Surface Acoustic Wave Velocity Research Articles

Temperature dependent angular dispersions of surface acoustic waves on GaAs

We measure the phase velocities of surface acoustic waves (SAWs) propagating at different crystal orientations on (001)-cut GaAs substrates and their temperature dependance. We design and fabricate sets of interdigital transducers (IDTs) to induce 4 μm SAWs via the inverse piezoelectric (PZE) effect between the PZE [110] direction (set as θ = 0°) and the non-PZE [100] direction (θ = 45°) on GaAs. We also prepare ZnO film sputtered GaAs substrates in order to launch SAWs efficiently by IDTs even in the non-PZE direction. We quantify acoustic velocities between 1.4 and 300 K from the resonant frequencies in the S11 parameter using a network analyzer. We observe parabolic velocity–temperature trends at all θ-values both on GaAs and ZnO/GaAs substrates. Below 200 K, in ZnO/GaAs substrates slower SAW modes appear around the [110] direction, which are unseen at RT.

Anomalies in the Complex Parameters of the Transparent Ferroelectric Ceramics PLZT Near the Diffused Phase Transition

The main objectives of the paper were to study the anomalies in the electrophysical parameters of the transparent ferroelectric ceramics of the PLZT (X/65/35) system near the diffuse phase transition, and to measure the complex sets of dielectric, elastic and piezoelectric parameters of those materials over a wide frequency range. The ferroelectric ceramics of the system (Pb1-xLax)(Zr0,65Ti0,35)O3 with lanthanum content were chosen as the object of the study. The experimental samples of ferroelectric PLZT ceramics were obtained by the hot pressing method. The complex parameters of the experimental samples were measured by the piezoelectric resonance analysis method using the software package PRAP. The sets of complex elastic, dielectric and piezoelectric parameters of PLZT (6.5/65/35) ceramics were obtained. The anomalies in the behavior of surface acoustic waves velocity and attenuation for PLZT (7.5/65/35) ceramics near the temperature of diffused phase transition were found and discussed.

Development of Methods of Acoustic Microscopy Inspection for Monitoring of Structure and Properties of Coatings for Various Purposes

The paper presents an algorithm for evaluating the physical properties of coatings for various purposes using the methods of acoustic microscopy (AMD-methods). The results of the experiments revealed a region of reduced adhesion, cracks under coatings. The obtained dispersion dependence of velocities of surface acoustic waves and the thickness of coatings of different physical nature.

The method of measuring the velocity of surface acoustic waves by laser probing

The method of measuring the velocity of surface acoustic waves by laser probing

Study of laser-induced surface acoustic wave propagating on materials with machined surfaces based on wavelet analysis

The present paper is concerned with the calculation of the dispersion curves of surface acoustic waves (SAWs) propagation on materials with machined surfaces. Using a DPSS (Diode Pumped Solid State) laser as the excitation source, experiments are performed on the surfaces of silicon wafer, steel and aluminum alloy plates respectively. The theoretic analysis shows that the location of the wavelet coefficients peaks at different scales in time-frequency domain are related to the arrival times of surface acoustic waves with different frequencies. The wavelet transform using the Sym8 wavelet is applied to the time-frequency analysis of weakly-dispersive SAWs and the propagation velocities of SAWs with different frequencies are calculated by extracting relevant data. Combined with the nanoindentation experiments, the relationships between the variation trend of the SAWs' dispersion curves and the surface properties of the materials are analyzed. The repeatability of the experimental method and analysis method is also verified by multiple experiments on different materials, the results indicate that the dispersion curves of multiple groups of signals on the propagation path have good consistency.

Electroacoustical constants and Rayleigh surface acoustic wave propagation characteristics of calcium aluminate silicate Ca2Al2SiO7 single crystals

Electroacoustical constants (, , and dij) of calcium aluminate silicate Ca2Al2SiO7 piezoelectric single crystals, which have the tetragonal structure with the point group , were evaluated. The normalized first-order temperature coefficients of all the constants were determined between −30 and 120 °C at 10 kHz frequency, e.g., for and were 69.3 and 87.6, and for d14 and d36 were −338.4 and 552.4 ppm/°C, respectively. The Rayleigh surface acoustic wave (SAW) velocities for the fundamental X- and Z-cuts of the crystals were theoretically calculated. The results were supported by the SAW velocities measured for the Z-cut of the crystal, proving the accuracy of the electroacoustic constants determined in this study.

Effects of helium production, displacement damage on mechanical properties and surface acoustic wave in austenitic stainless steels and martensitic steel

The effects of helium production, displacement damage on mechanical properties and microstructures were investigated in some specimens such as austenitic stainless steels of SUS304 and SUS316 and a high chromium martensitic steel of HCM12A steels irradiated in a high fluence irradiation facility (HIT) of the University of Tokyo. The simultaneous dual ion (nickel plus helium ions) irradiations were adopted to simulate nuclear irradiation environments such as fast reactor and fusion reactor at HIT to 1 or 10 dpa and to 0, 1, 10, and 100 appm-He at 500, 550, and 600 °C. Thin foils for a transmission electron microscopy (TEM) were prepared with a focused ion beam (FIB) micro-sampling system. After the irradiation, the microstructures were observed by a transmission electron microscope and the irradiation hardening was measured by nano-indentation technique. In this study, the efficient of non-destructive measurement method of surface acoustic wave (SAW) excited by laser beam on the detection of radiation hardening behavior was also examined. Irradiation hardening was observed and the increment was tended to increase with dpa and He/dpa, which was especially effective in the condition of 100 appmHe/dpa even at 550 °C. Non-linear effect on amplitude of the excited SAW was also observed on the ion irradiated materials, and the propagation velocity of SAW was tended to be increased with irradiation dose. It was found that the behaviors of SAWs results were correlated with the changes of mechanical properties.

Fast surface acoustic wave solution method based on the generalized Green’s function

The characteristics of generalized Green’s function elements with different materials and cuts are analyzed. The real part has only one zero crossing point that corresponds to a free surface acoustic wave (SAW) when the imaginary part of elements H33 is zero. Moreover, the signs of the real part on two sides of the zero crossing point are opposite. A fast SAW solution algorithm is developed on the basis of the characteristics of H33. Free surface SAW velocity vf is obtained by searching the zero crossing point of H33, and metal surface SAW velocity vm is obtained by searching the zero crossing point of an effective permittivity that is smaller than vf. A numerical simulation is performed. Results show that the obtained SAW velocity and electromechanical coupling coefficients are consistent with the reported results. Moreover, the calculation time of the proposed SAW solution method is approximately 10% of the existing methods, which verify its feasibility.

Three-dimensional finite element simulation of Love mode surface acoustic wave in layered structures including ZnO piezoelectric film and diamond substrate

Three-dimensional (3D) finite element method (FEM) was used to simulate the surface acoustic wave (SAW) propagation properties in layered structures including ZnO piezoelectric film and diamond substrate. The excitation conditions of Love mode and Rayleigh mode SAWs are discussed considering the ZnO crystal orientation and the SAW propagation direction which are specified using Euler angles (α, β, γ). The phase velocity and electromechanical coupling coefficient K2 of Love mode SAW in the ZnO/diamond structure are provided as functions of the normalized ZnO layer thickness hZnO/λ and the Euler angles (α, β, γ). The results show that the maximum K2 of 4.26% is reached at hZnO/λ = 0.3 and (α, β, γ) = (0°, 90°, 0°) for Love mode SAW; the associated phase velocity is 3436 m/s and the temperature coefficient of frequency (TCF) value is −26.5 ppm/°C. The TCF properties are greatly improved by adding a SiO2 layer between the ZnO film and the diamond substrate. A zero TCF can be obtained when the normalized SiO2 thickness hSiO2/λ is 0.25 and the hZnO/λ is 0.2, where the corresponding K2 is 3.26% and the phase velocity is 3126 m/s.

Influence of Boron Adding on the Acoustic Materials Signature Curves for Computing of Surface Acoustic Wave Velocities of Ti64 Alloys

Influence of Boron Adding on the Acoustic Materials Signature Curves for Computing of Surface Acoustic Wave Velocities of Ti64 Alloys

First measurement of the full elastic constants of Ni-based superalloy René 88DT

The full elastic constants of Ni-based superalloy René 88DT were measured for the first time using a recently developed method that matches the computed surface acoustic wave (SAW) velocities from an elastodynamic model with experimental velocities of SAWs that are generated and detected with a femtosecond laser. The experimental measurements were performed on several grains of a polycrystalline sample without the need of growing a single crystal. The computed Young's modulus from the resultant elastic constants agrees with the literature values, lending confidence on our measured elastic constants: C11=267.1, C12=170.5, and C44=107.6 (GPa).

High-Temperature SAW Resonator Sensors: Electrode Design Specifics.

Surface acoustic wave (SAW) sensors are steadily paving the way to wider application areas. Their main benefit consisting in the possibility of wireless interrogation with the radio frequency interrogation signal being the only energy source for the reradiated signal. This feature is getting more and more attractive with the growing demand in monitoring multiple industrial objects difficult to access by wired sensors in harsh environments. Among such wider applications, the possibility of making measurements of temperature, deformation, vibrations, and some other parameters at temperatures in the range of 300 °C-1000 °C look quite promising. This paper concentrates on specific features of the SAW resonator-based sensors operation at this temperature range. High-temperature influences the material choice and thus the properties of SAW resonators design peculiarities intended for use at high temperature. It is suggested that preferable designs should use synchronous resonators with relatively thick electrodes (10% of wavelength) based on Ir or Pt alloys while benefiting from the possibilities of specific designs that could reduce the negative impact of thick electrodes on the manufacturing in quantity. This solution benefits from lower resonance frequency scatter because of the automatic compensation of SAW velocity decrease due to electrode metallization ratio increase. This compensation originates from the resonance frequency increase that is related to the decrease of the Bragg bandwidth defined by the reflection. It is shown in modeling examples that the value of metallization ratio at which this compensation occurs is close to 65%-70%.

SAW propagation characteristics of TeO3/3C-SiC/LiNbO3 layered structure

Surface acoustic wave (SAW) devices based on Lithium Niobate (LiNbO3) single crystal are advantageous because of its high SAW phase velocity, electromechanical coupling coefficient and cost effectiveness. In the present work a new multi-layered TeO3/3C-SiC/128° Y-X LiNbO3 SAW device has been proposed. SAW propagation properties such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of the TeO3/SiC/128° Y-X LiNbO3 multi layered structure is examined using theoretical calculations. It is found that the integration of 0.09λ thick 3C-SiC over layer on 128° Y-X LiNbO3 increases its electromechanical coupling coefficient from 5.3% to 9.77% and SAW velocity from 3800 ms−1 to 4394 ms−1. The SiC/128° Y-X LiNbO3 bilayer SAW structure exhibits a high positive TCD value. A temperature stable layered SAW device could be obtained with introduction of 0.007λ TeO3 over layer on SiC/128° Y-X LiNbO3 bilayer structure without sacrificing the efficiency of the device. The proposed TeO3/3C-SiC/128° Y-X LiNbO3 multi-layered SAW structure is found to be cost effective, efficient, temperature stable and suitable for high frequency application in harsh environment.

Analysis of Surface Acoustic Wave Propagation Velocity in Biological Function-Oriented Odor Sensor

We describe the measurement of surface acoustic wave (SAW) velocities to identify five odorant molecules by using a SAW device system. We derive a new frequency equation for SAWs propagating in the SAW device system with Cynops pyrrhogaster lipocalin (Cp-Lip1) protein, in order to identify five odorant molecules, R-limonene (R-Lim), ethyl butyrate (Eth), 2-isobutylthiazole (Iso), benzophenone (Ben), and 2-acetylthiazole (Ace). We developed a method to identify these odorant molecules combined with the Cp-Lip1 odorant-binding protein. Our frequency equation can satisfactorily predict different odorant molecules in the Cp-Lip1 SAW device. Moreover, our data suggest that the propagation velocity of the SAWs mostly relate to the density and concentration of the Cp-Lip1 odorant molecule mixtures. At the same sample concentration, the propagation velocity depends on the density. For the same odorant molecule, the propagation velocity decreases with increasing concentration.

Measurement of Surface Acoustic Wave Velocity Curves of Silicon Crystal by Ultrasonic Method

Measurement of Surface Acoustic Wave Velocity Curves of Silicon Crystal by Ultrasonic Method

Optimization of measurement step of surface acoustic wave velocity in non-homogeneous medium

The method of measurement of space distribution of the surface acoustic wave velocity in nonhomogeneous medium is considered. It is shown that the spatial resolution and error of measurement of the surface acoustic wave velocity are dependent on the magnitudes and its ratio dependents on the step of measurement. The optimization method of the spatial resolution and precision measurement of the surface acoustic wave velocity is proposed. The method is based on the measurement by minimum step size and next processing of the experiment data.

Temperature dependence of elastic properties in austenite and martensite of Ni-Mn-Ga epitaxial films

Using surface acoustic waves (SAW) the elastic properties of 500 nm thick epitaxial off-stoichiometric Ni-Mn-Ga films prepared by sputtering on MgO substrate were determined in a broad temperature range both in austenite and martensite and across the martensitic transformation. At room temperature the films were in non-modulated martensite with tweed-like microstructure. Structural and magnetic studies proved that the martensitic structure can be considered homogenous on the scale of surface waves owing to the fine twinning. Measured angular dependence of SAW velocities indicated that the averaged in-plane tetragonal structure can be used for the calculation of elastic coefficients in martensite. The phase velocity of SAW showed an anomaly around the phase transition temperature due to changes of the shear elastic coefficients, c'and c44. During cooling there was a gradual softening of c' in austenite. The softening turned to stiffening at the onset of the martensitic transformation while c44 sharply decreased. The shear coefficients for martensite and paramagnetic austenite of the film are comparable to Ni-Mn-Ga bulk single crystal. No significant effect of magnetic field on elastic coefficients was detected in agreement with the bulk.

Detecting self-ion irradiation-induced void swelling in pure copper using transient grating spectroscopy

Irradiation-induced void swelling remains a major challenge to nuclear reactor operation. Swelling may take years to initiate and often results in rapid material property degradation once started. Alloy development for advanced nuclear systems will require rapid characterization of the swelling breakaway dose in new alloys, yet this capability does not yet exist. We demonstrate that transient grating spectroscopy (TGS) can detect void swelling in single crystal copper via changes in surface acoustic wave (SAW) velocity. Scanning transmission electron microscopy (STEM) links the TGS-observed changes with void swelling-induced microstructural evolution. These results are considered in the context of previous work to suggest that in situ TGS will be able to rapidly determine when new bulk materials begin void swelling, shortening alloy development and testing times.

Inherent losses induced absorptive acoustic rainbow trapping with a gradient metasurface

Acoustic rainbow trapping represents the phenomenon of strong acoustic dispersion similar to the optical “trapped rainbow,” which allows spatial-spectral modulation and broadband trapping of sound. It can be realized with metamaterials that provide the required strong dispersion absent in natural materials. However, as the group velocity cannot be reduced to exactly zero before the forward mode being coupled to the backward mode, such trapping is temporary and the local sound oscillation ultimately radiates backward. Here, we propose a gradient metasurface, a rigid surface structured with gradient perforation along the wave propagation direction, in which the inherent thermal and viscous losses inside the holes are considered. We show that the gradually diminished group velocity of the structure-induced surface acoustic waves (SSAWs) supported by the metasurface becomes anomalous at the trapping position, induced by the existence of the inherent losses, which implies that the system's absorption reaches its maximum. Together with the progressively increased attenuation of the SSAWs along the gradient direction, reflectionless spatial-spectral modulation and sound enhancement are achieved in simulation. Such phenomenon, which we call as absorptive trapped rainbow, results from the balanced interplay among the local resonance inside individual holes, the mutual coupling of adjacent unit cells, and the inherent losses due to thermal conductivity and viscosity. This study deepens the understanding of the SSAWs propagation at a lossy metasurface and may contribute to the practical design of acoustic devices for high performance sensing and filtering.

Imaging surface acoustic wave dynamics in semiconducting polymers by scanning ultrafast electron microscopy

Understanding the mechanical properties of organic semiconductors is essential to their electronic and photovoltaic applications. Despite a large volume of research directed toward elucidating the chemical, physical and electronic properties of these materials, little attention has been directed toward understanding their thermo-mechanical behavior. Here, we report the ultrafast imaging of surface acoustic waves (SAWs) on the surface of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film at the picosecond and nanosecond timescales. We then use these images to measure the propagation velocity of SAWs, which we then employ to determine the Young's modulus of P3HT. We further validate our experimental observation by performing a semi-empirical transient thermoelastic finite element analysis. Our findings demonstrate the potential of ultrafast electron microscopy to not only probe charge carrier dynamics in materials as previously reported, but also to measure their mechanical properties with great accuracy. This is particularly important when in situ characterization of stiffness for thin devices and nanomaterials is required.