Sun Fei, Guo Shuwei, Li Borui, Liu Yichao, He Sailing «An Acoustic Metamaterial Lens for Acoustic Point-to-Point Communication in Air» Акустический журнал, 65, № 1, с. pp. 1-6 (2019)

Acoustic metamaterials have become a novel and effective way to control sound waves and design acoustic devices. In this study, we design a 3D acoustic metamaterial lens (AML) to achieve point-to-point acoustic communication in air: any acoustic source (a speaker) in air enclosed by such an AML can produce an acoustic image where the acoustic wave is focused (the field intensity is at a maximum, and the listener can receive the information), while the acoustic field at other spatial positions is low enough that listeners can hear almost nothing. Unlike a conventional elliptical reflective mirror, the acoustic source can be moved around inside our proposed AML. Numerical simulations are given to verify the performance of the proposed AML.

Tong Yunzhe  Wei Wang, Fan Jun, Wang Bin «Acoustic Scattering from a Cylindrical Shell with Double Internal Rigid Plates» Акустический журнал, 65, № 1, с. pp. 7-13 (2019)

The acoustic scattering from an infinite cylindrical shell with double internal rigid plates at normal incidence is studied by theoretical and experimental approaches. The two rigid plates are attached to the shell along lines parallel to the shell axis symmetrically. The dominant feature of frequency-angle spectra is the interference fringes caused by the reflection waves of attachments in the illuminated region and specular reflection. For a cylindrical shell with double internal plates, there may be several attachments in the illuminated region simultaneously. There will be bright spots when two interference fringes caused by two attachments in the illuminated region intersect, while only interference fringes can be observed for one attachment in the illuminated region. Theoretical and experimental results show that the number of attachments in illuminated region can significantly affect the scattering characteristics, and it is a prominent feature to identify the location of internal plates.

Zhou Fulin, Wang Bin, Fan Jun, Peng Zilong «Theoretical and Numerical Studies on in vacuo Structural Admittance of an Infinite, Coated Cylindrical Shell» Акустический журнал, 65, № 1, с. pp. 14-22 (2019)

Studying the interaction of sound with a coated cylindrical shell immersed in water is essential for improving existing underwater target detection and classification algorithms. According to the impedance theory of sound scattering, in vacuo structural admittance describes the relationship between the sonar-induced forces and the resulting vibration on the surface, which can be used to solve the problem of the acoustic scattering and radiation. In this work, we investigate numerically and theoretically the structural admittance of a coated cylindrical shell. Analytical expressions of the structural admittance are derived for different external forces: a plane acoustic wave, a normal point force, and a random noise field. The structural admittance is also numerically evaluated. The results show that the structural admittance is independent of exterior medium and fluid loading. According to the impedance theory of sound scattering, the scattered field of a coated cylindrical shell is calculated by combining the structural-, acoustic-, and internal-admittance matrices. Because of the non-local property of structural surface admittance, we build an algebraic model of a coated object by nonlinear curve fitting and study a local approximation of the structural admittance. We also find that simplifying the large matrices is useful for research on structural vibrations. Thus, this work presents a systematic study of the acoustic scattering characteristics of structural admittance of an infinite, coated cylindrical shell.

Zakhidov E.A., Kokhkharov A.M., Kuvondikov V.O., Nematov Sh.K., Tazhibaev I.I. «A Low-Frequency Photoacoustic Spectrometer with an RGB Light-Emitting Diode for Evaluating Photosynthetic Activity in Plant Leaves» Акустический журнал, 65, № 1, с. pp. 90-95 (2019)

A photoacoustic spectrometer based on a three-colored light-emitting diode (with peak emission wavelengths of 465, 525, and 640 nm) designed to determine the intensity of photosynthesis in different deep layers of plant leaves is described. The physical properties of the photoacoustic signal were studied at different wavelengths and light modulation frequencies. It was shown that the proposed spectrometer can be employed for quantitative evaluation of heat dissipation and photochemical assimilation of the absorbed light energy in this medium.

Milekhina O.N., Nechaev D.I., Supin A.Ya. «Frequency Range of Compression for Discrimination of Acoustic Signals with Complex Spectra» Акустический журнал, 65, № 1, с. pp. 96-102 (2019)

Psychophysical experiments on listeners with normal hearing were conducted to discriminate the rippled spectra of an acoustic signal against maskers with different positions of the spectral band relative to the signal band. As the signal level changed from 50 to 80 dB SPL, the on-frequency masker level changed by 29 dB, whereas the low-frequency masker level (the position of the center of the spectral band was from –1.25 to –1 octave relative to the signal) changed by 8.7–9.8 dB. These results are interpreted as 0.3 dB/dB compression of responses to the signal and no compression of the effect of low-frequency maskers. If the spectral bands of the signal and masker partially overlap, discrimination of the spectral structure occurs predominantly in the part of the spectrum that does not overlap the masker spectrum and is subjected to low-frequency masking that is not compressed.

Wang Ping, Shi Yizhe, Jiang Jinyang, Kong Lu, Gong Zhihui «Generalized Sidelobe Canceller for Ultrasound Imaging based on Eigenvalue Decomposition» Акустический журнал, 65, № 1, с. pp. 123-131 (2019)

The improved generalized sidelobe canceller (GSC) based on eigenvalue decomposition beamforming technique for ultrasound imaging is proposed. Firstly, the signal subspace is obtained by performing eigenvalue decomposition on the covariance matrix of received data. Secondly, the weighting vector of GSC is divided into adaptive and non-adaptive two parts. Then the non-adaptive part is projected into the signal subspace to obtain a new steer vector. Subsequently, based on the orthogonal complementary space of the new steer vector, the blocking matrix is constructed. Finally, the weighting vector is updated by projecting the final weighting vector into the signal subspace. In order to verify the proposed algorithm, the simulations of the point targets and the cyst phantom were conducted in Field II. The experimental results indicate that the proposed method has better resolution and contrast ratio than the conventional algorithms. In addition, the algorithm is robust to noises. Furthermore, combining with coherence factor, the contrast ratio of the proposed algorithm can be further improved in comparison with a conventional GSC with coherence factor.