Excitation Of Surface Acoustic Waves Research Articles

Bending and splitting of spoof surface acoustic waves through structured rigid surface

Abstract In this paper, we demonstrated that a 90°-bended imaging of spoof surface acoustic waves with subwavelength resolution of 0.316λ can be realized by a 45° prism-shaped surface phononic crystal (SPC), which is composed of borehole arrays with square lattice in a rigid plate. Furthermore, by combining two identical prism-shaped phononic crystal to form an interface (to form a line-defect), the excited spoof surface acoustic waves can be split into bended and transmitted parts. The power ratio between the bended and transmitted surface waves can be tuned arbitrarily by adjusting the defect size. This acoustic system is believed to have potential applications in various multifunctional acoustic solutions integrated by different acoustical devices.

Excitation and time resolved spectroscopy of SAW harmonics up to GHz regime in photolithographed GaAs devices

In this work, we demonstrate the excitation of surface acoustic waves (SAW) harmonics up to GHz regime in photolitographed devices fabricated on gallium arsenide (GaAs) by acting on the IDT metallization ratio among the finger width and pitch. Specifically, we observed up to the 13th harmonic, which corresponds to a frequency of about 1.7 GHz. Moreover, we employed time-resolved spectroscopy for isolating the shape of the SAW bandpass-filter response (for each harmonic) eliminating the interference between acoustic and electromagnetic waves. Notably, the extracted SAW spectra are characterized by a bandwidth which remains constant for the different harmonic modes, unlike the case of traditional SAW filters (having a 0.5 metallization ratio) where the pass band increases with the working frequency. These results are relevant for applications where high frequencies and multiple harmonics excitation are desirable, or where quantitative measurements of the direct SAW signal are required.

Vector network analyzer measurement of the amplitude of an electrically excited surface acoustic wave and validation by X-ray diffraction

Surface acoustic waves are used in magnetism to initiate magnetization switching, in microfluidics to control fluids and particles in lab-on-a-chip devices, and in quantum systems like two-dimensional electron gases, quantum dots, photonic cavities, and single carrier transport systems. For all these applications, an easy tool is highly needed to measure precisely the acoustic wave amplitude in order to understand the underlying physics and/or to optimize the device used to generate the acoustic waves. We present here a method to determine experimentally the amplitude of surface acoustic waves propagating on Gallium Arsenide generated by an interdigitated transducer. It relies on Vector Network Analyzer measurements of S parameters and modeling using the Coupling-Of-Modes theory. The displacements obtained are in excellent agreement with those measured by a very different method based on X-ray diffraction measurements.

Enhanced surface acoustic wave cell sorting by 3D microfluidic-chip design

We demonstrate an acoustic wave driven microfluidic cell sorter that combines advantages of multilayer device fabrication with planar surface acoustic wave excitation. We harness the strong vertical component of the refracted acoustic wave to enhance cell actuation by using an asymmetric flow field to increase cell deflection. Precise control of the 3-dimensional flow is realized by topographical structures implemented on the top of the microchannel. We experimentally quantify the effect of the structure dimensions and acoustic parameter. The design attains cell sorting rates and purities approaching those of state of the art fluorescence-activated cell sorters with all the advantages of microfluidic cell sorting.

Piezoelectric Ca3NbGa3Si2O14 crystal: crystal growth, piezoelectric and acoustic properties

Ca3NbGa3Si2O14 (CNGS), a five-component crystal of lanthanum-gallium silicate group, was grown by the Czochralski method. The parameters of the elementary unit cell of the crystal were measured by powder diffraction. The independent piezoelectric strain coefficients \(d{}_{11}\) and \(d_{14}\) were determined by the triple-axis X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves (SAW) were studied by high-resolution X-ray diffraction at BESSY II synchrotron radiation source. The velocity of SAW propagation and power flow angles in the \(Y\)-, \(X\)- and \(yxl/{+}36^\circ\)-cuts of the CNGS crystal were determined from the analysis of the diffraction spectra. The CNGS crystal was found practically isotropic by its acoustic properties.

Evaluation of annealing and double ion beam irradiation by a laser-induced and laser-detected surface acoustic wave diagnostic system

The effects of annealing and double ion irradiation on nuclear structural materials were investigated using a novel, non-destructive, non-contact diagnostic method. A laser-induced and laser-detected surface acoustic wave (SAW) was adopted as a diagnostic system. The SAWs propagation velocity and the SAWs vibration velocity along the normal direction of the surface were measured to investigate mechanical properties of the substrates. Change of the shear modulus was detected in the annealed substrates. Non-linear effect on amplitude of the excited SAW was observed on the double ion irradiated materials. The potential of the SAW diagnostic system for assessing nuclear structural materials was demonstrated.

Surface Acoustic Wave Excitation Using a Pulse Wave

Surface acoustic waves (SAWs) excited by bursts of sinusoidal waves have been used in various applications. However, the SAW actuators used for this purpose are expensive because each SAW transducer must be equipped with a radio frequency linear amplifier and a function generator. To simplify the driving circuits of these actuators, SAW excitation using a pulse wave is proposed in this report. Simulated results for an equivalent circuit of a single interdigital transducer and measurements of SAWs excited by pulse waves are presented. The generation of tactile sensations using a SAW excited by a pulse wave is also reported. Furthermore, the power requirements for SAW excitation by a sinusoidal wave and by a pulse wave are compared.

Excitation of Surface Acoustic Wave on a Glass Substrate Using a LiNbO3 Piece

Surface acoustic waves (SAWs) are used in many applications. Here, we consider application of SAWs to actuators, which require relatively large vibration amplitudes. In conventional applications, a SAW propagates on a LiNbO3 substrate that serves as an elastic medium. This implies that the maximal size of a SAW transducer is limited by the LiNbO3 wafer size. Better actuators require larger-size SAW transducers. Here, we propose a transducer in which an excited SAW propagates on an inexpensive elastic medium (indirect excitation method). The method combines a piezoelectric material and a non-piezoelectric material substrate. These two materials are coupled. Electric energy is provided by an interdigital transducer (IDT). We designed and studied three different transducer configurations. To determine the optimal configuration, various materials and their combinations were considered with the proposed method. Electrical and mechanical characteristics were quantified in terms of the frequency response of admittance and vibration response, respectively. A suitable combination of materials was determined after measuring and analyzing the properties of different transducers. For this combination, the vibration velocity of the novel transducer was as large as that obtained using the conventional direct excitation method.

Rayleigh and Wood anomalies in the diffraction of acoustic waves from the periodically corrugated surface of an elastic medium

By the use of the Rayleigh method we have calculated the angular dependence of the reflectivity and the efficiencies of several other diffracted orders when the periodically corrugated surface of an isotropic elastic medium is illuminated by a volume acoustic wave of shear horizontal polarization. These dependencies display the signatures of Rayleigh and Wood anomalies, usually associated with the diffraction of light from a metallic grating. The Rayleigh anomalies occur at angles of incidence at which a diffracted order appears or disappears; the Wood anomalies here are caused by the excitation of the shear horizontal surface acoustic waves supported by the periodically corrugated surface of an isotropic elastic medium. The dispersion curves of these waves in both the nonradiative and radiative regions of the frequency-wavenumber plane are calculated, and used in predicting the angles of incidence at which the Wood anomalies are expected to occur.

Piezoelectric tube rotation effect owing to surface acoustic wave excitation

It is shown experimentally that a macroscopic cylindrical solid shaped like a piezoelectric tube can be rotated due to the excitation of surface acoustic waves (SAWs) with different amplitudes propagating in opposite directions along the solid's surface. A unidirectional SAW transducer covering the whole cylindrical surface has been used for ac voltage excitation of waves with unequal amplitudes in both directions. The pattern of such a transducer consists of a periodic comb structure with two electrodes of different width per period. An external torque is not applied to the tube and, from the outside, its movement looks like a motion under the action of an internal force. The observed mechanical response of the piezoelectric cylindrical tube to excitation of waves is due to an angular momentum of SAWs, the value of which has been directly calculated from experimental results.

An improved Mach-Zehnder acousto-optic modulator on a silicon-on-insulator platform

The interdigital transducer (IDT) of the traditional Mach-Zehnder (MZ) acousto-optic modulator on a silicon-on-insulator (SOI) platform is located outside its two arms. The crest and trough of the surface acoustic wave (SAW) are used to modulate the two arms of the MZ interferometer so as to achieve a high modulation efficiency. Therefore, the distance between the two arms must be odd multiples of half acoustic wavelength. However, since the substrate is usually not uniform, the wavelength of the SAW changes as it transmits through the surface of the device. As a result, the exact distance between the two arms is difficult to choose. On the other hand, the SAW losses a portion of energy after passing through the first arm of the MZ interferometer, so the modulation of the second arm becomes much weaker. To solve these problems, we propose a new structure where its IDT is situated in the middle of the two arms of the MZ interferometer. With this scheme, the two arms of the MZ interferometer are located exactly at the crest and the trough of the SAW, while they are modulated with equal strength. In this paper, we first use the finite element method to simulate the acoustic frequency and the surface displacement of the excited SAW. Then we deduce the refractive index variations of all layers according to their acousto-optic effects. After that, we analyze the influences of different factors on the acousto-optic modulation efficiency, including the type and size of waveguide, the thickness of zinc oxide (ZnO) layer, and the area it covers, the number of electrodes, etc. These parameters are accordingly optimized to enhance the modulation efficiency. Modeling result based on COMSOL Multiphysics indicates that when the width of the strip waveguide is 6 m, the ZnO layer covers only the area under the IDT and has a thickness of 2.2 m, and the number of the electrodes is 50, the effective refractive index variation of the waveguide reaches 4.0810-4 provided that the amplitude of the driving voltage is 1 V. This value is 12% higher than that of the traditional structure.

Acoustic Properties of La3Ga5.3Ta0.5Al0.2O14 Crystal

Development and search for new advanced materials of the lanthanum gallium silicate group with unique thermal properties is of great importance for the development of acoustoelectronics based on volume and surface acoustic waves. The processes of surface acoustic wave excitation and propagation in the La 3 Ga 5.3 Ta 0.5 Al 0.2 O 14 crystal was studied using a double − crystal X − ray diffractometer with a BESSY II synchrotron radiation source. The X − ray diffraction spectra of acoustically modulated crystals were used to measure the surface acoustic wave velocity and power flow angles in different acoustic cuts of the La 3 Ga 5.3 Ta 0.5 Al 0.2 O 14 crystal.

Directional excitation of the designer surface acoustic waves

We propose an efficient design route to realize directional excitation of the structure-induced surface waves for airborne sound. The whole system consists of a periodically corrugated rigid plate combining with a pair of asymmetric narrow slits. The directional excitation of the mimicked surface waves stems from the destructive interference between the evanescent waves emitted from the double slits. The directionality can be switched conveniently by tuning the external frequency. The theoretical prediction is validated well by simulations and experiments. Promising applications can be anticipated such as in designing compact devices for airborne sound.

Acoustic properties of La3Ga5.3Ta0.5Al0.2O14 crystal

Development and search for new advanced materials of the lanthanum gallium silicate group with unique thermal properties is of great importance for the development of acoustoelectronics based on volume and surface acoustic waves. The processes of surface acoustic wave excitation and propagation in the La3Ga5.3Ta0.5Al0.2O14 crystal was studied using a double-crystal X-ray diffractometer with a BESSY II synchrotron radiation source. The X-ray diffraction spectra of acoustically modulated crystals were used to measure the surface acoustic wave velocity and power flow angles in different acoustic cuts of the La3Ga5.3Ta0.5Al0.2O14 crystal.

Исследование объемных акустических волн СВЧ-диапазона, возбужденных встречо-штыревым преобразователем

Excitation of bulk and surface acoustic waves with the interdigital transducer (IDT), which is deposited on the surface of piezoelectric crystal, is widely used in the development of devices in acoustoelectronics and in the design of the microwave acousto-optic deflectors. Excitation of bulk acoustic waves by IDT in the devices on surface acoustic waves leads to the appearance of spurious signals. At the same time excitation of bulk acoustic waves with IDT from the surface of lithium niobate crystals allows creating high frequency acousto-optic deflectors, which makes possible to significantly simplify the technology of their production. Therefore, significant attention is paid to the task of excitation and distribution of bulk acoustic waves with IDT including recent times by the method of simulation of their excitation and distribution. The obtained theoretical results require experimental verification. This paper documents the visualization of acoustic beams excited with IDT from the XY-surface of lithium niobate crystals. The Bragg cells with LiNbO3 crystals coated with IDT with a different period of electrodes were manufactured for the experimental research of excitation and distribution of bulk acoustic waves. Visualization results have shown that the acoustic waves excited with IDT distribute in both the Fresnel zone and the Fraunhofer zone. The length of these zones is caused by individual elementary emitters of which consists the IDT (by their size). At the same time the far zone for IDT is located at distances much greater than the actual size of the LiNbO3 crystals. This peculiarity is not always taken into account when calculating diffraction. The achieved results can be used to design high-frequency acousto-optic devices, as well as in the development of devices based on surface acoustic waves.

Controlling nanomagnet magnetization dynamics via magnetoelastic coupling

We demonstrate that elastic interactions between nanomagnets in a periodic array can determine the magnetic response according to the nanoscale array geometry. These findings are attributed to magnetoelastic coupling of the spin dynamics with simultaneously excited surface acoustic waves. Specifically, we observe three manifestations of this effect: pinning of the magnetic resonance frequency over an extended range of applied magnetic fields, generation of additional modes whose frequency can differ by more than 100% from the intrinsic element response, and an enhancement of the Fourier amplitude of the magnetic mode at crossovers with mechanical modes. Simulations of the dynamics in the presence of coupling between magnetic and mechanical degrees of freedom are in good agreement with the experiment. This suggests that magnetization dynamics can be controlled by rational structural design on the nanoscale even when the magnetostatic interactions are negligible.

Microfluidic resonant cavities enable acoustophoresis on a disposable superstrate.

We demonstrate surface acoustic wave (SAW) induced microparticle manipulation in a microstructured disposable glass-polymer composite superstrate, positioned on a piezoelectric substrate with a single, slanted SAW transducer. An excited SAW was coupled from the piezoelectric substrate into the superstrate, which acted as a transversal resonator structure. We show that the energy transmitted into the superstrate allowed acoustophoretic particle manipulation, while the wide frequency response of the SAW transducer enabled tuneable pressure distributions confined by the microchannel layout. The configuration provides a significant tolerance in positioning - making assembly easy.

High frequency microfluidic performance of LiNbO3 and ZnO surface acoustic wave devices

Rayleigh surface acoustic wave (SAW) devices based on 128° YX LiNbO3 and ZnO/Si substrates with different resonant frequencies from ∼62 MHz to ∼275 MHz were fabricated and characterized. Effects of SAW frequency and power on microfluidic performance (including streaming, pumping, and jetting) were investigated. SAW excitation frequency influenced the SAW attenuation length and hence the acoustic energy absorbed by the liquid. At higher frequencies (e.g., above 100 MHz), the SAW dissipated into liquid decays more rapidly with much shorter decay lengths. Increasing the radio frequency (RF) frequencies of the devices resulted in an increased power threshold for streaming, pumping, and especially jetting, which is attributed to an increased absorption rate of acoustic wave energy. ZnO SAW devices could achieve similar streaming, pumping, and jetting effects as well as frequency effect, although the SAW signals are relatively weaker.

Cell detachment and label-free cell sorting using modulated surface acoustic waves (SAWs) in droplet-based microfluidics

We present a droplet-based surface acoustic wave (SAW) system designed to viably detach biological cells from a surface and sort cell types based on differences in adhesion strength (adhesion contrast) without the need to label cells with molecular markers. The system uses modulated SAW to generate pulsatile flows in the droplets and efficiently detach the cells, thereby minimizing the SAW excitation power and exposure time. As a proof of principle, the system shows efficient sorting of HEK 293 from A7r5 cells based on adhesion contrast. Results are obtained in minutes with sorting purity and efficiency reaching 97% and 95%, respectively.

Piezoelectric La3Ga5.3Ta0.5Al0.2O14 crystal: growth, crystal structure perfection, piezoelectric, and acoustic properties

A five-component crystal of lanthanum–gallium silicate group La3Ga5.3Ta0.5Al0.2O14 (LGTA) was grown by the Czochralski method. The LGTA crystal possesses unique thermal properties and substitution of Al for Ga in the unit cell leads to a substantial increase of electrical resistance at high temperatures. The unit cell parameters of LGTA were determined by powder diffraction. X-ray topography was used to study the crystal structure perfection: the growth banding normal to the growth axis were visualized. The independent piezoelectric constants d 11 and d 14 were measured by X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves were studied by the double-crystal X-ray diffraction at the BESSY II synchrotron radiation source. The analysis of the diffraction spectra of acoustically modulated crystals permitted the determination of the velocity of acoustic wave propagation and the power flow angles in different acoustic cuts of the LGTA crystal.