleigh-type waves on Lithium Niobate via parallelised Newtonian flow phase tracking

Micro-Electromechanical System Surface Acoustic Wave (MEMS SAW) devices are key technological enablers in RF telecommunications filters, inertial systems and biosensors. Recent developments in Focused SAW (FSAW) device design demand high quality, high resolution dispersion data for multiple in-plane directions, typically presented as a slowness curve, to facilitate design. Very few slowness curves are available in the literature for free surfaces not aligned to the crystallographic axes except in a few special cases. The first major novelty in the present work is a bespoke computational approach to solving this problem with a distinct theoretical basis. After a brief summary of the motivation, the mathematical formulation and its theoretical footing are outlined. The most important algorithms are given as pseudocode, and source code, datasets and extended visualisation available online are referenced. The structure of the method is illustrated via application to the bulk wave problem. The model is then applied to Lithium Niobate to generate new results characterising SAW propagation velocity for all in-plane directions over one full circle of plane inclinations. These results are presented as a two-dimensional velocity surface. This new data constitutes the second area of novelty herein. Finally, the applicability of the work to FSAW design is indicated by examining the RMS variation of propagation velocity for different cut plane inclinations.

Propagation Velocity of Flames in Inert-Diluted Stoichiometric Propane-Air Mixtures: Pressure and Temperature Dependence

The flammable propane–air mixtures raise specific safety and environmental issues in the industry, storage, handling and transportation; therefore dilution of such mixtures has gained significant importance from the viewpoint of fire safety, but also due to nitrogen oxide’s emission control through flameless/mild combustion. In this paper, the propagation of the flame in C3H8-air-diluent stoichiometric gaseous mixtures using Ar, N2 and CO2 as diluents was investigated. Data were collected from dynamic pressure-time records in spherical propagating explosions, centrally ignited. The experiments were done on stoichiometric C3H8-air + 10% diluent mixtures, at initial pressures within 0.5–2.0 bar and initial temperatures within 300–423 K. The flame velocity was determined from laminar burning velocities obtained using the pressure increase in the incipient stage of flame propagation (when the pressure increase is lower than the initial pressure). The experimental propagation velocities were compared with computed ones obtained from laminar burning velocities delivered by kinetic modeling made using the GRI mechanism (version 3.0) with 1D COSILAB package. The thermal and baric coefficients of propagation velocity variation against the initial temperature and pressure are reported and discussed.

Effects of Dispersion and Multi-Path Propagation in Partial Discharges Location

Dispersion and multi-path propagation distort partial discharge (PD) pulses that travel along power cables. This article proposes a theoretical framework that models the PD source location error owing to these effects. Regarding dispersion, a closed-form expression is proposed to estimate the PD bandwidth reduction at the cable ends, as well as the expected location error due to propagation velocity variation. A new expression is proposed for the difference of times of arrival (TOAs), which exhibits dependence with frequency. Multi-path propagation also introduces a non-linear dependence with frequency in the TOAs, which leads to location errors when the echo is very close to the main PD signal. Three location algorithms (based on cross-correlation, phase increment, and energy criterion) are investigated under noise, dispersion, and multi-path conditions. Simulation results show that the energy criterion algorithm is very sensitive to dispersion, but it is robust to multi-path propagation. The algorithm based on phase increments is the most sensitive to noise. Finally, the best location method for noisy, highly dispersive, multi-path propagation is the one based on cross-correlation.

The variation of propagation velocity according to substrate material of band pass filter

Background/Objectives: The SAW filter has a frequency characteristic determined by the geometry of the IDT electrode, and is widely used as a band-pass filter for passing only a signal having a specific frequency.Methods/Statistical analysis: The features of this filter are high stability and reliability and enable mass production using semiconductor processes.Findings: The MCB process lift off method was used to fabricate the filter to solve the difficulties of the SAW filter process. In particular, we fabricated ZnO thin films with excellent c-axis preferential orientation, high resistivity of more than 106Ωcm, and flat surfaces, and fabricated SAW filters using ZnO thin films as deposition conditions suitable for application to SAW filters. ZnO thin films deposited under conditions of RF power of 150W, chamber pressure of 10mTorr, substrate temperature of 200 ° C and gas mixture ratio of Ar/O2 of 50/50 as sputtering gas have excellent c-axis preferential orientation, high specific resistance and flat surface shape. Then, ZnO piezoelectric thin film was deposited on SiO2 substrate by RF magnetron sputtering method and the SAW filter was fabricated by the MCB lift off method to analyze the frequency characteristics. In addition, compared with the SAW filter fabricated on the LiNbO3 substrate, which is a piezoelectric substrate.Improvements/Applications: The propagation speed of the SAW filter using the ZnO thin film was determined by the variation of the center frequency due to the deposition of the ZnO thin film.

Modeling dispersion of partial discharges due to propagation velocity variation in power cables

Existing models for partial discharge (PD) propagation based on a single attenuation constant are unable to explain how each frequency component travels with a different propagation velocity. This paper proposes a new model based on a complex propagation term whose real component does not depend on the frequency (f), and whose imaginary part is modeled with a second order polynomial in f. The proposed model explains how the PD is attenuated, delayed, and dispersed due to the fact that each frequency component is differently delayed.A closed-form expression is proposed for the PD peak value and width, and a method to derive the model parameters from a reference model existing in the bibliography. Simulation results show that the peak value and width of the propagated PD pulse are similar to those obtained with the proposed model. Additionally, the proposed model provides the velocity of each PD frequency component, which is crucial to get an accurate estimation of the PD source location.The parameters of the proposed model have been estimated using a vector network analyzer for a XLPE cable. These results have been compared to the measurement obtained in a medium voltage test bench where intentionally induced PDs have been captured and processed, confirming the results of attenuation, delay and dispersion predicted by the proposed model.

Tight focusing of femtosecond radially polarized light pulses through a dielectric interface.

Based on the Richards-Wolf vector diffraction theory, we have derived the expressions for the electric field and the propagation velocity of femtosecond radially polarized light pulses focused by a high numerical aperture (NA) objective. The intensity distribution in the focus, wavefront spacings, and propagation velocity variation near the focus are investigated in detail by using numerical calculations. It is found that the propagation velocity of focused ultrashort light pulses changes dramatically near the focus, and the propagation velocity of the focused laser pulse is strongly dependent on the NA of an objective and the refractive index of media. Moreover, the usual propagation velocity of light pulses, as expected, decreases as the refractive index of media increases.

Temperature dependent signal propagation velocity: possible indicator for mv cable dynamic rating

Insulation temperature is the critical parameter for dynamic rating of underground power cables. Power cables on medium voltage (MV) level are too numerous and widespread to economically justify solutions like optical fibers as temperature sensors, often employed for high voltage power cables. This paper proposes to utilize the propagation velocity of high frequency signals as indicator for MV cable dynamic rating. Laboratory scale tests are performed for both PILC and XLPE cables. Test results show that the high frequency signal propagation velocity for XLPE insulation increases with the temperature rise while PILC cable shows opposite behavior. The variation of propagation velocity with temperature is consistent with the variation of permittivity measured on test samples of both materials. The variation of propagation velocity of XLPE is confirmed by data of a power cable in service subjected to strong load cycling monitored over a week. Field data on propagation velocity also matches load variation observed for a PILC cable for load cycling recorded over one week. From laboratory tests and field measurements, it seems feasible to extract thermal information from MV cables for dynamic rating by means of high frequency propagation velocity.

Timelapse ultrasonic tomography for measuring damage localization in geomechanics laboratory tests.

Variation of mechanical properties in materials can be detected non-destructively using ultrasonic measurements. In particular, changes in elastic wave velocity can occur due to damage, i.e., micro-cracking and particles debonding. Here the challenge of characterizing damage in geomaterials, i.e., rocks and soils, is addressed. Geomaterials are naturally heterogeneous media in which the deformation can localize, so that few measurements of acoustic velocity across the sample are not sufficient to capture the heterogeneities. Therefore, an ultrasonic tomography procedure has been implemented to map the spatial and temporal variations in propagation velocity, which provides information on the damage process. Moreover, double beamforming has been successfully applied to identify and isolate multiple arrivals that are caused by strong heterogeneities (natural or induced by the deformation process). The applicability of the developed experimental technique to laboratory geomechanics testing is illustrated using data acquired on a sample of natural rock before and after being deformed under triaxial compression. The approach is then validated and extended to time-lapse monitoring using data acquired during plane strain compression of a sample including a well defined layer with different mechanical properties than the matrix.

Novel joint TOA/RSSI-based WCE location tracking method without prior knowledge of biological human body tissues.

This paper proposes a novel joint time of arrival (TOA)/received signal strength indicator (RSSI)-based wireless capsule endoscope (WCE) location tracking method without prior knowledge of biological human tissues. Generally, TOA-based localization can achieve much higher localization accuracy than other radio frequency-based localization techniques, whereas wireless signals transmitted from a WCE pass through various kinds of human body tissues, as a result, the propagation velocity inside a human body should be different from one in free space. Because the variation of propagation velocity is mainly affected by the relative permittivity of human body tissues, instead of pre-measurement for the relative permittivity in advance, we simultaneously estimate not only the WCE location but also the relative permittivity information. For this purpose, this paper first derives the relative permittivity estimation model with measured RSSI information. Then, we pay attention to a particle filter algorithm with the TOA-based localization and the RSSI-based relative permittivity estimation. Our computer simulation results demonstrates that the proposed tracking methods with the particle filter can accomplish an excellent localization accuracy of around 2 mm without prior information of the relative permittivity of the human body tissues.

Assessment of muscle stiffness using a continuously scanning laser‐Doppler vibrometer

A stand-alone and low-cost elastography technique has been developed using a single continuously scanning laser Doppler vibrometer. This elastography technique is used to measure the propagation velocity of surface vibrations over superficial skeletal muscles to assess muscle stiffness. Systematic variations in propagation velocity depending on the contraction level and joint position of the biceps brachii were demonstrated in 10 subjects. This technique may assist clinicians in characterizing muscle stiffness (or tone) changes due to neuromuscular disorders.

Key Features of Hip Hop Dance Motions Affect Evaluation by Judges

The evaluation of hip hop dancers presently lacks clearly defined criteria and is often dependent on the subjective impressions of judges. Our study objective was to extract hidden motion characteristics that could potentially distinguish the skill levels of hip hop dancers and to examine the relationship between performance kinematics and judging scores. Eleven expert, six nonexpert, and nine novice dancers participated in the study, where each performed the "wave" motion as an experimental task. The movements of their upper extremities were captured by a motion capture system, and several kinematic parameters including the propagation velocity of the wave were calculated. Twelve judges evaluated the performances of the dancers, and we compared the kinematic parameters of the three groups and examined the relationship between the judging scores and the kinematic parameters. We found the coefficient of variation of the propagation velocity to be significantly different among the groups (P < .01) and highly correlated with the judging scores (r = -0.800, P < .01). This revealed that the variation of propagation velocity was the most dominant variable representing the skill level of the dancers and that the smooth propagation of the wave was most closely related to the evaluation by judges.

Observed cumulative time delay between second harmonic and fundamental component of pressure wave fields propagating through ultrasound contrast agents

To our knowledge, despite several studies on the propagation velocity of pressure wave fields through ultrasound contrast agents (UCAs) have been conducted, the variation of propagation velocity between the fundamental and second harmonic component generated during the propagation of ultrasound through UCAs has not been studied yet. For this purpose, transmission and backscattering measurements of pressure wave fields propagating through gelatin phantoms containing cylindrical cavities of different diameter, filled with different concentrations [0 to 240 μL/L] of SonoVue® contrast agent, are conducted. Different frequencies [2, 2.5, and 3 MHz] and mechanical indices [0.05, 0.1, and 0.2] are investigated. Moreover, measurements obtained with Definity® contrast agent are also analyzed. Results show the occurrence of a cumulative delay between the time signals related to the second harmonic and fundamental component, suggesting a smaller propagation velocity for the second harmonic as compared to the fundamental component. Moreover, this delay increases with increasing microbubble concentration and diameter of the cavity, it depends on mechanical index and frequency, and, most importantly, it is not observed in the absence of UCAs. These results may be relevant for contrast-enhanced ultrasonography, providing new possibilities to increase contrast-to-tissue ratios and to quantify UCA concentrations.

Validation of a thermal bias control technique for Coda Wave Interferometry (CWI)

The Coda Wave Interferometry (CWI) analysis serves to monitor the variation of propagation velocity in a heterogeneous medium with high precision (10−3% in relative terms). In combination with acoustoelastic theory, this type of analysis offers an NDT method for stress evaluation and/or damage detection. Since the CWI method is intended to evaluate extreme levels of accuracy, the presence of bias under certain circumstances can undermine evaluation results and/or test repeatability. In this paper, we offer a bias control technique involving the use of a second (reference) specimen for CWI analysis that is designed to compensate: (1) the thermally-induced velocity variation due to environmental temperature fluctuations; and (2) bias originating from experimental procedures. The presentation of this technique contains both a theoretical analysis and experimental protocol for the purpose of implementation. Furthermore, comparisons of experimental results have been included in order to demonstrate the utility of this bias control technique under laboratory conditions.

Multi-datum based estimation of near-surface full-waveform redatuming operators

Abstract A complex near surface can impact the quality of land data, despite the fact that the geology below the near surface complexities can be laterally smooth. Redatuming with operators based on a high-frequency parameterization in terms of traveltimes and simple geometric spreading factors will fall short if there are large lateral and vertical variations in propagation velocity and buried anomalies in the near surface layer. Recently, a method was introduced that can estimate the involved redatuming operators in a full-waveform sense. Application to synthetic data shows an uplift to the redatuming quality, but residual imprint is still observed. In this paper an extension is introduced that estimates redatuming operators based on two datum reflections simultaneously. In this way the full-waveform estimation process becomes more robust and shows another level of improvement for synthetic data. This conclusion is further amplified by the results obtained on field data from an area with a severe near-surface problem.

Variations in propagation velocity of muscle-fiber action potentials in individual motor units during voluntary contractions

muscle-fiber conduction velocity can be measured in humans in vivo during either voluntary or electrically elicited contractions. Its measure provides a window into the membrane electrophysiological properties of the muscle fibers, which cannot be directly measured, because the velocity of

Surface Current Density Mapping for Identification of Gastric Slow Wave Propagation

The magnetogastrogram (MGG) records clinically relevant parameters of the electrical slow wave of the stomach noninvasively. Besides slow wave frequency, gastric slow wave propagation velocity is a potentially useful clinical indicator of the state of health of gastric tissue, but it is a difficult parameter to determine from noninvasive bioelectric or biomagnetic measurements. We present a method for computing the surface current density from multichannel MGG recordings that allows computation of the propagation velocity of the gastric slow wave. A moving dipole source model with hypothetical as well as realistic biomagnetometer parameters demonstrates that while a relatively sparse array of magnetometer sensors is sufficient to compute a single average propagation velocity, more detailed information about spatial variations in propagation velocity requires higher density magnetometer arrays. Finally, the method is validated with simultaneous MGG and serosal electromyography measurements in a porcine subject.

Monitoring of trabecular bone induced microdamage using a nonlinear wave‐coupling technique

Bone tissue contains microcracks which may affect its mechanical properties as well as the whole trabecular structure. The relationship between crack density and bone strength is nevertheless poorly understood. Efficient nonlinear (NL) ultrasound methods have been widely developed for nondestructive testing and geophysical applications to detect microdamage. Moreover it has been reported that elastic nonlinearities increase with induced damage. We propose to monitor trabecular bone microdamage using a NL wave coupling technique. Ultrasonic short bursts times of flight (TOF) are modulated as result of NL interaction with a low‐frequency (LF) wave in the medium. TOF modulation (TOFM), or propagation velocity variations, are directly related to NL elasticity variations. This technique allows measuring the instantaneous TOFM as a function of the LF pressure. It is thus possible to analyze separately elasticity variations in tension and in compression, and to distinguish the tension to compression phase from the compression to tension phase (hysteresis). In several trabecular bone samples, different TOFM amplitudes in tension and in compression are observed, probably due to microdamage. For increasing damage levels progressively induced by quasi‐static compression testing, linear and nonlinear ultrasound parameters are compared to biomechanical parameters.

Ultrasound elasticity assessment of in vivo human achilles tendons during a quick-release exercise

An ultrasound (US) axial transmission technique has been developed to assess in vivo real time tendon biomechanical properties during calibrated exercises. The US propagation velocity changes are indeed related to the tendon visco-elasticity variations. We propose to monitor the propagation velocity changes during a very short period of time corresponding to the tendon/muscle complex release just after a sub-Maximal Voluntary isometric Contraction (MVC). This measurement is repeated for several sub-MVC amplitudes. The propagation velocity variations, linearly related to the torque measurements, allow to estimate a stiffness index, essentially due to the Series Elastic Component of the Achilles tendon. This study has been performed in collaboration with the UMR 6600 (UTC, France), and we have used the Ergometer they developed a few years ago. The US device is composed of a 1.8 MHz US probe (1 emitter, 20 receivers), and an electronic module (Althaïs Technologies, France) allowing real time and synchronous acquisitions of US RF signals and auxiliary inputs (Torque, angular position). Four healthy subjects were asked to develop several submaximal voluntary isometric contractions, and the sole was suddenly released (sub MVC to relaxed state, 2s, 2kHz). This protocol was repeated two times with foot and probe repositioning.

Dispersion and PD detection in shielded power cable [Feature article

Dispersion, the variation in propagation velocity with frequency, is one of those phenomena that people in the field of partial discharge (PD) detection have talked about since at least the early 1980s, but which is lacking a formal treatment in the literature. When one of the authors recently published an analytic theory of PD propagation in shielded power cable, both reviewers said "dispersion, dispersion". They believed that dispersion was important but gave no evidence for that assertion. In fact, as shown below, dispersion in shielded power cable has little if any impact on measurement of PD magnitude because the Fourier components of the pulse attenuate to insignificance before they can disperse to a degree that would cause appreciable change in the peak pulse amplitude or integral of the pulse waveform. However, dispersion does cause some distortion of the pulse shape that has implications for PD location, as it has a second-order effect on the timing of the peak PD amplitude relative to other pulses in the pulse train caused by multiple reflections from the ends of the cable. A Gaussian PD pulse in the time domain will have a Fourier spectrum that is also Gaussian in the frequency domain. If the Fourier components in the frequency domain propagate down the cable at differing velocities, the waveform to which they add will vary as a function of distance propagated, and the energy in the PD pulse is likely to spread out in time, which would have an effect on wide band PD detection no matter what the means of detection.

Digital Equivalent Circuits for Acoustic Field Based on Discrete Huygens' Modeling

A digital equivalent circuit for a three-dimensional acoustic field is developed on the basis of the discrete Huygens' model (DHM) in which the propagation and scattering of waves are simulated as the sequences of impulses scattering as Huygens' principle states. The scattering matrix of a DHM element for propagation velocity variation is first derived. Applying the z transformation to the scattering matrix, the transfer function in the z-domain is then derived. The transmission characteristic is numerically discussed in comparison with the analog equivalent circuit model.