Acoustic Field Simulation Research Articles

Numerical simulation of acoustic field under mechanical stirring* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11674207 and 11674206).

The present study analyzes the effect of stirring on ultrasonic degradation experiments through acoustic field distribution, which provides a guidance for further improvement of the degradation rate of organic solutions. It is known that in order to eliminate the standing wave field formed by ultrasonic radiation in the water tank, the liquid in the water tank needs to be stirred and the corresponding distribution of acoustic field is simulated by using the finite element method (FEM). The standing wave leads to an uneven distribution of the acoustic field when it is not stirred, and disappears after being stirred, which increases the cavitation area in the ultrasonic cleaning tank. Then, the degradation experiment with agitation is carried out. The experimental results show that the degradation rate of the solution is higher than that when there is no agitation, which confirms the importance of the acoustic field distribution to ultrasonic degradation. In addition, it is clear that with the increase of the stirring speed, the degradation rate increases first and reaches a maximum at 600 rpm before decreasing. Finally, the distribution of flow field is simulated and analyzed.

Mechanical Analysis and Experimental Research on Ultrasonic Levitated Conical Rotor Piezoelectric Actuator

This work presents a novel conical rotor non-contact piezoelectric actuator based on the principle of near-field acoustic levitation. The conical rotor is levitated and driven by a single stator, while generating two orthogonal standing waves and superimposing a travelling wave vibration on the stator. A frequency sensitivity analysis is conducted for the stator structural parameters, based on a dynamics calculation. An acoustic field simulation is conducted and the sound pressure distribution is obtained. The acoustic radiation force is calculated at different voltages and frequencies. A prototype is fabricated, and the vibration characteristics are experimentally obtained. A test system is built for the actuator, and the conical rotor successfully achieves levitation and rotation. The levitation height and rotation speed of the 3.37[Formula: see text]g rotor are 0.4[Formula: see text]mm and 2300[Formula: see text]r/min, respectively. The acoustic simulations are validated experimentally and show reasonable agreement.

Ultrasound frequency effect on soybean protein: Acoustic field simulation, extraction rate and structure

This study endeavored to develop a method to evaluate the effect of ultrasound frequency on soybean protein extraction. In the ultrasonic frequencies range from 20 to 52 kHz, 28, 35, and 45 kHz were predicted to be the resonance frequencies in the ultrasound-assisted extraction (UAE) process of soybean protein by simulating the acoustic field distribution. The absolute sound pressure and the relative standard deviation could be well-coordinated via frequency regulation. The extraction experiment of soybean protein showed that the extraction rate was improved significantly (p < 0.05) with the aid of ultrasound. The extraction effect was optimal at 28 kHz and the extraction rate was improved to 73.35 g/100 g from 46.09 g/100 g of control under the same condition. The structure of the extracted protein was analyzed by the spectrum to further explore the mechanism of the effect of ultrasonic frequency. Spectral analysis showed that 20, 28, and 35 kHz had a significant influence on the structure of protein molecules. Therefore, acoustic field simulation can be used as one effective method for selecting ultrasonic frequency, which could help to optimize equipment and improve efficiency.

Seabed seismic wave simulation by finite difference time domain scheme in marine environment with complex seafloor topography

The studying of the excitation and propagation characteristics of seabed seismic waves in a complex marine environment is of great significance in investigating seafloor physical and mechanical properties and exploring resources. At present, the research of time-domain seabed seismic waves is mostly restricted in a marine environment with horizontal stratification, but the actual geological conditions of seafloor are relatively complex, and the numerical solutions obtained under ideal assumption are quite different from those in an actual complex environment. To master the propagation characteristics of seabed seismic wave in the environment that is closer to the actual one, a complex and long range model including layers of water, soft mud and bedrocks is designed in the paper, where non-horizontal seafloor topography with a dipping and uplifting structure is considered. The staggered-grid finite difference method with 2nd-order accuracy in time and 10th-order accuracy in space is used to simulate the seabed seismic waves under such a complex marine environment. Meanwhile, multi axial perfectly matched layer is used as an artificial boundary condition to ensure the numerical long-term stability in a liquid-solid medium. Considering the dipping structure, the acoustic signals excited by sources at different positions of the model are compared to determine the favorable style of source excitation for Scholte interface wave receiving. Through the time-domain waveform of the calculated acoustic field, the propagation characteristics of the seabed seismic wave in the complex marine environment are analyzed. The results show that the staggered-grid finite difference method with high-order spatial accuracy can improve the dispersion problem in numerical calculation. The multi-axial perfectly matched layer used to replace the traditional perfectly matched layer can solve the instability problem in the numerical simulation of acoustic field in liquid-solid media for a long range. Through the comparison among the acoustic signal amplitudes excited by sources at different positions, a better performance can be achieved when the source-receiver is placed along the updip direction. In such a case, the acoustic signal is stronger, which is more advantageous to receive and analyze the Scholte interface wave. In the complex seabed model with a dipping and uplifting structure, the uplift of seafloor bedrock changes the propagation direction of Scholte wave, which makes it possible to receive Scholte wave at shallower depth.

Optimization of piezotransducer dimensions for quasicollinear paratellurite AOTF

The method of quasicollinear acousto-optic tunable filters (AOTFs) piezoelectric transducer dimensions optimization is presented. The AOTFs with large interaction length apply the bulk acoustic wave (BAW) reflection from the input optical facet. Optimization is based on spectral approach to simulation of the BAW field in anisotropic media and Raman–Nath equations numerically solved for the inhomogeneous acoustic field. It was found that variation of the transducer dimensions can minimize RF power consumption of the AOTF. Comparison of the optimized transducer dimensions with those commonly used in quasicollinear paratellurite AOTFs showed that it is possible to improve the AOTF energy efficiency in about 2 times. It was shown that acoustic field simulation results obtained for one AOTF geometry can be applied to the other geometries but for equivalent frequency providing the same ultrasound beam ray spectrum width. It was also shown that when choosing the quasicollinear AOTF with reflection geometry, one should not rely only on the AO figure of merit value, since the energy efficiency of such AOTF type will be determined by the product of the AO figure of merit and the AOTF efficiency, which takes into account the change in the acoustic beam width in the reflection process. The results aim at improving the design of AOTFs for ultrashort laser pulse shaping.

A High-Frequency Phased Array System for Transcranial Ultrasound Delivery in Small Animals.

Existing systems for applying transcranial focused ultrasound (FUS) in small animals produce large focal volumes relative to the size of cerebral structures available for interrogation. The use of high ultrasonic frequencies can improve targeting specificity; however, the aberrations induced by rodent calvaria at megahertz frequencies severely distort the acoustic fields produced by single-element focused transducers. Here, we present the design, fabrication, and characterization of a high-frequency phased array system for transcranial FUS delivery in small animals. A transducer array was constructed by micromachining a spherically curved PZT-5H bowl (diameter = 25 mm, radius of curvature = 20 mm, fundamental frequency = 3.3 MHz) into 64 independent elements of equal surface area. The acoustic field generated by the phased array was measured at various target locations using a calibrated fiber-optic hydrophone, both in free-field conditions as well as through ex vivo rat skullcaps with and without hydrophone-assisted phase aberration corrections. Large field-of-view acoustic field simulations were carried out to investigate potential grating lobe formation. The focal beam size obtained when targeting the array's geometric focus was [Formula: see text] mm in water. The array can steer the FUS beam electronically over cylindrical volumes of 4.5 mm in diameter and 6 mm in height without introducing grating lobes. Insertion of a rat skullcap resulted in substantial distortion of the acoustic field ( [Formula: see text]% [Formula: see text]); however, phase corrections restored partial focal quality ( [Formula: see text]% [Formula: see text]). Using phase corrections, the array is capable of generating a trans-rat skull peak negative focal pressure of up to ~2.0 MPa, which is sufficient for microbubble-mediated blood-brain barrier permeabilization at this frequency.

Non-linear embedding of acoustic cross-spectral density matrices through diffusion maps.

Based on the notion of similarity or "distance" between cross-spectral density matrices (CSDMs), a recent analysis of matched-field source localization in a stochastic ocean waveguide provided evidence that geodesic distances between CSDMs could be employed to estimate the source location in range and depth. For M acoustic sensors configured as a vertical array, these M×M matrices were estimated from source and replica fields propagated to the array and interpreted as points in a Riemannian manifold whose dimension is M2. Because they serve as fundamental constructs for many source localization algorithms, visualizations of CSDM manifolds are illustrated here in an attempt to gain insight into this geometric approach by using simulated acoustic fields propagated through an ocean waveguide with internal wave-induced variability. The manifold is treated as an undirected, weighted graph whose nodes are CSDMs with edges (weights) describing a measure of similarity between nodes. A non-linear dimensionality reduction technique, diffusion maps, is applied to project these high-dimensional matrices onto a three-dimensional subspace using a spectral decomposition of the graph in an attempt to grasp relationships among such matrices. The mapping is designed to preserve the notion of distance between matrices, allowing for a meaningful visualization of the high-dimensional manifold.

Construction of axisymmetric equivalent sources to facilitate the simulation of nonlinear acoustic fields in therapeutic ultrasound

The development of new clinical applications of therapeutic ultrasound has been accompanied by efforts to standardize simulation methods for predicting nonlinear ultrasound fields. Although software tools for simulating nonlinear ultrasound propagation are increasingly available, computational burdens remain high, especially for fields characterized by strong focusing and significant harmonic content. Because nonlinear effects in such fields accumulate primarily over a short axial distance within the focal lobe, the nonlinear field can be approximated by considering an equivalent source with a similarly shaped focal lobe in the linearly focused beam. If an axisymmetric equivalent source can be identified, even strongly nonlinear fields can be accurately simulated with minimal computational burden using the Khokhlov-Zabolotskaya- Kuznetsov model. This approach has been implemented and validated in water for several real sources using only a simple set of linear field measurements to characterize the focal lobe of each source. To demonstrate the breadth of utility of this approach, holograms of non-axisymmetric fields distorted by phantoms were also used to define equivalent sources and estimate in situ nonlinear fields. Fast holography measurements combined with equivalent-source simulations can efficiently characterize the impact of different phantom geometries on nonlinear fields. [Work supported by NIH R01EB025187 and R01EB007643, and RSF 19-12-00148.]

Dimensionality reduction of cross-spectral density matrices using diffusion map projections

Cross-spectral density matrices (CSDMs) constructed for matched-field source localization in an ocean waveguide are both Hermitian and positive semi-definite, allowing them to be interpreted in a non-Euclidean geometric framework as “points” in a Riemannian manifold. This abstract matrix representation can be used to construct distance metrics on the manifold, and distances between pairs of such matrices provide a measure of similarity between the true source CSDM and various replica CSDMs. With this geometric interpretation, the shortest “distance” between pairs of source/replica CSDMs represents an estimate of the source location obtained from acoustic field amplitude and phase acquired on a vertical array [Finette and Mignerey, JASA 143 (2018)]. In this presentation, visualizations of CSDM manifolds obtained from simulated acoustic fields propagating in an ocean waveguide with internal wave-induced variability are illustrated to gain insight into this approach to passive source localization. Since the original manifold resides in a high-dimensional space determined by the number of sensors, manifold learning using diffusion maps is employed to reduce the dimensionality but constrained to retain the relative distance relationships among the CSDMs. The original manifold is projected down to three dimensions for visualization. [Work supported by the Office of Naval Research.]

Characterization and Optimization of Acoustic Field for Curved Array Probe

The focusing principle and acoustic field characteristics of curved array probe are studied. Delay laws are first computed in the same way as linear array probe, and its effects on the axial acoustic pressure distributions are quantitatively examined. It is shown that the maximum points of axial acoustic pressure occur at positions deviating from the predefined focal depths. To further analyze the focusing principle of curved array probe, simulations of acoustic field are conducted under different settings of focal depth and active aperture size. It reveals that the circular array profile and the inconsistent electronic delay laws make the pulsed ultrasonic waves unable to constructively interfere at target positions. Subsidiary beams arise and further interfere with the axial acoustic pressure distributions of the main beam. To control the transmitted acoustic field, and thus customize the inspection strategy, an optimized delay law calculation scheme is proposed. The good behavior is well validated both by theoretical calculation and experimental examination.

Numerical Simulation of Acoustic Fields Induced by a Flow Past an Oscillating Solid

The paper presents two computational techniques that do not require a change in the topology of the mesh to simulate the flow around oscillating bodies. The first technique uses the immersed boundary method, the second technique uses the method of deformed meshes. The capabilities of these two approaches are demonstrated by solving model problems in a two-dimensional formulation for simulating acoustic fields generated by an oscillating cylinder, both single and in the presence of a fixed cylindrical body, in a subsonic flow.

LIPUS far-field exposimetry system for uniform stimulation of tissues in-vitro: development and validation with bovine intervertebral disc cells

Therapeutic Low-intensity Pulsed Ultrasound (LIPUS) has been applied clinically for bone fracture healing and has been shown to stimulate extracellular matrix (ECM) metabolism in numerous soft tissues including intervertebral disc (IVD). In-vitro LIPUS testing systems have been developed and typically include polystyrene cell culture plates (CCP) placed directly on top of the ultrasound transducer in the acoustic near-field (NF). This configuration introduces several undesirable acoustic artifacts, making the establishment of dose-response relationships difficult, and is not relevant for targeting deep tissues such as the IVD, which may require far-field (FF) exposure from low frequency sources. The objective of this study was to design and validate an in-vitro LIPUS system for stimulating ECM synthesis in IVD-cells while mimicking attributes of a deep delivery system by delivering uniform, FF acoustic energy while minimizing reflections and standing waves within target wells, and unwanted temperature elevation within target samples. Acoustic field simulations and hydrophone measurements demonstrated that by directing LIPUS energy at 0.5, 1.0, or 1.5 MHz operating frequency, with an acoustic standoff in the FF (125–350 mm), at 6-well CCP targets including an alginate ring spacer, uniform intensity distributions can be delivered. A custom FF LIPUS system was fabricated and demonstrated reduced acoustic intensity field heterogeneity within CCP-wells by up to 93% compared to common NF configurations. When bovine IVD cells were exposed to LIPUS (1.5 MHz, 200 μs pulse, 1 kHz pulse frequency, and ISPTA = 120 mW cm−2) using the FF system, sample heating was minimal (+0.81 °C) and collagen content was increased by 2.6-fold compared to the control and was equivalent to BMP-7 growth factor treatment. The results of this study demonstrate that FF LIPUS exposure increases collagen content in IVD cells and suggest that LIPUS is a potential noninvasive therapeutic for stimulating repair of tissues deep within the body such as the IVD.

Phased Array Detection Parameters for Electron Beam Welds in CFETR Vacuum Vessel Port Stubs

The China Fusion Engineering Testing Reactor (CFETR) vacuum vessel (VV) port stub was formed by electron beam welding (EBW). In this article, the phased array ultrasonic testing (PAUT) method was introduced for testing the quality of the weld. First, the acoustic field simulation and analysis of the EBW of 316L austenitic stainless steel were carried out with different frequency probes, then the microstructure of electron beam welds were observed by microscopic metallographic to analyze the influence of the type and influence of probe, finally fabricating the reference test blocks according to the NB/T47013-2015 standard to conducting the PAUT experiment. The test results show that the type of probe has less influence on the signal-to-noise ratio (SNR) and localization of the detection of large-thickness austenitic stainless steel electron beam welds under low-frequency conditions. The SNR of EBW detection was gradually decreased as the frequency of the probe increases under the same type of probe. In the direction of depth of the EBW, with the increase in the depth, the weld microstructure size becomes finer, so the sector scan image of $\phi ~1$ -mm side drilled hole (SDH) near the upper weld was severely distorted, while the sector scan image of $\phi ~1$ -mm SDH near the lower EBW was relatively good.

Aerosol aggregation through modulated symmetrically opposing acoustic field in normal 16-sided waveguide coupled with resonators

Aerosol control is a big revolution in production and use of submicronic particles. Developing a novel aerosol control technology in the area is the study objective of this paper. Attributing to the aerosol control potential in acoustics, a normal 16-sided aerosol aggregation chamber (pelletier dish) symmetrically installed with 16 poles of Helmholtz sound source (HSS) is successfully used to aggregate smog aerosols. The aerosols are generated by the combustion of chemical material. In the acoustic conditions of 2, 4, 8 and 16 beams of opposing waves, the shapes of aerosol distribution always display as the specific aerosol petals of number equaling to the operating number of HSS. With the increase of the operating number, the removal effectiveness rises gradually to 1.5 wavelengths, obviously larger than half wavelengths achieved in the previous study. The results are repeatability in experiment, and especially the aerosol aggregation can be pre-designed by acoustic field simulation.

Enhanced Low‐Frequency Monopole and Dipole Acoustic Antennas Based on a Subwavelength Bianisotropic Structure

AbstractHigh‐efficiency sound emission is crucial in practical scenarios, such as sonar system and acoustic communication. However, the efficient emission of the low‐frequency sound source is difficult because of the large acoustic radiation reactance from the ambient medium. Here, a subwavelength bianisotropic hybrid Mie resonator (BHMR) is proposed, which has shown excellent capability in converting a central monopole source into the enhanced monopole and dipole acoustic antennas at low frequency. The simulated acoustic field distributions and far‐field radiations of the BHMR demonstrate that the enhanced omnidirectional and directional antennas are induced by the monopole and dipole resonances, respectively. A BHMR sample is further fabricated and the enhancements of the monopole and dipole acoustic antennas by the BHMR are experimentally verified. The miniature BHMR offers an alternative way to achieve the enhanced low‐frequency monopole and dipole antennas that are highly desirable for loudspeaker design and acoustic communication.

Acoustic sound speed profile inversion based on orthogonal matching pursuit

The estimation of ocean sound speed profiles (SSPs) requires the inversion of an acoustic field using limited observations. Such inverse problems are underdetermined, and require regularization to ensure physically realistic solutions. The empirical orthonormal function (EOF) is capable of a very large compression of the data set. In this paper, the non-linear response of the sound pressure to SSP is linearized using a first order Taylor expansion, and the pressure is expanded in a sparse domain using EOFs. Since the parameters of the inverse model are sparse, compressive sensing (CS) can help solve such underdetermined problems accurately, efficiently, and with enhanced resolution. Here, the orthogonal matching pursuit (OMP) is used to estimate range-independent acoustic SSPs using the simulated acoustic field. The superior resolution of OMP is demonstrated with the SSP data from the South China Sea experiment. By shortening the duration of the training set, the temporal correlation between EOF and test sets is enhanced, and the accuracy of sound velocity inversion is improved. The SSP estimation error versus depth is calculated, and the 99% confidence interval of error is within ±0.6 m/s. The 82% of mean absolute error (MAE) is less than 1 m/s. It is shown that SSPs can be well estimated using OMP.

Simulation of acoustic fields emitted by ultrasonic phased array in austenitic steel weld**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474308, 11574343, and 11774377).

Ultrasonic inspection of austenitic steel weld is a great challenge due to skewed and distorted beam in such a highly anisotropic and inhomogeneous material. To improve the ultrasonic measurement in this situation, it is essential to have an in-depth understanding of ultrasound characteristics in austenitic steel weld. To meet such a need, in the present study we propose a method which combines the weld model, Dijkstra’s path-finding algorithm and Gaussian beam equivalent point source model to calculate the acoustic fields from ultrasonic phased array in such a weld. With this method, the acoustic field in a steel-austenitic weld-steel three-layered structure for a linear phase array transducer is calculated and the propagation characteristics of ultrasound in weld are studied. The research results show that the method proposed here is capable of calculating the acoustic field in austenitic weld. Additionally, beam steering and focusing can be still realized in the austenitic steel weld and the beam distortion is more severe in the middle of weld than at other positions.

Simulation of acoustic backscattered field from a medium with randomly distributed fibers

Common assumptions in quantitative ultrasound include that the medium is homogeneous and isotropic and has diffuse scattering conditions. In some soft tissues, due to the presence of fiber-like structures, the medium is anisotropic and has a periodic scattering condition. Skeletal muscle is an example in which the fibers are highly aligned, a coherent scattering condition appears. Using the closed form solution of acoustic backscattered field from immersed finite cylindrical targets, this work presents a simulation study of a medium containing randomly distributed fibers. The effective scatterer diameter and average backscatter coefficient of the medium are calculated and compared with the change in fiber orientation. The effects of other parameters such as number of fibers and their lengths are also analyzed. In addition, different distributions of parameters such as normal or uniform distributions are considered, and their effects on the backscattered field are studied.

Effect of acoustic streaming on continuous flow sonocrystallization in millifluidic channels

This work is concerned with the effect of ultrasound on mixing and consequently on crystallization in millifluidic channels. An ultrasonic horn with frequency of 20 kHz was placed inside a vessel with a well-defined geometry containing a single capillary tube with internal diameter (I.D.) of 1.55 or 3.2 mm operated with a fluid flow rate between 1 and 17.6 ml/min. This system was employed to produce crystals of adipic acid in the range of 15–35 µm. The effect of ultrasound on flow patterns, residence time distribution (RTD) and cooling crystallization were investigated experimentally and numerically. Simulations of acoustic and velocity fields inside the millichannel acting as crystallizer allowed characterizing the acoustic streaming generated within it. In the large capillary, especially at small flow rates, acoustic streaming influenced the flow field, inducing vortices and leading to significant changes in RTD. Conversely, in the small capillary, ultrasound affected the flow field and the RTD negligibly, and a laminar velocity profile with straight streamlines was obtained. As a consequence, different crystallization behaviours were observed in the two capillaries; in particular, while the mean crystal size increased with the sonication residence time in the 1.55 mm I.D. capillary, it decreased in the 3.2 mm I.D. capillary. This difference highlights the importance of considering acoustic streaming when designing sonocrystallizers.

Numerical simulation of acoustic fields in formation generated by linear phased array acoustic transmitters during logging while drilling

The monopole acoustic transmitters of existing logging while drilling (LWD) tools rarely have directional radiation capacity. Only a small amount of energy is radiated to geological structures outside the borehole, which presents a significant challenge for acoustic reflection LWD. In this study, a method is proposed to enhance the amplitudes of P-P waves reflected from unknown reflection boundaries during LWD, based on the directional radiation technology of linear phased array (LPA) acoustic transmitters. Waveforms in the formation generated by a monopole acoustic transmitter and LPA acoustic transmitters are numerically simulated using the finite-difference time-domain and real axis integration methods. The influences of LPA parameters on formation P waves and the application effects of LPA acoustic transmitters in acoustic reflection LWD are also analyzed. The simulation results show that the characteristics of formation P waves when using the LPA acoustic transmitter differ from those when using the monopole transmitter. The main radiated acoustic beam of formation P waves can be controlled by adjusting the LPA parameters. The main beam angular width decreases with the increase of the element number; the main beam deflection angle is affected by the delay time between the excitation signals applied to adjacent elements; and the amplitude weighting of the excitation signals applied to all elements has a slight effect on the main beam angular width. With an appropriate choice of the LPA parameters, the amplitudes of reflected P-P waves are significantly increased in acoustic reflection LWD. Therefore, compared with the monopole acoustic transmitter, the LPA acoustic transmitter can be utilized to effectively improve the capacity of acoustic LWD tools for detecting the reflectors away from the borehole. The findings of this study provide a novel approach to designing next-generation acoustic reflection LWD tools.