Acoustic Pulse Research Articles

О некоторых возможностях многочастотного дистанционного зондирования водной поверхности

This study is aimed at expanding the number of measured parameters to analyze the features of the formation of surface waves under the influence of wind. The paper develops an original approach to obtaining information on the variability of the short-wavelength part of the wave spectrum (examples are given for wavelengths from about 50 cm to 2 cm in 6 intervals) and the long-wave component of the wave spectrum (> 1 m) in marine conditions. Retrievable information about waves will allow studying the interaction of wind simultaneously with the short-wave and long-wave components of the wave spectrum and will be in demand by scientists involved in numerical modeling of the wave climate and interested in refining the model of near-surface wind interaction with waves. In addition, new information about the short-wave part of the wave spectrum in different wavelength ranges will improve the accuracy of near-surface wind speed retrieval from remote sensing data. This work is devoted to a theoretical analysis of slope variance retrieved from reflected acoustic pulses for different radiation frequencies depending on the near-surface wind speed and swell wave height. A study was made of the measured slope variances of large-scale waves, compared to the radiation wavelength, in six intervals depending on the wind speed and swell height. It is shown that the use of difference slope variances of the large-scale wave makes it possible to get rid of the influence of swell in the case of mixed waves and obtain a better correlation with the wind speed. A method is proposed for retrieving the declination degree for the spectrum of wave heights in given intervals of radiation wavelengths. Within the framework of this method, it is possible to retrieve the boundary wave numbers for each radiation wavelength.

Experimental investigations of indirect noise due to modulation of axial vorticity and entropy upstream of a choked nozzle

An experimental cold-gas study of the response of a choked convergent–divergent nozzle to swirl perturbations is presented. The perturbations were obtained by means of upstream unsteady tangential injections into initially steady flows with different values of steady background swirl. The swirl perturbations induced changes in the axial mass-flow rate, due to either their ingestion or evacuation by the nozzle. This in turn caused a downstream acoustic response. For low-intensity background swirl the responses were found to be similar to those obtained without steady background swirl. Perturbations of a high-intensity background swirl led to different effects. For long injection times, the negative mass-flow rate modulation occurred in two stages. The first stage was similar to that of the background-swirl free case. The second stage occurred after a short time delay, and induced a much stronger negative acoustic response. This unexpected behavior suggests that a significant part of the tangentially injected fluid flows upstream inducing an accumulation of swirl, which is – after tangential injection is ceased – suddenly cleared out through the nozzle. A scaling rule for the amplitudes of these acoustic responses is reported. Furthermore, quasi-steady models, based on steady-state measurements are proposed. These models predict the downstream acoustic response amplitude within a factor two. Additionally, preliminary empirical evidence of the effect of swirl on the downstream acoustic response due to the interaction of entropy patches with a choked nozzle is reported. This was obtained by comparison of sound produced by abrupt radial or tangential sonic injection, upstream from the choked nozzle, of air from a reservoir at room temperature to that from a reservoir with a higher stagnation temperature. Because the mass flow through the nozzle does not increase instantaneously, the injected higher-enthalpy air accumulates upstream of the injection-port position in the main flow. This eventually induces a large downstream acoustic pulse when tangential injection is interrupted. The magnitude of the resulting sound pulse can reach that of a quasi-steady response of the nozzle to a large air patch with a uniform stagnation temperature equal to that of the upstream-injected heated air. This hypothesis is consistent with the fact that the initial indirect-sound pulse is identical to one obtained with unheated air injection. The authors posit that – given all of the insight gleaned from them in this case – acoustic measurements of indirect sound appear to be a potentially useful diagnostic tool.

The effects of nose bluntness on broadband disturbance receptivity in hypersonic flow

While nose bluntness is known to have a large impact on the stability of hypersonic vehicles, its influence on the freestream receptivity process has not been fully characterized for a wide range of conditions. This paper investigates the effects of nose bluntness on the second mode receptivity coefficients and the development of boundary layer disturbances over two 7° half-angle circular blunt cones at Mach 10 after perturbation with broadband freestream pulses of different types. The cones have nose radii of 9.525 mm (case B) and 5.08 mm (case I). Unsteady direct numerical simulation (DNS) and linear stability theory (LST) results compare well and predict stronger second mode growth for case I in all pulse cases. Unsteady DNS also shows variations in extramodal excitation between the cones depending on freestream disturbance type. Spectral receptivity coefficients are generated by decomposing the unsteady DNS data into discrete frequency Fourier modes, which are then corrected with LST N-factors. Fast acoustic disturbances demonstrate minimal variation in receptivity coefficients, while temperature and vorticity disturbances have much higher coefficients in case I. Planar slow acoustic pulses induce stronger disturbances outside of the second mode in case I, resulting in higher peak receptivity coefficients. Results show significant variation in receptivity response based on nose bluntness, pulse geometry, and the type of incident perturbation.

Microenergy acoustic pulse therapy restores function and structure of pelvic floor muscles after simulated birth injury.

BackgroundThe mechanisms of the microenergy acoustic pulse (MAP) therapy on restoring structure and function of pelvic floor muscles (PFM) after simulated birth injury are not well understood.MethodsA total 24 female Sprague-Dawley rats were randomly grouped into sham control (sham), vaginal balloon dilation and ovariectomy (VBDO), VBDO + β-aminopropionitrile (BAPN, an irreversible LOX inhibitor), and VBDO + BAPN and treated with MAP (n=6 in each group). The MAP therapy was administered 2 times per week for 4 weeks with 1-week washout, the functional and histological studies were conducted in all 24 rats. The viscoelastic behavior of the PFM, including iliococcygeus (IC) and pubococcygeus (PC), was examined with a biomechanical assay. The structure of the PFM was assessed by immunofluorescence and Masson’s trichrome staining.ResultsThe leak point pressure (LPP) assay demonstrated that the MAP therapy group had higher LPPs compared to that of VBDO and BAPN groups. In the sham group, the muscular stiffness (K) of IC muscle was significantly higher than that of PC muscle while the pelvic floor muscle rebound activity (MRA) of PC muscle was stronger than that of IC muscle (291.26±45.33 and 241.18±14.23 N/cm2, respectively). Both VBDO and BAPN decreased the MRA and increased the K in both IC and PC. Histologic examination revealed increased fibrous tissue (collagen) and degeneration of muscle fibers in both VBDO and BAPN groups. MAP therapy significantly reduced the collagen content and improved the architecture of muscle fibers.ConclusionsMAP appears to restore the structure and function of PFM by regenerating muscular fibers and improving biomechanical properties in an animal model of simulated birth injury.

Improving Quality Control Methods to Test Strengthening Technologies: A Multilevel Model of Acoustic Pulse Flow

This article describes an approach that makes it possible to substantiate quality control criteria and methods to improve strengthening technologies. The approach was used to test the quality of products made using these technologies and analyze different strengthening methods applied to structural materials. In the experiment, samples of welded joints subjected to various types of strengthening were used that underwent acoustic emission (AE) testing. The results of quick evaluations produced by the proposed multilevel model of acoustic pulse flow were compared with the results of long-term cyclic tests to make a conclusion about the effectiveness of the approach being discussed. To improve strengthening quality control, a method is proposed that can be applied to complex and large-sized structures in the construction industry.

Experimental studies and simple numerical modeling of underwater electric discharges.

At present, underwater electric pulsed discharges are used in a wide range of modern applications. During the development of a system for generating underwater acoustic pressure pulses, a numerical model is an essential tool for guiding the design and interpreting the data. Developing a complex one-dimensional numerical code, like those presented in the literature, requires a substantial dedicated effort. Unfortunately, previous work trying to use simple and elegant theoretical models developed many decades ago reported a fundamental issue, apparently related to the input data. The present work performs a detailed analysis of the real meaning of the voltage measured across an underwater discharge and clarifies the correct way the power input to a simple two-phase model should be calculated. Based on accurate measurements, a phenomenological methodology to obtain the input data is demonstrated, with theoretical predictions obtained from the simple two-phase model being successfully compared with the experimental evidence obtained from both the present work as well as from other reliable data presented in the literature.

Microenergy acoustic pulse therapy restores urethral wall integrity and continence in a rat model of female stress incontinence.

To determine the outcomes and mechanisms of microenergy acoustic pulse (MAP) therapy in an irreversible rat model of female stress urinary incontinence. Twenty-four female Sprague-Dawley rats were randomly assigned into four groups: sham control (sham), vaginal balloon dilation and ovariectomy (VBDO), VBDO + β-aminopropionitrile (BAPN), and VBDO + β-aminopropionitrile treated with MAP (MAP). MAP therapy was administered twice per week for 4 weeks. After a 1-week washout period, all 24 rats were evaluated with functional and histological studies. The urethral vascular plexus was examined by immunofluorescence staining with antibodies against collagen IV and von Willebrand factor (vWF). The urethral smooth muscle stem/progenitor cells (uSMPCs) were isolated and functionally studied in vivo and in vitro. Functional study with leak point pressure (LPP) measurement showed that the MAP group had significantly higher LPPs compared to VBDO and BAPN groups. MAP ameliorated the decline in urethral wall thickness and increased the amount of extracellular matrix within the urethral wall, especially in the urethral and vaginal elastic fibers. MAP also improved the disruption of the urethral vascular plexus in the treated animals. In addition, MAP enhanced the regeneration of urethral and vaginal smooth muscle, and uSMPCs could be induced by MAP to differentiate into smooth muscle and neuron-like cells in vitro. MAP appears to restore urethral wall integrity by increasing muscle content in the urethra and the vagina and by improving the urethral vascular plexus and the extracellular matrix.

Vortex beam interactions for the measurement of nonlinear acoustic behaviour

Spatially shaped optical fields have been widely implemented for remote sensing, enhanced imaging and communications. Many of these principles can be readily translated into acoustics, where acoustic fields that carry orbital angular momentum (OAM) have gained considerable interest in recent years. These spatially shaped fields can provide unique acoustic interactions with materials and gasses as they propagate that can be leveraged to create novel sensor technologies. We will present a technique to amplify the visibility of nonlinear acoustic effects in gasses, via the controlled interference of acoustic pulses that carry OAM. This amplification allows accurate determination of the nonlinear parameter with acoustic pressures that are 66dB lower than a direct measurement of pulse chirping. In controlled conditions, non-linear parameters can be directly measured; however, variations in environmental parameters can lead to ambiguity, which can be addressed through the use of a trained Support Vector Machine machine learning approach. This will allow measurements in variation in the nonlinear parameter 0.01 with over 99.5% accuracy and 0.001 with over 75% accuracy based on single measurements, where repeated measurements can further reduce the power requirements and increase accuracy. This approach can be used for monitoring changes in air quality and if extended to other frequencies could be used for monitoring fatiguing in metals.

Calibration of a focused passive cavitation detector using bubble shock waves

In microbubble-mediated therapeutic ultrasound, a focused passive cavitation detector (PCD) is often used to measure the bubbles’ acoustic emissions, providing useful signals for treatment monitoring. However, calibrating a spherically focused PCD is challenging, due to the difficulty of generating a spherical wave that matches the PCD’s surface curvature. Here, a PCD was calibrated using broadband shock waves generated by inertial collapses of single microbubbles. Microbubbles were diluted to a very low concentration, flowed through a wall-less gel channel, and sonicated using single-cycle, 0.5-MHz-centre-frequency, 1-MPa acoustic pulses. The focused PCD to be calibrated and a reference needle hydrophone captured their emissions. The sensitivity and phase response of the PCD relative to the reference hydrophone was calculated from the single bubble signals. For comparison, the PCD was also calibrated using a focused emitter as a sound source (Rich and Mast, JASA, 2015). The nominal PCD sensitivities obtained using the two methods agreed within 1% ± 14% within the PCD’s bandwidth (2–10 MHz). The calibration data from the bubble method was then used to correct the PCD’s signal distortions. Our method recovered the impulse waveform of the bubble-generated shock wave from the raw PCD signal, where such a waveform was not previously observed.

On the possibility of electrostatically generated infrasound during thunderstorms

Acoustic emissions from lightning discharges are usually attributed to two mechanisms. The audible part of their spectrum mainly results from the shock wave generated by the heating of the lightning channel. On the other hand, the infrasonic component is associated with the conversion to sound of the electrostatic energy stored in the thundercloud. While there is a broad scientific consensus on the former mechanism, the latter process is still controversial. The electrostatic mechanism was proposed by C. T. R. Wilson in 1921 and can be summarized as follows. Due to the electrostatic repulsion of the charged particles, the pressure within a thundercloud is lower than outside. At discharge, the electrostatic field collapses, and the sudden air volume contraction produces an acoustic pulse. This work examines the existing theoretical models of the electrostatic mechanism with the data observed for thundercloud dimensions, charge densities, and total charges. Our results show that, although possible, this mechanism, as currently described, cannot explain observations. Our findings might support the hypothesis that the heating of the lightning channel is responsible for the generation of both infrasound and audible sound. However, a definitive answer remains precluded and requires a better understanding of cloud formation and electrification processes.

Quarter acoustic period pulse compression using stimulated Brillouin scattering in PF-5060.

The pulse duration of the near quarter-acoustic period (τa) is demonstrated in transient stimulated Brillouin scattering (SBS) pulse compression by the suppressing Stokes trailing-edge broadening at high intensities. A theoretical analysis reveals that the difficulty in attaining the transient compression limit is caused by the broadening of the Stokes trailing edge owing to insufficient pump depletion, and this undesirable phenomenon can be significantly suppressed by a high SBS gain coefficient. An average pulse duration of ∼1.05 τa was experimentally achieved in transient compression with a high-energy efficiency of over 30%. Benefiting from energy back conversion, compression below the transient SBS limit (< τa) also occurred when the pump peak power was increased to 150 MW.

What Is COVID 19 Teaching Us about Pulmonary Ultrasound?

In lung ultrasound (LUS), the interactions between the acoustic pulse and the lung surface (including the pleura and a small subpleural layer of tissue) are crucial. Variations of the peripheral lung density and the subpleural alveolar shape and its configuration are typically connected to the presence of ultrasound artifacts and consolidations. COVID-19 pneumonia can give rise to a variety of pathological pulmonary changes ranging from mild diffuse alveolar damage (DAD) to severe acute respiratory distress syndrome (ARDS), characterized by peripheral bilateral patchy lung involvement. These findings are well described in CT imaging and in anatomopathological cases. Ultrasound artifacts and consolidations are therefore expected signs in COVID-19 pneumonia because edema, DAD, lung hemorrhage, interstitial thickening, hyaline membranes, and infiltrative lung diseases when they arise in a subpleural position, generate ultrasound findings. This review analyzes the structure of the ultrasound images in the normal and pathological lung given our current knowledge, and the role of LUS in the diagnosis and monitoring of patients with COVID-19 lung involvement.

Piezoelectric potential-enhanced output and nonlinear response range for self-powered sensor on curved surface

Triboelectric nanogenerator (TENG)-based dynamics sensors usually suffer from low output and nonlinear response (inconsistent sensitivity) in wider detection range, especially at curved state. Here, we investigated the influence of piezoelectric potential and dipole moment on electrical output of TENG by fabricating four modes of TENGs with different polarized PVDF and working modes. Moreover, piezoelectric potential can be utilized to tune the interfacial energy band structure by piezotronic effect, which significantly improves the sensing performance of TENG-based pressure sensor, achieving linear response and high sensitivity in a wider range. In application, such sensor is good at human-body monitoring, such as acoustic wave, pulse wave and respiratory wave.

Acoustic Analog Signal Processing for 20–200 MeV Proton Sound Detectors

Proton sound detectors rely on sensing the weak thermoacoustic signals emitted by the fast energy deposition at the end of the beam penetration path through the energy absorber. The energy of the ions/protons is first converted into heat, and then, into pressure by a thermodynamic process. The pressure signal propagates through the energy absorber, and it is read by an acoustic sensor, which, in turn, converts the pressure wave into an analog electrical voltage. Such an analog signal is digitalized by the analog front-end. Its digital representation is used for the measurement of the beam depth. This emerging technique attracts attention in both physics experiments and medical applications (hadron therapy). This article investigates the signal-to-noise-ratio performance in proton sound detectors exploring all critical steps that lead to both reduction of the power of the electrical signal and noise power increasing. Nonetheless, this article proposes specific technical solutions to mitigate such signal-to-noise-ratio degradations with particular attention to higher energy (i.e., 200 MeV) proton beams, which are crucial for medical applications, and where the maximum achievable signal-to-noise ratio can be 50/60 dB lower than 20 MeV acoustic pulses.

Spectral and temporal behavior of a quasi-collinear AOTF in response to acoustic pulses: simulations and experiments.

This paper is dedicated to the study of an AOTF whose selectivity and side lobes are controlled thanks to acoustic square pulses with different and relatively low acoustic power. The behavior of the transmission function of a quasi-collinear acousto-optical tunable filter in TeO2 is analyzed. The filter is used with acoustic pulses above 12 µs to manipulate the selectivity and with an electric power up to 600 mW to control the side lobes of the filtered spectrum. Using acoustic pulses requires working under a regime of a long optical pulse. The temporal response of the filter was considered to find the best parameters to perform the experiments. The selectivity was controlled from 1.3 nm to 2.5 nm with the use of acoustic pulses. The manipulation of the acoustic power applied to the filter improved the performance of the side lobe levels in regards to the main one from -9dB to -12dB.

Enhanced Near-Field Interference Suppression Scheme for the Non-Cooperative Underwater Acoustic Pulse Detection of the Towed Linear Array

Near-field interference suppression for a towed linear array (TLA) is investigated in this paper. The existing eigencomponent association (ECA) scheme and multiple signal classification interference suppression (MUSIC-IS) scheme require the prior information of a target bearing in order to achieve satisfactory performance. To improve this, we propose the use of an enhanced ECA (EECA) scheme that achieves interference suppression in a non-cooperative scenario. It identifies non-target eigenvectors by scanning the tail direction zone of the TLA. With the non-target-only eigenvectors subtracted, the beam power spectrum of the EECA manifests null troughs at the target bearings. Numerical simulations show the superiority of the EECA method. This method can effectively suppress strong interference without prior information, capture a target even at a low signal-to-interference (SIR) level of −25 dB, and obtain dozens of dB processing gains compared to the ECA and MUSIC-IS.

Comparison of Transcranial Focused Ultrasound and Transcranial Pulse Stimulation for Neuromodulation: A Computational Study

ObjectiveThe objective of the study was to investigate transcranial wave propagation through two low-intensity focused ultrasound (LIFU)–based brain stimulation techniques—transcranial focused ultrasound stimulation (tFUS) and transcranial pulse stimulation (TPS). Although tFUS involves delivering long trains of acoustic pulses, the newly introduced TPS delivers ultrashort (∼3 μs) pulses repeated at 4 Hz. Accordingly, only a single simulation study with limited geometry currently exists for TPS. We considered a high-resolution three-dimensional (3D) whole human head model in addition to water bath simulations. We anticipate that the results of this study will help researchers investigating LIFU have a better understanding of the effects of the two different techniques. ApproachWith an objective to first reproduce previous computational results, we considered two spherical tFUS transducers that were previously modeled. We assumed identical parameters (geometry, position, and imaging data set) to demonstrate differences, purely because of the waveform considered. For simulations with a 3D head data set, we also considered a parabolic transducer that has been used for TPS delivery. ResultsOur initial results successfully verified previous modeling workflow. The tFUS distribution was characterized by the typical elliptical profile, with its major axis perpendicular to the face of the transducer. The TPS distribution resembled two mirrored meniscus profiles, with its widest diameter oriented parallel to the face of the transducer. The observed intensity value differences were theoretical because the two waveforms differ in both intensity and time. The consideration of a realistic 3D human head model resulted in only a minor distortion of the two waveforms. SignificanceThis study simulated TPS administration using a 3D realistic image-derived data set. Although our comparison results are strictly limited to the model parameters and assumptions made, we were able to elucidate some clear differences between the two approaches. We hope this initial study will pave the way for systematic comparison between the two approaches in the future.

A low-effort and inexpensive methodology to determine beam separation distance of multi-foci FLDI

A new method is presented to measure the separation distance between probing volumes of closely spaced multi-foci Focused Laser Differential Interferometers (FLDI). The accuracy and precision of this distance measurement directly translate into the quality of convection velocity measurements performed by means of arrays of FLDI. The suggested method is based on the detection of a propagating weak blast wave, generated with a simple and inexpensive apparatus using an automotive spark plug. Demonstration is conducted using an FLDI with two foci (D-FLDI). The generated blast wave is probed at multiple distances from its source to verify its weakening into an acoustic pulse, which offers ideal conditions to the proposed methodology. D-FLDI separation distance measurement using the new approach is compared to measurements using beam profiler images and to the alternative currently established in the literature, based on the FLDI response to a moving weak lens. Tests are made on varying internal configurations of the D-FLDI, while the distance between the two systems is kept constant. Results show the present method to have improved accuracy and robustness in comparison with the moving lens approach, while requiring significantly less effort. Measured separation distances obtained from blast wave detections in a single location are within 0.5 % of the reference value measured through the beam profiler. This procedure is therefore a practical and reliable alternative to the measurement using beam profiler imaging, with similar quality. Its advantages concern associated costs, flexibility when measuring in constrained spaces such as in proximity to walls, and applicability to systems in which beam imaging is not an option, such as multi-point line FLDI.

POS-772 SHEAR WAVE BASED ELASTOGRAPHY POINT QUALIFICATION IN THE EVALUATION OF RENAL PARENCHYMA STIFFNESS IN KIDNEY TRANSPLANT RECIPIENTS UNDERGOING GRAFT BIOPSY

Shear wave elastography (SWE) is an ultrasound technique that measures tissue stiffness non-invasively. In SWE, a real-time short-duration acoustic push pulse generates shear waves travelling perpendicular to the main US beam. Renal biopsy remains the gold standard in assessing rejection and chronicity in kidney transplantation. However, biopsy remains imperfect, with limitations and inherent risks, including sampling errors, allograft trauma with multiple needle pass attempts, and significant interobserver variation in interpreting biopsy samples among pathologists.

Investigation of a Novel Acoustic Levitation Technique Using the Transition Period Between Acoustic Pulse Trains and Electrical Driving Signals.

Acoustic levitation is considered one of the most effective noncontact particle manipulation methods, along with aerodynamic, ferromagnetic, and optical levitation techniques. It is not restricted by the material properties of the target. However, existing acoustic levitation techniques have some drawbacks that limit their potential applications. Therefore, in this article, an innovative approach is proposed to manipulate objects more intuitively and freely. By taking advantage of the transition periods between the acoustic pulse trains and electrical driving signals, acoustic traps can be created by switching the acoustic focal spots rapidly. Since the high-energy-density points are not formed simultaneously, the computation of the acoustic field distribution with complicated mutual interference can be eliminated. Therefore, compared to the existing approaches that created acoustic traps by solving pressure distributions using iterative methods, the proposed method simplifies the computation of time delay and makes it possible to be solved even with a microcontroller. In this work, three experiments have been demonstrated successfully to prove the capability of the proposed method including lifting a Styrofoam sphere, transportation of a single target, and suspending two objects. Besides, simulations of the distributions of acoustic pressure, radiation force, and Gor'kov potential were conducted to confirm the presence of acoustic traps in the scenarios of lifting one and two objects. The proposed tactic should be considered effective since the results of the practical experiments and simulations support each other.