Gulia P., Gupta A. «Effect of Sidewalls on Sound Transmission Loss Through Sonic Crystal» Акустический журнал, 64, № 6, с. pp. 665-672 (2018)

Sonic crystals are the periodic arrangements of scatterers embedded in a homogeneous material. Their ability to prevent sound wave to propagate in a particular range of frequency demonstrates their use as potential noise barriers. The sonic crystal considered in this work is an array of PVC cylinders (5×5) in air bounded by acrylic sheets. This paper studies the sound transmission loss in the sonic crystal by changing the location of the sidewalls. The optimized location of sidewalls of the sonic crystal to get wide band gap and high sound transmission loss has been investigated. To increase the transmission loss, a periodic structure having bi-periodicity, i.e., periodicity in two perpendicular directions is introduced. Both computational (Finite Element simulation) and experimental work has been performed to study the sound transmission loss and the band gaps. To bridge the gap between the two results, an improved finite element model has been proposed with an aim to replicate the experimental situation more closely. Generally, in experiments, insertion loss is calculated while numerically transmission loss is computed, and the two are compared. In this paper, a comparison between insertion loss and transmission loss has also been made numerically, which is compared with the experimental results.

Zhang Kang «An Analytical Inverse Approach to Design GRIN Lenses» Акустический журнал, 64, № 6, с. pp. 684-691 (2018)

An analytical inverse method to design lenses of isotropic inhomogeneous refractive index (RI) distribution is presented, where the wave ray propagation is described by the eikonal equation. We show that some particular RI distributions can be obtained by the angles of incidence and emergence when the rays pass through the surfaces of the lenses. This method is applied to design lenses that perfectly focus rays or bend them to arbitrary angles. In addition, gradient refractive index (GRIN) devices are proposed, able to generate self-bending acoustic beams and obtain illusion shadows of arbitrary objects. The ray tracing and finite elements method simulation results indicate the validity of the method. The method may have potential applications in designing acoustic and optic GRIN devices for controlling energy flux, such as medical imaging, therapeutic ultrasound, acoustic levitation, energy isolation, acoustic and optic camouflaging, etc.

Gu Xinzhong, Li Shunming «Convolution Quadrature Time-Domain Boundary Element Method for Two-Dimensional Aeroacoustic Noise Prediction» Акустический журнал, 64, № 6, с. pp. 731-741 (2018)

The computation of a compressible flow for aeroacoustic prediction is a challengeable work insofar as the fluctuation is usually very small in a sound field compared with the flow field. For the low Mach number considered in this study, a discrete vortex method in conjunction with fast multipole time-domain boundary element method is developed and applied to predict far-field sound resulting from a 2D vortex dominated flow. The flow field is simulated employing the classical discrete vortex method. The sound field scattered by solid bodies is determined by using a time-domain boundary element method combined with the convolution quadrature approach, by means of which the convolution integral is approximated by a quadrature formula utilizing a Laplace-domain fundamental solution. In addition, the fast multipole method is applied to improve the computational efficiency. Finally, several examples are presented to check the applicability and accuracy of the method. Numerical results indicate that the noise predicted by the present method agrees well with the experimental results, and the sound pressure levels of the cylinder models have a dipole-like directivity at vortex shedding frequency.

Cao Yonggang, Chen Qian, Zheng Huifeng, Lu Lidong, Wang Yuebing, Zhu Jiang «Study on the Mechanism of Ultrasonic Power Measurement Sensor based on Pyroelectric Effect» Акустический журнал, 64, № 6, с. pp. 789-795 (2018)

PVDF pyroelectric sensor has been widely applied in many fields, such as intruder alarm. Nowadays, this sensor shows a potential for ultrasonic power measurement. However, the transformation mechanism between the acoustic and pyroelectric signals has not been particularly studied until now. In this paper, a physical model was introduced for theoretical study of the mechanism of energy transformations. In addition, a simulation program based on finite-element analysis method was built up for analyzing the ultrasound propagation characteristics and the temperature rise on the PVDF, as well it predicted the waveform and amplitude of the generated pyroelectric signal. Besides that, a PVDF pyroelectric sensor was fabricated and used for acoustic power measurement experiment. Finally, the experiment and simulation results were compared, confirming that the physical model is suitable for pyroelectric sensor characteristics analysis. It can also provide useful suggestions for the design and fabrication of PVDF pyroelectric sensors with high sensitivity.