Surface Acoustic Wave Amplitude Research Articles

Coherent surface acoustic wave–spin wave interactions detected by micro-focused Brillouin light scattering spectroscopy

We investigated the interaction of surface acoustic waves and spin waves with spatial resolution by micro-focused Brillouin light scattering spectroscopy in a Co40Fe40B20(10 nm) ferromagnetic layer on a LiNbO3-piezoelectric substrate. We experimentally demonstrate that the magnetoelastic excitation of magnons by phonons is coherent by studying the interference of light scattered off generated magnons and annihilated phonons. We find a pronounced spatial dependence of the phonon annihilation and magnon excitation, which we map as a function of the magnetic field. The coupling efficiency of the surface acoustic waves (SAWs) and the spin waves is characterized by a magnetic field-dependent decay of the SAWs amplitude.

A toroidal SAW gyroscope with focused IDTs for sensitivity enhancement

A surface acoustic wave (SAW) gyroscope measures the rate of rotational angular velocity by exploiting a phenomenon known as the SAW gyroscope effect. Such a gyroscope is a great candidate for application in harsh environments because of the simplification of the suspension vibration mechanism necessary for traditional microelectromechanical system (MEMS) gyroscopes. Here, for the first time, we propose a novel toroidal standing-wave-mode SAW gyroscope using focused interdigitated transducers (FIDTs). Unlike traditional SAW gyroscopes that use linear IDTs to generate surface acoustic waves, which cause beam deflection and result in energy dissipation, this study uses FIDTs to concentrate the SAW energy based on structural features, resulting in better focusing performance and increased SAW amplitude. The experimental results reveal that the sensitivity of the structure is 1.51 µV/(°/s), and the bias instability is 0.77°/s, which are improved by an order of magnitude compared to those of a traditional SAW gyroscope. Thus, the FIDT component can enhance the performance of the SAW gyroscope, demonstrating its superiority for angular velocity measurements. This work provides new insights into improving the sensitivity and performance of SAW gyroscopes.

Status of X-ray Acoustooptics at the Institute of Microelectronics Technology Russian Academy of Sciences

The electrical measurement method, scanning electron microscopy method and high-resolution X-ray diffraction method have been used to investigate the process of the surface acoustic wave (SAW) propagation in a LiNbO3 ferroelectric crystal. Measurement of the amplitude-frequency response provides information on the losses in the acoustoelectronic device during the process of the SAW propagation. The scanning electron microscopy method permits to visualize the SAW on the surface of piezoelectric crystals in the real-time mode and to observe diffraction phenomena in acoustic beam. The X-ray diffraction method is sensitive to the crystal lattice distortions by surface acoustic wave and allows determining the SAW amplitudes.

Resonant excitation of vortex gyrotropic mode via surface acoustic waves

Finding new energy-efficient methods for exciting magnetization dynamics is one of the key challenges in magnonics. In this work, we present an approach to excite the gyrotropic dynamics of magnetic vortices through the phenomenon of inverse magnetostriction, also known as the Villari effect. We develop an analytical model based on the Thiele formalism that describes the gyrotropic motion of the vortex core including the energy contributions due to inverse magnetostriction. Based on this model, we predict excitations of the vortex core resonances by surface acoustic waves whose frequency is resonant with the frequency of the vortex core. We verify the model's prediction using micromagnetic simulations and show the dependence of the vortex core's oscillation radius on the surface acoustic wave amplitude and the static bias field. Our study contributes to the advancement of energy-efficient magnetic excitations by relying on voltage-induced driven dynamics, which is an alternative to conventional current-induced excitations.

Numerical study of microdevice with surface acoustic waves for separation of gas mixtures

Recently, it was shown that traveling surface acoustic waves (SAWs) can affect gas flow in microchannels. The effect of SAWs was studied in free-molecular flow regime, and it was shown that SAWs can induce separation of gas mixtures. In the present work, this effect is studied for denser flow regimes, which are more interesting from a practical point of view. The problem is studied numerically using own modification of the direct simulation Monte Carlo method on the example of a neon–argon mixture. The main finding is that SAWs still enhance separation of gas mixtures outflowing into vacuum through a microchannel under all studied rates of gas rarefaction up to Kn≈0.1. Another important practical result is that effect is present for wave speeds typical for existing SAWs (≈1000 m/s) and in a wide range of SAW amplitude to channel height ratios. Influence of other practical aspects, such as channel length, masses of species, and available magnitudes of material surface speed, are also briefly discussed.

Acoustically Stimulated Charge Transport in Graphene Film.

The process of acoustically stimulated charge transport in the graphene film on the surface of the YZ-cut of a LiNbO3 crystal was investigated. It was found that the dependence of the current in the graphene film on the frequency of the surface acoustic wave (SAW) excitation repeats the amplitude-frequency response of the SAW delay time line. It is shown that increasing the SAW amplitude leads to an increase in the current in the graphene film, and the current in the graphene film depends linearly on the amplitude of the high-frequency input signal supplied to the interdigital transducer (IDT, in dB). It is demonstrated that at a positive bias potential on the graphene film, the SAW propagation allows to change the direction of the current in the graphene film by changing the amplitude of the SAW. It is also shown that in the frequency range of the amplitude-frequency response of the SAW delay time line, the current in the graphene film can vary from positive to negative values depending on the frequency. The capability to control the SAW excitation frequency or the SAW amplitude makes it possible to control the value and direction of the current in the graphene film. The SAW propagation lets to collect and transport the photo-stimulated charges in the graphene film on the crystal surface.

Dual-comb ranging yields reliable surface acoustic wave amplitude measurements

Quantitative evaluation of mechanical movement at the picometer level found to be precise and accurate.

Flying electron spin control gates

The control of "flying” (or moving) spin qubits is an important functionality for the manipulation and exchange of quantum information between remote locations on a chip. Typically, gates based on electric or magnetic fields provide the necessary perturbation for their control either globally or at well-defined locations. Here, we demonstrate the dynamic control of moving electron spins via contactless gates that move together with the spins. The concept is realized using electron spins trapped and transported by moving potential dots defined by a surface acoustic wave (SAW). The SAW strain at the electron trapping site, which is set by the SAW amplitude, acts as a contactless, tunable gate that controls the precession frequency of the flying spins via the spin-orbit interaction. We show that the degree of precession control in moving dots exceeds previously reported results for unconstrained transport by an order of magnitude and is well accounted for by a theoretical model for the strain contribution to the spin-orbit interaction. This flying spin gate permits the realization of an acoustically driven optical polarization modulator based on electron spin transport, a key element for on-chip spin information processing with a photonic interface.

Focused surface acoustic wave induced nano-oscillator based reservoir computing

We demonstrate using micromagnetic simulations that a nanomagnet array excited by surface acoustic waves (SAWs) can work as a reservoir. An input nanomagnet is excited with focused SAW and coupled to several nanomagnets, seven of which serve as output nanomagnets. To evaluate memory effect and computing capability, we study the short-term memory (STM) and parity check (PC) capacities, respectively. The SAW (4 GHz carrier frequency) amplitude is modulated to provide a sequence of sine and square waves of 100 MHz frequency. The responses of the selected output nanomagnets are processed by reading the envelope of their magnetization states, which is used to train the output weights using the regression method. For classification, a random sequence of 100 square and sine wave samples is used, of which 80% are used for training, and the rest are used for testing. We achieve 100% training and 100% testing accuracy. The average STM and PC are calculated to be ∼4.69 and ∼5.39 bits, respectively, which is indicative of the proposed acoustically driven nanomagnet oscillator array being well suited for physical reservoir computing applications. The energy dissipation is ∼2.5 times lower than a CMOS-based echo-state network. Furthermore, the reservoir is able to accurately predict Mackey-Glass time series up to several time steps ahead. Finally, the ability to use high frequency SAW makes the nanomagnet reservoir scalable to small dimensions, and the ability to modulate the envelope at a lower frequency (100 MHz) adds flexibility to encode different signals beyond the sine/square waves classification and Mackey-Glass predication tasks demonstrated here.

Numerical study on the behavior of vapor bubbles during boiling with surface acoustic wave (SAW)

In this study, the dynamic mechanism of vapor bubble during boiling process under the effect of acoustic field was numerically investigated, by coupling the phase field method and thermo-viscous acoustic module. The purpose is to use the surface acoustic wave (SAW) to interfere with vapor bubbles in the boiling process, so as to realize control of boiling on the temporal and spatial scales while improving the boiling heat transfer capability. It is observed that the effect of SAW on bubble behaviors is related to the amplitude of SAW and the initial bubble size. For pool boiling case, at the critical displacement amplitude, tiny vortices form at the root of bubble during the bubble growth stage. The velocity amplitude induced by SAW in the liquid phase around bubble can reach up to 2.1 m/s, which is nearly twofold comparing to that without SAW effect. The vortices at the root of bubble disrupt the thermal boundary layer to a certain extent by creating ‘micro-turbulence’, thereby reducing the thermal resistance. Furthermore, the strong SAW effect for the large amplitude case causes one bubble to collapse into two separate bubbles after the bubble detaches from the heating surface. For flow boiling case, the SAW can break the growing bubbles along the flow direction, and the collapsed bubbles flow downstream with a maximum speed of 5 m/s, which is almost 12.5 times of that without acoustic excitation. The acoustic streaming can interrupt the growth of the boundary layer in the single-phase region, so that the subcooled fluid can rewet the microchannel wall in time. Thus, the growth of bubbles and flow instability are effectively inhibited, and flow boiling heat transfer is promoted. It is revealed that the SAW is an effective approach for the active control and enhancement of boiling heat transfer.

Determining Amplitudes of Standing Surface Acoustic Waves via Atomic Force Microscopy

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.

Nondestructive measurement of the grain size of laser cladding coatings using a laser ultrasonic method.

Due to the processing characteristics of laser cladding, the beads and joints of the laser cladding coatings have different grain sizes. We used the laser ultrasonic (LU) method to measure the distribution of the grain sizes of laser cladding coatings nondestructively. The surface acoustic wave amplitude was influenced by the grain size; hence, the amplitude varied for beads and joints because of their different attenuations. The spatial resolution of LU is higher than that of the traditional ultrasonic testing method, leading to a fringe distribution of the C-scan results in the scanning area. The LU results were verified through metallographic experiments. It was concluded that the LU method can be used to determine the grain sizes of coatings.

Ultrasonic investigation of the evaporation dynamics of subnanoliter droplets

With the development of ink jet printers or spotters for biological applications, the control size and homogeneity of small fluids as well as their successful deposition on various substrates has gained significant importance. We study the impingement process of such small droplets onto a solid substrate and investigate their evaporation and drying process by means of surface acoustic wave (SAW) transmission experiments. We observe a strong fluid-SAW interaction resulting in an attenuation which toward the end of the evaporation and drying process exhibits characteristic oscillations being related to temperature, SAW amplitude, and fluid properties such as viscosity and wetting angle. It is found that oscillations can only be seen in pinned, very flat droplets, while the pinning can be roughly controlled via the SAW amplitude. The frequency of those characteristic oscillations is superlinear with respect to temperature, rather proportional to the evaporation rate and can change drastically depending on the liquid used. In our experiments, isopropanol, ethanol, and water with various glycerol concentrations were loaded onto the SAW delay line. Based on the experimental results, simulations using the finite element method were performed. We find that a standing wave pattern within the droplet is responsible for the transmission oscillations. These findings might lead to new methods, e.g., sensory systems, being able to examine droplets according to their physical or chemical properties.

Thermoelastic modeling of laser-induced generation of strong surface acoustic waves

Short pulse laser irradiation of a substrate can generate pulses of surface acoustic waves (SAWs) capable of propagating long distances along the surface of the irradiated substrate. In this work, we use thermoelastic modeling of the generation of SAWs on a Si substrate to explore the effect of irradiation parameters, i.e., pulse duration, laser spot size, absorption depth, and spatial profile of the laser energy deposition, on the strength of the SAWs. A particular goal of this study is to establish the optimum conditions for maximizing the strength of the surface waves generated in the nonablative, thermoelastic irradiation regime. The simulations demonstrate that the highest strain amplitude of the laser-generated SAWs can be achieved for a laser spot size comparable to the characteristic length of the SAW propagation during the laser pulse. The amplitude of SAWs increases with the increase in the characteristic laser energy deposition depth, and laser pulses with sharper spatial energy deposition profiles (flat-top laser beams) produce stronger SAWs. For the optimal set of irradiation parameters, the strain amplitude of a SAW generated in Si in the thermoelastic regime can reach the levels of 10−4–10−3, which are sufficiently high for causing nonlinear sharpening of the wave profile and the formation of a shock front during the wave propagation from the laser spot. The computational predictions suggest the feasibility of a continuous generation of strong nonlinear pulses of SAWs, which may be utilized for driving the surface processes in thin film deposition, growth of two-dimensional materials, heterogeneous catalysis, and other applications.

Nonlinear Coupling of Phononic Resonators Induced by Surface Acoustic Waves

The rising need for hybrid physical platforms has triggered a renewed interest in the development of agile radio-frequency phononic circuits with complex functionalities. The combination of traveling waves with resonant mechanical elements appears as an appealing means of harnessing elastic vibration. In this work, we demonstrate that this combination can be further enriched by the occurrence of traveling surface acoustic waves (SAWs), induced by elastic nonlinearities, interacting with a pair of otherwise linear micron-scale mechanical resonators. Reduction of the resonator-gap distance and an increase in the SAW amplitude results in a frequency softening of the resonator-pair response that lies outside the usual picture of geometrical Duffing nonlinearities. The dynamics of the SAW excitation scheme allows further control of the resonator motion, notably leading to circular-polarization states. These results may pave the way toward versatile high-frequency phononic microelectromechanical-systems--nanoelectromechanical-systems circuits fitting both classical and quantum technologies.

Engineering the beat phenomenon of quasi-Rayleigh waves for regions with minimal Surface Acoustic Wave (SAW) amplitude

Surface Acoustic Waves (SAW) are prevalent in a variety of scientific fields. Typically, the ability to manipulate these surface waves has a significant impact on the efficacy of any SAW-based device. In this paper, we present a simple method for designing localized regions that have minimal SAW amplitude. These localized regions have valley-like drops in SAW amplitude and are achieved by using the spatial beat phenomenon of quasi-Rayleigh waves. Controlling the beat phenomenon allows us to manipulate where and how these localized regions appear in the waveguide. In particular, the localized regions can be designed to have variable widths and can be positioned consecutively due to minimal wave scattering. The design methodology and physics are described in detail, and several supplementary simulations are provided to demonstrate the efficacy of the proposed method. Lastly, we briefly discuss how the proposed approach could potentially be exploited to implement a localized high-pass filter and enables SAW wave propagation that avoids surface obstacles.

X-ray diffraction by surface acoustic waves

The possibilities are presented of X-ray diffraction methods for studying the propagation of surface acoustic waves (SAWs) in solids, including diffraction under total external reflection conditions and Bragg diffraction, using acoustically modulated X-ray multilayer mirrors and crystals. SAW propagation was studied using both meridional and sagittal diffraction geometries where the SAW wavevectors and X-ray photons are collinear or perpendicular, respectively. SAW propagation in a crystal leads to sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curve. The intensities and angular positions of these diffraction satellites are determined by the SAW wavelength, amplitude and attenuation. Therefore, diffraction methods allow the analysis of the SAW propagation process and determination of SAW parameters. The influence of X-ray energy on diffraction by acoustically modulated crystals is studied for the first time. It is shown that changes in the X-ray energy can change the angular region where diffraction satellites exist under conditions of total external reflection. By contrast, in the Bragg diffraction region changes in the X-ray photon energy lead to changes in the X-ray penetration depth into the crystal and redistribution of the diffracted intensity among diffraction satellites, but do not change the angular divergence between diffraction satellites on the rocking curve. It is also shown that, in X-ray diffraction on acoustically modulated crystals on a number of successive reflections, a decrease in interplanar spacing leads to an increase in the number of diffraction satellites and a redistribution of diffracted radiation between them.

Vibration enhanced cell growth induced by surface acoustic waves as in vitro wound-healing model

We report on in vitro wound-healing and cell-growth studies under the influence of radio-frequency (rf) cell stimuli. These stimuli are supplied either by piezoactive surface acoustic waves (SAWs) or by microelectrode-generated electric fields, both at frequencies around 100 MHz. Employing live-cell imaging, we studied the time- and power-dependent healing of artificial wounds on a piezoelectric chip for different cell lines. If the cell stimulation is mediated by piezomechanical SAWs, we observe a pronounced, significant maximum of the cell-growth rate at a specific SAW amplitude, resulting in an increase of the wound-healing speed of up to 135 ± 85% as compared to an internal reference. In contrast, cells being stimulated only by electrical fields of the same magnitude as the ones exposed to SAWs exhibit no significant effect. In this study, we investigate this effect for different wavelengths, amplitude modulation of the applied electrical rf signal, and different wave modes. Furthermore, to obtain insight into the biological response to the stimulus, we also determined both the cell-proliferation rate and the cellular stress levels. While the proliferation rate is significantly increased for a wide power range, cell stress remains low and within the normal range. Our findings demonstrate that SAW-based vibrational cell stimulation bears the potential for an alternative method to conventional ultrasound treatment, overcoming some of its limitations.

Flexible Printed Circuit Board as Novel Electrodes for Acoustofluidic Devices

Surface acoustic wave (SAW)-based acoustofluidics shows broad applications in biomedicine and chemistry. Conventional manufacturing process for SAW devices uses photolithography and metal deposition, thus requires accessing cleanroom facilities. This study presents an efficient and versatile technique based on a flexible printed circuit board (FPCB) for developing SAW acoustofluidic devices. By mechanically clamping interdigital electrodes (IDEs) made on the FPCB onto a piezoelectric substrate, SAWs can be effectively generated with an additional matching network. The SAW amplitudes were measured by a laser vibrometer, which increases with the applied input voltage. The FPCB-SAW device has been applied to actuate 10-μm microspheres to form strong streaming vortices inside a droplet, and to drive a sessile droplet for transportation on the substrate surface. The use of the FPCB rather than a rigid printed circuit board (PCB) can help cut down on the overall footprint of the device and save space. The low requirement in assembling the FPCB-SAW device can facilitate versatile acoustofluidic applications by providing fast prototyping devices.

Contactless Liquid Height and Property Estimation Using Surface Acoustic Waves

The propagation of surface acoustic waves over a solid plate is highly influenced by the presence of liquid media on the surface. At the solid–liquid interface, a leaky Rayleigh wave radiates energy into the liquid, causing a signification attenuation of the surface acoustic wave amplitude. In this study, we take advantage of this spurious wave mode to predict the characteristics of the media, including the volume or height. In this study, the surface acoustic waves were generated on a thick 1018 steel surface via a 5 MHz transducer coupled through an angle beam wedge. A 3D-printed container was inserted on the propagation path. The pulse-echo time-domain responses of the signal were recorded at five different volumes (0, 400, 600, 1000, and 1800 µL). With the aid of parametric CAD analysis, both the position and distance of the entire traveling wave in the liquid layer were modeled and verified with experimental studies. The results indicated that the average drop in the reflected wave amplitude due to liquid loading is −62.5% compared to the empty container, with a percentage of error within 10% for all cases. The localized-time frequency components of the reflected wave were obtained via a Short-Time Fourier Transform technique. Up to 10% reduction (500 KHz) in the central frequency was observed due to the liquid volume increasing. The method discussed herein could be useful for many applications, where some of the liquid’s parameters or the ultrasonic wave behavior in the liquid need to be assessed.