The ultrasonic cavitation and acoustic streaming have long been regarded as the dominant mechanisms for refining the solidification microstructure of Aluminum (Al) alloys. This work investigated the effects of low-intensity ultrasound on the solidification microstructure of 2219 Al alloy by setting an ultrasonic application angle of 15° and with the different depths (30 mm, 70 mm, and 110 mm). The experimental results show that low-intensity ultrasound can also achieve a significant refining effect on the microstructure. Comparative analysis of solidified microstructures across multiple samples revealed, for the first time, that low-intensity ultrasound refines grain morphology primarily through enhanced heterogeneous nucleation. By establishing a theoretical model between acoustic intensity (Ie) and heterogeneous nucleation energy (ΔG∗), the required low-intensity acoustic pressure amplitude (Pa′) for heterogeneous nucleation was determined. The calculation results are in good agreement with the experimental conclusions, thereby proposing a new mechanism for ultrasound to improve solidification microstructures. This work demonstrates that the ultrasonic cavitation and acoustic streaming are not necessary conditions for refining grain structures. Low-intensity ultrasound can also promote the refinement of Al alloy grain structures when satisfying the critical nucleation acoustic pressure conditions.
Integrated photoacoustic endoscopy and endoscopic ultrasound (PAE/EUS) are recognized as an effective method for detecting intestinal and intravascular diseases. Changes in the morphology and composition of the trachea are significant hallmarks of respiratory diseases. In this study, an acoustic-optic confocal probe was developed and integrated at the tip of a 2.1 mm diameter catheter to perform simultaneous PAE/EUS imaging. Phantom experimental results demonstrated that the catheter achieved a high lateral resolution of 11 µm, with an imaging depth of 12 mm, using an excitation energy of 1.5 μJ. Trachea from healthy and chronic obstructive pulmonary disease (COPD) rabbit models and in vivo were imaged by the PAE/EUS system. The results demonstrated that photoacoustic imaging could identify increases in the diameter and density of the tracheal microvessels, while ultrasound imaging provided detailed views of the tracheal submucosa. These findings underscore the potential of PAE/EUS in the diagnosis of COPD.
Photoacoustic microscopy (PAM) enables label-free, quantitative imaging of blood flow and oxygenation in vivo, offering critical insights into microvascular function and tissue metabolism. However, current flow quantification methods suffer from poor accuracy at extreme flow speeds and high computational costs. We present Hybrid Fourier-Derivative Analysis (HFDA), a new method based on frequency analysis of flow-induced modulations in photoacoustic amplitude. Compatible with standard raster scanning, HFDA adaptively integrates Fourier analysis for high-speed flow and derivative analysis for low-speed flow, achieving high accuracy and computational efficiency. Phantom studies validate the accuracy of HFDA across 0.2–20 mm/s, with errors typically less than 7 %. Compared to correlation-based methods, HFDA reduces computational time by 35-fold. In vivo demonstrations in mouse models of hypoxia and hypercapnia further underscore the potential of HFDA as a rapid and precise tool for blood flow quantification in functional and metabolic PAM studies.
It is a challenge to study the nucleation of cavitation bubbles, which critically depends on nanoscale morphological features. Our recent advances in synthesizing colloidal negative-curvature nanoparticles (NGC-NPs) offer a rare opportunity, in comparison to the conventional studies of bulk substrates, where it is difficult to obtain consistent and well-defined surface features. In order to quantitatively assess their effects, we exploit the radical-induced color change of [Fe(SCN)6]3−, which turned out to be a more convenient method than the bending of AgNWs and the fluorescence-based methods. We show that the NGC-NPs outperform positive-curvature nanoparticles (PSC-NPs) and homogeneous nucleation, in terms of promoting cavitation. The NGC-NPs provide a higher percentage of gas–solid interface, and thus reduces the activation barrier during the critical stage of bubble nucleation. This leads a higher probability of cavitation and transforms more energy from ultrasonication to radical formation and shockwaves.
The objective of this paper is to numerically investigate the thermodynamic effect during bubble collapse near a rigid boundary. A compressible fluid model is introduced to accurately capture the transient process of bubble shapes and temperature, as well as corresponding pressure, and velocity. The accuracy of the numerical model is verified by the experimental data of bubble shapes, and Keller-Kolodner equation as well as its thermodynamic equation. The results show that a bubble near the rigid boundary presents high-speed jet in collapse stage and counter jet in rebound stage, respectively. In the collapse stage, the bubble margin will shrink rapidly and do the positive work on the compressible vapor inside the bubble, then a significant amount of heat will be generated, and finally the generation of high-speed jet drives the low-temperature liquid outside the bubble to occupy the position of high-temperature vapor inside the bubble. In the rebound stage, the counter jet moving away from the rigid boundary takes part of heat away from the sub-bubble, which avoids the external work of the expansion of the sub-bubble and the temperature reduction caused by the dissipation effect of the vortex structure. In addition, the initial standoff has a significant effect on the thermodynamics of bubble oscillation. The temperature keeps increasing with the increase of the initial standoff in the collapse stage, while it shows a downward trend with the increase of the initial standoff in the rebound stage. That’s because the high-speed jet and counter jet of bubble gradually disappear when the initial standoff increases, which is the important reason for the opposite evolution trend of temperature in collapse and rebound stage.
Olga Krasulya, Anastasiya Smirnova, Vladimir Bogush
et al.
We studied the effect of ultrasonic activation of brine (3%) during salting on the degree of stability of colour parameters of pork with normal (NOR) and abnormal course of autolysis in the CIE Lab colour space. The mechanism of stabilisation of the colour of meat is attributed to donor–acceptor bonds of metmyoglobin (MetMb). The accumulation of excessive number of free electrons in the medium are capable of activating MetMb. This reduces the activity of meat, when the native participants of the metmyoglobin reductase system and their own antioxidant systems of meat are depleted.Based on the additive calculation of deviations (increase / decrease) by the coordinates L*, a*, b* in the CIE Lab system, and the total colour difference (ΔE) in control and experimental samples, recommendations were developed. To optimize the colour characteristics of all types of meat, both on the surface and in the thickness of the meat, the preliminary activation of a 3% brine in a low-frequency submersible ultrasonic unit is recommended. Moreover, preliminary cavitation activation of a 3% is more preferable to stabilise the colour of PSE – meat (pale, soft, exudative (watery),) brine in a flow-through installation.
Abstract The acoustic echo cannot be entirely removed by linear adaptive filters due to the nonlinear relationship between the echo and the far-end signal. Usually, a post-processing module is required to further suppress the echo. In this paper, we propose a residual echo suppression method based on the modification of dual-path recurrent neural network (DPRNN) to improve the quality of speech communication. Both the residual signal and the auxiliary signal, the far-end signal or the output of the adaptive filter, obtained from the linear acoustic echo cancelation are adopted to form a dual-stream for the DPRNN. We validate the efficacy of the proposed method in the notoriously difficult double-talk situations and discuss the impact of different auxiliary signals on performance. We also compare the performance of the time domain and the time-frequency domain processing. Furthermore, we propose an efficient and applicable way to deploy our method to off-the-shelf loudspeakers by fine-tuning the pre-trained model with little recorded-echo data.
Spin-orbit acoustics is determinant to provide new perspectives and functionalities for sound manipulations. Here the authors theoretically and experimentally demonstrate acoustic spin-orbit interaction enabling chiral sound-matter interactions with unprecedented applications.
In the development of automation industry, external force detection/monitoring is essential for the safety of human and machines. To detect or measure these forces easily, a static loading sensor is required. However, commercially available sensors are too bulky and cause installation difficulties in automated machines. A piezoelectric element is an electro-mechanical component wildly used for actuator sensing or harvesting applications. In this paper, a 10 N capacity thin piezoelectric force sensor is designed and tested for external static load detection. This paper considers that larger strain made by an external force on a proposed piezoelectric sensor generates higher voltage, thereby increasing its force estimation accuracy. Meanwhile, in most piezoelectric force sensors, a cantilever beam mechanism is usually adopted for its simple structure; however, large deformations seen in cantilever piezoelectric sensors are not proportional to its measuring accuracy nor force bearing capacity. Therefore, in this paper, an amplified trapezoidal shape mechanism is designed to convert external vertical load into horizontal displacement deformation in order to obtain higher voltage generation. The Taguchi optimization design method is proposed to analyze the key factors that affect the amplified mechanism design of the piezoelectric sensor. Moreover, static loading force applied on a piezoelectric component generates constant voltage that eventually decreases with time. This is because of its internal electric impedance property, which causes difficulty in static loading force estimation. To represent the theoretical model of the static force estimation in this paper, a chain scattering description matrix of a two-port network was proposed to represent the electric impedance in relation to the mechanical properties’ variation. The measured results demonstrate the accuracy of the proposed theoretical method which implies that the external force can be estimated by measuring its electric impedance variation, particularly the shift in resonance frequency Therefore, based on the developed theoretical model, a driving voltage with fixed frequency can measure its electric current in the same time, thereby achieving the external force monitoring technology.
Control engineering systems. Automatic machinery (General), Acoustics. Sound
Aiming at elucidating ultrasonic emulsification mechanisms, the interaction between a single or multiple acoustic cavitation bubbles and gallium droplet interface was investigated using an high-speed imaging technique. To our best knowledge, the moment of emulsification and formation of fine droplets during ultrasound irradiation were observed for the first time. It was found that the detachment of fine gallium droplets occurs from the water-gallium interface during collapse of big cavitation bubbles. The results suggest that the maximum size of cavitation bubble before collapsing is of prime importance for emulsification phenomena. Previous numerical simulation revealed that the collapse of big cavitation bubble is followed by generation of high-velocity liquid jet directed toward the water-gallium interface. Such a jet is assumed to be the prime cause of liquid emulsification. The distance between cavitation bubbles and water-gallium interface was found to slightly affect the emulsification onset. The droplet fragmentation conditions are also discussed in terms of the balance between (1) interfacial and kinetic energies and (2) dynamic and Laplace pressure during droplet formation.
In the application of photoacoustic human infant brain imaging, debubbled ultrasound gel or water is commonly used as a couplant for ultrasonic transducers due to their acoustic properties. The main challenge in using such a couplant is its discomfort for the patient. In this study, we explore the feasibility of a semi-dry coupling configuration to be used in photoacoustic computed tomography (PACT) systems. The coupling system includes an inflatable container consisting of a thin layer of Aqualene with ultrasound gel or water inside of it. Finite element method (FEM) is used for static and dynamic structural analysis of the proposed configuration to be used in PACT for infant brain imaging. The outcome of the analysis is an optimum thickness of Aqualene in order to meet the weight tolerance requirement with the least attenuation and best impedance match to recommend for an experimental setting.
This paper investigates the possibility of using long-term analysis of the zero-crossings of a speech signal for speaker identification. The applied method of identification is based on an analysis of the signal in measuring windows of a duration which should ensure the stationarity of the statical distributions of the time intervals between successive zero-crossings, in 16 pre-set time channels.
An objective method of defining the minimum length of the measuring window for a selected set of parameters is presented. It is based on the stationarity test and the ergodic theorem for stochastic processes, as is the transformation of the speech signal mentioned above. An experiment in speaker identification for 10 speakers with 10 repetitions for each speaker has been performed. The results obtained, in well exceeding 90 % correct identification for 30- and 40 second samples of the speech signal, have confirmed the practicality of the method of zero-crossing analysis for speaker identification.
The paper presents some experimental and theoretical results obtained in the examination of high power light diffraction (ND^{3+} laser) by ultrasound (4 MHz) in nonlinear liquids. The diffraction patterns differ from the usual results for the light of small intensity. The distributions of the light can be explained by the influence of the optical nonlinearity of the medium (3-rd harmonic light generation and frequency mixing). The theoretical description proposed appears to explain the experimental results.
A reversing, multistrip coupler device is presented that can find numerous applications in SAW devices. Fundamental theory and first experimental results are presented on an application of rmsc in SAW resonator.
The performance of four spectral techniques (FFT, AR Burg, ARMA and Arithmetic Fourier Transform AFT) for mean and maximum frequency estimation of the Doppler spectra is described. The mean frequency was computed as the first spectral moment of the spectrum with and without the noise subtraction. Different definitions of f_max were used: frequency at which spectral power decreases down to 0.1 of its maximum value, modified threshold crossing method [23] and novel geometrical method. "Goodness" and efficiency of estimators were determined calculating the bias and standard deviation of the estimated mean and maximum frequency of the computer simulated Doppler spectra. The power of analysed signals was assumed to have the exponential distribution function. The SNR ratios were changed over the range from 0 to 20 dB. The AR and ARMA models orders selections were done independently according to Akaike Information Criterion (AIC) and Singular Value Decomposition (SVD). It was found, that the ARMA model computed according to SVD criterion had the best overall performance and produced the results with the smallest bias and standard deviation. The preliminary studies of the AFT proved its attractiveness in real-time computation, but its statistical properties were worse than that of the other estimators. It was noticed that with noise subtraction the bias of f_mean decreased for all tested methods. The geometrical method of f_max estimation was found to be more accurate of other tested methods, especially for narrow band signals.