Showing papers on "Acoustic wave published in 2022"

Surface Acoustic Wave (SAW) Sensors: Physics, Materials, and Applications

Abstract: Surface acoustic waves (SAWs) are the guided waves that propagate along the top surface of a material with wave vectors orthogonal to the normal direction to the surface. Based on these waves, SAW sensors are conceptualized by employing piezoelectric crystals where the guided elastodynamic waves are generated through an electromechanical coupling. Electromechanical coupling in both active and passive modes is achieved by integrating interdigitated electrode transducers (IDT) with the piezoelectric crystals. Innovative meta-designs of the periodic IDTs define the functionality and application of SAW sensors. This review article presents the physics of guided surface acoustic waves and the piezoelectric materials used for designing SAW sensors. Then, how the piezoelectric materials and cuts could alter the functionality of the sensors is explained. The article summarizes a few key configurations of the electrodes and respective guidelines for generating different guided wave patterns such that new applications can be foreseen. Finally, the article explores the applications of SAW sensors and their progress in the fields of biomedical, microfluidics, chemical, and mechano-biological applications along with their crucial roles and potential plans for improvements in the long-term future in the field of science and technology.

Extended topological valley-locked surface acoustic waves

Abstract: Stable and efficient guided waves are essential for information transmission and processing. Recently, topological valley-contrasting materials in condensed matter systems have been revealed as promising infrastructures for guiding classical waves, for they can provide broadband, non-dispersive and reflection-free electromagnetic/mechanical wave transport with a high degree of freedom. In this work, by designing and manufacturing miniaturized phononic crystals on a semi-infinite substrate, we experimentally realized a valley-locked edge transport for surface acoustic waves (SAWs). Critically, original one-dimensional edge transports could be extended to quasi-two-dimensional ones by doping SAW Dirac "semimetal" layers at the boundaries. We demonstrate that SAWs in the extended topological valley-locked edges are robust against bending and wavelength-scaled defects. Also, this mechanism is configurable and robust depending on the doping, offering various on-chip acoustic manipulation, e.g., SAW routing, focusing, splitting, and converging, all flexible and high-flow. This work may promote future hybrid phononic circuits for acoustic information processing, sensing, and manipulation.

Extended topological valley-locked surface acoustic waves

Abstract: Stable and efficient guided waves are essential for information transmission and processing. Recently, topological valley-contrasting materials in condensed matter systems have been revealed as promising infrastructures for guiding classical waves, for they can provide broadband, non-dispersive and reflection-free electromagnetic/mechanical wave transport with a high degree of freedom. In this work, by designing and manufacturing miniaturized phononic crystals on a semi-infinite substrate, we experimentally realized a valley-locked edge transport for surface acoustic waves (SAWs). Critically, original one-dimensional edge transports could be extended to quasi-two-dimensional ones by doping SAW Dirac "semimetal" layers at the boundaries. We demonstrate that SAWs in the extended topological valley-locked edges are robust against bending and wavelength-scaled defects. Also, this mechanism is configurable and robust depending on the doping, offering various on-chip acoustic manipulation, e.g., SAW routing, focusing, splitting, and converging, all flexible and high-flow. This work may promote future hybrid phononic circuits for acoustic information processing, sensing, and manipulation.

Acoustic focusing and imaging via phononic crystal and acoustic metamaterials

Abstract: The effective operation of certain electronic, medical, industrial, and testing equipment relies on high-quality focusing and imaging capability, which also plays a vital role in the field of wave physics. Therefore, continuously improving the resolution capacity is essential. However, in a homogeneous medium dominated by the diffraction limit, the best resolution for wave focusing and imaging could only reach half the wavelength corresponding to the lowest operating frequency, significantly hindering the relevant application value. The development of phononic crystals (PCs) and acoustic metamaterials (AMMs) has realized sub-wavelength focusing and super-resolution imaging and attracted increasing research attention in physics, mechanics, engineering, and biomedical science. This Tutorial explained the basic principles and traditional methods of acoustic focusing and imaging. Then, the implementation principles and related research progress of sub-wavelength focusing and super-resolution imaging based on artificial acoustic devices, including but not limited to PCs and AMMs, were systematically discussed. Moreover, a method was introduced to realize sub-wavelength or sub-diffraction focusing by integrating these artificial devices into the time-reversal procedure. Finally, the potential development trends and practical application prospects were presented.

Electrical control of surface acoustic waves

Abstract: Acoustic waves at microwave frequencies are widely used in wireless communication and are potential information carriers in quantum applications. However, most acoustic devices are passive components, and the development of phononic integrated circuits is limited by the inability to control acoustic waves in a low-loss, scalable manner. Here we report the electrical control of gigahertz travelling acoustic waves at room temperature and millikelvin temperatures. We achieve phase modulation by tuning the elasticity of a lithium niobate acoustic waveguide via the electro-acoustic effect. This phase modulator is then used to build an acoustic frequency shifter based on serrodyne phase modulation, and phase modulators in a Mach–Zehnder interferometer configuration are used to create an electro-acoustic amplitude modulator. By tailoring the phase matching between acoustic and quasi-travelling electric fields, we achieve reconfigurable non-reciprocal modulation with a non-reciprocity of over 40 dB. To illustrate the potential of the approach in quantum applications, we show that our electro-acoustic modulator can provide coherent modulation of single-phonon-level acoustic waves at 50 mK. The electro-acoustic effect can be used to electrically control the phase velocity of travelling acoustic waves in a lithium niobate waveguide, and to construct devices that can modulate the phase, frequency and amplitude of acoustic waves, even at the limit of single phonons.

Acoustofluidic black holes for multifunctional in-droplet particle manipulation.

Abstract: Acoustic black holes offer superior capabilities for slowing down and trapping acoustic waves for various applications such as metastructures, energy harvesting, and vibration and noise control. However, no studies have considered the linear and nonlinear effects of acoustic black holes on micro/nanoparticles in fluids. This study presents acoustofluidic black holes (AFBHs) that leverage controlled interactions between AFBH-trapped acoustic wave energy and particles in droplets to enable versatile particle manipulation functionalities, such as translation, concentration, and patterning of particles. We investigated the AFBH-enabled wave energy trapping and wavelength shrinking effects, as well as the trapped wave energy-induced acoustic radiation forces on particles and acoustic streaming in droplets. This study not only fills the gap between the emerging fields of acoustofluidics and acoustic black holes but also leads to a class of AFBH-based in-droplet particle manipulation toolsets with great potential for many applications, such as biosensing, point-of-care testing, and drug screening.

On the acoustically induced fluid flow in particle separation systems employing standing surface acoustic waves - Part I.

Abstract: By integrating surface acoustic waves (SAW) into microfluidic devices, microparticle systems can be fractionated precisely in flexible and easily scalable Lab-on-a-Chip platforms. The widely adopted driving mechanism behind this principle is the acoustic radiation force, which depends on the size and acoustic properties of the suspended particles. Superimposed fluid motion caused by the acoustic streaming effect can further manipulate particle trajectories and might have a negative influence on the fractionation result. A characterization of the crucial parameters that affect the pattern and scaling of the acoustically induced flow is thus essential for the design of acoustofluidic separation systems. For the first time, the fluid flow induced by pseudo-standing acoustic wave fields with a wavelength much smaller than the width of the confined microchannel is experimentally revealed in detail, using quantitative three-dimensional measurements of all three velocity components (3D3C). In Part I of this study, we focus on the fluid flow close to the center of the surface acoustic wave field, while in Part II the outer regions with strong acoustic gradients are investigated. By systematic variations of the SAW-wavelength λSAW and channel height H, a transition from vortex pairs extending over the entire channel width W to periodic flows resembling the pseudo-standing wave field is revealed. An adaptation of the electrical power, however, only affects the velocity scaling. Based on the experimental data, a validated numerical model was developed in which critical material parameters and boundary conditions were systematically adjusted. Considering a Navier slip length at the substrate-fluid interface, the simulations provide a strong agreement with the measured velocity data over a large frequency range and enable an energetic consideration of the first and second-order fields. Based on the results of this study, critical parameters were identified for the particle size as well as for channel height and width. Progress for the research on SAW-based separation systems is obtained not only by these findings but also by providing all experimental velocity data to allow for further developments on other sites.

Perspectives on spintronics with surface acoustic waves

Abstract: Surface acoustic waves (SAWs) are elastic waves propagating on the surface of solids with the amplitude decaying into the solid. The well-established fabrication of compact SAW devices, together with well-defined resonance frequencies, places SAWs as an attractive route to manipulate the magnetization states in spintronics, all of which is made possible by the magnetostriction and magnetoelastic effects. Here, we review the basic characteristics of SAW devices and their interaction out-of-resonance and in-resonance with the magnetization in thin films. We describe our own recent results in this research field and closely related works and provide our perspectives moving forward.

Data-driven and physical property-based hydro-acoustic mode decomposition

Abstract: A data-driven and physical property-based hydrodynamic and acoustic mode decomposition method combining dynamic mode decomposition and Helmholtz decomposition is proposed. It allows decomposition and fast prediction of hydrodynamic and acoustic components of the flow field. The method is tested by a two-dimensional subsonic open cavity flow and a supersonic cold jet, and the hydrodynamic and acoustic features are revealed. For the cavity flow, it is found that the acoustic velocity inside the cavity is composed of several pairs of standing waves. The propagating trajectory of the acoustic waves in the cavity is well captured. The dynamic relation between the hydrodynamic and acoustic motion is investigated. For the supersonic jet, the method successfully identifies the screech in the far field and the “trapped wave” within the potential core.

Enhanced acoustofluidic mixing in a semicircular microchannel using plate mode coupling in a surface acoustic wave device

Abstract: In this study, we present enhanced acoustic mixing inside a semicircular microfluidic channel via acoustic streaming induced by acoustic plate modes (APMs) of a 500-μm-thick double-side polished lithium-niobate (LiNbO3) substrate. We demonstrated that the APMs supported by the LiNbO3 substrate can be excited by an interdigitated transducer (IDT) at higher frequencies, in addition to conventional surface acoustic waves (SAWs), and can generate stronger acoustic streaming flow (ASF) and stirring effects. Consequently, rapid and enhanced mixing processes were observed in the channel. We conducted full-wave modeling of the device with finite element (FE) simulation to elucidate the acoustic process and mixing behaviors of the APM-based approach. Subsequently, we fabricated the acoustofluidic device using a standard photolithographic process and a 3D-printed replica molding method. The measured excitation spectrum of SAW and APM agrees with the numerical prediction; additionally, experiments on mixing and 2 µm particle motion in the continuous channel flow validate the ability of the device to enhance micromixing using APM frequencies compared with that using SAWs in our device. Our approach enables distinctive APMs to be fully coupled to the SAW-based acoustofluidic platform, which potentially enables an integrated design for the use of SAW and APM frequencies, acoustic energy, and wave fields in a single system. Our results also suggest innovative applications of the conventional SAW acoustofluidic devices to extended frequency regimes via APMs without reducing the substrate thickness and IDT pitch.

Investigation and Analysis of Acoustojets by Spectral Element Method

Abstract: In this study, acoustic wave scattering in a homogeneous media by an obstacle is examined in the case of plane wave excitation and the formation of acoustic jets is explored. Spectral element method (SEM) is employed for the approximate solution of scattered acoustic waves’ calculations. An important finding of the study is the concurrence of whispering gallery modes and acoustic jet in the case of proper adjustment of structural parameters, which has not been reported before in the literature. Furthermore, numerical findings based on SEM calculations show that the main characteristics of acoustic jet can be explored and controlled by changing the targeted parameters. Microscopy and imaging applications utilizing acoustic wave can benefit from the conducted study presented in this manuscript.

Couplants in Acoustic Biosensing Systems

Abstract: Acoustic biosensors are widely used in physical, chemical, and biosensing applications. One of the major concerns in acoustic biosensing is the delicacy of the medium through which acoustic waves propagate and reach acoustic sensors. Even a small airgap diminishes acoustic signal strengths due to high acoustic impedance mismatch. Therefore, the presence of a coupling medium to create a pathway for an efficient propagation of acoustic waves is essential. Here, we have reviewed the chemical, physical, and acoustic characteristics of various coupling material (liquid, gel-based, semi-dry, and dry) and present a guide to determine a suitable application-specific coupling medium.

Acoustic Purcell Effect Induced by Quasibound State in the Continuum

Abstract: We study theoretically and experimentally the acoustic Purcell effect induced by quasi-bound states in the continuum (quasiBICs). A theoretical framework describing the acoustic Purcell effect of a resonant system is developed based on the system’s radiative and dissipative factors, which reveals the critical emission condition for achieving optimum Purcell factors. We show that the quasiBICs contribute to highly confined acoustic field and bring about greatly enhanced acoustic emission, leading to strong Purcell effect. Our concept is demonstrated via two coupled resonators supporting a Friedrich–Wintgen quasiBIC, and the theoretical results are validated by the experiments observing emission enhancement of the sound source by nearly two orders of magnitude. Our work bridges the gap between the acoustic Purcell effect and acoustic BICs essential for enhanced wave-matter interaction and acoustic emission, which may contribute to the research of high-intensity sound sources, high-quality-factor acoustic devices and nonlinear acoustics.

Microfluidic acoustic sawtooth metasurfaces for patterning and separation using traveling surface acoustic waves

Abstract: We demonstrate a sawtooth-based metasurface approach for flexibly orienting acoustic fields in a microfluidic device driven by surface acoustic waves (SAW), where sub-wavelength channel features can be used to arbitrarily steer acoustic fringes in a microchannel. Compared to other acoustofluidic methods, only a single travelling wave is used, the fluidic pressure field is decoupled from the fluid domain's shape, and steerable pressure fields are a function of a simply constructed polydimethylsiloxane (PDMS) metasurface shape. Our results are relevant to microfluidic applications including the patterning, concentration, focusing, and separation of microparticles and cells.

High-temperature EMAT with double-coil configuration generates shear and longitudinal wave modes in paramagnetic steel

Abstract: The non-contact nature of electromagnetic acoustic transducers (EMATs) allows a continuous operation at high temperatures without physical coupling. The existing high-temperature EMATs are mainly shear-wave EMATs, and there are few reports on shear-longitudinal wave or longitudinal-wave EMATs due to the low intensity of the horizontal magnetic field. However, a desirable EMAT design characteristic is the possibility of selecting to generate different acoustic wave modes for various engineering applications. In this paper, a high-temperature EMAT with a double-coil configuration on waveform generation in paramagnetic steel was studied. By adjusting the configuration relationship between the electromagnetic coil and the EMAT eddy-current coil, the selective generation of shear-wave, longitudinal-wave, and shear-longitudinal wave modes was realized. According to quantitative analysis of shear and longitudinal waves generated by the double-coil EMAT, the amplitude ratio of shear and longitudinal waves was about 1 when the diameter of the EMAT eddy-current coil was equal to the inner diameter of the electromagnetic coil. Furthermore, shear-wave mode and shear-longitudinal wave mode high-temperature EMATs were designed and fabricated. The EMAT was placed in a high-temperature environment to continuously measure the paramagnetic steel SUS304. The amplitudes of the shear wave and longitudinal wave at 500 °C decreased by 10.2 times and 3.8 times, respectively, compared with that at 25 °C. The designed EMAT can selectively generate and receive different bulk acoustic wave modes at high temperatures.

Microscopic analysis of sound attenuation in low-temperature amorphous solids reveals quantitative importance of non-affine effects

Abstract: Sound attenuation in low-temperature amorphous solids originates from their disordered structure. However, its detailed mechanism is still being debated. Here, we analyze sound attenuation starting directly from the microscopic equations of motion. We derive an exact expression for the zero-temperature sound damping coefficient. We verify that the sound damping coefficients calculated from our expression agree very well with results from independent simulations of sound attenuation. Small wavevector analysis of our expression shows that sound attenuation is primarily determined by the non-affine displacements' contribution to the sound wave propagation coefficient coming from the frequency shell of the sound wave. Our expression involves only quantities that pertain to solids' static configurations. It can be used to evaluate the low-temperature sound damping coefficients without directly simulating sound attenuation.

Three-dimensional heating and patterning dynamics of particles in microscale acoustic tweezers.

Abstract: Acoustic tweezers facilitate a noninvasive, contactless, and label-free method for the precise manipulation of micro objects, including biological cells. Although cells are exposed to mechanical and thermal stress, acoustic tweezers are usually considered as biocompatible. Here, we present a holistic experimental approach to reveal the correlation between acoustic fields, acoustophoretic motion and heating effects of particles induced by an acoustic tweezer setup. The system is based on surface acoustic waves and was characterized by applying laser Doppler vibrometry, astigmatism particle tracking velocimetry and luminescence lifetime imaging. In situ measurements with high spatial and temporal resolution reveal a three-dimensional particle patterning coinciding with the experimentally assisted numerical result of the acoustic radiation force distribution. In addition, a considerable and rapid heating up to 55 °C depending on specific parameters was observed. Although these temperatures may be harmful to living cells, counter-measures can be found as the time scales of patterning and heating are shown to be different.

Determining Amplitudes of Standing Surface Acoustic Waves via Atomic Force Microscopy

Abstract: Atomic force microscopy is a tool for characterizing surface acoustic waves, in particular for high frequencies, where the wavelength is too short to be resolved by laser interferometry. A caveat is, that the cantilever deflection is not equal to the amplitude of the surface acoustic wave. We show that the energy transfer from the moving surface to the cantilever instead leads to a deflection exceeding the surface modulation. We present a method for an accurate determination of surface acoustic wave amplitudes based on comparing force-curve measurements with the equation of motion of a driven cantilever. We demonstrate our method for a standing surface acoustic wave on a $\mathrm{Ga}\mathrm{As}$ crystal confined in a focusing cavity with a resonance frequency near 3 GHz.

Multifunctional acoustic holography based on compact acoustic geometric-phase meta-array

Abstract: Optical geometric-phase metasurfaces provide a robust and efficient means for light wave control by simply manipulating the spatial orientations of the in-plane anisotropic meta-atoms, where polarization conversion plays a vital role. However, the concept of acoustic geometric-phase modulation for acoustic field control remains unexplored because airborne acoustic waves lack a similar optical polarization conversion process. In this work, a new type of acoustic meta-atom with deep-subwavelength feature size is theoretically investigated and further applied to acoustic field engineering based on the emerged concept of acoustic geometric phase. Herein, tunable acoustic geometric-phase modulation of designated order is obtained via the near-field coupled orbital angular momentum transfer process, and the topological charge-multiplexed acoustic geometric phase endows our meta-arrays with multiple functionalities. Our work extends the capacity of the acoustic geometric-phase meta-arrays in high-quality acoustic field reconstruction and offers new possibilities in multifunctional acoustic meta-holograms.

Fully resonant magneto-elastic spin-wave excitation by surface acoustic waves under conservation of energy and linear momentum

Abstract: We report on the resonant excitation of spin waves in micro-structured magnetic thin films by surface acoustic waves (SAWs). The spin waves as well as the acoustic waves are studied by micro-focused Brillouin light scattering spectroscopy. Besides the excitation of the ferromagnetic resonance, a process which does not fulfill momentum conservation, also the excitation of finite-wavelength spin waves can be observed at low magnetic fields. Using micromagnetic simulations, we verify that during this excitation both energy and linear momentum are conserved and fully transferred from the SAW to the spin wave.

Modeling and analysis of a dual-acoustic-driver thermoacoustic heat pump

Abstract: Thermoacoustic heat pumps (TAHPs) can be used for heating and/or cooling purposes. Current designs of travelling-wave TAHPs normally employ a single acoustic driver and rely on a looped pipe to establish and maintain the required acoustic field. The resultant system is thereby bulky and expensive, detracting from the structure simplicity and low-cost advantages of thermoacoustic technology. To address this issue, this paper investigates the dual-acoustic-driver concept that can significantly increase the system’s compactness. Theoretical analyses are conducted for the dual-acoustic-driver TAHP, and the acoustic and temperature fields in the thermoacoustic core are examined. Parametric studies are undertaken to investigate the effects of acoustic drivers on the acoustic and thermal characteristics of the TAHP. It is found that, as the frequency of acoustic drivers changes, the acoustic field in the thermoacoustic (TA) core could be dominated by a standing, traveling, or hybrid standing-traveling wave. The temperature distribution within the TA core and temperature difference between the core ends will change accordingly. Results show that the temperature difference is non-zero only when the acoustic field contains a traveling-wave component. To obtain a large temperature difference, the acoustic drivers should be driven near resonance frequencies at which the acoustic field is hybrid and the pressure amplitude is large. This study gains new insights into the working mechanisms behind the dual-acoustic-driver TAHP concept, paving the way for developing compact, efficient, and high-power-density TAHPs for industrial waste heat recovery.

Investigation of effective parameters on streaming-induced acoustophoretic particle manipulation in a microchannel via three-dimensional numerical simulation

Abstract: Particle manipulation using ultrasonic standing waves has gained increased attention in recent years as it is efficient and noninvasive. In order to predict the effects of acoustic streaming on the concentration of particles in the actual microchannel geometry, this paper presents a 3D numerical study on the transient motion of microparticles suspended in a liquid-filled microchannel, considering the mixed standing and traveling waves. The motion was generated by the acoustic radiation force and acoustic streaming-induced drag force arising from an imposed bulk acoustic wave and the hydrodynamic drag. The acoustic streaming patterns in the 3D microchannel were investigated using the limiting velocity method. In addition, the effects of the 3D streaming pattern in an acoustofluidic device on the acoustophoretic motion of microparticles were evaluated. The concentration of polystyrene particles was simulated for many particles with diameters of 0.5, 2, and 5 μm released from random initial locations. The obtained results indicate a balance between the flow rate and the particle diameter to achieve the highest concentration percentage. Increasing the height increased the concentration of large 5-μm-diameter particles to more than 80%. By doubling the length of the piezoelectrically actuated region, the concentration of 2-μm particles improved by approximately 20%. Finally, increasing the viscosity of the fluid by using a 50% glycerol-in-water mixture resulted in a greater effect of acoustic streaming. This study can provide helpful guidance for optimizing the design of acoustofluidic devices to enhance experiments.