METHOD OF EXCITATION OF QUASI LONGITUDINAL ACOUSTIC WAVES IN LAYERED STRUCTURES

The analysis of methodological possibilities of excitation of quasi-longitudinal (QL) acoustic waves of the megahertz frequency range in layered structures GaN-on-sapphire is studied and carried out. Volume-type transducers polarized by plate thickness are used to generate and detect QL waves. It is concluded that quasilongitudinal modes (QL) can be excited by this method – the so-called Anisimkin (AN) waves, for which the displacement plane is localized in the film plane and the displacement direction is directed along the wave vector.

Application of wideband laser-ultrasonic spectroscopy for non-destructive control of porosity in carbon plastics with various volume content of carbon fiber

In this work, to obtain the frequency dependences of the phase velocity of longitudinal acoustic waves in composite materials, we use the method of broadband laser-ultrasonic spectroscopy, based on laser thermo-optical excitation of broadband acoustic pulses. Unidirectional carbon fiber reinforced plasticsampes with different volume contents of the matrix and fiber were taken as objects of study.For the studied samples, the frequency dependences of the phase velocity were obtained in the spectral range of 0.8 – 10 MHz, and the existence of the phase velocity dispersion in this range was shown. The phase velocity dispersion of longitudinal acoustic waves in the sample was calculated using the phase spectra of the probe ultrasonic pulse and the pulse transmitted through the sample under study. It is also shown that the relative dispersion of the phase velocity characterizes the porosity of the sample, and the higher the porosity, the greater the relative dispersion. Empirical relations obtained for the relationship between porosity and relative dispersion can be used for the operational non-destructive assessment of the porosity of composites. The results obtained can be useful both for quality control of the materials obtained with the aim of modernizing manufacturing technologies and for predicting the behavior of structures and parts of this material under external loads.

Акустооптические свойства сплавов на основе германия, селена, кремния и теллура

We examined the acoustical, optical and acousto-optical properties amorphous alloys based on germanium, selenium, silicium and tellurium. The phase velocities of longitudinal acoustic waves and the value of acousto-optic figure of merit of the tellurium-based compounds were measured using the infrared sources of light radiation on the wavelength λ = 3.39 μm. We measured the acousto-optic figure of merit of germanium single crystal in case of diffraction on the acoustic modes along [110] and [111].

Simulation of Acoustic Propagation in 3D Viscoelastic Inhomogeneous Media with Application to Medical Shear Wave Elastography

This paper proposes a new numerical framework to simulate ultrasound wave propagation in 3D viscoelastic heterogeneous media based on the elastodynamic wave equation including a 3D second-order time-domain perfectly matched layer formulation. A finite difference discretization of this formulation is presented, along with a stability analysis. The resulting model is capable of simulating 3D shear and longitudinal acoustic waves for arbitrary source geometries and excitations, together with arbitrary initial and boundary conditions. A simulation example is provided to show the application of our proposed method for tissue elastography imaging. Specifically, the propagation of shear waves from a localized lesion to the surrounding normal tissue is examined.