Acoustical Physics最新文献

Cracks are one of the most common damages to thin plates. Therefore, rapid and accurate detection of cracks is of great significance in the nondestructive testing of thin plates. Most existing nondestructive testing technologies focus on crack localization rather than the quantification of the crack length and orientation. Therefore, this paper proposes a damage index, considering the wave attenuation during propagation, to quantify the crack length and orientation. Lamb waves are transmitted and received by a circular sensor array. Based on the abnormal reflection of the A0 mode of Lamb waves, the reflections at cracks are extracted by the Hilbert transform. The influence of the crack length and orientation are studied parametrically, and the relations between the proposed damage index and crack length and angle are given based on regression analysis.

In this study, phonon crystal structures embedded in acoustic black holes are discussed. The low-frequency band gap is widened by exploiting the low-frequency, broadband and multimode properties of the acoustic black hole. The energy band properties of the acoustic crystal structure embedded in an acoustic black hole are calculated by means of a finite element method. The mechanism of band gap generation is investigated. The vibration transfer characteristics of finite period structures are analyzed. The influence of the structural parameters of the acoustic black hole is analyzed. The results show that the acoustic crystal structure embedded in an acoustic black hole has multiple band gaps in the 500 Hz band and the band gap coverage is increased to 45.18%. The starting bandgap is 16.10% lower than before embedding in the acoustic black hole and the width of the first bandgap expands to 173.03% of that before embedding in the acoustic black hole. The onset and termination frequencies of the first band gap are mainly determined by the vibrational modes of the scatterer and the acoustic black hole structure. The vibrational transfer of the finite period structure is analyzed and shows good damping characteristics in the bandgap interval. Finally, vibration experiments verify the vibration damping effect of the proposed coupled acoustic black hole phononic crystal, and the relevant findings of this paper can be used in the vibration damping design of plate structures, enriching the experience of research related to acoustic black holes.

High-intensity focused ultrasound (HIFU) is widely used in the treatment of benign and malignant tumors due to its advantages of noninvasiveness and high therapeutic efficiency. However, how to improve the efficiency of heat deposition in a short period of time is a key problem during HIFU thermal ablation. The acoustic cavitation excited by pulse HIFU has been proven to achieve HIFU efficiency enhancement. However, the real-time monitoring of acoustic cavitation is still an issue. In this study, a real-time detection method of acoustic cavitation is established based on self-sensing ultrasound, and the synergistic effect of acoustic cavitation excited by pulse HIFU is researched. The influences of the output power, pulse duration, irradiation depth on cavitation duration are respectively discussed by using the established cavitation detection method compared passive cavitation detection (PCD). The relationship between cavitation intensity and synergistic effect is discussed. The results have shown that the cavitation detection can real-time measure cavitation duration compared with PCD. In addition, during the cavitation detection of pulse HIFU, the synergistic effect of acoustic cavitation is obvious in HIFU ablation.

The article describes the methodology and presents the results of a model quantitative assessment of the efficiency of solving the problem of detecting and tracking a low-noise underwater object using three algorithms for spatial signal processing at the output of a multielement array—the nonadaptive Bartlett algorithm, the Capon algorithm, and the Capon algorithm, combined with a projection procedure for limiting the signal power of strong local sources.

A method is proposed for reconstructing the acoustic parameters of a medium by iterative processing of the coherence matrices of the acoustic field of random sources, for some of which their power density is known. The possibilities of increasing the stability and accelerating the convergence of the method are discussed. The reconstruction results are compared with the functional-analytical approach based on the processing of the scattering amplitude.

Almost no diffraction broadening of self-collimation beams and their easy crossing with low crosstalk offer new opportunities for acoustic wave manipulation. Here, we flexibly steer the self-collimation beam based on the total internal reflection of an airborne square lattice sonic crystal. The properly designed crystal/air interface may serve well as a total internal reflection mirror of the self-collimation beam, with which we are able to achieve the highly controllable beam reversal, snaking and crossing. Our scheme can be extended to more interesting beam steering, and have potential applications in constructing high-density integrated acoustic circuits.

The study analyzes the basic properties of the scalar wavenumber-frequency spectrum of turbulent pressures, representing the total energy of the wave components of the turbulent pressure field with a given wave vector modulus. Consideration of the scalar spectrum, which has independent applied significance, makes it possible to visualize the energy distribution of turbulent pressures in a wide range of frequencies and wave numbers. Based on well-known vector wave field models, relations are proposed for estimating the relative scalar spectrum. The degree and nature of the parametric influence of the Mach and Reynolds numbers are determined.