Surface Acoustic Wave Velocity Research Articles

Wideband Surface Acoustic Wave Resonator With Good Temperature Stability Using LiNbO3 on Glass.

Currently, wideband surface acoustic wave (SAW) devices are in demand. However, SAW resonators with a large coupling factor have a large negative temperature coefficient of frequency (TCF). In this work, we developed a new hetero acoustic layer (HAL) structure combining LiNbO3 (LN) and a glass with a low coefficient of thermal expansion (CTE), called ABC-G glass, to obtain the resonator with both large bandwidth (BW) and low TCF. The bulk and leaky SAW (LSAW) velocities of ABC-G glass were measured by ultrasonic microspectroscopy (UMS) technology, and its positive temperature coefficient of velocity (TCV) was confirmed. The (0°, 101°, 0°) and (0°, 120°, 0°) LNs are selected for experiments. The measured results show impedance ratio (Z-ratio) and BW as high as 82 dB and 12%, respectively. The measured TCFs reach -27 ppm/°C and -24 ppm/°C at resonance and antiresonance frequency, respectively, which are significantly improved compared with LN/Quartz (Qz). Ladder filters composed of three LN/ABC-G resonators are prototyped using a T-type configuration, and the insertion loss lower than 1 dB with a fractional bandwidth (FBW) of 15.0% was demonstrated. At the same time, no spurious response was observed up to 10 GHz. The results shown in this work prove the high performance of the LN/ABC-G structure in applications requiring good temperature stability, large BW, and out-of-band spurious-free characteristics.

Влияние геометрических параметров на распространение SH-волн в пьезоэлектрической/пьезомагнитной пластине

The propagation features of horizontally polarized shear waves in a magnetoelectroelastic composite plate in contact with vacuum are investigated within the quasi-static approximation. The plate consists of rigidly coupled piezoelectric and piezomagnetic layers. It is assumed that there are no mechanical stresses on the outer surfaces, and the magnetic potential is zero. Depending on the nature of the specified electrical conditions, problems with electrically open and electrically closed external surfaces are considered. The wave process is initiated by the action of a remote source of harmonic oscillations and is assumed to be steady. The solution of the problems is constructed in Fourier images as an expansion into a set of exponentials. Dispersion equations of the problems, which are presented in a matrix form convenient for numerical implementation, were obtained. Using the example of the PZT-5H/CoFe2O4 plate, the effect of the thickness of each of its layers on the transformation features of phase and group velocities of surface acoustic waves with horizontal polarization (SH-SAW) is established. When changing the geometric parameters, either the plate thickness or the thickness of one of its layers was fixed. Within the framework of the problem with electrically closed external surfaces, significant differences in the behavior of velocities were established depending on the thickness of the piezoelectric and piezomagnetic layers. The conditions for the maximum and minimum effect of the thickness of each layer on the behavior of the 2nd and subsequent SH-SAW modes were determined. It is shown that in the presence of a very thin piezomagnetic layer in the plate, the behavior of the 2nd SAW mode changes significantly: both the mode output frequency and the asymptotic value of the velocity increase. The regularities of the effect of changing the thickness of the piezoelectric and piezomagnetic layers of the plate on the transformation of the electromagnetic-mechanical coupling coefficient in a wide frequency range were revealed. The obtained results are given in dimensionless parameters and can be of interest in the development of new functionally oriented materials, the assessment of their performance characteristics, as well as in the creation of highly efficient devices operating on surface acoustic waves.

Continuous crystal growth and homogeneity of 2-inch Ca3Ta(Ga,Al)3Si2O14 bulk single crystals

Continuous crystal growth and homogeneity of 2-inch Ca3Ta(Ga,Al)3Si2O14 bulk single crystals

Optimization of the method for determining the velocity of surface acoustic waves

The methodological aspects of measuring the velocity of Rayleigh surface waves are considered. The main attention is paid to the method for determining the change in surface wave velocity under the influence of certain factors on the object of study. The main sources of error in determining the change in surface acoustic wave velocity are discussed. The use of a transducer with rigidly connected elements for exciting and recording surface acoustic waves to determine the change in velocity is examined. A distinctive feature of such a transducer is the stable measurement base length, which eliminates the need for its determination during the measurement process. It is shown that the main sources of decreased surface acoustic wave measurement accuracy are the temperature instability of the measuring equipment and the transducer, as well as the instability of the acoustic contact layer between the transducer ele-ments and the object of study. The instability of the acoustic contact is caused by the uncertainty in the distribution of the coupling fluid between the transducer and the specimen during the bonding process, leading to changes in the acoustic signal propagation time. The source of temperature instability is random changes in the ambient temperature. Another source of such instability is the heating of equipment elements due to the release of heat when electrical and acoustic energy pass through them. This is particularly important for the transducer, where electrical energy is converted into acoustic energy, as a significant portion of it is transformed into heat. The magnitude of temperature instability arising from prolonged system operation, as well as the instability caused by the installation of the transducer on the object of study, is experimentally evaluated. The use of a reference sample to compensate for the temperature instability of the measurement system is considered. The possibility of using a measurement scheme with a reference sample to reduce temperature instability and the error caused by the instability of the acoustic contact between the transducer and the object of study is analyzed.

A new FEM-based approach on the modeling of stress-induced velocity shift of piezoelectric surface acoustic wave resonators

A new FEM-based approach on the modeling of stress-induced velocity shift of piezoelectric surface acoustic wave resonators

A novel gyroscope based on the slow surface acoustic wave in a phononic metamaterial

Limited to the direct modulation on the surface acoustic wave (SAW) by the rotation, the conventional SAW gyroscopes incur weak Coriolis effects and gyroscopic effects. In this paper, we innovatively utilize a phononic metamaterial (PM) operated at whispering-gallery modes (WGMs) as the vehicle for the Coriolis effect rather than SAW itself. The gyroscopic effects of this PM are investigated, and a new SAW gyroscope is subsequently proposed based on the slow SAW in PM. We show, combining theoretical modeling and finite element method simulation, that the rate of rotation can linearly induce the splitting of WGMs and modulate the phase velocity of SAW down to 4600 m/s (initial phase velocity of 5355 m/s); the direction of rotation results in the chiral symmetry of the PM vibration and the asymmetric distribution of the transmissive SAW. Besides, the proposed SAW gyroscope measures the angular velocity by detecting the phase shift resulting from rotation-dependent slow SAW in PM, obtaining a sensitivity of 0.016 deg/Hz when 50-cell PM. Compared with the existing SAW gyroscopes based on phase velocity modulation, the gyroscopic gain factor in this paper is enhanced by 430–1600 times. This work jumps out of the framework of directly modulating SAW in gyroscopes and provides an innovative scheme of the indirect modulations from the rotation-dependent PM on SAW, showing excellent performance and potential for angular velocity measurement in extreme environments.

Single-Ended Surface Acoustic Wave Pressure Resonators

Surface acoustic wave (SAW) sensors exhibit advantageous attributes for pressure detection, including compact dimensions, cost-effectiveness, facile integration, elevated sensitivity, and a high quality factor (Q value). In this study, the single-ended resonant configuration of SAW pressure sensing element based on ST-X cut quartz was simulated and fabricated. The influence of the interdigitated transducer (IDT) and applied pressure on the resonance frequency of SAW were simulated and analyzed. The designed phase velocity (3159.344 m s−1) without IDT is closest to the theoretical phase velocity (3158 m s−1) of SAW propagation in the substrate, and the relative error is about 0.043%. The designed phase velocity of SAW dropped to 3149.198 m s−1 due to the loading of the IDT mass. With an increase in applied pressure from 0 to 350 kPa, the resonance frequency of the SAW decreases from 157.05 to 154.02 MHz, yielding a maximum linear pressure sensitivity of approximately 8.6 kHz kPa−1. The measured center frequencies of the fabricated single-ended SAW devices are predominantly clustered around 157 MHz, exhibiting a deviation of 0.46 MHz from the simulated results. The present work establishes a foundation for subsequent experimental investigations into pressure sensing.

Application of Graphene in Acoustoelectronics.

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the YZ-cut of a LiNbO3 ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO3 substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of Λ=60 μm was fabricated on the surface of the LiNbO3 crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude-frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass.

The influence of hydrogenation on propagation of surface acoustic waves in structural steel with nanocrystalline layer

The influence of the surface layer with nanocrystalline structure (NCS), electrolytical hydrogen charging with different intensities and their complex effect on the velocity of surface acoustic waves (SAW) was studied on the 40X steel. Changes in the NCS parameters under hydrogen action were revealed. Using SAW with frequencies of 1; 3 and 6 MHz, the distribution of properties through the surface layer thickness was estima­ted. A decrease in the SAW velocity is shown for the layer with NCS versus the matrix metal, as well as for the hydrogen charged metal versus the non-hydrogenated one. A non-monotonic de­pen­dence of the change in SAW velocity on the hydrogen charging intensity of the steel was established. The dependence of the SAW velocity on the frequency was observed for the hydrogen charged steel, thus indicating a non-homogeneous distribution of changes in properties through the depth. The surface NCS layer is a barrier for the hydrogen permea­tion into the steel depth under hydrogen charging at ic = 0.1 mA/cm2

ELECTROMECHANICAL PROGRAMMER FOR ACOUSTOELECTRONIC SENSORS OF PHYSICAL QUANTITIES

An electromechanical programmer is described, intended for programming an acoustoelectronic angular displacement meter, constructed on the basis of the effect of dependence of the phase velocity of surface acoustic waves on the direction of propagation relative to the crystallographic axis of a piezoelectric sound conductor.

Modeling acoustic characteristics of artificial bone alloys for medical and surgical use under thermodynamic conditions

Modeling acoustic characteristics of artificial bone alloys for medical and surgical use under thermodynamic conditions

Generation of GHz surface acoustic waves in (Sc,Al)N thin films grown on free-standing polycrystalline diamond wafers by plasma-assisted molecular beam epitaxy

Abstract Telecommunication of the next generation demands filters that can operate in the 10 GHz range with sufficient bandwidths. For surface-acoustic-wave (SAW) devices this prerequisite translates into high sound velocities and high piezoelectric couplings. Wurtzite AlN on diamond, which exploits the strong piezoelectricity of AlN with the very high SAW velocity of diamond, has been considered a promising platform. A significant boost (up to a factor of 4) of the piezoelectric response can be obtained by alloying AlN with Sc. Here, the main challenge lies in the synthesis of highly-oriented thin (Sc,Al)N films on diamond. In this work, we aim at establishing a platform for SAW devices using plasma-assisted molecular beam epitaxy for the deposition of Sc0.2Al0.8N on diamond. We investigate the structural properties related to SAW generation gearing towards applications at high frequencies. To this end, we prepare (Sc,Al)N thin films using plasma-assisted MBE on polished polycrystalline diamond wafers and demonstrate the efficient generation of SAW modes with frequencies up to 8 GHz. Systematic studies of the dependence of the SAW velocity and electromechanical coupling coefficient on the Sc0.2Al0.8N film thickness is presented for various SAW modes. Our result demonstrates the potential of this material combination for future application that requires large bandwidth in the ultra-high frequency range.

Design and Characterization of SAW-Based Wireless and Passive Temperature Sensing System

Abstract The Surface Acoustic Wave (SAW) temperature sensor has received significant attention due to its wirelessly-powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, antennas, and transceiver circuit. The SAW resonator utilized in this system was based on Aluminum Nitride (AlN) thin film, which exhibits high SAW velocity and excellent piezoelectric properties. To completely investigate the performance of the SAW resonator, simulation and experiments were conducted. Upon connecting the SAW sensor to the temperature sensing system via the antenna, the reflection peak of the SAW resonator was clearly observed in the spectrum of the return signal. Additionally, during the temperature tests, the response frequency displayed almost linear behavior as the temperature increased from 30°C to 150°C. The fitted temperature coefficient of frequency (TCF) was 30.68ppm/°C, indicating that the wireless temperature sensing system has high temperature sensitivity.

Velocity of subsonic and hypersonic surface acoustic waves on silicon with native oxide layer

The anisotropic dependence of the velocity of surface acoustic waves (SAW) on silicon is explored using surface Brillouin light scattering. Measurements of the SAW velocity are compared to a numerical model that takes into account the native thin amorphous oxide layer formed at the top surface of the silicon wafer. The model accounts for material loss and provides a relative estimate for the backscattered intensity resulting from the ripple effect. For the (100) sample considered, a thickness of 4 nm fits well with experimental data, considering material constants of amorphous silica for the oxide. A global phase velocity decrease of −11 m/s per nanometer of silica thickness is predicted for surface phonons at frequencies around 16 GHz.

Evaluation of surface corrosion damage in thin plates by Zero-Group Velocity Lamb waves based on PVDF comb transducers

Evaluation of surface corrosion damage in thin plates by Zero-Group Velocity Lamb waves based on PVDF comb transducers

Microstructural and material property changes in severely deformed Eurofer-97

Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ∼30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ∼0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties.

Probing phonon focusing, thermomechanical behavior, and moiré patterns in van der Waals architectures using surface acoustic waves

Surface acoustic waves (SAWs) propagate along solid-air, solid-liquid, and solid-solid interfaces. Their characteristics depend on the elastic properties of the solid. Combining transmission electron microscopy (TEM) experiments with molecular dynamics (MD) simulations, we probe atomic environments around intrinsic defects that generate SAWs in vertically stacked two-dimensional (2D) bilayers of MoS2. Our joint experimental-simulation study provides insights into SAW-induced structural and dynamical changes and thermomechanical responses of MoS2 bilayers. Using MD simulations, we compute mechanical properties from the SAW velocity and thermal conductivity from thermal diffusion of SAWs. The results for Young’s modulus and thermal conductivity of an MoS2 monolayer are in good agreement with experiments. The presence of defects, such as nanopores which generate SAWs, reduces the thermal conductivity of 2D-MoS2 by an order of magnitude. We also observe dramatic changes in moiré patterns, phonon focusing, and cuspidal structures on 2D-MoS2 layers.

Metamaterial control of the surface acoustic wave streaming jet

The phenomenon of surface acoustic wave (SAW) streaming, where a streaming jet is created, occurs when an SAW propagating on the surface of a solid interacts with water, and underpins the increasingly important area of SAW microfluidics. A key characteristic of the streaming jet is the Rayleigh angle, i.e. the angle at which the jet is formed relative to the surface normal of the solid, which is determined by the ratio of the velocity of the acoustic wave in the fluid and in the solid. Although the ability to dynamically tune this angle would offer a novel tool for microfluidic control, the SAW velocity is normally fixed by the characteristics of the solid and liquid material properties. In this paper we show, using finite element method modelling, that changing the SAW Rayleigh wave phase velocity by patterning a metamaterial array, consisting of square annular holes, onto the surface of an SAW device can change the acoustic streaming Rayleigh angle by approximately a factor of two, in good agreement with calculations based on the change in velocity.

Remote measurement of material elastic property at elevated temperature with grating laser ultrasonic testing

ABSTRACT As a pivotal elastic property, elastic modulus plays a crucial role in characterising the mechanical performance of materials. To achieve the convenient and remote measurement of the elastic modulus of materials at elevated temperatures, a method based on diffracted grating laser-induced narrowband surface acoustic waves (SAW) is proposed. The design scheme of the diffraction grating is disclosed, and a CCD camera is deployed to confirm the generated grating pattern and determine the actual grating period. Delving into the viability of an effortless and reliable procedure for calculating elastic modulus is discussed. The elastic modulus determined by the SAW does not depend on the exact Poisson’s ratio, which can be calculated from the SAW velocity with a given, less precise value for Poisson’s ratio. Experimental results of the three metals are in line with the reference values, and the elastic modulus at elevated temperature is successfully measured remotely, thereby verifying the feasibility of the proposed method.

Growth of ferroelectric lithium niobate-tantalate LiNb(1-x)TaxO3 crystals

Growth of ferroelectric lithium niobate-tantalate LiNb(1-x)TaxO3 crystals