Acoustical Physics最新文献

The inverse problem of acoustic sounding of a three-dimensional nonstationary medium is considered, based on the Cauchy problem for the wave equation with a sound speed coefficient depending on the spatial coordinates and time. The data in the inverse problem are measurements of time-dependent acoustic pressure in some spatial domain. Using these data, it is necessary to determine the positions of local acoustic inhomogeneities (spatial sound speed distributions), which change over time. A special idealized sounding model is used, in which, in particular, it is assumed that the spatial sound speed distribution changes little in the interval between source time pulses. With such a model, the inverse problem is reduced to solving three-dimensional Fredholm linear integral equations for each sounding time interval. Using these solutions, the spatial sound speed distributions are calculated in each sounding time interval. When a special (plane-layer) geometric scheme for the location of the observation and sounding domains is included in the sounding scheme, the inverse problem can be reduced to solving systems of one-dimensional linear Fredholm integral equations, which are solved by well-known methods for regularizing ill-posed problems. This makes it possible to solve the three-dimensional inverse problem of determining the nonstationary sound speed distribution in the sounded medium on a personal computer of average performance for fairly detailed spatial grids in a few minutes. The efficiency of the corresponding algorithm for solving a three-dimensional nonstationary inverse sounding problem in the case of moving local acoustic inhomogeneities is illustrated by solving a number of model problems.

In communication systems, when the loudspeaker and the microphone are coupled together, it creates acoustic echoes. With the increasing demand for mobile communication and online conference, it is urgent to solve the problem of acoustic echo cancellation (AEC) in communication systems. Due to the existence of nonlinear distortion, background noise and other reasons, traditional AEC methods can no longer solve the problem of echo cancellation well. Although some traditional methods consider the problem of nonlinear distortion, the effect of echo suppression is still not ideal. In this paper, we propose an echo cancellation method based on frequency domain mask, which is defined as a supervised speech separation problem. The use of the temporal convolutional network and optimal ratio mask to obtain the predicted mask, as well as the use of SISNR as the loss function, have been shown to effectively reduce echo in double-talk, nonlinear distortion, and background noise. This method is a significant advancement in the field of AEC and can be used in for mobile communication and online conference.

The acoustic properties of suspensions based on pure glycerol and diamond powder with a particle size of 1–2 μm and different concentrations were studied using a resonator with a longitudinal electric field. A disk resonator made of langasite with round electrodes on both sides of the plate with a frequency of 4.1 MHz, operating on a longitudinal acoustic wave, was completely immersed in a liquid container with the studied suspension. Based on the measured frequency dependences of the real and imaginary parts of the electric impedance of the resonator using an equivalent electromechanical circuit, the longitudinal elastic modulus and longitudinal viscosity coefficient of the samples were determined. Comparison of the experimental dependences of the longitudinal elastic modulus, viscosity coefficient, and longitudinal acoustic wave velocity on the volume concentration of diamond particles in the suspension with the calculated dependences demonstrated good agreement.

This work introduces a method of one-dimensional deconvolution with Tikhonov regularization for enhancing three-dimensional optoacoustic images in vivo. The method employs adaptive self-calibration to eliminate frequency-dependent distortions associated with ultrasound propagation and detection. By adapting to the inhomogeneous frequency characteristics of the examined medium, the method eliminates the need for additional calibration experiments. The processing time for three-dimensional optoacoustic data of size 200 × 200 × 100 voxels is less than 5 ms, facilitating the real-time enhancement of angiographic images and improving the effective spatial resolution by more than 50%.

A finite element method is presented for calculating hydrodynamic noise excited by turbulent fluid fluctuations in the presence of an elastic body. The conventional approach to solving this problem by direct solution of the Lighthill equation requires a large amount of calculations. It is demonstrated that the situation is considerably simplified when noise components are calculated at relatively low frequencies, which correspond to wavelengths that exceed the dimensions of the turbulent zone. In this case, the noise field can be expressed in terms of turbulent fluctuations in pressure on the surface of an elastic body, which is found in the incompressible fluid approximation. The article is based on a report presented at the IX Russian Conference “Computational Experiment in Aeroacoustics and Aerodynamics,” Svetlogorsk, September 26–October 1, 2022.

The numerical method is proposed for predicting the far-field noise using Ffowcs Williams–Hawkings (FW–H) equation with high-order finite-difference method for the time derivative. The results of this method for second-, fourth-, and sixth-order finite difference approximations are compared with that of analytic applications, such as monopole and dipole. It is observed that the use of the high-order time derivatives is an efficient approach to improve the prediction accuracy of the radiated acoustic pressure, particularly when the temporal resolution is not sufficiently high owing to the limited time step size. Our findings in this study provide evidence that for higher-order approximations, the RMS error for the first and second derivatives is smaller. In addition, the RMS error for the sixth-order approximation decreases considerably compared to that for the second-order approximation, with an increase in the number of points per period. This study and its results are expected to serve as a guide for noise prediction, indicating the temporal accuracies of the acoustic analogy according to the high-order approximation of time derivatives.