Abstract: —It is shown that the transmission function of an acousto-optic device remains unchanged for variations in the acoustic drift angle and acoustic column width when the distance traveled by the incident light in the acoustic column is maintained. In some cases, this invariance simplifies theoretical analysis of acousto-optic interaction. PubDate: 2019-07-01

Abstract: The article investigates the possibility of reconstructing a reflector image using the compressive sensing (CS) method based on an incomplete set of echo signals measured by an antenna array in double or triple scanning mode. For comparison, we also considered reflector reconstruction methods used in ultrasonic testing (UT): the correlation, combined SAFT (C-SAFT), and maximum entropy (ME) methods. The last method allows reconstruction of superresolution images from an incomplete set of measured echo signals. Numerical and model experiments have demonstrated the possibility of reconstructing a reflector image with superresolution for a significant decrease in the amount of data used. Reconstructed CS images were compared with images reconstructed by other methods. PubDate: 2019-07-01

Abstract: The approach of resolving analysis the cross-flow relative motion streamline on the cross-flow straight blade is presented to predict the rotation aerodynamic noise performance of cross-flow fan by solving the dipole source term of Ffowcs Williams and Hawkings equation, while the cross-flow fan is applied in the indoor unit of split-type air-conditioner and operated in the rated condition. The calculating results of the method are respectively drawn by programming in Matlab computational language, and compared with the results of CAA numerical simulation and noise experiment. There are some differences in the distribution condition of aerodynamic force fluctuation amplitude on the blade surface, and sound pressure in the related frequency on the indoor unit casing, or on the sphere far field, between the streamline computation approach and numerical simulation. The orders of magnitudes of these calculating results solved by the analysing streamline method are similar with that attained by the numerical simulation. The resolving analysis approach has the characteristics of decreasing the computing cost and not constructing the acoustics grid model of fan, compared with the numerical simulation. The error between the result of numerical simulation and noise test is larger than that between the result of theoretical calculation and noise test, so the approach could be used for the rotation aerodynamic noise analysis of the cross-flow fan. PubDate: 2019-07-01

Abstract: —For broadband modulation of the intensity of optical radiation, the tandem arrangement two acousto-optic (AO) Bragg cells are proposed in which acoustic waves propagate in opposite directions. The device allows modulation of optical radiation in the acoustic frequency band of ~6 MHz at four times the frequency of the sound. The possibility of switching the modulation frequency from 2f to 4f, where f is the frequency of sound, by simply turning the output polarizer is demonstrated. The method is experimentally tested for modulating radiation with a wavelength of 0.63 × 10–4 cm using two AO cells made of paratellurite operating at a center frequency of 22 MHz. PubDate: 2019-07-01

Abstract: — The article investigates the response of composite skin-stringer joint to broadband acoustic loading. To describe the frequency and spatial structure of the acting sound field, the study used a model of a field completely correlated over the surface of a sample with a uniform frequency spectral density. The finite element method (FEM) was used to simulate the response of the joint in the 50–1550 Hz frequency band at different total sound pressure levels. To validate the FEM, a series of experiments on a vibration table were carried out, in which vibration simulated acoustic loading. The data obtained were used as the input data for integrating the equations of motion. The results of calculating of the RMS strains in the zone of maximum stresses showed good convergence with the experimental results. For samples containing simulated defects, the resonance frequencies and dynamic response parameters were calculated. Comparison of these results with experimental data characterizing the change in the resonance frequency as a function of defect size made it possible to specify the applied failure criterion and adapt the FEM for analyzing the durability of the composite joint. PubDate: 2019-07-01

Abstract: In this study, we used passive acoustic thermometry to measure the core (acoustic brightness) temperature in a subject’s forearm while applying warming ointments to the skin. A decrease of 3–6°C in the acoustic brightness temperature was recorded in the first 5–10 min. After this, the acoustic brightness temperature returned to the level prior to application of the ointment. We attribute the decrease in core temperature to the use of a gel at room temperature in the measurements. On the one hand, the application of a cold gel to the skin should reduce the superficial blood flow. However, the use of warming ointments temporarily blocked this process. As a result, cold blood from near-surface capillaries entered the internal tissues of the forearm, cooling the tissue. The effect was taken into account in the heat conduction equation with blood flow by changing a parameter used in the equation: the temperature of flowing blood. The time dependence of the acoustic brightness temperature calculated with the heat conduction equation is consistent with the experimental data. PubDate: 2019-07-01

Abstract: Nowadays, biodiesel is considered as an important alternative source of energy. In this work, we introduce theoretically a phononic crystal (PnC) model acts as a biodiesel sensor. Such a sensor can detect and measure biodiesel physical properties efficiently. The sensor configuration is a 1D PnC structure and a defect layer filled with biodiesel in-between. Using the transfer matrix method, the transmission spectrum of the biodiesel PnC structure is calculated. We pay more attention to the resonant peak (the transmitted peak inside the band gap), which is related directly to the biodiesel properties. The obtained simulated results have revealed that the resonant peak is very sensitive to the physical properties of biodiesel. Also, the resonant peak position is highly affected by the biodiesel layer thickness, temperature, and pressure applied to the PnC structure. Moreover, we obtained a high \(Q\) value for the biodiesel sensor at room temperature up to the value of 1980. PubDate: 2019-07-01

Abstract: Modified discrete source method and diagram equation method are used to develop two algorithms for solving a three-dimensional scattering problem in the case of scattering from an acoustically soft or acoustically hard doubly periodic rough surface. Calculations use the efficient algorithm developed earlier for determining a periodic Green’s function in the problem of diffraction by a grating consisting of bodies of revolution. For the algorithm based on the diagram equation method, applicability conditions are determined. The two methods are compared in application to a sine-shaped doubly periodic surface. Fulfillment of both the energy conservation law and the boundary condition at the central surface element is verified. Dependences of reflected harmonic amplitudes on wave parameter and angle of incidence of plane waves are plotted. PubDate: 2019-07-01

Abstract: The frequency dispersion of the sound propagation speed in a marine waveguide makes it possible to compress an acoustic signal with an increase in its intensity. The paper presents the results of experimental research of this effect during the propagation of a broadband acoustic signal from a parametric array in shallow water. The parametric array provided single-mode excitation for the marine waveguide. The possibility of compressing a broadband signal during its propagation in shallow water with special selection of the frequency modulation mode is discussed. Waveguide dispersion leads to an increase in the efficiency of parametric radiation in shallow water. PubDate: 2019-07-01

Abstract: A high-frequency diffraction problem is considered for a Gaussian beam incident parallel to the axis of a strongly elongated spheroid. The parabolic equation method in spheroidal coordinates is used to construct the leading order term of the field asymptotics in the boundary layer near the surface in the form of an integral containing Whittaker functions. The field amplitudes on the surface of a perfectly hard spheroid are computed. High-frequency diffraction effects are discussed. PubDate: 2019-07-01

Abstract: An adaptive modal MUSIC algorithm is constructed to localize an acoustic source by a vertical array operating under conditions of incomplete information on a waveguide propagation channel . The results of statistical modeling are presented, which demonstrate the probabilities of correct source localization versus the input signal-to-noise ratio and the sample size. The method is validated by its application to the experimental data observed in the Ladoga Lake. It is shown that this method ensures greater stability of the estimation procedure to mismatch between the true and expected signal replica compared to the conventional element-space MUSIC. PubDate: 2019-07-01

Abstract: The problem of diffraction by an elongated body of revolution with impedance boundary conditions is studied. The case of axial incidence of a high-frequency wave is considered. The diffraction process is described using the parabolic equation method. A Volterra-type boundary integral equation is derived with the aid of Green’s theorem. An iterative numerical solution is constructed for the problem of diffraction by a thin impedance cone. PubDate: 2019-07-01

Abstract: A finite element method is used for three-dimensional numerical simulation of hydro- and seismoacoustic waves in shallow water, generated by harmonically oscillating sources. The features of acoustic waves in water, seismic waves in the bottom layer, and surface waves at the fluid–bottom interface are analyzed. The results of 3D numerical simulation are presented with illustrations of the amplitude wave distribution in contacting media for different source depths. PubDate: 2019-07-01

Abstract: The paper presents an estimate for the viscosity and its increment (“magneto-viscous” effect) in a thin wall layer of a magnetic fluid column oscillating in a tube under the action of a strong transverse magnetic field. The viscosity is calculated using an expression derived with two different theoretical approaches. For calculations, published experimental results are used, discussed previously under the assumption of no field-dependent viscosity. A comparative analysis is performed for the estimates of the “wall viscosity” obtained using dynamic elasticity along with the magnetization curve and static elasticity coefficient. The meaning of the obtained results on the magneto-viscous effect for detecting interparticle aggregation is pointed out. PubDate: 2019-07-01

Abstract: The effect of acoustic emission is used to study the acoustic radiation accompanying the combustion of flammable substances (alcohols, acetone, crude oil, and petroleum products), and experimental and calculated research results are presented. A set of time series and peak amplitude-frequency responses was formed that characterize the acoustic signals generated by these burning substances. The number of samplings recorded every 22 μs lies in the range of 1.5. × 106 up to 9.7 × 106. Fractal R/S analysis of time series demonstrates the fundamental possibility of identifying (recognizing) the nature of a burning substance. The dependence of the Hurst index H on the nature of a substance is established, and its numerical values are obtained. PubDate: 2019-07-01

Abstract: The study analyzes experimental data on amplitude–time parameters p+, p–, t+, t–, tR+, tR– of the first positive and negative phases of acoustic waves in the atmosphere from different pulsed sources. The experimental data are compared with numerical simulation results for spherically and cylindrically symmetrical propagation of a blast wave in homogeneous air. Comparison reveals the features of how the stability of the atmospheric boundary layer influences the parameters and shape of acoustic signals propagating in it. Approximations are given for the experimental values p–, t– and tR– of the recorded acoustic signals for a wide range of variations in the source energy values of 10–8 < Q < 1010 kg TNT and distances of 1 < R/Q1/3 < 4 × 104 m/kg1/3 to them. PubDate: 2019-07-01

Abstract: The features of propagation of low-frequency tonal and pulsed acoustic signals generated at sea to land have been experimentally and theoretically studied. The accuracy in determining signals characteristics and, in particular, transmission losses using relatively simple measuring instruments (a hydrophone placed in a small water-filled container) is shown. The results of the calculating estimates for the sound field parameters on the coast formed by a source operating in the water layer are demonstrated. The calculations done by a program that uses a parabolic equation in the horizontal plane and vertical waveguide modes. PubDate: 2019-05-01

Abstract: The propagation of detonation waves in a channel filled with a bubbly liquid that suddenly widens is investigated. Possible scenarios for the dynamics of detonation waves after their transition to the widening part of the channel are analyzed. The influence of the volume content of a combustible gas and the geometric parameters of the channel on the propagation and breakdown of the detonation wave has been established. PubDate: 2019-05-01

Abstract: In this paper, the acoustic field excited by a single force with arbitrary direction in a semi-infinite elastic space is studied and its mathematical expressions are obtained. It shows that there are many complex behaviors when the elastic wave reaches the free boundary. The numerical simulation shows that there are several kinds of waves in the semi-infinite elastic space: direct P wave, direct SV wave, SP wave propagating along the free surface which can generate Head wave and Rayleigh wave. The forming mechanism of the SP wave and Rayleigh wave is specially studied. The waveforms at the observation point on the free surface of the semi-infinite space contain only direct P wave and direct SV wave when the SV wave incident angle is within the critical reflection angle. However, if the incident angle from the source to the observation point is exceeding to the critical reflection angle, not only direct P and direct SV wave but also the SP wave and Rayleigh wave are all be generated. It is focused on the relationships of the direction of single force to the excitation intensity of each wave. The relationship of each wave packet to the single force and observation direction is obtained and analyzed. PubDate: 2019-05-01

Abstract: The paper demonstrates for the first time the possibility of using aluminum nitride–scandium as an effective piezoelectric material in composite acoustic resonators on synthetic diamond substrates. Composite resonators based on an Al/(Al, Sc)N/Mo/(100) diamond piezoelectric layered structure with three Sc concentrations have been studied in the frequency range of 0–20 GHz. It is shown that such resonators can be excited in a wide frequency range from 0.2 to 20 GHz with Q factors relatively on par with similar devices using pure aluminum nitride. The quality parameter Qf ≈ 3 × 1014 Hz in a resonator sample based on the Al/Al0.7Sc0.3N/Mo/(100) diamond structure is comparable to the similar record value for composite resonators on diamond substrates and thin-film piezoelectric AlN transducers. The maximum values of the squared effective electromechanical coupling coefficient for composite BAW resonators increased by almost an order of magnitude upon replacing an AlN with an ASN film. PubDate: 2019-05-01