Surface Acoustic Wave Applications Research Articles

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.

Density functional theory insights of phonons modes behaviours in AlScN for surface acoustic wave applications

In this work, we investigate the phonons modes behaviors of scandium-doped aluminum nitride (Sc-AlN) using first-principles density functional theory (DFT). We analyze the phononic dispersion, phonon density of states, group velocity, and Raman spectra of ScAlN for various scandium concentrations and compare them with undoped AlN. Our results show that Sc doping is significantly affect the phononic properties of AlN, including the formation of defect states within the phononic band gap and changes in the group velocities of phonon modes. Our analysis reveals that the introduction of Sc dopants causes a notable narrowing of the phononic band gap in AlN. Additionally, we observe a zero group velocity in the band gap, indicating the suppression of phononic transmission through the material. Moreover, Sc doping also affects the Raman spectrum of AlN, by inducing new vibrational modes. The known E2(high) peak in the Raman spectrum of AlN shifts to lower frequencies upon Sc doping, and new peaks appear due to the interactions of scandium and the AlN lattice. Our findings highlight the importance of understanding the effects of dopants on the phononic properties of AlScN and have implications for the design and optimization of AlScN-based devices for acoustic wave applications

Application of Shear Horizontal Surface Acoustic Wave (SH-SAW) Immunosensor in Point-of-Care Diagnosis.

Point-of-care testing (POCT), also known as on-site or near-patient testing, has been exploding in the last 20 years. A favorable POCT device requires minimal sample handling (e.g., finger-prick samples, but plasma for analysis), minimal sample volume (e.g., one drop of blood), and very fast results. Shear horizontal surface acoustic wave (SH-SAW) biosensors have attracted a lot of attention as one of the effective solutions to complete whole blood measurements in less than 3 min, while providing a low-cost and small-sized device. This review provides an overview of the SH-SAW biosensor system that has been successfully commercialized for medical use. Three unique features of the system are a disposable test cartridge with an SH-SAW sensor chip, a mass-produced bio-coating, and a palm-sized reader. This paper first discusses the characteristics and performance of the SH-SAW sensor system. Subsequently, the method of cross-linking biomaterials and the analysis of SH-SAW real-time signals are investigated, and the detection range and detection limit are presented.

Acoustofluidics: A Versatile Tool for Micro/Nano Separation at the Cellular, Subcellular, and Biomolecular Levels

AbstractSeparation of micro/nanoparticles, such as cellular, subcellular and biomolecular, has attracted increasing attention because of their remarkable potential applications in various fields, including chemistry, physics, medicine, etc. Among different micro/nanoparticle separation methods, acoustofluidics, which combines acoustics and microfluidics, has drawn the interest of researchers due to its biocompatibility, high efficiency and free labeling. In this review, the basic constitutions, mechanisms, and materials of acoustofluidics are described. Subsequently, sorts of delicately designed acoustofluidic devices, including diverse bulk acoustic wave (BAW) microfluidics and surface acoustic wave (SAW) microfluidics, are discussed, covering principles, advantages, limitations and applications in separation. Besides the introduction of advances of micro/nanoparticle separation in the BAW microfluidics, the SAW microfluidics are elaborated in detail with a focus on various configurations of interdigital transducers (IDTs), comprising straight IDT, slanted‐finger IDT, chirped IDT and focused IDT. Microfluidic systems of the acoustofluidics involve the forms of straight channels, serpentine channels, and droplets. Additionally, besides simply structured acoustofluidics, acoustofluidics integrated with other structures are also mentioned. Finally, the prospects and limitations of acoustofluidics in micro/nanoparticle separation are also discussed. The acoustofluidics reviewed here is envisioned as a versatile tool for micro/nanoparticle separation at the cellular, sub‐cellular, and biomolecular levels.

Integrated transparent surface acoustic wave technology for active de-fogging and icing protection on glass

There have been great concerns on poor visibility and hazardous issues due to fogging and ice/frost formation on glass surfaces of windshields, windows of vehicles/airplanes, and solar panels. Existing methods for their monitoring and removal include those active ones (such as using resistance heating) or passive ones (such as using surface icephobic treatments), which are not always applicable, effective or reliable. In this study, we proposed a novel strategy by implementing transparent thin film surface acoustic wave (SAW) devices by directly coating ZnO films onto glass substrate and studied their de-fogging, active anti-icing and de-icing mechanisms using the SAW technology. Effects of powers and wavelengths of SAW devices were investigated and influences of acousto-heating and surface hydrophobic treatments were evaluated. Results showed that de-fogging time was dramatically decreased with the increase of SAW powers when the thin film-based SAW devices were exposed to humid air flow for different durations. The icing accretion was significantly delayed under the applied SAW agitation, and SAW application has also effectively promoted de-icing on glass substrate, due to the interfacial nanoscale vibration and localized heating effect.

Manipulation of flying and single excitons by GHz surface acoustic waves

An important prerequisite for quantum communication networks is the transfer and manipulation of single particles on a chip as well as their interconversion to single photons for long-range information exchange. GHz acoustic waves are versatile tools for the implementation of these functionalities in hybrid quantum systems. In particular, flying excitons propelled by GHz surface acoustic waves (SAWs) can potentially satisfy this prerequisite. In this article, we review recent works on the application of GHz SAWs to realize flying excitons in semiconductor-based systems. Most importantly, we have identified suitable two-level centers for the storage of single excitons, thus forming single excitonic qubits, and interconverted them to single photons with a very high emission rate dictated by the GHz-SAW pumping. The work covered here paves the way for on-chip, exciton-based qubit manipulation.

Biological Effects and Applications of Bulk and Surface Acoustic Waves on In Vitro Cultured Mammal Cells: New Insights.

Medical imaging has relied on ultrasound (US) as an exploratory method for decades. Nonetheless, in cell biology, the numerous US applications are mainly in the research and development phase. In this review, we report the main effects on human or mammal cells of US induced by bulk or surface acoustic waves (SAW). At low frequencies, bulk US can lead to cell death. Under specific intensities and exposure times, however, cell proliferation and migration can be enhanced through cytoskeleton fluidization (a reorganization of the actin filaments and microtubules). Cavitation phenomena, frequencies of resonance close to those of the biological compounds, and mechanical transfers of energy from the acoustic pressure could explain those biological outcomes. At higher frequencies, no cavitation is observed. However, USs of high frequency stimulate ionic channels and increase cell permeability and transfection potency. Surface acoustic waves are increasingly exploited in microfluidics, especially for precise cell manipulations and cell sorting. With applications in diagnosis, infection, cancer treatment, or wound healing, US has remarkable potential. More mechanotransduction studies would be beneficial to understand the distinct roles of temperature rise, acoustic streaming and mechanical and electrical stimuli in the field.

Current Development in Interdigital Transducer (IDT) Surface Acoustic Wave Devices for Live Cell In Vitro Studies: A Review.

Acoustics have a wide range of uses, from noise-cancelling to ultrasonic imaging. There has been a surge in interest in developing acoustic-based approaches for biological and biomedical applications in the last decade. This review focused on the application of surface acoustic waves (SAW) based on interdigital transducers (IDT) for live-cell investigations, such as cell manipulation, cell separation, cell seeding, cell migration, cell characteristics, and cell behaviours. The approach is also known as acoustofluidic, because the SAW device is coupled with a microfluidic system that contains live cells. This article provides an overview of several forms of IDT of SAW devices on recently used cells. Conclusively, a brief viewpoint and overview of the future application of SAW techniques in live-cell investigations were presented.

Surface acoustic wave controlled skyrmion-based synapse devices

Magnetic skyrmions, which are particle-like spin structures, are promising information carriers for neuromorphic computing devices due to their topological stability and nanoscale size. In this work, we propose controlling magnetic skyrmions by electric-field-excited surface acoustic waves in neuromorphic computing device structures. Our micromagnetic simulations show that the number of created skyrmions, which emulates the synaptic weight parameter, increases monotonically with increases in the amplitude of the surface acoustic waves. Additionally, the efficiency of skyrmion creation is investigated systemically with a wide range of magnetic parameters, and the optimal values are presented accordingly. Finally, the functionalities of short-term plasticity and long-term potentiation are demonstrated via skyrmion excitation by a sequence of surface acoustic waves with different intervals. The application of surface acoustic waves in skyrmionic neuromorphic computing devices paves a novel approach to low-power computing systems.

Revisiting the Electroacoustic Phenomenon in the Presence of Surface Acoustic Waves.

Recently, one has been observing abundant studies on the application of surface acoustic waves (SAWs) in solid substrates for manipulating liquids and particulates in micron-to-nanometer thick films and channels and in porous media. At these length scales, contributions of SAWs to the electrical double layer (EDL) of ions and of the latter to particulates and flow may become appreciable. However, the nature of the interplay between SAWs and EDLs is unknown. We demonstrate the contribution of a SAW to the near-equilibrium electrical and ion-concentration fields in an EDL near inert and piezoelectric substrates. In particular, we concentrate on the leakage of transient and steady components of electrical potential through the excited EDL. Far from the solid, the leakage may be interpreted by different models of the EDL to give information about the EDL characteristic relaxation time, ζ-potential, and the Stern layer therein. In addition, the analysis given here may explain observed SAW-induced electrochemical effects on piezoelectric substrates.

Application of surface acoustic wave to enhance the photocatalytic degradation efficiency of methylene blue

The TiO2 thin film was grown on a [Formula: see text] Y-axis cut, X-axis propagation lithium niobate substrate by radio frequency magnetron sputtering to fabricate a surface acoustic wave device. The sputtering ratios of argon to oxygen at 20% and post-annealing temperature at [Formula: see text]C for 3 h were controlled to improve the photocatalytic activity of TiO2 thin film. The effects of work frequency and input voltage of the surface acoustic wave device on the methylene blue photocatalytic degradation efficiency of the TiO2 thin film were investigated. The TiO2 thin film was vibrated at radio frequency by surface acoustic wave device to increase the scattering and reactive frequency for methylene blue in liquid. The surface acoustic wave device operated at 28.65 MHz work frequency and 0.95 V input voltage revealed the highest photocatalytic degradation efficiency of methylene blue. Compared to the TiO2 thin film combined with and without surface acoustic wave device, the surface acoustic wave device enhanced the TiO2 thin film photocatalytic degradation efficiency to 46%.

Cantilever damage evaluation using impedance-loaded SAW sensor with continuous wavelet analysis and machine learning

To monitor the health of large-scale structures, a wireless measurement system, such as a bridge, is required. One of the methods of monitoring the health of large-scale structures involves the application of an impedance-loaded wireless surface acoustic wave (SAW) sensor. Additionally, a pressure-sensor-loaded SAW sensor can detect the vibration of a cantilever. In this study, a continuous wavelet transform (CWT) is adopted to analyze the sensor responses. The CWT results obtained were classified into two categories based on the attenuation at each frequency, which include the exponential or linear type. Furthermore, machine learning was applied to evaluate cantilever damage. The results indicate that a high accuracy evaluation of damage is feasible with the proposed method.

Highly coupled leaky surface acoustic wave on hetero acoustic layer structures based on ScAlN thin films with a c-axis tilt angle

In this paper, we present hetero acoustic layer (HAL) structures based on ScAlN thin films with a c-axis tilt angle. The surface acoustic wave (SAW) excitation modes and their propagation characteristics for different Euler angles (0°, θ, ψ) of the ScAlN thin film are analyzed using the finite element method. We find that the acoustic field distribution of HAL structures can be adjusted by rotating their Euler angles and that normal SAWs are suppressed; however, leaky SAWs (LSAWs) with significantly improved electromechanical coupling coefficients (K 2) are excited. A maximum K 2 of 14% can be obtained for shear horizontal (SH)-type LSAWs, which is almost 7 times larger than that of the previously reported normal SAW Sezawa mode. Moreover, the optimized HAL structure consisting of (0°, 90°, 60°) ScAlN thin film/SiO2/AlN/Si simultaneously possesses a larger K 2, a wider bandwidth, and a higher Q value, which is promising for the design and application of wideband SAW devices with high performance.

Epitaxial Growth of Sc0.09Al0.91N and Sc0.18Al0.82N Thin Films on Sapphire Substrates by Magnetron Sputtering for Surface Acoustic Waves Applications.

Scandium aluminum nitride (ScxAl1−xN) films are currently intensively studied for surface acoustic waves (SAW) filters and sensors applications, because of the excellent trade-off they present between high SAW velocity, large piezoelectric properties and wide bandgap for the intermediate compositions with an Sc content between 10 and 20%. In this paper, the growth of Sc0.09Al0.91N and Sc0.18Al0.82N films on sapphire substrates by sputtering method is investigated. The plasma parameters were optimized, according to the film composition, in order to obtain highly-oriented films. X-ray diffraction rocking-curve measurements show a full width at half maximum below 1.5°. Moreover, high-resolution transmission electron microscopy investigations reveal the epitaxial nature of the growth. Electrical characterizations of the Sc0.09Al0.91N/sapphire-based SAW devices show three identified modes. Numerical investigations demonstrate that the intermediate compositions between 10 and 20% of scandium allow for the achievement of SAW devices with an electromechanical coupling coefficient up to 2%, provided the film is combined with electrodes constituted by a metal with a high density.

Polymeric liquid layer densified by surface acoustic wave.

Creating densified and stable liquid is a straightforward strategy for the fabrication of strong and ultra-stable amorphous or glassy materials. The current study has discovered that a liquid polymeric thin film is densified under the application of a high frequency surface acoustic wave (SAW). The experimental evidence is the decrease in film thickness and the increase in refractive index, measured by ellipsometry, of polyisobutylene thin films deposited on the solid substrates, when a high frequency SAW (39.5 MHz) is applied to the system. Further investigations by polarization-resolved single molecule fluorescence microscopy have demonstrated that the rotational motion of fluorescent probes doped inside the liquid film is retarded and the dynamical heterogeneity is reduced. The results demonstrate that the application of SAW of high frequency makes the thin polymeric liquid film densified and more dynamically homogeneous.

Removal of spoiling materials from solar panel surfaces by applying surface acoustic waves

Surface acoustic wave (SAW) technologies have been widely utilized for sensitive surface cleaning and particle steering applications in micro-electro-mechanical system (MEMS). This study investigates application of SAWs for cleaning of solar PV panel surfaces. Spoiling of photovoltaic (PV) solar panel surfaces is one of major problems that can reduce energy efficiency of PV solar energy systems in outdoor conditions. Rough mechanical cleaning methods can easily damage surface of panels and hence they can reduce efficient working life-span of panels. Therefore, sensitive and electronically controllable self-cleaning techniques are needed to keep PV panel surface cleaner. This study presents a theoretical analysis for detachment phenomenon of dust particles in interaction with SAWs. These analysis considers adhesion forces and effects of gravity in cleaning process and results reveal underlying mechanisms involving in particle detachment process. We derive sufficient conditions that are required for removal of a dust particle from inclined panel surfaces in case of SAW interactions. Experimental studies are conducted with spoiled PV solar panels, and cleaning effects of SAWs on solar panel surface are demonstrated.

Theoretical analysis of high electromechanical coupling surface acoustic wave propagating on lead-free Na0.5Bi0.5TiO3–BaTiO3 single crystal

The propagation properties of surface acoustic wave (SAW) on the Na0.5Bi0.5TiO3–BaTiO3 (NBBT) substrate with different crystal cuts were theoretically analyzed by Finite Element Method (FEM). The calculated results, for the NBBT with the optimized electrode type and thickness, indicate the existence of Rayleigh and Sezawa modes with high electromechanical coupling factor K2 ~18% and ~6.8% respectively, which are considerably higher than that of the conventional lithium niobate (LiNbO3) single crystal for SAW applications. The research provides a comprehensive understanding of the SAW propagation characteristics of lead-free NBBT, and explores the promising applications of NBBT in wideband SAW devices.

Influence of Waterproof Films on the Atomization Behavior of Surface Acoustic Waves.

One of the reasons why commercial application of surface acoustic wave (SAW) atomization is not possible is due to the condensation of aerosol droplets generated during atomization, which drip on the interdigitated transducer (IDT), thereby causing electrodes to short-circuit. In order to solve this problem, a SU-8-2002 film coating on an IDT is proposed in this paper. The waterproof performance of the film coating was tested on a surface acoustic wave (SAW) device several times. The experimental results reveal that the film coating was robust. The experiment also investigated the effects of the SU-8-2002 film on atomization behavior and heating.

Nanoacoustofluidics: Unprecedented fluid manipulation via controlled MHz-order vibration at the nanoscale

Manipulation of fluids and colloids at the nanoscale is made exceptionally difficult by the dominance of surface and viscous forces. The use of MHz-order vibration has dramatically expanded in microfluidics, enabling fluid manipulation, atomization, and microscale particle/cell separation. We find even more powerful results at the nanoscale, with the key discovery of a new mechanism of acoustic wave-fluid motion interaction. We show that MHz-order surface acoustic waves (SAW) can manipulate fluids and fluid droplets within fully transparent, high-aspect ratio 5–150 nm tall, 10–100 μm wide, 5 mm long nanoslits fabricated via a direct, room temperature bonding method for lithium niobate (LN). The application of SAW causes fluid draining and pumping, developing ∼1 MPa pressure through the nanoslit structure. The mechanism of specific draining pattern is well explained by a detailed theoretical model based on the nonlinear acoustic vibration phenomenon in nanoscale channels. We also show how individual fluid droplets of only 1–10 fl are propelled by incident SAW in the nanoslit structure, entrapping them at locally widened regions along the nanoslit due to the capillary pressure difference. Our results indicate MHz-order SAW as a powerful tool for fluid manipulation in nanoscale.

Surface-Acoustic-Wave Induced Ferromagnetic Resonance in Fe Thin Films and Magnetic Field Sensing

Resonant magnetoelastic coupling (MEC) is demonstrated in an Fe thin film epitaxially grown on a piezoelectric GaAs substrate with application of subgigahertz surface acoustic waves (SAWs). The frequency at which resonant MEC is achieved is reduced far below 1 GHz by the application of a small in-plane magnetic field. Moreover, the resonance, observable by attenuation and velocity changes of the SAW, can be switched on and off by a small (0.1 oC) angular rotation of this in-plane field. This angular sensitivity makes SAW-ferromagnet devices attractive for sensing applications, such as wireless, battery-free, and interrogable magnetic-field monitors. Using a simple magnetization dynamics model that takes into account the Fe magnetic anisotropy and the softening of the magnetic precession modes, we are able to describe the observed salient features.