Acoustical Physics最新文献

A possibility of constructing wide-angle diffraction models using Fourier series decomposition of the propagation operator of one-way wave equations is investigated. The propagation operator is considered as a function of the propagation step, reference wavenumber, and transversal Laplacian operator, which appears under the square-root of the pseudodifferential operator in the theory of one-way equations. It is shown that in this operator formalism, Fourier series decomposition approximates the one-way propagator by a weighted sum of exponential propagators, whose structure is similar to the propagator of the standard or small-angle parabolic equation. The exact propagator is modified using Hermite interpolation polynomials in order to achieve two crucial properties that guarantee fast convergence of the Fourier series: propagator periodicity and continuity of its derivatives. It is demonstrated that for three-dimensional diffraction problems, contrary to the standard split-step Padé approach, the proposed wide-angle propagation model allows for using efficient numerical methods and operator splitting procedures available for the standard parabolic equation. As a result, it is possible to organize computations separately along each of the two coordinate axes that are perpendicular to the predominant direction of wave propagation.

The properties of a speech burst of closure are studied by using a database of 39 speakers with single-digit and multi-digit numerals and parallel recording of signals on a telephone handset and a directional microphone. A speech burst is detected by short-term and long-term detectors of spectral-temporal inhomogeneities and by a detector for the measure of similarity between the eigenfunctions of a consonant burst spectrum and a current speech burst spectrum. The probability for the presence of a voiced or voiceless closure is estimated in the spaces of an amplitude spectrum and a group delay spectrum from the ratio between the energies in the high- and low-frequency regions. The place of articulation for a back-lingual consonant influences the probability distribution for the duration of the interval between the onsets of a speech burst and a vowel, for the frequency of a peak with a maximum amplitude in the high-frequency region, for the ratio between the energies in the spectral regions of high and low frequencies of a speech burst, and also for the measure of similarity between the eigenfunctions of a consonant burst spectrum and a current speech burst spectrum.

Abstract—The article presents the results of an experiment on assessing subjective indicators of acoustic perceptibility by pedestrians (experts) of a vehicle approaching at a constant speed and some conclusions. Subjective indicators of perceptibility were defined as the distance between the vehicle and the expert, at the moment when the expert heard (recorded) the sound of an approaching car, as well as the time of the car’s approach to the expert at that moment. Subjective indicators of perceptibility are compared with the objective parameters of car noise measured in accordance with UN Regulation no. 138: the sound pressure level, its frequency response, and the sound level. The study is motivated by the problem of traffic safety of electrified vehicles with low noise, which include, in particular, electric cars and electric scooters. The article publishes the first results of a research paper devoted to increasing the perceptibility of low-noise vehicles for pedestrians without damaging the acoustic ecology of cities and suburbs.

The propagation of slit shear waves in a quasi-symmetric structure of piezoelectrics of the 4mm symmetry class has been theoretically studied. It has been shown that taking into account the unequal level of loss and gain in piezoelectrics results in either intersection, touching, or convergence of two modes at the point of their degeneracy (singular point) in the shear wave spectrum. It has been found that the intersection of the mode spectra occurs only in the case of equal loss and gain magnitudes (a PT-symmetric structure). Based on this, it is concluded that using the pattern of the spectra near a singular point, it is possible to determine the level of imbalance of gain and loss in piezoelectric waveguides. As in the case of a purely PT-symmetric structure, the frequency dependence of the amplitude at an exceptional point of a quasi PT-symmetric structure (with a rather small difference in loss and gain levels) exhibits a very narrow peak, which opens up the possibility of creating hypersensitive sensors based on them. Thus, it has been shown that even at unequal loss and gain levels in piezoelectrics (a quasi PT-symmetric structure), it is possible to obtain a structure with all the characteristics of a PT-symmetric structure.

A practical task of testing samples of various metals using the principles of nonlinear acoustics is being solved. A surface acoustic wave (surfactant), whose propagation process, due to nonlinear effects, is accompanied by generation of a wave of doubled frequency, was used for testing. An experimental device is used to monitor the structural state of a metal sample by recording a change in the nonlinear acoustic parameter (NAP). To excite surfactants, a wedge transducer with a resonance frequency of 1 MHz was used. The transmitted wave was recorded with a wedge transducer with a resonance frequency of 2 MHz. It has been shown that the NAP for the tested materials in the initial state has different values not only for materials belonging to different classes, but also for materials belonging to the same structural class and having different chemical compositions (12Kh17G9AN4 and 12Kh18N10Т). A plastic deformation by 2% does not lead to a NAP change for the AMg6 alloy and 12Kh17G9AN4, 20Kh13N4G9, and 10KhSND steels. The NAP change by 2% as a result of a plastic deformation for the 12Kh18N10T and 08Kh17N4M3 stainless steels is caused by a change in their phase compositions associated with the martensitic transformation. The presented data on the change in the NAP from early stages of the elastoplastic deformation to a predestruction for AMg6 and 10KhSND steels demonstrate the possibility of using it as a prognostic criterion for the limiting state of the material.