SAW Power Research Articles

The Interaction between Surface Acoustic Wave and Quantum Hall Effects

Abstract Surface Acoustic Wave (SAW) is a powerful technique for investigating quantum phases appearing in two-dimensional electron systems. The electrons respond to the piezoelectric field of SAW through screening, attenuating its amplitude and shifting its velocity, which is described by the relaxation model. In this work, we systematically study this interaction using orders of magnitude lower SAW amplitude than that in previous studies. At high magnetic fields when electrons form highly correlated states such as the quantum Hall effect, we observe an anomalously large attenuation of SAW while the acoustic speed remains considerably high, inconsistent with the conventional relaxation model. This anomaly exists only when the SAW power is sufficiently low.

Effects of surface acoustic waves on droplet impact dynamics

HypothesisSurface acoustic waves (SAW) propagating along a solid surface can significantly affect the dynamics of droplet impact. Although droplet impact in presence of SAW has been attempted recently, here, we investigate the effects of surface wettability, droplet size, impact velocity, and SAW power on the impact and spreading dynamics along with post-impact oscillation dynamics of a drop. ExperimentsHere, we study droplet impact on a surface exposed to traveling SAW produced using an interdigitated electrode patterned on a piezoelectric substrate. The effects of Weber number (We), surface wettability, and SAW power on the impact and spreading dynamics and post-impact oscillation dynamics are studied. FindingsOur study unravels that the interplay between capillary and viscous forces, and inertia forces arising due to pre-impact kinetic energy and SAW-induced bulk acoustic streaming underpins the phenomena. Remarkably, we find that the effect of SAW on droplet impact dynamics is predominant in the case of a hydrophilic (HPL) substrate at a higher SAW power and smaller We and hydrophobic (HPB) substrate irrespective of SAW power. Our study reveals that the maximum droplet spreading diameter increases with SAW power at smaller We for an HPL surface whereas it is independent of SAW power at higher We. Post-impact oscillation of a droplet over an HPL surface is found to be overdamped with a smaller amplitude compared to an HPB substrate, and a faster decay in oscillation amplitude is observed in the case of an HPB surface and higher We. Our study provides an improved understanding of droplet impact on a surface exposed to SAW that may find relevance in various practical applications.

Analysis of Extracellular Vesicles Lysing using Surface Acoustic Wave Resonator

The integration of a Y-channel microfluidic system with an annular SAW device developed using MEMS technology has built an efficient platform for mixing and lysing of extracellular vesicles. The travelling SAW used in this study operating at a frequency of 50 MHz is capable of generating surface acoustic waves stream on a liquid sample inside a Y-chamber. At a height of 80µm the PDMS chamber and a liquid sample flow rate of 10µl/min can produce a mixing method that is able to generate gas bubbles that cause the occurrence of microcavities which are the agents of the extracellular vesicle lysing mechanism. This method of rupturing extracellular vesicles through cavitation techniques results in cell rupture through a combination of shear force and pressure changes without destroying proteins and nucleic acids. The Bradford assay is used to observe the increased presence of proteins resulting from the rupture of extracellular vesicles after exposure to acoustic waves. Based on the results, it can be concluded that the most optimal SAW exposure time and power is at 20dBM and 60 seconds. Through this test it can also be observed that a longer exposure period will generate heat which results in the degradation of the proteins that come out of the extracellular vesicles. It can be concluded that the results of this study prove that mechanical method of integrating an annular -SAW device and a Y-channel PDMS microfluidic chamber for micro-mixing, the analysis of biological cells and lysing mechanism can be achieved more effectively compared to conventional methods.

The Separation of Blood Components Using Standing Surface Acoustic Waves (SSAWs) Microfluidic Devices: Analysis and Simulation.

The separation of blood components (WBCs, RBCs, and platelets) is important for medical applications. Recently, standing surface acoustic wave (SSAW) microfluidic devices are used for the separation of particles. In this paper, the design analysis of SSAW microfluidics is presented. Also, the analysis of SSAW force with Rayleigh angle effect and its attenuation in liquid-loaded substrate, viscous drag force, hydrodynamic force, and diffusion force are explained and analyzed. The analyses are provided for selecting the piezoelectric material, width of the main microchannel, working area of SAW, wavelength, minimum input power required for the separation process, and widths of outlet collecting microchannels. The design analysis of SSAW microfluidics is provided for determining the minimum input power required for the separation process with appropriated the displacement contrast of the particles.The analyses are applied for simulation the separation of blood components. The piezoelectric material, width of the main microchannel, working area of SAW, wavelength, and minimum input power required for the separation process are selected as LiNbO3, 120 μm, 1.08 mm2, 300 μm, 371 mW. The results are compared to other published results. The results of these simulations achieve minimum power consumption, less complicated setup, and high collecting efficiency. All simulation programs are built by MATLAB.

Acoustic charge transport in a n-i-n three terminal device

We present an unconventional approach to realize acoustic charge transport devices that takes advantage from an original input region geometry in place of standard Ohmic input contacts. Our scheme is based on a n-i-n lateral junction as electron injector, an etched intrinsic channel, a standard Ohmic output contact and a pair of in-plane gates. We show that surface acoustic waves are able to pick up electrons from a current flowing through the n-i-n junction and steer them toward the output contact. Acoustic charge transport was studied as a function of the injector current and bias, the SAW power and at various temperatures. The possibility to modulate the acoustoelectric current by means of lateral in-plane gates is also discussed. The main advantage of our approach relies on the possibility to drive the n-i-n injector by means of both voltage or current sources, thus allowing to sample and process voltage and current signals as well.

Theoretical Analysis and Design of Non-Collinear Guided-Wave Acousto-Optic Devices

A numerical analysis is presented about the performance of non-collinear acousto-optic interaction in LiNbO3 guiding structures. To get the optimal design for a higher diffraction, the SAW power required for 100% diffraction (P 100) dependences on the length of acousto-optic (AO) interactions, guided optical mode, waveguide depth and driving frequency are investigated. Some valuable results are obtained for design of guided-wave acousto-optic devices.

Guided-wave acousto-optic diffraction in AlxGa1−xN epitaxial layers

The acousto-optic (AO) diffraction of guided optical waves from surface acoustic waves in AlxGa1−xN layers grown on sapphire substrates by Migration Enhanced Metalorganic Chemical Vapor Deposition (MEMGCVD™) technique was studied at the optical wavelengths of 442 and 633nm and acoustic wavelength of 16μm. In the near-to-Bragg diffraction regime, the diffraction efficiency from 90% to 95% was attained at SAW powers of 0.28 and 0.72W for the blue and red light, respectively. The simulation using photo-elastic and electro-optic constants reported in literature revealed the prevailing contribution of the photo-elastic effect to the AO diffraction. The calculated SAW power required to attain the diffraction maximum was about seven times larger than the measured values. This discrepancy implies that the photo-elastic constants of AlN and GaN available from literature are underestimated. The increase in the diffraction efficiency with the decreasing optical wavelength is in a good agreement with the theoretical prediction. This feature makes AlGaN very promising for AO applications in the deep UV region.

Interaction of surface acoustic waves with a two-dimensional electron gas in the presence of spin splitting of the Landau bands

The absorption and variation of the velocity of a surface acoustic wave of frequency f=30 MHz interacting with two-dimensional electrons are investigated in GaAs/AlGaAs heterostructures with an electron density n=(1.3–2.8)×1011cm2 at T=1.5–4.2K in magnetic fields up to 7 T. Characteristic features associated with spin splitting of the Landau level are observed. The effective g factor and the width of the spin-split Landau bands are determined: g*≅5 and A=0.6 meV. The greater width of the orbital-split Landau bands (2 meV) relative to the spin-split bands is attributed to different shielding of the random fluctuation potential of charged impurities by 2D electrons. The mechanisms of the nonlinearities manifested in the dependence of the absorption and the velocity increment of the SAW on the SAW power in the presence of spin splitting of the Landau levels are investigated.

Acoustooptic modulator using the Stark effect and stress-induced bandgap changes

An analysis of the semiconductor multiple-quantum-well (MQW) acoustooptic modulator is performed. The strain and electric-field components generated by surface acoustic waves (SAW's) in a multilayered semiconductor piezoelectric structure are presented. The effects of a SAW propagation on the modulator optical parameters are studied. Two kinds of SAW effects in the modulator structure are taken into account: the variation of the excitonic energies of the MQW due to strain and the companion electric field generated by the SAW is determined. The hole's effective mass change induced by the SAW is analyzed and included in the Schrodinger equation. The optical absorption coefficient spectra of the modulator as a function of the SAW power is presented. Experimental results concerning optical absorption variations of quantum-well structures produced by various SAW powers are shown.

Scattering of SAW at discontinuities: some numerical experiments

In developing models to characterize the metallic-finger step discontinuity in SAW devices on piezoelectric substrates it is important to estimate the SAW reflection coefficients and the effect of other modes at step discontinuities. In the literature perturbation approximations, finite element methods and various phenomenological parameter-fitting using experimental data are among the techniques which have been exploited. In this paper, a nonperturbation approximation method, which attempts to parallel some well-established techniques used in solving electromagnetic waveguide-discontinuity problems, is explored as an alternate numerical procedure for calculating SAW reflections. Implementing such a method requires that the full solution to SAW propagation in the free and in the layered regions be obtained. Thus, for a free-to-metallized discontinuity, the two SAW phase velocities, the total SAW power now in the free region and in the layered region, and the electroacoustic fields, must be calculated. In this paper the reflection problem is formulated as an optimization problem subject to the necessary scattering parameter constraints. Numerical experiments are described, and the results of calculations for reflectivity are compared to perturbation approximations, nonperturbation approximations and the available experimental data for the effects of energy storage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sputter Deposition for High Power Durable SAW Electrodes

DC magnetron sputtering of Al and Al alloy is studied to fabricate high power durable SAW electrodes. Experiments on SAW resonators as a test medium show that the time to failure is inversely proportional to the cube of SAW power in the sputtered Al films. Structure analyses and measurements on static stress reveal the following: the reduced static stress has a significant effect on higher durability to SAW power in the sputtered Al electrodes, and in addition, reduction of grain size in the films results in higher resistance to mechanical migration.

Temperature variation of SAW power flow angle

The power flow angle of surface acoustic waves in quartz not on a crystalline axis of symmetry is shown to vary rapidly with temperature. Experimental results and theoretical calculations are presented demonstrating the dependence of the acoustic power flow angle on a doubly rotated cut of quartz.

Discrimination of pulsed and CW signals using SAW power cepstrum analysis

The application of a surface acoustic wave power cepstrum analyser to the problem of automatic discrimination of pulsed and CW interference signals is discussed. The SAW processor can analyse signals of duration up to 25 μs and bandwidth 6 MHz and with suitable frame-to-frame tagging of the processor output it is possible to discriminate responses due to CW interference yielding an unambiguous record of the input pulse.

Radiation Patterns of Bulk Modes from a Finite Interdigital Transducer on Y-Z LiNbO3

Radiation patterns of bulk acoustic modes from a finite in- terdigital transducer on Y-Z LiNb03 were found using moment method and then compared with the experimental results. The power density radiation patterns of shear and longitudinal bulk modes were computed as functionsof the radiation angle, the electrode metallization ratio, and the frequency. It was shown that a SAW transducer can be very effi- ciently used for shear bulk wave excitation. For instance, at the sec- ond harmonic of the Rayleigh wave the percentage power of the shear, longitudinal, and SAW is 67.2,26.4, and 6.4 percent, respectively. The bulk power density distribution versus radiation angle does not change in form with a change in the metallization ratio. The SAW power density increases with increasing values of the metallization ratio.

Asymmetric distribution of SAW power flux emitted from LFM IDT

According to the prediction of theories, both acoustic power flux distribution between the right and left acoustic ports emitted from LFM IDT is asymmetric. By means of optical diffraction, we have detected the distribution of acoustic fields excited by the LFM IDT. Three unapodized LFM IDT which have different parameters are studied. These transducers with aluminum electrodes were deposited on the piezoelectric substrates of YZ‐LiNbO3. The experimental results show that the SAW power run radiated from the high frequency port of LFM IDT is found to be stronger than that from the low frequency one. The asymmetry increases with the number of the finger pairs, but decreases with the band width. In general, the asymmetry increases with the excited frequency but the relation is not monotonic. Some theoretical models are taken for numerical evaluation of the asymmetric distribution. The comparison between the theoretical curves and the experimental results are presented and discussed briefly. However, in the theoretical calculations the mode‐conversion from SAW into BAW induced by the interdigital electrodes, has not been taken into consideration.

Actively controlled SAW power divider

The operation and construction of a new actively controlled SAW power divider is presented. The amount of power delivered to either of two outputs can be controlled with a voltage less than +30 V. The two essential components of this device are a SAW magic tee fabricated on yz LiNbO3 and an acoustoelectric phase shifter which uses silicon air-gap coupled to the LiNbO3.