Acoustic Radiation Research Articles

COMPACT ANALYTICAL MODEL FOR ELECTROMAGNETIC DISK-SHAPED UNDERWATER TRANSDUCER

This paper proposes a mathematical model for a disk-type pulsed electrodynamic transducer operating in the low-frequency range. A well-known architecture of an electromagnetic acoustic radiator with a helical coil and a conducting disk is studied. In the work, the equations of the electromechanical system in the form of the Lagrange-Maxwell equations are built with the use of the Green's functions of a plane axisymmetric acoustic problem to estimate the reaction force of the fluid. A comparison is made between the results of a numerical solution of the obtained equations and direct numerical calculation in the COMSOL finite element analysis software. The resulting model shows good qualitative agreement with the results of finite element calculations while allowing calculations with a variation for all main model parameters required to design the transducer.

Boundary Integral Neural Networks for Acoustic Radiation Prediction from Noisy Boundary Data

Boundary Integral Neural Networks for Acoustic Radiation Prediction from Noisy Boundary Data

Acoustic black hole immersed sonoreactor for high-efficiency cavitation treatment

Developing innovative sonoreactors to enhance acoustic processing efficiency holds immense importance in the field of sonochemistry. Traditional immersed sonoreactors (TISs) mainly produce cavitation at the probe tip, with a relatively weak cavitation around the probe, resulting in posing challenges for high-efficiency cavitation treatment. Here we propose an acoustic black hole immersed sonoreactor (ABHIS) in longitudinal-flexural coupled vibration, enabling high-efficiency cavitation treatment by unleashing the cavitation potential of the probe. The symmetrical structure of the probe is altered to introduce a coupling of flexural vibration mode, and an acoustic black hole (ABH) profile is integrated to further enhance both flexural wave number and amplitude. In this paper, we present a systematic theoretical design method for ABHIS and compare its performance with TIS using finite element method (FEM). An ABHIS prototype is fabricated and subjected to experimental tests and cavitation observation. The results demonstrate that our theoretical analysis model accurately predicts the frequency characteristics of ABHIS. The proposed ABHIS exhibits satisfactory dynamic characteristics, with significantly increased vibration displacement and acoustic radiation ability compared to TIS. Importantly, the ABH design significantly expands ultrasonic cavitation regions and enhances acoustic radiation intensity of ABHIS resulting in a substantial improvement in acoustic processing efficiency.

Acoustic radiation by cavitation bubbles near solid boundaries with modified wettability

Acoustic radiation by cavitation bubbles near solid boundaries with modified wettability

Differentiating Benign from Malignant Causes of Splenomegaly: Is Acoustic Radiation Force Impulse Elastography Helpful?

Purpose: To evaluate the ability of acoustic radiation force impulse (ARFI) elastography in differentiating benign from malignant etiologies of splenomegaly based on differences in splenic stiffness. Materials and Methods: Between September 2020 and November 2022, we evaluated 40 patients with splenomegaly—defined by a splenic long axis greater than 13 cm and/or a short axis greater than 6 cm, without visible focal or infiltrative mass lesions—using abdominal ultrasound at our university hospital. Each patient also underwent a standardized ARFI elastographic assessment of the enlarged spleen, with data collected prospectively. We then retrospectively analyzed the cases with confirmed etiologies of splenomegaly from their final medical reports. Mean ARFI velocities (MAV) were compared across patients with splenomegaly due to malignant infiltration (MIS) from hematological malignancy, congestive splenomegaly (CS) due to portal or splenic vein congestion/occlusion, and immune-related splenomegaly (IRS) associated with systemic infectious or autoimmune diseases. Results: Among the 40 patients with splenomegaly, 21 (52.5%) were diagnosed with malignant infiltrative splenomegaly (MIS), 11 (27.5%) with congestive splenomegaly (CS), and 8 (20%) with immune-related splenomegaly (IRS). The mean ARFI velocities (MAV) for the MIS, CS, and IRS groups were 3.25 ± 0.68 m/s, 3.52 ± 0.47 m/s, and 2.84 ± 0.92 m/s, respectively. No significant differences were observed in splenic stiffness (MAV) among these groups. Conclusions: Differentiating between benign and malignant etiologies of splenomegaly based on stiffness differences observed in ARFI elastography is not feasible. Larger prospective studies are necessary to validate these findings.

Automated interferometric stand for determination of amplitude-frequency characteristics of acoustic emitters

An automated interferometric stand (AIS) was created to determine the amplitude-frequency characteristics of acoustic emitters in the range from 0.5 to 200 kHz. The created AIS contains a unit for generating acoustic sinusoidal excitation pulse packets and a recording unit. The unit for generating acoustic pulse packets includes a generator of sinusoidal signals, a microprocessor unit for pulse packets generation and the AIS synchronization, a power amplifier of a sinusoidal signal to create a sufficient power of the acoustic emitter excitation signal. The recording unit includes a Michelson interferometer with a sound-conducting rod in one of the arms. One of the ends of the rod has a mirror surface. The other end is connected to the acoustic emitter through an acoustic contact. The length of the sound-conducting rod is 50 cm, which is enough to ensure measurements at the lower limit of the frequency range of the acoustic emitter radiation. The propagation time of the acoustic wave in the rod is of the order of 75 microseconds. As the end of the rod vibrates due to acoustic excitation, the initial path difference of the optical beams in the interferometer will change, causing a change in the intensity of the illumination produced by the interfering beams. These changes are recorded by photodiode in the other arm of the interferometer. After the photodiode signal is amplified in the amplifier, it is fed to the analog-to-digital converter, the output of which is transferred to the buffer memory, where the discretized values of the response signal amplitude during the time of the measuring pulse are accumulated. The control algorithm of the AIS is carried out with the help of developed software. The results of measuring the amplitude-frequency characteristics of mass-produced broadband acoustic emitters using AIS proved the satisfactory convergence of the obtained frequency responses with the passport data of these serial devices frequency responses. The amplitude-frequency characteristic of experimental sample of a piezoelectric acoustic emitter, made for research on the detection and identification of internal defects in laminated composite structures and "composite-concrete" adhesive joints, was obtained.

Acoustic radiation force impulse (push pulse)-induced lung hemorrhage: investigating the effect of ultrasound contrast agent in rabbits.

Acoustic radiation force impulse (ARFI) elastography and contrast-enhanced ultrasonography (CEUS) are emerging techniques that are becoming common in ultrasound examinations. We previously reported that ARFI (push pulse) induced lung hemorrhage in rabbits, indicating that greater risks are associated with ARFI than with conventional ultrasound. In this study, we assessed the risk of lung hemorrhage under a combination of ARFI elastography and CEUS, considering potential exacerbation of ARFI-induced lung hemorrhage as a result of the ultrasound contrast agent (UCA) used in CEUS. Twenty-three rabbits were divided into non-UCA and UCA groups. ARFI exposure parameters were set at six mechanical index (MI) levels (0.29, 0.45, 0.60, 0.88, 1.0, 1.39) in non-UCA groups and five MI levels (0.29, 0.66, 0.88, 0.97, 1.25) in UCA groups. Lung exposure was performed bilaterally through the intercostal space in each rabbit. Lung damage was assessed through macroscopic and microscopic observation post euthanasia. Lung hemorrhage was detected at MI0.3 levels of 0.88 or higher. Logistic regression analyses showed that MI0.3 was a statistically significant factor for occurrence of lung hemorrhage in both non-UCA and UCA groups, and the MI0.3 threshold (ED05) for inducing lung hemorrhage was 0.68 and 0.71, respectively. However, multivariate logistic regression and linear regression analyses across all samples indicated that UCA did not significantly affect the occurrence or area of lung hemorrhage. This study demonstrates that UCA does not significantly worsen ARFI-induced lung hemorrhage in terms of occurrence or severity. However, risks and benefits of ARFI elastography on the lung should be considered, irrespective of UCA administration.

Optimization of MR-ARFI for Human Transcranial Focused Ultrasound.

Magnetic resonance acoustic radiation force imaging (MR-ARFI) is an exceptionally promising technique to non-invasively confirm targeting accuracy and estimate exposure of low-intensity transcranial focused ultrasound stimulation. MR-ARFI uses magnetic field motion encoding gradients to visualize the MR phase changes generated by microscopic displacements at the ultrasound focus. Implementing MR-ARFI in the human central nervous system has been hindered by 1) phase distortion caused by subject motion, and 2) insufficient signal-to-noise ratio at low (<1.0 MPa) ultrasound pressures. The purpose of this study was to optimize human MR-ARFI to allow reduced ultrasound exposure while at the same time being robust to bulk and physiological motion. We demonstrate that a time series of single-shot spiral acquisitions, while triggering ultrasound on and off in blocks, provides ARFI maps that with correction are largely immune to bulk and pulsatile brain motion. Furthermore, the time series approach allows for a reduction in ultrasound exposure per slice while improving motion robustness with reduced scan time. The focused ultrasound beam can be visualized in an 80 second scan with our protocol, enabling iteration for image-guided targeting. We demonstrated robust ARFI signals at the expected target in 4 participants. Our results provide persuasive proof-of-principle that MR-ARFI can be used as a tool to guide ultrasound-based precision neural circuit therapeutics.

Prediction of splash noise in a rectangular tank under longitudinal periodic excitation

Sloshing phenomena within fuel tanks have emerged as a significant contributor to noise in hybrid and high-end vehicles, particularly as other sources of noise, such as those from the engine and transmission system, minimized. The manifestation of noise during sloshing results from the dynamic interplay between the fluid within the tank and both its surrounding structures and the fluid itself. “Splash noise” is an acoustic phenomenon which arises due to pressure fluctuations induced by fluid-fluid interactions during sloshing. Thus, the generation of splash noise encompasses a multi-physics process involving fluid flow and acoustic radiation. Accurate prediction of splash noise is crucial for implementing measures to mitigate it during the design phase. The current paper proposes a hybrid approach for predicting splash noise within a rectangular tank. The first step in the methodology is to predict the flow field within the tank, from which acoustic sources are computed. These sources are then utilized to calculate the sound propagation based on the acoustic analogy. To emulate a regime dominated by fluid-fluid interactions, periodic longitudinal excitations are imposed on the rectangular tank, both with and without baffles. Parameters such as fluid free-surface profile, tank wall pressures, and radiated sound pressure levels are systematically calculated and subsequently validated against experimental results available in the existing literature.

Acoustic Radiation Patterns of Different Polygon Piston Surfaces

Transducers are used in acoustic remote sensing and several other modern applications. The radiating surface geometry of a single acoustic transducer affects its beam pattern and has a cumulative effect on the overall performance of an array configuration. In addition, the transducers with polygon radiating surfaces provide more compact structure in an array than the circular pistons due to their flat surface edges. However, until now, the radiation patterns of acoustic polygonal pistons have not been exclusively studied and documented. In this study, the directional factors of acoustic pistons with polygonal surfaces of three to ten sides were derived analytically from the first principle using the Rayleigh integral. These directional factors were used to synthesise and characterise the radiation patterns of the piston sources in comparison with the baffled circular piston of an equivalent surface area. The rectangular, the triangular, and the rest of the polygons have the same performance with the circular piston when the surface diameter is not higher than 0.5λ, 0.28λ and 0.43λ, respectively. The main lobe of the acoustic emissions from the square is very close to that of the circular piston whose diameter is greater than a wavelength while that of the rectangle is wider. The results show that the radiating surface perimeter and symmetry are the two most critical factors affecting the beam characteristics of a piston source rather than the surface area or the number of sides. The theoretical results were validated using the finite element method with an excellent compliance.

High-Performance SAW-Based Microfluidic Actuators Composed of Sputtered Al–Cu IDT Electrodes

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the significant influence of electrode resistivity and density on acoustic wave propagation, an Al–Cu film with 65 at% Al was selected as the IDT electrode material. The selected Al–Cu film demonstrated a resistivity of 6.0 × 10−5 Ω-cm and a density of 4.4 g/cm3, making it suitable for SAW-based microfluidic actuator applications. XRD analysis revealed that the Al–Cu film consisted of a physical mixture of Al and Cu without the formation of Al–Cu alloy phases. The film exhibited a fine-grained microstructure with an average crystallite size of 7.5 nm and surface roughness of approximately 6 nm. The SAW device fabricated with Al–Cu IDT electrodes exhibited excellent acoustic performance, resonating at 143 MHz without frequency shift and achieving an insertion loss of −13.68 dB and a FWHM of 0.41 dB. In contrast, the Au electrode-based SAW device showed significantly degraded acoustic characteristics. Moreover, the SAW-based microfluidic module equipped with optimized Al–Cu IDT electrodes successfully separated 5 μm polystyrene (PS) particles even at high flow rates, outperforming devices with Au IDT electrodes. This enhanced performance can be attributed to the improved resonance characteristics of the SAW device, which resulted in a stronger acoustic radiation force exerted on the PS particles.

Wearable Ultrasound System Using Low-Voltage Time Delay Spectrometry for Dynamic Tissue Imaging.

Wearable ultrasound is emerging as a new paradigm of real-time imaging in freely moving humans and has wide applications from cardiovascular health monitoring to human gesture recognition. However, current wearable ultrasound devices have typically employed pulse-echo imaging which requires high excitation voltages and sampling rates, posing safety risks, and requiring specialized hardware. Our objective was to develop and evaluate a wearable ultrasound system based on time delay spectrometry (TDS) that utilizes low-voltage excitation and significantly simplified instrumentation. We developed a TDS-based ultrasound system that utilizes continuous, frequency-modulated sweeps at low excitation voltages. By mixing the transmit and receive signals, the system digitizes the ultrasound signal at audio frequency (kHz) sampling rates. Wearable ultrasound transducers were developed, and the system was characterized in terms of imaging performance, acoustic output, thermal characteristics, and applications in musculoskeletal imaging. The prototype TDS system is capable of imaging up to 6cm of depth with signal-to-noise ratio of up to 42dB at a spatial resolution of 0.33mm. Acoustic and thermal radiation measurements were within clinically safe limits for continuous ultrasound imaging. We demonstrated the ability to use a 4-channel wearable system for dynamic imaging of muscle activity. We developed a wearable ultrasound imaging system using TDS to mitigate challenges with pulse echo-based wearable ultrasound imaging systems. Our device is capable of high-resolution, dynamic imaging of deep-seated tissue structures and is safe for long-term use. This work paves the way for low-voltage wearable ultrasound imaging devices with significantly reduced hardware complexity.

Vibro-acoustic suppression of metamaterial plates in multi-bandgaps

This paper delves into the vibration and acoustic radiation properties of a metamaterial plate integrated with grouped local resonators (GLRs). The GLRs, consisting of multiple spring-mass resonators arranged in various configurations such as series, parallel, and periodic arrangements, are shown to significantly influence the structural performance of the plate. An advanced Fourier series is implemented to articulate the displacement functions and surface acoustic pressure of the plate. By utilizing the energy principle, a vibro-acoustic coupling model is developed to describe the interaction between the metamaterial plate and the external acoustic field. The theoretical framework is rigorously validated against finite element method simulations, yielding highly congruent results. The local resonance bandgap behavior is explored, and the results reveal that the arrangement and connection strategy of the GLRs determine the stopband characteristics. Multiple resonators connected in series lead to an increased number of stopbands and more pronounced attenuation valleys, whereas multiple resonators connected in parallel or arranged in a periodic array result in an unchanged number of stopbands but a significantly wider stopband bandwidth. Furthermore, transmission characteristic assessments substantiate the vibration dampening efficacy of GLRs, and the marked suppressions in flexural wave propagation are demonstrated within the multiple merged bandgaps. These insights advance the comprehension of localized resonance phenomena in metamaterials and inform the development of sophisticated noise and vibration control strategies.

Acoustic Waves Coupling with Polydimethylsiloxane in Reconfigurable Acoustofluidic Platform.

Acoustofluidics is a promising technology that leverages acoustic waves for precise manipulation of micro/nano-scale flows and suspended objects within microchannels. Despite many advantages, the practical applicability of conventional acoustofluidic platforms is limited by irreversible bonding between the piezoelectric actuator and the microfluidic chip. Recently, reconfigurable acoustofluidic platforms are enabled by reversible bonding between the reusable actuator and the replaceable polydimethylsiloxane (PDMS) microfluidic chip by incorporating a PDMS membrane for sealing the microchannel and coupling the acoustic waves with the fluid inside. However, a quantitative guideline for selecting a suitable PDMS membrane for various acoustofluidic applications is still missing. Here, a design rule for reconfigurable acoustofluidic platforms is explored based on a thorough investigation of the PDMS thickness effect on acoustofluidic phenomena: acousto-thermal heating (ATH), acoustic radiation force (ARF), and acoustic streaming flow (ASF). These findings suggest that the relative thickness of the PDMS membrane (t) for acoustic wavelength (λPDMS) determines the wave attenuation in the PDMS and the acoustofluidic phenomena. For t/λPDMS≈O(1), the transmission of acoustic waves through the membrane leads to the ARF and ASF phenomena, whereas, for t/λPDMS≈O(10), the acoustic waves are entirely absorbed within the membrane, resulting in the ATH phenomenon.

Numerical simulation of impulse-induced surface acoustic waves for elastography purposes using k-Wave simulation toolbox

As elastography, an emerging medical imaging strategy, advances, surface acoustic waves have been utilized to examine superficial tissues quantitatively. So far, most studies are experimental, and a numerical method is needed to cost-effectively investigate surface acoustic wave generation and propagation for technical development and optimization purposes. This study aims to develop a reliable numerical method for simulating impulse-induced surface acoustic waves using the k-wave simulation toolbox. According to the physical process of surface acoustic wave based elastography, the proposed simulation method consists of two stages: compressional wave simulation and elastic wave simulation, which aim to generate acoustic radiation force impulse and elastic waves, respectively. The technical procedures were demonstrated by a wave simulation on a water–tissue model. Meanwhile, three acoustic radiation force modeling methods were adopted. The compressional wave simulation showed that the three force modeling methods could produce similar force distribution in space but largely different amplitudes. The elastic wave simulation confirmed the feasibility of numerically generating surface acoustic waves. The reliability of the simulated waves was verified by a quantitative comparison between the numerically acquired sound speeds and their theoretical expectations and by a qualitative comparison between the numerically generated waves and the experimental observations under similar conditions. In summary, this study confirms k-wave as an effective numerical method for simulating surface acoustic waves for elastography purposes. This study provides an immediate simulation platform for investigating Scholte waves, the surface acoustic wave at a liquid–solid interface, and also, a potential numerical framework to investigate other surface acoustic waves.

Joint subarray acoustic tweezers enable controllable cell translation, rotation, and deformation

Contactless microscale tweezers are highly effective tools for manipulating, patterning, and assembling bioparticles. However, current tweezers are limited in their ability to comprehensively manipulate bioparticles, providing only partial control over the six fundamental motions (three translational and three rotational motions). This study presents a joint subarray acoustic tweezers platform that leverages acoustic radiation force and viscous torque to control the six fundamental motions of single bioparticles. This breakthrough is significant as our manipulation mechanism allows for controlling the three translational and three rotational motions of single cells, as well as enabling complex manipulation that combines controlled translational and rotational motions. Moreover, our tweezers can gradually increase the load on an acoustically trapped cell to achieve controllable cell deformation critical for characterizing cell mechanical properties. Furthermore, our platform allows for three-dimensional (3D) imaging of bioparticles without using complex confocal microscopy by rotating bioparticles with acoustic tweezers and taking images of each orientation using a standard microscope. With these capabilities, we anticipate the JSAT platform to play a pivotal role in various applications, including 3D imaging, tissue engineering, disease diagnostics, and drug testing.

Assessment of wood quality for Sape making: Vibroacoustic analysis and machine learning classification

Sape is a popular traditional musical instrument from Sarawak, Malaysia. This instrument is handmade and differs in wood, dimension, design, etc. This impedes the preservation and promotion of the Sape tradition, as well as the development of new Sape instruments. Wood is the primary factor affecting Sape sound, and this study aimed to evaluate the quality of three commonly used types of wood in the instrument manufacturing. Rectangular wood samples were fashioned and tested for physical, vibroacoustic, and timbre characteristics using a flexural vibration test. The objective was to identify the top features influencing the sound quality and develop a reliable method for classifying wood quality. Results showed that Adau wood had the highest quality, followed by Merbau and Tapang wood. Four key features, including acoustic radiation damping coefficient, spectral flux, spectral centroid, and inharmonicity, were selected by the MRMR algorithm and used to train and test various classifiers in MATLAB. The decision tree classifier achieved 98.1% accuracy in predicting wood quality. This study demonstrates the potential of using machine learning to classify Sape wood quality and provides a useful guide for its production. The findings could contribute to the preservation and advancement of this cultural tradition.

Linear pressure waves in mono- and poly-disperse bubbly liquids: Attenuation and propagation speed in slow and fast and evanescent modes

Using volumetric averaged equations from a two-fluid model, this study theoretically investigates linear pressure wave propagation in a quiescent liquid with many spherical gas bubbles. The speed and attenuation of sound are evaluated using the derived linear dispersion. Mono- and poly-disperse bubbly liquids are treated. To precisely describe the attenuation effect, some forms of bubble dynamics equations and temperature gradient models are employed. Focusing on the dissipative effect, we analyze the stop band that occurs in the linear dispersion relation. In the two-fluid model, even if the dissipation effect is considered, the inconvenience that the wavenumber diverges to infinity in the resonance frequency cannot be resolved. Additionally, the validity of terminating that wavenumber value in the middle of the frequency is demonstrated. To determine a linear dispersion relation that can exactly predict thermal conduction and acoustic radiation, wave propagation velocities and attenuation coefficients are compared with some experimental data and existing models. The results show that thermal conduction and acoustic radiation should be set appropriately to accurately predict the propagation velocity and attenuation except in the high frequency range, the phase velocity in the resonance frequency range, or the attenuation in the high frequency range.

Acoustic black hole effect enhanced micro-manipulator

Microparticle manipulation is a critical concern across various fields including microfabrication, flexible electronics and tissue engineering. Acoustic-activated sharp structures have been designed as simple and flexible tools to manipulate microparticles with their good compatibility, fast response, and broad tunability. However, there still lacks rational acoustic-structure design for effective energy concentration at the acoustic-activated sharp structures for microparticle manipulation. Here, we present the acoustic black hole (ABH) effect as enhancement for the acoustic micro-manipulator. It provides great reliability, simplicity and ease of use, supporting custom design of high-throughput patterning modes. Moreover, compared to commonly used configurations, such as cylindrical or conical microneedles, those microneedles with ABH profile exhibit superior acoustic energy focusing at the tip and induce stronger acoustofluidic effects. The average acoustic flow velocity induced by the ABH microneedle is 154 times greater than that of the conical one and 45 times greater than that of the cylindrical microneedle. Besides, the average acoustic radiation force (ARF) produced by the ABH microneedle against acrylic microparticles is about 319 times greater than that of the cylindrical one and 16 times greater than that of the conical one. These results indicate that ABH design significantly enhances microparticle manipulation. We demonstrate this concept with ABH effect enhanced microparticle manipulation and study the parameters influencing its performance including operating frequency, operating voltage and particle diameter. Furthermore, considering the flexibility of this system, we employ it for various patterning and high-throughput microparticle manipulation. This work paves the way for controllable microparticle manipulation, holding great potential for applications in microfabrication and biomedicine.

SAW-driven directional clearance of bacteria on submerged surfaces

The process of bacterial film formation on submerged surfaces commences with the attachment of bacteria to the substrate. Appropriate combinations of topology and surface chemistry have been explored to prevent biofilm anchoring at the solid–liquid interface. However, the failure to actively remove bacteria from solid surfaces within a fluid in a directional manner results in bacterial backflow onto those surfaces, thus leading to secondary contaminations. Herein, inspired by the biology broom of the ciliary beating system, we propose an active surface sweeper mechanism assisted by charged particles and surface acoustic waves (SAW) to facilitate the directional clearance of bacteria. Through the synergistic effect of charge trapping and acoustic propelling, the sweeper system demonstrates an effective inhibition of bacterial adhesion in the initial stage of biofilm formation. Utilizing SAW for twenty seconds yields a remarkable 94.8% efficiency in bacterial clearance, with antibacterial adhesion efficiency up to 92.4% and 98.8% for Escherichia coli and Staphylococcus aureus, respectively. Moreover, the accompanying theoretical force modeling offers a comprehensive mechanistic insight into the relationship between acoustic streaming and bacteria repelling. The motion analysis of bacteria-loaded particles suggests that the acoustic radiation force, rather than the Strokes force, determines the clearance direction of bacteria.