Peculiarities of the Acoustic Wave Propagation in Diamond-Based Multilayer Piezoelectric Structures as “Me1/(Al,Sc)N/Me2/(100) Diamond/Me3” and “Me1/AlN/Me2/(100) Diamond/Me3” under Metal Thin-Film Deposition

New theoretical and experimental results of microwave acoustic wave propagation in diamond-based multilayer piezoelectric structures (MPS) as “Me1/(Al,Sc)N/Me2/(100) diamond/Me3” and “Me1/AlN/Me2/(100) diamond/Me3” under three metal film depositions, including the change in the quality factor Q as a result of Me3 impact, were obtained. Further development of our earlier studies was motivated by the necessity of creating a sensor model based on the above fifth layered MPS and its in-depth study using the finite element method (FEM). Experimental results on the change in operational checkpoint frequencies and quality factors under the effect of film deposition are in satisfactory accordance with FEM data. The relatively small decrease in the quality factor of diamond-based high overtone bulk acoustic resonator (HBAR) under the metal layer effect observed in a wide microwave band could be qualified as an important result. Changes in operational resonant frequencies vs. film thickness were found to have sufficient distinctions. This fact can be quite explained in terms of the difference between acoustic impedances of diamond and deposited metal films.

Two-Dimensional Composite Acoustic Metamaterials of Rectangular Unit Cell from Pentamode to Band Gap

Pentamode metamaterials have been receiving an increasing amount of interest due to their water-like properties. In this paper, a two-dimensional composite pentamode metamaterial of rectangular unit cell is proposed. The unit cells can be classified into two groups, one with uniform arms and the other with non-uniform arms. Phononic band structures of the unit cells were calculated to derive their properties. The unit cells can be pentamode metamaterials that permit acoustic wave travelling or have a total band gap that impedes acoustic wave propagation by varying the structures. The influences of geometric parameters and materials of the composed elements on the effective velocities and anisotropy were analyzed. The metamaterials can be used for acoustic wave control under water. Simulations of materials with different unit cells were conducted to verify the calculated properties of the unit cells. The research provides theoretical support for applications of the pentamode metamaterials.

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

Acoustic propagation in seawater is an important aspect of scientific investigation. However, the impact of the THz scale frequencies for acoustic propagation is not included in the studies. Thus, a finite element analysis of such propagation in a seawater medium is presented in this paper applying THz frequencies. A transmitter (circular with a diameter of 14 mm, a thickness of 3 mm) and a rectangular receiver (20×10×0.5 mm3) are designed to trace the variations in the propagation mediums. A propagation medium of seawater (70×40×60 mm3) with ice and softwood is modelled. A scale of frequencies (1 kHz to 1 THz) is applied to trace the impact on the propagation pattern. It is found that THz range frequencies provide a very small wavelength. As a result, the potential propagation distance is very small. As such, the sound pressure level, displacements of the receiver and pressure field shows very rapid drops in the magnitude. This work considers only 70 mm as propagation distance, yet the sharp decrement of performance parameters suggests that it is rather inconvenient to achieve useful efficiency using THz frequencies for acoustic propagation.