Surface Acoustic Wave Amplitude Research Articles

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.

Holographic measurement of surface acoustic wave parameters in crystals

The theoretical basis of a specialized technique for applying digital holographic interferometry to measure the parameters of surface acoustic waves is presented, a measuring system for visualization and quantitative analysis of the parameters of ultralow-amplitude high-frequency oscillations arising in electronic devices using surface acoustic waves is developed, and experimental results of the study of surface acoustic waves in crystals of lithium niobate are obtained. In this case, to ensure the possibility of recording precision double-exposure interferograms of high-frequency surface acoustic waves, a picosecond pulsed laser with two-stage frequency multiplication was used as a radiation source, and to increase the spatial resolution of the system with the possibility of observing a wide field of view, an adjustable optical zoom of the incoming image was applied to the matrix input (based on charge-coupled devices) of the recording camera and digital zoom was used for obtained interferogram. We achieved the measuring sensitivity of the surface acoustic waves amplitude and spatial-temporal resolution allowing visualization and measurement of surface acoustic waves with amplitudes of the order of 1 nm and frequencies of the order of 10 MHz, which is far beyond the capabilities of standard methods of holographic interferometry.

A study of interaction surface acoustic wave with localized surface plasmon resonance

A surface acoustic wave (SAW) has the ability to manipulate droplets, and a localized surface plasmon resonance (LSPR) is expected to be utilized for biosensors. By integrating both of them on a single substrate, it is possible to create a new microfluidic system. In order to achieve this goal, the interaction the SAW with the LSPR was investigated by fabricating the substrate and measuring. As a result, it was found that the reflectance characteristics of the LSPR decreased and the spectrum shift in the short wavelength direction was observed during the SAW generated. The reason was experimentally considered and found that the LSPR was influenced from the temperature distribution on the SAW device. On the other hand, the increase of the SAW amplitude was observed by the LSPR excited. The results obtained indicate that control of the temperature is necessary to integrate the SAW and LSPR on the same substrate.

Chip-based sensing for release of unprocessed cell surface proteins in vitro and in serum and its (patho)physiological relevance.

To study the possibility that certain components of eukaryotic plasma membranes are released under certain (patho)physiological conditions, a chip-based sensor was developed for the detection of cell surface proteins, which are anchored at the outer leaflet of eukaryotic plasma membranes by a covalently attached glycolipid, exclusively, and might be prone to spontaneous or regulated release on the basis of their amphiphilic character. For this, unprocessed, full-length glycosylphosphatidylinositol-anchored proteins (GPI-AP), together with associated phospholipids, were specifically captured and detected by a chip- and microfluidic channel-based sensor, leading to changes in phase and amplitude of surface acoustic waves (SAW) propagating over the chip surface. Unprocessed GPI-AP in complex with lipids were found to be released from rat adipocyte plasma membranes immobilized on the chip, which was dependent on the flow rate and composition of the buffer stream. The complexes were identified in the incubation medium of primary rat adipocytes, in correlation to the cell size, and in rat as well as human serum. With rats, the measured changes in SAW phase shift, reflecting specific mass/size or amount of the unprocessed GPI-AP in complex with lipids, and SAW amplitude, reflecting their viscoelasticity, enabled the differentiation between the lean and obese (high-fat diet) state, and the normal (Wistar) and hyperinsulinemic (Zucker fatty) as well as hyperinsulinemic hyperglycemic (Zucker diabetic fatty) state. Thus chip-based sensing for complexes of unprocessed GPI-AP and lipids reveals the inherently labile anchorage of GPI-AP at plasma membranes and their susceptibility for release in response to (intrinsic/extrinsic) cues of metabolic relevance and may, therefore, be useful for monitoring of (pre-)diabetic disease states.

Non-destructive characterization of surfaces and thin coatings using a large-bandwidth interdigital transducer.

This paper deals with non-destructive testing of thin layer structures using Rayleigh-type waves over a broad frequency range (25-125 MHz). The dispersion phenomenon was used to characterize a layer-on-substrate-type sample comprising a thin layer of platinum 100 nm thick on a silicon substrate. The originality of this paper lies in the investigation of different ways of generating surface acoustic waves (SAWs) with large bandwidth interdigital transducers (IDTs) as well as the development of a measuring device to accurately estimate the SAW phase velocity. In particular, this study focuses on comparing the performance (in terms of SAW amplitude and bandwidth) of different excitations imposed on IDTs. The three types of excitations are burst, impulse, and chirp. The interest of chirp excitation compared to the other two types was clearly demonstrated in terms of the SAW bandwidth and amplitude of displacement. With these IDT transducers, measurements could be performed over a wide frequency band (20-125 MHz), and consequently, dispersion curves could be obtained over a wide frequency band with a range of velocity variations in the order of 100 m/s. Under these conditions, an extremely accurate estimate of the phase velocity as a function of the frequency could be obtained using a Slant Stack transformation. Finally, from these experimental dispersion curves and theoretical dispersion curves, an accurate estimate of the thickness of the layer could be obtained by inversion. This estimated thickness was then confirmed using profilometer measurements.

Effects of helium production, displacement damage on mechanical properties and surface acoustic wave in austenitic stainless steels and martensitic steel

The effects of helium production, displacement damage on mechanical properties and microstructures were investigated in some specimens such as austenitic stainless steels of SUS304 and SUS316 and a high chromium martensitic steel of HCM12A steels irradiated in a high fluence irradiation facility (HIT) of the University of Tokyo. The simultaneous dual ion (nickel plus helium ions) irradiations were adopted to simulate nuclear irradiation environments such as fast reactor and fusion reactor at HIT to 1 or 10 dpa and to 0, 1, 10, and 100 appm-He at 500, 550, and 600 °C. Thin foils for a transmission electron microscopy (TEM) were prepared with a focused ion beam (FIB) micro-sampling system. After the irradiation, the microstructures were observed by a transmission electron microscope and the irradiation hardening was measured by nano-indentation technique. In this study, the efficient of non-destructive measurement method of surface acoustic wave (SAW) excited by laser beam on the detection of radiation hardening behavior was also examined. Irradiation hardening was observed and the increment was tended to increase with dpa and He/dpa, which was especially effective in the condition of 100 appmHe/dpa even at 550 °C. Non-linear effect on amplitude of the excited SAW was also observed on the ion irradiated materials, and the propagation velocity of SAW was tended to be increased with irradiation dose. It was found that the behaviors of SAWs results were correlated with the changes of mechanical properties.

Fast time-domain laser Doppler vibrometry characterization of surface acoustic waves devices

This paper explores experiments and an in-depth analysis of surface acoustic waves (SAW) imaging using scanning laser Doppler vibrometry. Optical measurements allow visualization of wave propagation and resonance patterns in SAW devices as well as the detection of loss sources and undesired responses, such as escaping acoustic beams, unwanted reflections and acoustic crosstalk. We also report the characterization of a gas sensor based on electro-acoustic delay lines operating at 78.8MHz and featuring a maximum SAW amplitude of 0.6nm due to 33dBm burst excitation. In addition to conventional full C-Scan (3200 points) of the structure, we report a series of B-Scans (430 points) referenced to the device geometry. The latter provides the same valuable information on SAW device operation with more versatility for graphical analysis and more than 10 times faster measurement times. Such capabilities have implications for the engineering of acoustic and sensor applications. In order to extend the analysis of the performance of SAW sensors, we discuss different experimental approaches using numerical simulation, radiofrequency and interferometric measurements. The present study highlights several approved SAW device characterization techniques and methods, the means of their optimization as well as applications for improving SAW device performances.

Enhancing the sensitivity of three-axis detectable surface acoustic wave gyroscope by using a floating thin piezoelectric membrane

A new type of surface acoustic wave (SAW) gyroscope was developed on a floating thin piezoelectric membrane to enhance sensitivity and reliability by removing a bulk noise effect and by importing a higher amplitude of SAW. The developed device constitutes a two-port SAW resonator with a metallic dot array between two interdigital transducers (IDTs), and a one-port SAW delay line. The bulk silicon was completely etched away, leaving only a thin piezoelectric membrane with a thickness of one wavelength. A voltage controlled oscillator (VCO) was connected to a SAW resonator to activate the SAW resonator, while the SAW delay line was connected to the oscilloscope to monitor any variations caused by the Coriolis force. When the device was rotated, a secondary wave was generated, changing the amplitude of the SAW delay line. The highest sensitivity was observed in a device with a full acoustic wavelength thickness of the membrane because most of the acoustic field is confined within an acoustic wavelength thickness from the top surface; moreover, the thin-membrane-based gyroscope eliminates the bulk noise effect flowing along the bulk substrate. The obtained sensitivity and linearity of the SAW gyroscope were ∼27.5 µV deg−1 s−1 and ∼4.3%, respectively. Superior directivity was observed. The device surface was vacuum-sealed using poly(dimethylsiloxane) (PDMS) bonding to eliminate environmental interference. A three-axis detectable gyroscope was also implemented by placing three gyrosensors with the same configuration at right angles to each other on a printed circuit board.

Pulse picker for synchrotron radiation driven by a surface acoustic wave.

A functional test for a pulse picker for synchrotron radiation was performed at Diamond Light Source. The purpose of a pulse picker is to select which pulse from the synchrotron hybrid-mode bunch pattern reaches the experiment. In the present work, the Bragg reflection on a Si/B4C multilayer was modified using surface acoustic wave (SAW) trains. Diffraction on the SAW alters the direction of the x rays and it can be used to modulate the intensity of the x rays that reach the experimental chamber. Using electronic modulation of the SAW amplitude, it is possible to obtain different scattering conditions for different x-ray pulses. To isolate the single bunch, the state of the SAW must be changed in the short time gap between the pulses. To achieve the necessary time resolution, the measurements have been performed in conical diffraction geometry. The achieved time resolution was 120 ns.

Non-contact detection of low carbon steel using laser generated ultrasound at high temperature

Theoretical and experimental studies on non-contact detection of high temperature metal using laser ultrasound are carried out. Based on the theory of laser ultrasound, effects of high temperature on the laser generated surface acoustic wave (SAW) are discussed. Results of simulation show that the velocity and the amplitude of SAW will decrease with the increase of the temperature. An experimental system was set up, which in a non-contact mode, by utilizing a point laser source to generate the SAW, and an interferometer to detect the SAW signal. The corresponding experimental results have verified the feasibility of the numerical simulation and the achieved result of the relationship between the velocity of SAW and the temperature. The research findings provide a potential application for online monitoring of high temperature metal.

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.

3D measurement and simulation of surface acoustic wave driven fluid motion: a comparison.

The characterisation of the fluid motion induced by the acoustic streaming effect is of paramount interest for novel microfluidic devices based on surface acoustic waves (SAWs), e.g. for a detailed description of the achievable mixing efficiency and thus the design of such devices. Here, we present for the first time a quantitative 3D comparison between experimental measurements and numerical simulations of the acoustic streaming induced fluid flow inside a microchannel originating from a SAW. On the one hand, we performed fully three-dimensional velocity measurements using the astigmatism particle tracking velocimetry. On the other hand, we derived a novel streaming force approach solving the damped wave equation, which allows fast and easy 3D simulations of the acoustic streaming induced fluid flow. Furthermore, measurements of the SAW amplitude profile inside the fluid filled microchannel were performed. Based on these results, we obtained a very good agreement between the velocity measurements and the simulations of the fluid flow demonstrating the importance of comprising the actual shape of the SAW amplitude profile for quantitatively reliable simulations. It is shown that the novel streaming force approach is a valid approximation for the simulation of the acoustic streaming induced fluid flow, allowing a rapid and simple estimation of the flow field of SAW based microfluidic devices.

Laboratory X-ray characterization of a surface acoustic wave on GaAs: the critical role of instrumental convolution

Surface acoustic waves of micrometre wavelength travelling on a monocrystal give diffraction satellites around each Bragg peak in an X-ray diffraction diagram. By using a four-crystal monochromator, a secondary two-crystal analyser and masks reducing the footprint to the part of the crystal containing the acoustic modulation, it is possible to observe these satellites on a GaAs (001) surface using a laboratory diffractometer. The finite extension of the satellite diffraction rods and of the crystal truncation rod perpendicular to the surface leads to geometrical correction factors when convoluted with the instrumental resolution function, which had previously been ignored. The calculation of these geometrical correction factors in the framework of the kinematic approximation allows the determination of the surface acoustic wave amplitude, and the study of its attenuation and its dependence on radiofrequency power and duty cycle. The ability to perform such determinations with a laboratory diffractometer should prove useful in optimizing surface acoustic waves, which are presently used in a broad range of condensed matter physics studies.

Attenuation of 7 GHz surface acoustic waves on silicon

We measured the attenuation of GHz frequency surface acoustic waves (SAWs) on the Si (001) surface using an optical pump-probe technique at temperatures between 300 and 600 K. SAWs are generated and detected by a 700 nm Al grating fabricated by nanoimprint lithography. The grating for SAW generation is separated from the grating for SAW detection by $\ensuremath{\approx}150\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$. The amplitude of SAWs is attenuated by coupling to bulk waves created by the Al grating, diffraction due to the finite size of the source, and the intrinsic relaxational Akhiezer damping of elastic waves in Si. Thermal phonon relaxation time and Gr\"uneisen parameters are fitted using temperature-dependent measurement. The $fQ$ product of a hypothetical micromechanical oscillator limited by Akhiezer damping at this frequency is $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{13}$ Hz.

Fast-response and low-loss surface acoustic wave humidity sensor based on bovine serum albumin-gold nanoclusters film

The impact of ambient air humidity on surface acoustic wave (SAW) propagation in structures consisting of bovine serum albumin (BSA) and bovine serum albumin - gold nanoclusters (BSA-Au NCs) films deposited on YZ lithium niobate (LiNbO3) substrate has been investigated. The BSA-Au NCs film deposited on the surface of LiNbO3 significantly reduced the low-humidity value of the SAW transmission loss and considerably improved its long-term stability as compared to the BSA film. The amplitude of the output signal of the BSA-Au NCs on LiNbO3 SAW delay line was measured as a function of relative humidity (RH) at the steady-state conditions and as a function of time upon the step-like RH variation. An observed decrease in the transmitted SAW amplitude with increasing RH was explained in terms of the acoustoelectric attenuation. The response and recovery times of the structure with BSA-Au NCs on LiNbO3 SAW delay line upon abrupt humidity changes were on the order of 0.2s. No impact of RH variation on the SAW propagation was observed in the structures with BSA-Au NCs films deposited on metalized LiNbO3 substrate surface. The time-stable, fast-response and low-loss BSA-Au NCs on LiNbO3 SAW humidity sensor has been applied for monitoring the human respiration by detecting moisture contained in the exhaled air.

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.

Injection of a single electron from static to moving quantum dots

We study the injection mechanism of a single electron from a static quantum dot into a moving quantum dot. The moving quantum dots are created with surface acoustic waves (SAWs) in a long depleted channel. We demonstrate that the injection process is characterized by an activation law with a threshold that depends on the SAW amplitude and on the dot-channel potential gradient. By sufficiently increasing the SAW modulation amplitude, we can reach a regime where the transfer has unity probability and is potentially adiabatic. This study points to the relevant regime to use moving dots in quantum information protocols.

Localized Effect of Light Diffraction by Capillary Wave

The localized effect of light diffracted by a capillary wave is discovered by changing the wave amplitude. The localized range is related to the wave number and the amplitude. The dependence of the half maximum localized angle on the wave number and amplitude is analytically derived. Meanwhile, the analytic angular distribution of the diffraction light in the localized range is obtained. Experiments are carried out to achieve diffraction patterns to confirm the localized effect and to measure the angular distribution of the diffraction light intensity as well as to determine the localized range scales corresponding to different wave amplitudes. Theoretical curves of the light intensity angular distribution and localized interval widths related to surface acoustic wave amplitudes are compared with the experimental data. The experimental results agree well with the theoretical prediction.

Surface acoustic wave propagation in graphene film

Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.