Narrow Results

This paper presents an analysis of wave dispersion behavior in electrode–piezoelectric–electrode sandwich structures, considering surface effects (SE). The sandwich structure was situated atop an orthogonally anisotropic viscoelastic substrate. This paper aims to explore the surface effects on the dispersion characteristics of piezoelectric sandwich nanoplates embedded with viscoelastic substrates, integrating frequency-wave number curves and phase velocity-wave number curves. The displacement field of the nanoplate was derived using the sinusoidal shear deformation theory, and governing equations were established through Hamilton’s principle and surface constitutive equations. Subsequently, equations of motion were obtained based on the nonlocal strain gradient theory (NSGT), and characteristic equations were developed using harmonic solutions. The study thoroughly examined the effects of scale, viscoelasticity, and surface properties on wave propagation characteristics. The results reveal that scale effects significantly influence the dispersion curves of nanoplates, depending on the wave number, and emphasize the necessity of considering the surface effects of electrode layers. Notably, a reduction in thickness leads to an upward trend in both frequency and phase velocity curves. Furthermore, the Winkler modulus and shear modulus play a pivotal role in enhancing frequency stiffness, while increases in the damping coefficient and voltage result in a decrease in both frequency and phase velocity.

This paper proposes a new radial membrane acoustic metamaterial (RMAM) structure, wherein a layer membrane substrate is covered with a rigid ring (polymethyl methacrylate frame and aluminum lump). The dispersion relationships, transmission spectra and displacement fields of the eigenmodes of this radial membrane acoustic metamaterial are studied with FEM. In contrast to the traditional radial phononic crystals (RPCs), the proposed structures can open bandgaps (BGs) in lower frequency range (0–300 Hz). Simulation results show that the physical mechanism behind the bandgaps is the coupling effects between the rotational vibration of aluminum lump and the transverse vibration of membrane. Geometrical parameters which can adjust the bandgaps’ widths or positions are analyzed. Finally, we investigate the axial sound transmission loss of this acoustic metamaterial structure, and discuss the effects of factor loss, membrane thickness and the number of layers of unit cell on the axial sound transmission loss. Dynamic effective density proves the accuracy of the FEM results. This kind of structure has potential application in pipe or circular ring structure for damping/noise reduction.

The Half Heusler alloy (HHA) MnCrP has been studied theoretically for structural, elasto-mechanical and phonon properties. The structure is optimized and the calculated structural parameters are close to the literature. This optimized data is used to estimate three independent second-order cubic elastic constants $C_{11}$, $C_{12}$ and $C_{44}$. The mechanical stability criteria are explored by these constants and further used to estimate the elastic moduli; Young’s, bulk and shear modulus. The mechanical parameters like Poisson’s ratio, Pugh’s ratio, anisotropic factor, Cauchy pressure, shear constant, Lame’s constants, Kleinman parameter are also calculated and discussed. Discussions reveal the ductile nature, ionic behavior, anisotropic nature and mechanical stability of MnCrP. The metallic nature, compressibility, stiffness and interatomic forces of material are also described. Furthermore, the Debye temperature, where the collective vibrations shifts to an independent thermal vibrations, is also calculated. Longitudinal and transverse sound velocities are also obtained to investigate the phonon modes of oscillation. These phonon modes confirm the stability of the alloy as no negative phonon frequencies in the phonon-dispersion curves. These curves are used to estimate the reststrahlen band where light reflects 100% and the suitability of material is checked for Far Infrared (FIR), photographic, optoelectronic devices and sensors.

In this paper, we study the band gaps (BGs) of new proposed radial phononic crystal (RPC) structure composed of multilayer sections. The band structure, transmission spectra and eigenmode displacement fields of the multilayer RPC are calculated by using finite element method (FEM). Due to the vibration coupling effects between thin circular plate and intermediate mass, the RPC structure can exhibit large BGs, which can be effectively shifted by changing the different geometry values. This study shows that multilayer RPC can unfold larger and lower BGs than traditional phononic crystals (PCs) and RPC can be composed of single material.

The propagation of sound through plane layered structures is considered, with emphasis on three-layers made up of thick isotropic plates coupled with a thin anisotropic one. Modes are obtained by means of the transition terms method (TTM) based upon the use of the reflection and transmission coefficients. This method differs from the root searching methods (RSM) of dispersion equations such as, for instance, the Newton–Raphson method. The TTM provides dispersion curves with very little computation time. It unifies the dual representation of the dispersion curves: either complex wave numbers versus the real frequency, or complex frequencies versus the real wave number. The application to various cases of three-layer structures allows us to check the validity of the method and to discuss the connection between the TTM and Cremer's correspondence principle.

Guided waves sensitivity to environmental and operational conditions, especially temperature fluctuations, is one of the major problems when the method is considered for real engineering applications. The aim of this paper is to propose a novel dispersion curves extraction method for waveguides affected by nonuniform transient temperature field. Essentially, the method is based on a simple and robust approach, consisting in a few series of modal analyses for a representative part of the inspected structure. To consider the effect of temperature, a thermal stress calculation based on finite element method is presented. In this way, for different wave lengths, the mode shapes and corresponding natural frequencies can be obtained by solving some thermal-eigenvalue problems. To test the theoretical thermal effect of the dispersion curves a experiment on an isotropic plate is conducted. Those theoretical dispersion curves, consisting of only dominant modes, are compared with dispersion curves obtained from experiment. Finally, this method is used to extract the dispersion curves of the aero-engine casing considering the nonuniform temperature field. The results not only give us insight to how temperature affects Lamb wave velocities in different frequency ranges but also will help those extracting dispersion curves for waveguides affected by nonuniform transient temperature field.

We report on our systematic and detailed study of fabrication and characterization of polyaniline (PA) prepared by vacuum deposition and polystyrene (PS) prepared by dip coating method thin film optical waveguides. The four-layer consisting of substrate (glass)/PA/PS/air has been used for demonstrating polarization filter action.

The properties of ultrasonic Lamb waves, such as relatively small attenuation and high sensitivity to structural changes of the object being investigated, allow performing of non-destructive testing of various elongated structures like pipes, cables, etc. Due to the dispersion effect of Lamb waves, a waveform of the received informative signal is usually distorted, elongated and overlapping in the time domain. Therefore, in order to investigate objects using the ultrasonic Lamb waves and to reconstruct the dispersion curves, it is necessary to know the relationship between frequency, phase and group velocities and thickness of the plate. The zero-crossing technique for measurement of phase velocity of Lamb waves (the A₀ and S₀ modes) has been investigated using modelled dispersed signals and experimental signals obtained for an aluminium plate having thickness of 2 mm. A comparison between two reconstruction methods of Lamb wave phase velocity dispersion curves, namely, the two-dimensional fast Fourier transform (2D-FFT) and zero-crossing technique, along with the theoretical (analytical) dispersion curves is presented. The results indicate that the proposed zero-crossing method is suitable for use in reconstruction of dispersion curves in the regions affected by strong dispersion, especially for the A₀ mode.

In the present paper, the theory of generalized thermo-microstretch elasticity has been employed to study the propagation of straight and circular crested waves in microstretch thermoelastic plates bordered with inviscid liquid layers (or half-spaces), with varying temperature on both sides. The secular equations governing the wave motion in both rectangular and cylindrical plates have been investigated. The results in the case of thin (long wavelength) and thick (short wavelength) plates have also been obtained and discussed as special cases of this work. The secular equation in the case of microstretch coupled with thermoelastic, micropolar thermoelastic and thermoelastic plates can be obtained from the present analysis by an appropriate choice of relevant parameters. The results have been deduced and compared with the relevant publications available in the literature at the appropriate stages of this work. Finally, the analytical developments have been illustrated numerically for aluminum–epoxy-like material sandwiched in the inviscid liquid. The computer simulated results in respect of phase velocity, attenuation coefficient, specific loss factor of energy dissipation and relative frequency shift due to liquid layers on both sides of the plate are presented graphically.

The majority of ultrasonic characterizations are done on thermoplastics, with just a few articles available on the characterization of thermoset resin characteristics. A non-destructive methodology for monitoring fatigue and static deformation induced by mechanical loading on a fiber-reinforced plastic is presented. However, these materials’ dynamics of elastic waves are considerably more complicated. A large part was devoted to the calculation of dispersion curves of guided waves in composites. Therefore, this study presents a thorough description of the Glass/Epoxy system by comparing ultrasonic and mechanical data. Ultrasonic wave propagation at high frequencies, functioning as a dynamic mechanical deformation, may be utilized to calculate longitudinal and shear moduli during static and dynamic loading. The evolution of attenuation and velocity during loading is linked to the significant changes that occur during the aging process. The experimental transfer function is determined by the Fourier transform of all the obtained ultrasonic echoes.

This paper discusses the value added by using a single vector sensor over a conventional pressure-only hydrophone for geoacoustic inversions. Inversion methods based on genetic algorithms are used to estimate the seabed properties. Synthetic signals of impulsive arrivals first are modeled using KRAKEN and RAM propagation models, each being modified to predict components of the vector field. While KRAKEN is utilized to directly compute dispersion curves, RAM provides full-field results that require the application of time warping to separate the modal arrivals. Combinations of dispersion curves utilizing all vector sensor channels are compared to curves estimated with the pressure-only channel. Within the time warping analysis, both binary masking and band-pass filter masking methods are applied to compare stability of results. The environment modeled for the synthetic analysis and inversion method utilize sound speed profiles measured during the Monterey Bay 2019 at-sea experiment and assume a sediment layer of constant thickness overlying a deeper sub-bottom type. White noise is added to the synthetic data at different signal-to-noise ratios to evaluate the impact of signal excess on the results. A hybrid optimization approach is used to improve the results of the genetic algorithm method. The analysis with synthetic data is consistent with the analysis of broadband, impulsive data collected from the experiment, indicating that the additional information from the vertical velocity channel further improves the geoacoustic parameter estimates.

Based on the theory of liner piezoelectric elastic, the governing equations of the coupled waves are reduced to Bessel and Laplace equation. The boundary conditions imply that the displacements, shear stress, electric potential and electric displacement are continuous across the interface between the layer and the substrate together with the traction free at the surface of the layer. The electrically open and short conditions at cylinder surface are applied to solve the problem. The effect of the initial stress on the phase velocity and the electromechanical coupling factor are discussed in detail for piezoelectric ceramics PZT-5H, substrate for Aluminum. We find that the initial stress has an important effect on the SH wave propagation in a circular cylindrical layered structure.