Excitation Waveform Research Articles

Robust Waveform Design of Ultrasound Arrays for Medical Imaging.

Sound speed is an effective parameter in designing an optimal beamformer. In conventional ultrasound imaging systems, the beamformer is designed assuming a fixed value of speed, whereas the speed in a tissue is not known precisely and also may fluctuate by a great value. The errors in estimating sound speed may lead to a severe degradation in the reconstructed image, as mainlobe width and sidelobe level of the beampattern are sensitive to the speed variations. In this paper, we consider the design of a transmit beamformer, which is robust to the speed variations. The problem is formulated as a convex optimization problem versus the covariance matrix of the excitation waveforms to obtain a beampattern with predefined mainlobe width and a minimum sidelobe level for all possible variations of speed. Then, by eigen-analysis of the obtained covariance matrix, a set of nonidentical single-carrier short-pulses for the excitation waveforms were designed. Various simulations indicate that the proposed method can yield a robust beampattern whose mainlobe width and sidelobe level almost remain constant by 10% speed variations. In contrast, the beampatterns obtained by nonrobust methods suffer extensive changes.

Realistic FDTD GPR Antenna Models Optimized Using a Novel Linear/Nonlinear Full-Waveform Inversion

Finite-difference time-domain forward modeling of ground-penetrating radar (GPR) is becoming regularly used in model-based interpretation methods, such as full-waveform inversion (FWI) and machine learning schemes. Oversimplifications in such forward models can compromise the accuracy and realism with which real GPR responses can be simulated, which degrades the overall performance of interpretation techniques. A forward model must be able to accurately simulate every part of the GPR problem that affects the resulting scattered field. A key element, especially for near-field applications, is the antenna system. Therefore, the model must contain a complete description of the antenna, including the excitation source and waveform, the geometry, and the dielectric properties of any materials in the antenna. The challenge is that some of these parameters are not known or cannot be easily measured, especially for commercial GPR antennas that are used in practice. We present a novel hybrid linear/nonlinear FWI approach that can be used, with only knowledge of the basic antenna geometry, to simultaneously optimize the dielectric properties and excitation waveform of the antenna and minimize the error between real and synthetic data. The accuracy and stability of our proposed methodology are demonstrated by successfully modeling a 1.5-GHz commercial antenna from Geophysical Survey Systems, Inc. Our framework allows accurate models of GPR antennas to be developed without requiring detailed knowledge of every component of the antenna. This is significant because it allows commercial GPR antennas, regularly used in GPR surveys, to be more readily simulated.

Low-temperature helium plasma generated at atmospheric pressures by non-standard field applicator

Low-temperature helium plasmas were sustained using radio frequency excitation waveforms in a cylindrical glass tube, both in steady state and flowing conditions.

High-Volume-Rate 3-D Ultrasound Imaging Based on Synthetic Aperture Sequential Beamforming With Chirp-Coded Excitation.

Three-dimensional (3-D) ultrasound imaging is a promising modality for many medical applications. Unfortunately, it generates voluminous data in the front end, making it unattractive for high-volume-rate portable medical applications. We apply synthetic aperture sequential beamforming (SASB) to greatly compress the front-end receive data. Baseline 3-D SASB has a low volume rate, because subapertures fire one by one. In this paper, we propose to increase the volume rate of 3-D SASB without degrading imaging quality through: 1) transmitting and receiving simultaneously with four subapertures and 2) using linear chirps as the excitation waveform to reduce interference. We design four linear chirps that operate on two overlapped frequency bands with chirp pairs in each band having opposite chirp rates. Direct implementation of this firing scheme results in grating lobes. Therefore, we design a sparse array that mitigates the grating lobe levels through optimizing the locations of transducer elements in the bin-based random array. Compared with the baseline 3-D SASB, the proposed method increases the volume rate from 8.56 to 34.2 volumes/s without increasing the front-end computation requirement. Field-II-based cyst simulations show that the proposed method achieves imaging quality comparable with baseline 3-D SASB in both shallow and deep regions.

Sonic boom induced window rattle in indoor environments

The perceptual environment inside homes ensonified by sonic booms consists mainly of the transmitted indoor boom sound, rattle from items in loose contact with vibrating structures, and structural vibrations that may be felt or seen. In this presentation, measurements of window rattle from a recent laboratory study conducted inside the Interior Effects Room at NASA Langley Research Center will be summarized. Low amplitude sonic booms were reproduced at the facility exterior, which induced rattle in several distressed windows that were interchanged in the facility wall. The indoor sound field, the combined transmitted boom and window rattle sound, was measured at seven microphones placed inside the test room. The “rattle only” sound was recovered by subtracting the “boom only” sound, which was computed by convolving a measured room impulse response with the exterior excitation waveform, from each microphone measurement. In total, predicted low booms from fourteen different vehicles, each at three loudness levels, ensonified forty-two different window rattle conditions. Each measurement was repeated six times in both a lively and damped room configuration. This database of 148,176 rattle measurements enabled objective comparisons of rattle produced by different aircraft, at different booms levels and for different window rattle conditions.

Impact of excitation waveform on the frequency stability of electrostatically-actuated micro-electromechanical oscillators

In this paper, the frequency stability of high-Q electrostatically-actuated MEMS oscillators with cubic restoring forces, and its relation with the amplitude, the phase and the shape of the excitation waveform, is studied. The influence on close-to-the carrier frequency noise of additive processes (such as thermomechanical noise) or parametric processes (bias voltage fluctuations, feedback phase fluctuations, feedback level fluctuations) is taken into account. It is shown that the optimal operating conditions of electrostatically-actuated MEMS oscillators are highly waveform-dependent, a factor that is largely overlooked in the existing literature. This simulation-based study covers the cases of harmonic and pulsed excitation of a parallel-plate capacitive MEMS resonator.

Separation control by a microfabricated SDBD plasma actuator for small engine turbine applications: influence of the excitation waveform

Small engines will be finding increasing applications in unmanned aerial vehicles (UAVs), drones and helicopters. However, their turbomachines exhibit lower efficiencies than those of large scale engines. In this context, the aerodynamic losses in the low-pressure turbines (LPTs) are largely accountable to flow separation at low Reynolds numbers operation, i.e. in cruise conditions. Active flow control is a promising technology to suppress separation, thus reducing losses, fuel consumption rates and therefore emissions.The present paper is focused on the experimental investigation of the potentialities of a Single Dielectric Barrier Discharge Plasma Actuator (SDBDPA) to reattach the separated flow at a Reynolds number of 2⋅104. The influence of the high voltage (HV) waveform supplying the SDBDPA on both flow separation control and device power dissipation was studied.The investigated SDBDPA was manufactured by microfabrication techniques. Photolithography ensured thin metal deposition with high manufacturing reliability control. Due to the possible device degradation during operation, emphasis was put in selecting thin film materials that could withstand the plasma environment. Schott alkali-free borosilicate glass substrate was chosen as dielectric, while a multilayer tungsten (W)/titanium nitride (TiN) as electrode material.The experimental approach comprised the actuator testing over a curved wall plate, designed with a shape to reproduce the suction surface of a LPT rotor blade and installed in closed loop wind tunnel test section. The SDBDPA was located at the front side of the adverse pressure gradient area, in order to control flow separation.Different HV excitation waveforms (sinus, triangle and square) and amplitudes were tested and compared, aiming to identify the input signal that gave the best flow control authority and device energy conversion efficiency. The applied voltage and the discharge current were acquired in order to determine the actuator dissipated power. Two-dimensional (2-D) flow velocity measurements were carried out by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV).Velocity results showed that the extension of the separation area was reduced by actuation. Moreover, when the actuator was on, the boundary layer thickness and the negative velocity magnitude decreased. Their reduction increased with the applied voltage (i.e. higher power dissipations). At comparable peak-to-peak applied voltages, the sinus waveforms slightly outperformed the other waveforms; however, while the sinus and triangle ones had comparable power dissipation, the square wave always dissipated the most.

Continuous Fluorescence Depletion Anisotropy Measurement of Protein Rotation.

Protein rotation in viscous environments can be measured by fluorescence depletion anisotropy (FDA) which combines long lifetimes of chromophore triplet states with the sensitivity of fluorescence excitation and detection. FDA achieves sensitivity well beyond that attainable by the more common technique of time-resolved phosphorescence anisotropy (TPA). We have now combined benefits of both time-domain and frequency-domain FDA into a single continuous technique (CFDA). Intensity and polarization of a single laser beam are modulated continuously according to a complex, repeating waveform. Fluorescence signals excited from triplet-forming fluorescent probes are digitized over recurring waveform periods by a high-speed signal averager. CFDA experiments typically involve substantial ground state depletion. Thus signals, unlike those of TPA, are not linear in the exciting light intensity and simple data analysis based on such linearity is not appropriate. An exact solution of the coupled diffusion and triplet production/decay equation describing CFDA within individual data points has been combined with simulated annealing optimization to extract triplet and anisotropy decay kinetics from experimental data. Related calculations compare possible excitation waveforms with respect to rotational information provided per fluorescence photon. We present CFDA results for the model system of eosin conjugates of carbonic anhydrase, BSA and immunoglobulin G in 90% glycerol at various temperatures and initial cellular results on eosin-IgE bound to 2H3 cell Type I Fcε receptors. We explore how CFDA reflects rotational parameters of heterogeneous systems and discuss challenges of extending this method to single cell microscopic measurements.

Manipulation of the plasma-dust layer in high-frequency discharge with an additional alternative phase

Abstract. In this paper, the properties of complex plasma and the manipulation of plasma-dust layer in high-frequency discharge with an additional alternative phase have been investigated. The computer simulation of the high-frequency capacitive discharge has been carried out under the influence of an additional alternative phase on the basis of the particle-in-cell and Monte Carlo (PIC / MCC) methods. The parameters describing the kinetic and transport properties (density and temperature of electrons, electron and ion heating rates) of complex plasma of high-frequency capacitive discharge have been obtained. The charging processes of dust particles, the forces acting on dust particles, as well as the equilibrium positions of the dust particles in the plasma have been studied. A method for manipulating particles of micro and nano sizes in a low-temperature complex plasma has been developed. The results have shown that the dust charge can be tuned by the properties of the excitation waveform and in connection with it we have suggested that the dust component of the plasma can be heated through a variation of the excitation waveforms via a mechanism similar to second-order Fermi acceleration. G M T Английский Испанский Итальянский Казахский Китайский Трад Китайский Упр Корейский Русский Турецкий Французский Английский Испанский Итальянский Казахский Китайский Трад Китайский Упр Корейский Русский Турецкий Французский Звуковая функция ограничена 200 символами Настройки : История : Обратная связь : Donate Закрыть

Studying Townsend and glow modes in an atmospheric-pressure DBD using mass spectrometry

Ambient molecular beam mass spectrometry has been employed to examine the effects of the mode of operation and the excitation waveform on the ionic content of a helium-based atmospheric-pressure parallel plate dielectric barrier discharge. By applying 10 kHz microsecond voltage pulses with a nanosecond rise times and 10 kHz sinusoidal voltage waveforms, distinctly different glow and Townsend modes were produced, respectively. Results showed a significant difference in the dominant ion species between the two modes. In the Townsend mode, molecular oxygen ions, atomic oxygen anions and nitric oxide anions are the most abundant species, however, in the glow mode water clusters ions and hydrated nitric oxygen anions dominate. Several hypotheses are put forward to explain these differences, including low electron densities and energies in the Townsend mode, more efficient ionization of water molecules through penning ionization and charge exchange with other species in glow mode, and large temperature gradients due to the pulsed nature of the glow mode, leading to more favorable conditions for cluster formation.

Magnetic Field Analysis for Dimensional Resonance in Mn–Zn Ferrite Toroidal Core and Comparison With Permeability Measurement

This paper studies the calculation method of core loss and magnetic state in Mn-Zn ferrites under an arbitrary waveform excitation. The effective dielectric constant, which is caused by a thin high-resistive layer at the grain boundary, is treated as a modification of Ohm's law by using an equivalent circuit. This procedure enables us to calculate both the dimensional resonance and eddy-current loss. To confirm the accuracy of the proposed model, the size dependence of the complex permeability and core loss of the toroidal core is analyzed. These results show a good agreement with the experimental measurement in the megahertz region. By using the same model, the core loss mechanism excited by a triangular-wave current is analyzed. In the low-frequency region, the core loss is suppressed by the reduction of a steep change in magnetic flux. However, the core loss near the resonant frequency is increased at the turning point of the current wave, where the time derivative of the current changes discontinuously and a higher harmonic component is induced.

Antenna terminals based on ultra‐compact retrodirective antenna arrays

A novel physical effect of angular super-resolution based on the direction-of-arrival information sampling using highly oscillatory evanescent harmonics in dense antenna array environment is demonstrated theoretically and experimentally. This phenomenon enables realisation of novel, ultra-compact antenna terminals (ATs) with superdirective radiation patterns and spatial auto-focusing characteristics for any direction of arrival of the excitation waveform. The use of these ATs should enhance the signal-to-noise ratio at the receiver, increase overall energy efficiency of the wireless communication or power transmission systems and lead to substantially lower interference and EM pollution across the wireless network area. Special attention is given to the antenna array operating in the presence of a flat metal ground plane or a ground plane with EM band-gap structure. Near-field scattering phenomena arising as a result of the antenna array coupling to the ground planes of both types and their effects on the far-field radiation patterns are analysed in detail. The results of the study should be important for the development of the electrically compact ATs to be employed in the energy-efficient wireless communication systems including the Internet-of-Things, wireless sensor networks and wireless powering systems.

Simple method for RF pulse measurement using gradient reversal.

To develop and evaluate a simple method for measuring the envelope of small-tip radiofrequency (RF) excitation waveforms in MRI, without extra hardware or synchronization. Gradient reversal approach to evaluate RF (GRATER) involves RF excitation with a constant gradient and reversal of that gradient during signal reception to acquire the time-reversed version of an RF envelope. An outer-volume suppression prepulse is used optionally to preselect a uniform volume. GRATER was evaluated in phantom and in vivo experiments. It was compared with the programmed waveform and the traditional pick-up coil method. In uniform phantom experiments, pick-up coil, GRATER, and outer-volume suppression + GRATER matched the programmed waveforms to less than 2.1%, less than 6.1%, and less than 2.4% normalized root mean square error, respectively, for real RF pulses with flip angle less than or equal to 30°, time-bandwidth product 2 to 8, and two to five excitation bands. For flip angles greater than 30°, GRATER measurement error increased as predicted by Bloch simulation. Fat-water phantom and in vivo experiments with outer-volume suppression + GRATER demonstrated less than 6.4% normalized root mean square error. The GRATER sequence measures small-tip RF envelopes without extra hardware or synchronization in just over two times the RF duration. The sequence may be useful in prescan calibration and for measurement and precompensation of RF amplifier nonlinearity. Magn Reson Med 79:2642-2651, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Optimization of Plasma Actuator Excitation Waveform and Materials for Separation Control in Turbomachinery

Different input waveforms applied to a Single Dielectric Barrier Discharge Plasma Actuator (SDBDPA) were compared for flow separation control on low-pressure turbines (LPTs). The investigated Reynolds number (Re) was 2·104. The work aim was the device optimization in terms of materials and excitation conditions for enhancing its durability and performances. The SDBDPA was manufactured by microfabrication techniques. Device materials that could withstand the plasma environment were selected. Sine, square and triangle waveforms were compared in terms of actuator dissipated power and induced velocity. At comparable peak-to-peak applied voltage, the sinus outperformed the other waveforms, while the square dissipated the most.

Noise properties of Fourier deconvolution for time-domain electromagnetic soundings

The transient electromagnetic method (TEM) is widely used for mapping the earth’s subsurface resistivity structures, e.g., for groundwater or mineral exploration, using airborne and ground-based systems. Data from TEM surveys can be modified using Fourier deconvolution to correct for instrument drift, increase apparent bandwidth, or alter the apparent excitation waveform, e.g., to fuse or compare measurements from different systems, for visual presentation purposes, or to make the data compatible with a specific processing or inversion code. Although this method has been applied in several studies, little attention has been devoted to its properties with regard to noise. Using a generic analytical system model and examples featuring synthetic and field data, we perform a detailed analysis of the noise properties of Fourier deconvolution in the context of TEM. We find that although the effects from stationary noise are trivial, effects from nonstationary noise are less intuitive and more severe, e.g., causing on-time noise phenomena to degrade off-time data. In general, we observe that the method decreases the signal-to-noise ratio, and our recommendation is therefore that Fourier deconvolution should only be applied when it is desirable for presentation purposes or when strictly necessary for processing or inversion.

Effects of dwell time of excitation waveform on meniscus movements for a tubular piezoelectric print-head: experiments and model

In inkjet applications, it is normal to search for an optimal drive waveform when dispensing a fresh fluid or adjusting a newly fabricated print-head. To test trial waveforms with different dwell times, a camera and a strobe light were used to image the protruding or retracting liquid tongues without ejecting any droplets. An edge detection method was used to calculate the lengths of the liquid tongues to draw the meniscus movement curves. The meniscus movement is determined by the time-domain response of the acoustic pressure at the nozzle of the print-head. Starting at the inverse piezoelectric effect, a mathematical model which considers the liquid viscosity in acoustic propagation is constructed to study the acoustic pressure response at the nozzle of the print-head. The liquid viscosity retards the propagation speed and dampens the harmonic amplitude. The pressure response, which is the combined effect of the acoustic pressures generated during the rising time and the falling time and after their propagations and reflections, explains the meniscus movements well. Finally, the optimal dwell time for droplet ejections is discussed.

Comparison of static hysteresis models subject to arbitrary magnetization waveforms

PurposeThis paper aims to compare different static history-independent hysteresis models (mathematical-, behavioural- and physical-based ones) and a history-dependent hysteresis model in terms of parameter identification effort and accuracy.Design/methodology/approachThe discussed models were tested for distorted-excitation waveforms to explore their predictions of complex magnetization curves. Static hysteresis models were evaluated by comparing the calculated and measured major and minor static hysteresis loops.FindingsThe analysis shows that the resulting accuracy of the different hysteresis models is strongly dependent on the excitation waveform, i.e. smooth excitations, distorted flux waveforms, transients or steady-state regimes. Obtained results show significant differences between predictions of discussed static hysteresis models.Research limitations/implicationsThe general aim was to identify the models on a very basic and limited set of measured data, i.e. if possible using only the measured major static loop of the material. The quasi-static major hysteresis loop was measured at Bmax = 1.5 T.Practical/implicationsThe presented analysis allows selection of the most-suited hysteresis model for the sought-for application and appraisal of the individual limitations.Originality/valueThe presented analysis shows differences in intrinsic mechanisms to predict magnetization curves of the majority of the well-known static hysteresis models. The results are essential when selecting the most-suited hysteresis model for a specific application.

Estimating the penetration depth of stress corrosion cracks using time-reversal acoustics—A Numerical Study

It has been shown experimentally that it is feasible to use time-reversal elastic nonlinearity diagnostics (TREND) to estimate the penetration depth of stress corrosion cracks (SCC) in steel samples. TREND is a method to focus elastic waves energy to a point in space in order to probe that point for damage. High frequencies are used to probe near the surface, while low frequencies are used to probe deeper into the material. Depth estimation of a crack is important to determine when a critical size of defect is reached. This paper aims at a parametric analysis of the time reversal focusing process by means of numerical simulations. The influence of excitation frequency and waveform on the focal spot size and penetration depth are analyzed. An in-house simulation framework based on a commercial Finite Element (FE) solver is used to perform a series of numerical simulations of time-reversal focusing in a steel sample with a curved crack. Results of this study could help to understand the relationship between the vibration responses measured at the sample’s surface and crack-wave integrations at different penetration depths. Ultimately, this knowledge can be used to optimize the experimental setup and facilitate the interpretation of experimental results.

A software solution to dynamically reduce metallic distortions of electromagnetic tracking systems for image-guided surgery.

Electromagnetic tracking systems (EMTS) have achieved a high level of acceptance in clinical settings, e.g., to support tracking of medical instruments in image-guided interventions. However, tracking errors caused by movable metallic medical instruments and electronic devices are a critical problem which prevents the wider application of EMTS for clinical applications. We plan to introduce a method to dynamically reduce tracking errors caused by metallic objects in proximity to the magnetic sensor coil of the EMTS. We propose a method using ramp waveform excitation based on modeling the conductive distorter as a resistance-inductance circuit. Additionally, a fast data acquisition method is presented to speed up the refresh rate. With the current approach, the sensor's positioning mean error is estimated to be 3.4, 1.3 and 0.7mm, corresponding to a distance between the sensor and center of the transmitter coils' array of upto 200, 150 and 100mm, respectively. The sensor pose error caused by different medical instruments placed in proximity was reduced by the proposed method to a level lower than 0.5mm in position and [Formula: see text] in orientation. By applying the newly developed fast data acquisition method, we achieved a system refresh rate upto approximately 12.7 frames per second. Our software-based approach can be integrated into existing medical EMTS seamlessly with no change in hardware. It improves the tracking accuracy of clinical EMTS when there is a metallic object placed near the sensor coil and has the potential to improve the safety and outcome of image-guided interventions.

Iron-Loss and Magnetic Hysteresis Under Arbitrary Waveforms in NO Electrical Steel: A Comparative Study of Hysteresis Models

This paper presents a comparative study of different static hysteresis models coupled to the parametric magneto-dynamic model of soft magnetic steel sheets. Both mathematical and behavioral as well as physically based approaches are discussed with respect to the ability to predict the dynamic hysteresis loop shape and iron loss under arbitrary excitation waveforms. Both current- as well as voltage-driven excitation cases are evaluated. The presented analysis discusses and points out advantages and limitations of the majority of the well-known static hysteresis models. In this way, it supports the selection of adequate hysteresis models for the specific application, i.e., smooth excitations, distorted flux waveforms, transients, or steady-state regimes. Comparisons against measurements for a M400-50A electrical steel over a wide range of magnetic flux density and frequencies for both sinusoidal and arbitrary excitations are analyzed. In the analysis hysteresis loop shapes, power losses as well as NRMS errors of individual loop sections are compared.