Acoustic Wave Devices Research Articles

The cell elastic modulus sensing based on surface acoustic wave devices

Abstract Elastic modulus is an important parameter to reflect the status of the cell. In this work, the elastic modulus of liquid and cancer cell were studied based on the delay line type surface acoustic wave (SAW) device. Firstly, the finite element method (FEM) was used to analyse and design the sensor, a cavity was etched on the propagation path. After the acoustic wave transmit through the cavity, the transmission parameter was disturbed by the material in the cavity. The phase shift of the S21 parameter of the SAW sensor was used to detect the elastic modulus of liquid or cell in the cavity.

Time-resolved imaging of GHz acoustic vibrations at arbitrary frequencies using asynchronous periodic probe laser pulses

We present a technique for imaging gigahertz surface acoustic waves in the time domain at arbitrary frequencies, in which acoustic waves are excited asynchronously to the optical probe pulse train used to detect them. We apply this approach to the two-dimensional imaging of electrically excited single-frequency surface acoustic waves on a GaAs substrate with a deposited interdigital transducer. This technique significantly increases the possible fields of application for gigahertz acoustic wave device imaging.

Control of the preferentially orientated growth of Sr2TiSi2O8 crystals in a SrO – TiO2 – SiO2 – Al2O3 – K2O parent glass

A polar glass-ceramic containing Sr-fresnoite Sr2TiSi2O8 (STS) as single crystalline phase was developed through the controlled crystallization of a parent glass composition containing SrO, TiO2, SiO2, K2O, and Al2O3. The objective of this work is to obtain a piezoelectric substrate exhibiting a well-defined orientation of the polar direction of the STS crystals over a depth suitable for the design of surface acoustic waves (SAW) devices. For that purpose, the crystallization mechanism of the parent glass was first studied by Differential Scanning Calorimetry (DSC). Based on this study, heat treatments were applied to transform the glass into glass-ceramics. Two aspects were investigated: i). The influence of the surface state of parent glass and of its environment on the nucleation of preferentially orientated STS crystals at the surface of the parent glass; ii). The growth of a preferentially orientated crystallized layer from the surface into the bulk. The microstructures of resulting glass ceramics were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). We demonstrate that growth of the surface crystallized layer is governed by diffusion mechanisms through a transition glass composition separating the crystalized layer and the subjacent parent glass. The control of the growth rate of the crystalline layer plays the key role to keep a high and constant orientation of the (002) STS plans parallel to the surface of the substrate.

Ultralow electric-field poling of LiNbO3 single-crystal devices

The LiNbO3 (LNO) single crystal receives wide applications in nonvolatile memories, surface acoustic wave devices, and electro-optic modulators. However, engineering of antiparallel domain patterns within micrometer-sized devices generally requires a poling voltage more than a few thousands of volts. The high poling voltage could invoke dielectric breakdown. Here, we found an effective method to increase the local electric field significantly for domain nucleation at the interfaces of an etched LNO mesa in contact to two concave side electrodes, while the electric field across the protruding intra-electrode area can be lower by 10 times after the metal diffusion at the surface. Subsequent piezoresponse force microscopy mapping shows the nucleating domains to grow up through the entire intra-electrode area. This method is universal and analogous to other ferroelectric devices for the realization of low-voltage operations.

Rayleigh waves in viscoelastic piezoelectric half-space with cladding structures: An analytic Legendre-Laguerre polynomial method

Piezoelectric materials are widely used in surface acoustic wave devices. Many piezoelectric materials themselves have viscoelastic properties, and their surface wave characteristics, especially the attenuation characteristics still needs to be explored. This article proposes a Legendre-Laguerre orthogonal polynomial method to solve the Rayleigh wave problems in a viscoelastic piezoelectric half space with a covering layer. The proposed method compensates for the inherent shortcomings of traditional Laguerre polynomials in solving layered half spaces: the normal stress and electric displacement are discontinuous. The correctness of the method was verified through literature comparison and finite element simulation. At the same time, by utilizing the orthogonality of the Legendre-Laguerre polynomial, the integral analytical formula encountered in the solution process is derived, which improves the computational efficiency by more than ten times. Through the analysis and discussion of the dispersion and attenuation curves, it is found that the piezoelectric effect can suppress the attenuation of Rayleigh waves; the piezoelectric and viscous properties of the covering layer mainly affect attenuation at high frequencies, while those of the half space layer mainly affect attenuation at low frequencies of high-order modes.

Controllable manipulation of surface waves via a ferromagnetic elastic metasurface

In this paper, we study the propagation of surface waves on an A-shape metasurface, whose structure of the unit-cell is composed regularly of an A-shape surface column (made of steel), a thin magnetorheological plate and a soft thick rubber base. On the basis of the commercial program COMSOL Multiphysics, finite element method (FEM) analyses are carried out. The localization of elastic waves surrounding the surface allows surface waves to be distinguished among various complex wave modes. By adjusting the geometry, the A-shape surface column can be transformed from snowflake to A-shape. Owing to the C3v symmetry system, a Dirac cone of surface wave is observed in a snowflake metasurface. When the surface column changes to A-shape, the C3v symmetry is broken, making the Dirac cone vanish and a new band gap of surface waves arise. The band gap can be opened or closed by changing a geometric parameter, which determines the shape of the surface column changing from gadarene A-shape to snowflake or even upturned A-shape. Furthermore, we discover that although the topological phases of the gadarene A-shape and upturned A-shape metasurfaces are opposite, they share overlapped band gaps. Based on this phenomenon, we design a topological insulator for surface waves, whose super-cell is composed of gadarene A-shape units and upturned A-shape units. Through the calculation of the super-cell band structure, we observe the topologically protected interface states (TPISs). Subsequently, we design several waveguides whose paths are controllable. Up to now, most of the existing metasurfaces are made of passive materials, whose properties cannot be adjusted in real time, making them inconvenient for engineering applications when external conditions are changed. Therefore, we use tunable magnetorheological elastomer (MRE) to control the properties of the topological insulators. The stiffness of the surface layer can be converted by applying a magnetic field, which makes the topological metasurface controllable. These intelligent topological insulators may find important applications in the design of surface acoustic wave (SAW) devices.

Piezoelectric layer guided in-plane surface waves with flexoelectricity and gradient effects

With the rapid advancement of 5 G technology, the demand for surface acoustic wave (SAW) devices is experiencing exponential growth. Precisely forecasting the speed at which Rayleigh waves propagate, taking into account size effects and flexoelectric properties, is vital for enhancing SAW device design. To address this need, the study explores Rayleigh wave propagation in a stratified system consisting of a nanoscale piezoelectric guiding layer atop an isotropic elastic substrate. The governing equations, boundary conditions, and interface continuity conditions between the guiding layer and substrate are established through the Hamiltonian principle. Following this, the dispersion equations for Rayleigh waves under electric open-circuit and electric short-circuit conditions are derived and solved numerically. Additionally, the effects of flexoelectricity, inertial gradients, strain gradients, electric field gradients, and the piezoelectric guiding layer thickness on the phase velocity of Rayleigh waves are extensively explored. Our findings indicate that flexoelectricity and strain gradients elevate the phase velocity, while inertial gradients and electric field gradients result in a decrease in the phase velocity. As the frequency of Rayleigh waves increases, the impact of these factors becomes more prominent. In addition, it is observed that electric field gradients play a less significant role compared to inertial gradients and strain gradients. The findings of this study could offer valuable insights for the advancement of miniaturized SAW devices designed for high-frequency service.

Design optimization of surface acoustic wave devices and investigation of fabricated devices under temperature, humidity and steam environments

Surface Acoustic Wave (SAW) technique is one of the most promising Micro Electro Mechanical Systems (MEMS) based detection methods for a variety of applications. SAW sensor is based on the modulation of Rayleigh waves that travel near the surface of a piezoelectric substrate. Advent of MEMS technology has led to the development of SAW sensors which are widely used in chemical sensing, medical, industrial, telecommunication and biological applications. The main focus of this paper is to devise and characterize a generic SAW structure and study the acoustic properties at various environmental conditions before depositing the sensing layer/analyte for any particular application. In this work, a SAW device was designed using COMSOL Multiphysics for a resonant frequency of 100 MHz with 40 μm wavelength on Lithium Niobate (LiNbO3) piezoelectric substrate. The optimized device structure was fabricated using thin film deposition and UV photolithography. The resonant frequency of the fabricated device (97.63 MHz) matched closely with the simulation results (100 MHz) and theoretical results (100 MHz). The device was subjected to various environmental conditions to study the influence on the resonant frequency. The SAW structure showed a resonant frequency shift of 90 KHz in steam environment, ∼ 1 MHz when heated to 150 °C and ∼ 120 KHz when exposed to 80% RH. The device exhibited a linear shift in resonant frequency under all tested environmental conditions with a consistent baseline and good repeatability.

Simultaneous Protein Adsorption and Viscosity Measurement using Micropillar-Enhanced Acoustic Wave (μPAW) Device for Pharmaceutical Applications

At the early stages of drug development, the amount of drug materials is rather limited. In this case, viscosity measurement is often postponed to the later stages, where grams of proteins can be produced. Therefore, it is necessary to develop a viscometer capable of measuring the viscosity with high accuracy while requiring low sample volume. This study presents a novel viscosity measurement technique based on measuring the resonance frequency and motional resistance of a micropillar-enhanced acoustic wave (μPAW) device. The μPAW was developed by fabricating micropillars on the quartz crystal microbalance substrate in order to achieve ultra-high sensitivity, thanks to a unique coupling between the micropillar and the resonator. The experimental measurements demonstrated a nonlinear relationship between the density and viscosity of the fluid and the response of μPAW. A calibration correlation was developed using the response of μPAW in aqueous glycerol and sucrose solutions. The measurements were then extended using high-concentration BSA solutions as the model of protein solution. The main advantage of the μPAW device in this work over other viscometers is the ability to simultaneously measure solution viscosity and protein adsorption on the surface. This is a huge step forward in the development of sensing systems for the pharmaceutical industry, where real-time sensing of target biological proteins and measuring the viscosity of a solution is required.

Analysis Method for the Influence of Parasitic Surface Conductivity on Silicon-Based Surface Acoustic Wave Devices

Analysis Method for the Influence of Parasitic Surface Conductivity on Silicon-Based Surface Acoustic Wave Devices

Analysis of different wave characteristics in a fiber-reinforced thermo-piezoelectric rotating medium influenced by gravity

Fiber-reinforced polymer composites possess a lightweight nature, corrosion resistance, high strength, and specific stiffness. As a result, they play a crucial role in the construction and rehabilitation of structures, providing reinforcement with their versatile and beneficial properties. Owing to this, proposed mathematical model is intended to give a detailed analysis of the characteristics of surface waves in a homogeneous, transversely isotropic fiber-reinforced thermo-piezoelectric (FRTPC) composite half-space rotating with uniform angular frequency including Coriolis and centrifugal forces. Recently proposed Moore–Gibson–Thompson thermoelasticity theory with two-temperature is employed to describe the mathematical framework. The free surface is considered to be stress free, electrically shorted/charge free, and thermally insulated/isothermal. The FRTPC structure is analytically modeled by the Strength of Materials technique with the Rule of Mixtures approach. Normal mode technique is used to derive the expression for mechanical stresses, electrical displacement, and temperature gradient. Depending upon four different boundary conditions, corresponding secular equations are derived for the considered half-space. The influence of rotation, gravity, fiber volume fraction, and two-temperature on different wave characteristics (phase velocity, attenuation coefficient, specific loss, and frequency shift) is demonstrated graphically considering PZT-5H epoxy material. Numerical simulation indicates that wave propagates at a finite speed in the FRTPC medium in the case of MGT thermoelastic theory, rather than the infinite speed in the classical thermoelasticity model. The present mathematical study may find its application in designing of gyroscopes, rotation sensors, temperature sensors, and other pyro/piezoelectric surface acoustic wave devices.

Coherent optical coupling to surface acoustic wave devices

Surface acoustic waves (SAW) and associated devices are ideal for sensing, metrology, and hybrid quantum devices. While the advances demonstrated to date are largely based on electromechanical coupling, a robust and customizable coherent optical coupling would unlock mature and powerful cavity optomechanical control techniques and an efficient optical pathway for long-distance quantum links. Here we demonstrate direct and robust coherent optical coupling to Gaussian surface acoustic wave cavities with small mode volumes and high quality factors (>105 measured here) through a Brillouin-like optomechanical interaction. High-frequency SAW cavities designed with curved metallic acoustic reflectors deposited on crystalline substrates are efficiently optically accessed along piezo-active directions, as well as non-piezo-active (electromechanically inaccessible) directions. The precise optical technique uniquely enables controlled analysis of dissipation mechanisms as well as detailed transverse spatial mode spectroscopy. These advantages combined with simple fabrication, large power handling, and strong coupling to quantum systems make SAW optomechanical platforms particularly attractive for sensing, material science, and hybrid quantum systems.

Love wave propagation in a trigonal piezoelectric material layer of 32 crystal class

This paper analytically investigates the propagation characteristics of Love waves in a 32 trigonal piezoelectric layer resting on an elastic substrate. The governing electromechanical equations are derived and dispersion equations are obtained for two electrically open and short conditions. For a numerical study, a structure consisting of an α-quartz layer bonded onto a diamond substrate is considered. The influence of electrical boundary conditions on the mechanical and electrical responses is presented and discussed. The numerical results of dispersion curves indicate that phase velocities of all modes initiate at the shear wave velocity of the substrate and the phase velocity of the first mode approaches the velocity of the Bleustein–Gulyaev (BG) wave at high wavenumbers. Despite hexagonal piezoelectric material, the real and imaginary parts of the response mode shapes do not have identical distribution in a structure containing a piezoelectric material of crystal class 32. In addition, the present study provides a theoretical foundation for the design and application of surface acoustic wave (SAW) devices.

Deposition and structural investigation of uniform AlN(100) films at wafer scale through RF magnetron sputtering

a-axis-oriented AlN(100) films are identified as promising candidates for surface acoustic wave devices owing to their high transversal-acoustic velocity. Achieving uniform films across a wafer scale is crucial for enhancing device performance and minimizing manufacturing costs. In this study, we employ radio-frequency magnetron sputtering to deposit AlN(100) films on 2-in Si(100) wafers. We further examine the influence of various process parameters on the nonuniformity of film thickness and structural properties, including crystallite size, microstrain, and dislocation density. The optimization of parameters leads to the selection of a gas flow ratio of N2:Ar = 4:7, a sputtering power of 160 W, and a substrate temperature of 350 °C. Under these optimized conditions, the AlN films not only demonstrate a preferred (100) orientation and remarkable crystallinity, as indicated by a full width at half maximum of the X-ray diffraction peak of just 0.03°, but also achieve an optimal film thickness nonuniformity of 1.66 %. Our results offer valuable insights for the wafer-scale fabrication of AlN(100) films, potentially enhancing industrial production yields and reducing costs.

Rational Design of a Surface Acoustic Wave Device for Wearable Body Temperature Monitoring.

Continuous monitoring of vital signs based on advanced sensing technologies has attracted extensive attention due to the ravages of COVID-19. A maintenance-free and low-cost passive wireless sensing system based on surface acoustic wave (SAW) device can be used to continuously monitor temperature. However, the current SAW-based passive sensing system is mostly designed at a low frequency around 433 MHz, which leads to the relatively large size of SAW devices and antenna, hindering their application in wearable devices. In this paper, SAW devices with a resonant frequency distributed in the 870 MHz to 960 MHz range are rationally designed and fabricated. Based on the finite-element method (FEM) and coupling-of-modes (COM) model, the device parameters, including interdigital transducer (IDT) pairs, aperture size, and reflector pairs, are systematically optimized, and the theoretical and experimental results show high consistency. Finally, SAW temperature sensors with a quality factor greater than 2200 are obtained for real-time temperature monitoring ranging from 20 to 50 °C. Benefitting from the higher operating frequency, the size of the sensing system can be reduced for human body temperature monitoring, showing its potential to be used as a wearable monitoring device in the future.

Efficient Generation of Plasma‐Activated Aerosols with High Concentrations of Reactive Species via Silicon Dioxide Coated Surface Acoustic Wave Devices

AbstractAn effective method to deliver plasma‐activated water onto contaminated surfaces is with a surface acoustic wave (SAW) nebulizer that can efficiently produce plasma‐activated aerosols. While higher reactive species concentrations in the plasma‐activated aerosols promote more efficient bacterial inactivation and hence reduce the amount of aerosols needed to completely eradicate the bacteria colonies, higher concentrations of reactive species themselves are found to lead to lower nebulization rates due to the increased electrical conductivity of the solution. To circumvent this problem, it is shown that coating the SAW substrate with a thin insulating layer of silicon dioxide (SiO2) can significantly mitigate the nebulization rate reduction. Specifically, when the electrical conductivity increases from 0.25 to 4.0 mS cm−1, the 62% drop in the nebulization rate is observed with the uncoated SAW devices is substantially reduced to 19% simply with the SiO2 coating. This can be attributed to the synergistic effects of increased wettability and the suppression of the electrical body force acting on the liquid film. The concomitant increase in the bacterial colony reduction from 17% to 76% demonstrates this solution to be a facile yet effective way of enhancing the efficiency for spray‐based bacterial inactivation on contaminated surfaces.

Simultaneously realizing reversal of piezoelectric coefficient and enhancement of piezoresponse by chromium-doping in aluminum nitride films

Polarity inversion is an interesting phenomenon in non-centrosymmetric wurtzite-structured aluminum nitride (AlN), which offers an important platform to establish acoustic devices with heteropolar junctions. However, previous studies showed that switching polarity generally resulted in only reversing the piezoelectric coefficient (d33) in AlN films. Here, we discovered that appropriate Cr-doping would not only allow to reverse d33 but also improve piezoelectric response in the c-axis oriented AlN films by co-sputtering dual targets of Cr and Al. Specifically, the d33 was reversed from +2.6 pC/N for the undoped AlN to −2.6 pC/N for the 6.2 at. % Cr-doped CrxAl(1−x)N films. As the Cr-doping ratio increased to 9.3 at. %, d33 was −7.0 pC/N, which was 1.7 times higher than that of the undoped AlN films. Independent PFM phase image measurement offered further evidence of the polarity inversion by comparing the undoped and 9.3 at. % Cr-doped CrxAl(1−x)N films. This work offers a simple doping strategy that allows for simultaneous reversal of piezoelectric coefficient and enhancement of piezoresponse. As a result, it establishes a promising foundation for the design and development of acoustic wave devices featuring heteropolar junctions.

A Complete LTspice Simulation Model for SAW Devices

A complete circuit model of Surface Acoustic Wave (SAW) devices with straight interdigital transducers is presented. This equivalent circuit can be implemented in LTspice and contains variable design characteristics that can be easily changed to see their effect on the electrical response of the final SAW device design. Later a two port Surface Acoustic Wave device with 13-finger-IDT electrodes is fabricated and its electrical characterization is examined using a vector network analyzer. The test results are then compared with the equivalent circuits’ simulation output results for the verification. The results show an acceptable agreement between the experimental and simulation results for a wide frequency range. This paper offers an easy method to create an equivalent LTSpice model to determine the electrical response of a SAW device before fabrication. The model can also be used to simulate the behaviour of the circuits containing SAW devices using LTSPICE tool.

On propagation behavior of shear wave in piezoelectric-sandwiched structure

This paper delves into the analysis of shear wave propagation with a sandwiched structure comprising a piezoelectric layer and an elastic layer, with a transversely isotropic layer in between. The frequency equation has been derived following Biot’s theory. The dimensionless phase velocities numerical values are computed and visually depicted to demonstrate their dependencies on anisotropy, piezoelectricity, initial stress and porosity in a comparative manner. The explicit demonstration of the relationship between each parameter and the geometry has been presented. The observation shows that as porosity in the medium increases, the phase velocity also increases. Furthermore, the existence of medium anisotropy results in a decrease in the phase velocity of shear waves. Moreover, a correlation is observed where higher tensile initial stress within the medium leads to a corresponding reduction in the phase velocity of shear waves. We conclude that considered parameters (viz. piezoelectricity, anisotropy, porosity, initial stress and thickness of layers) affect the velocity profile of the shear waves significantly. This study holds practical significance in the development of innovative-layered composites, surface acoustic wave (SAW) devices and sensors utilizing intelligent piezoelectric devices for engineering purposes.

Ferroelectric Hysteresis Measurement in the Lithium Niobate‐Lithium Tantalate Single‐Crystalline Family: Prospects for Lithium Niobate‐Tantalate

Poling and structuring of ferroelectric domains form the basis for developing prospective applications using materials from the lithium‐niobate (LN) family. Applications range from second harmonic generation to electro‐optic modulators or surface acoustic wave devices. In the work presented here, hysteresis measurements are used as a standard method to quantitatively determine the poling properties of these ferroelectrics, including their spontaneous polarization Ps as well as their forward and reverse coercive fields Ec,+ and Ec,−. Systematic measurements that depend on parameters such as the ramp rate R of the applied poling voltage and the waiting time twait between domain inversions are investigated and compared between the congruent variants of LN, lithium tantalate (LT), their magnesium‐doped analogues, and stoichiometric LN. For bulk magnesium‐doped LN, for example, it is found that the resulting coercive field strongly depends on the speed of the voltage ramp, with values ranging from 11 to 21 kV mm−1. These investigations are used as fundamental input for poling ferroelectric lithium niobate‐tantalate solids (LNT), a system that offers a high potential for tuning the material parameters beyond what is possible for LN or LT.