Search

This review article presents insights into acoustic interactions with semiconductors, exploring a continuum from electron dynamics to exciton behavior while highlighting recent developments in organic material systems. Various aspects of acoustic interactions, encompassing the manipulation of electrons and their transport mechanisms for applications in the fields of acoustoelectric and acousto-optics, explored by studying surface acoustic wave (SAW) devices integrated with inorganic and organic semiconductors, are presented here. SAWs are guided waves propagating along a piezoelectric material surface, inducing acoustic strain and piezoelectric fields within a semiconductor upon contact. These fields create a dragging force, transferring energy and momentum into the semiconductor, which manipulate and transport charge carriers, thereby generating an acoustoelectric current. Furthermore, SAW can influence exciton dynamics via type-II as well as type-I band-edge modulations, leading to alterations in their spatial distribution, causing transport of electron–hole pairs as distinct charge carrier packets and as bound pairs, respectively, along the SAW path. This paper explores advancements in these phenomena, shedding light on innovative applications and, especially, novel insights into the dynamic interplay between acoustics and organic semiconductor physics. The review concludes by outlining challenges and prospects in the field of SAW and semiconductor interactions, providing a roadmap for future research endeavors. [ABSTRACT FROM AUTHOR]

The displacement of a single electron enables exciting avenues for nanotechnology with vast application potential in quantum metrology, quantum communication and quantum computation. Surface acoustic waves (SAW) have proven itself as a surprisingly useful solution to perform this task over large distance with outstanding precision and reliability. Over the last decade, important milestones have been achieved bringing SAW-driven single-electron transport from first proof-of-principle demonstrations to accurate, highly-controlled implementations, such as coherent spin transport, charge-to-photon conversion, or antibunching of charge states. Beyond the well-established piezoelectric gallium-arsenide platform, first realisations of acousto-electronic transport have also been carried out on the surface of liquid helium that promises unique stability and coherence. In this review article, we aim to keep track of this remarkable progress in SAW-driven transport of electron qubits by explaining these recent achievements from basic principles, with an outlook on follow-up experiments and near-term applications. [ABSTRACT FROM AUTHOR]

A theory is presented for the amplification of a surface acoustic wave (SAW) due to its interaction with conduction electrons in gate-controlled epitaxial graphene (epigraphene) on a SiC substrate. It is assumed that the SAW is launched onto the substrate in the direction of an external dc electric field applied to the graphene sample and causing the conduction electrons to drift at a speed greater than the speed of the SAW. The wavelength of the SAW is assumed to be shorter than the mean free path of the electrons, so that the quantum regime of interaction of those electrons with the SAW is realized. The Green's function method is used to calculate the SAW gain as a function of the electron concentration in epigraphene and the external dc electric field strength. It is shown that the substrate-induced band gap in the electronic spectrum of epigraphene leads to a significant (at least an order of magnitude) increase in the SAW gain as compared to the case of gapless graphene. In addition, the opening of the band gap results in a non-monotonic dependence of the SAW gain on the electron concentration, controlled by the gate voltage applied to the graphene sample. This dependence is characterized by the presence of a distinct maximum at a certain value of electron concentration (of about 2 × 10 12 cm−2 for typical values of the other parameters involved), which distinguishes it from the monotonic concentration dependence of the SAW gain in gapless graphene. [ABSTRACT FROM AUTHOR]

Telecommunication of the next generation demands filters that can operate in the 10 GHz range with sufficient bandwidths. For surface-acoustic-wave (SAW) devices this prerequisite translates into high sound velocities and high piezoelectric couplings. Wurtzite AlN on diamond, which exploits the strong piezoelectricity of AlN with the very high SAW velocity of diamond, has been considered a promising platform. A significant boost (up to a factor of 4) of the piezoelectric response can be obtained by alloying AlN with Sc. Here, the main challenge lies in the synthesis of highly-oriented thin (Sc,Al)N films on diamond. In this work, we aim at establishing a platform for SAW devices using plasma-assisted molecular beam epitaxy for the deposition of Sc0.2Al0.8N on diamond. We investigate the structural properties related to SAW generation gearing towards applications at high frequencies. To this end, we prepare (Sc,Al)N thin films on polished polycrystalline diamond wafers and demonstrate the efficient generation of SAW modes with frequencies up to 8 GHz. Systematic studies of the dependence of the SAW velocity and electromechanical coupling coefficient on the Sc0.2Al0.8N film thickness is presented for various SAW modes. Our result demonstrates the potential of this material combination for future application that requires large bandwidth in the ultra-high frequency range. [ABSTRACT FROM AUTHOR]

The phenomenon of surface acoustic wave (SAW) streaming, where a streaming jet is created, occurs when an SAW propagating on the surface of a solid interacts with water, and underpins the increasingly important area of SAW microfluidics. A key characteristic of the streaming jet is the Rayleigh angle, i.e. the angle at which the jet is formed relative to the surface normal of the solid, which is determined by the ratio of the velocity of the acoustic wave in the fluid and in the solid. Although the ability to dynamically tune this angle would offer a novel tool for microfluidic control, the SAW velocity is normally fixed by the characteristics of the solid and liquid material properties. In this paper we show, using finite element method modelling, that changing the SAW Rayleigh wave phase velocity by patterning a metamaterial array, consisting of square annular holes, onto the surface of an SAW device can change the acoustic streaming Rayleigh angle by approximately a factor of two, in good agreement with calculations based on the change in velocity. [ABSTRACT FROM AUTHOR]

The use of surface acoustic waves (SAW) in cell biology has gained high attention in the past years. Previous works show that SAW treatment of artificial wounds in vitro can accelerate wound healing by up to +135%. However, little is known about the mechanobiology behind these effects, and a stimulation has only been proven for continuous SAW signals so far. We here show that the stimulation efficacy observed in previous studies is preserved for pulsed stimuli applied to Madin-Darby canine kidney (MDCK-II) cells in wound healing assays on SAW chips at a resonance frequency f SAW = 160 MHz. Moreover, for a reproducible and reliable image analysis, we present the SegFormer-based deep learning algorithm Neural Cell Edge Detector for the cell edge segmentation and image binarization, that allows an automated determination of the stimulation efficacy. With these tools, we explore a wider range of applicable SAW intensities up to P in = 21 dBm (128 mW) with a maximum stimulation efficacy of E = 201%. We show that the order of magnitude of the stimulation effect is reproducible under the variation of SAW signal characteristics power P in, duty cycle D and pulse width τ, while the mean energy over time is constant. Below a distinct pulse duration limit τ = 100 ms, no direct stimulation effect was observed. From a mechanobiological point of view, these findings and time scales could narrow down the potentially triggered cellular mechanisms during the stimulation. [ABSTRACT FROM AUTHOR]

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 those 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. [ABSTRACT FROM AUTHOR]

We report on scalable heterointegration of superconducting electrodes and epitaxial semiconductor quantum dots (QDs) on strong piezoelectric and optically nonlinear lithium niobate. The implemented processes combine the sputter-deposited thin film superconductor niobium nitride and III–V compound semiconductor membranes onto the host substrate. The superconducting thin film is employed as a zero-resistivity electrode material for a surface acoustic wave resonator with internal quality factors Q ≈ 17 000 representing a three-fold enhancement compared to identical devices with normal conducting electrodes. Superconducting operation of ≈ 400 M H z resonators is achieved to temperatures T > 7 K and electrical radio frequency powers P r f > + 9 d B m . Heterogeneously integrated single QDs couple to the resonant phononic field of the surface acoustic wave resonator operated in the superconducting regime. Position and frequency selective coupling mediated by deformation potential coupling is validated using time-integrated and time-resolved optical spectroscopy. Furthermore, acoustoelectric charge state control is achieved in a modified device geometry harnessing large piezoelectric fields inside the resonator. The hybrid QD—surface acoustic wave resonator can be scaled to higher operation frequencies and smaller mode volumes for quantum phase modulation and transduction between photons and phonons via the QD. Finally, the employed materials allow for the realization of other types of optoelectronic devices, including superconducting single photon detectors and integrated photonic and phononic circuits. [ABSTRACT FROM AUTHOR]

Single crystalline AlN material is very attractive for the development of high temperature electronic devices owing to its high temperature resistance. However, at ultrahigh temperatures, AlN film still will be oxidized and metal electrodes used for the devices will aggregate and vaporize. The deterioration of the material and metal electrodes eventually fails the AlN-based devices. Here, we report a single crystalline AlN film-based ultrahigh temperature surface acoustic wave (SAW) device. By using a thin alumina (Al2O3) protection layer on surface, oxidation of the AlN piezoelectric film was effectively inhibited at high temperatures. A composite electrode based on multilayer structure of Pt-Rh and Al2O3 was designed and fabricated, with the Al2O3 layer as the diffusion barrier layers to suppressed inter-diffusion, agglomeration and vaporization of the metals. The results showed that the developed AlN SAW devices can withstand high temperatures, and work well at temperatures up to 1400 °C. [ABSTRACT FROM AUTHOR]

This paper proposes a class of high-performance surface acoustic wave (SAW) waveguides based on AlN-on-SiC substrates. Under the existing crystal growth and processing technology, these SAW waveguides offer excellent performance in single mode, low loss, ultra-broadband, operating at gigahertz frequencies. Quasi-Rayleigh SAWs can be excited by traditional interdigital transducers and guided freely with excellent efficiency. Based on these SAW waveguides, we further demonstrate SAW splitters and ring cavities with ultra-high qualities up to 107. These SAW components complement future integrated phononic circuits for high-frequency and compact acoustic manipulating, signal processing, sensing, computing, etc. [ABSTRACT FROM AUTHOR]

Langasite (LGS) based surface acoustic wave (SAW) sensors are widely used in high temperature circumstances due to their advantages of being passive and wireless. In this research, the platinum electrodes are deposited into the grooves of the LGS instead of on the surface to further improve the acoustic properties and prolong the lifetime of the resonators at high temperature. Proper MEMS fabrication techniques are proposed to fabricate such structures. The result of every step is evaluated, and the corresponding process parameters are optimized. With the optimal processes, two types of resonators with different Euler angles of (0∘, 22∘, 30∘) and (0∘, 22∘, 90∘) are fabricated on the LGS substrate. Furthermore, the process-influenced structure parameters such as metal ratio and sidewall angle are well investigated via a weak form nonlinear finite element method simulation model. The temperature dependence of the resonance frequency is measured, and the recorded thermal behaviors match well with the prediction of the simulation. In addition, the further endurance test shows that the devices could work at 1000 ∘C for 12 h. This research proves the validity of the grooved resonator structure and the prominent role of the simulation model in further optimizing the LGS-based SAW devices design. [ABSTRACT FROM AUTHOR]

Temperature and strain sensitivities of surface acoustic wave (SAW) and hybrid acoustic wave (HAW) Brillouin scattering (BS) in 1 ÎĽmâ€"1.3 ÎĽm diameter optical microfibers are simulated. In contrast to stimulated Brillouin scattering (SBS) from bulk acoustic wave in standard optical fiber, SAW and HAW BS, due to SAWs and HAWs induced by the coupling of longitudinal and shear waves and propagating along the surface and core of microfiber respectively, facilitate innovative detection in optical microfibers sensing. The highest temperature and strain sensitivities of the hybrid acoustic modes (HAMs) are 1.082 MHz/°C and 0.0289 MHz/ÎĽ ε, respectively, which is suitable for microfiber sensing application of high temperature and strain resolutions. Meanwhile, the temperature and strain sensitivities of the SAMs are less affected by fiber diameter changes, ranging from 0.05 MHz/°C/ÎĽm to 0.25 MHz/°C/ÎĽm and 1 Ă— 10âˆ'4 MHz/ÎĽ ε /ÎĽm to 5 Ă— 10âˆ'4 MHz/ÎĽ ε /ÎĽm, respectively. It can be found that that SAW BS for temperature and strain sensing would put less stress on manufacturing constraints for optical microfibers. Besides, the simultaneous sensing of temperature and strain can be realized by SAW and HAW BS, with temperature and strain errors as low as 0.30 °Câ€"0.34 °C and 14.47 ÎĽ ε â€"16.25 ÎĽ ε. [ABSTRACT FROM AUTHOR]

A delay line-type surface acoustic wave (SAW) gas sensor based on p-hexafluoroisopropanol phenyl (HFIPPH) functionalized multi-walled carbon nanotube (MWCNT) film is developed to detect organophosphorus dimethyl methylphosphonate (DMMP) vapor (a simulant of chemical nerve agent sarin). Inspired by the transfer process of Cu-based graphene, a uniform and size-controllable HFIPPH-MWCNT film is successfully prepared on the SAW device via a wet-etching transfer method. For the first time, we use the method of measuring the change of the sensor’s insertion loss to achieve the detection of ultra-low concentration DMMP vapor. The designed sensor exhibits a fast response/recovery time about 3 s/50 s, and a low detection limit of 0.1 ppm. Additionally, the stability and selectivity of the sensor and the influence of humidity on its response are evaluated through experiments. The acoustoelectric effect is proved to be the sensing mechanism of the sensor insertion loss response. [ABSTRACT FROM AUTHOR]

Higher-order topological insulator hosts both gapped edge states and in-gap corner states, which has garnered considerable attentions in the field of condensed matter physics, and most recently is further extended to the classical wave systems. Conventional acoustic metamaterials have intrinsic material and design limitations that prevent them from being used to create such states in subwavelength scale with function reconfigurability. Recently, the acoustic second-order topological insulators (SOTIs) composed of locally resonant metamaterials were reported to solve the problem, where the topological phase transition is induced by shrinking/expanding metamolecules. Here, we propose an acoustic SOTI in subwavelength scale by another protocol, i.e. gliding metamolecules, and the SOTI is pinned in the nontrivial region without the regular topological phase transition. Soda cans metamaterials in free space are utilized to support the spoof surface acoustic waves. With varying the introduced glided angle, the switching from the bulk to edge and corner states can be achieved accordingly. Furthermore, we not only experimentally observe this state switching process, but also illustrate the robustness of the topological corner states against various defects. Our results provide versatile ways to launch acoustic lower-dimensional topological states that might lead to interesting sound concentration applications. [ABSTRACT FROM AUTHOR]

The laser-generated surface acoustic wave (SAW) technique is a promising method to measure the mechanical properties of thin films quickly and nondestructively. Residual stress is inevitable during the processing and manufacturing of integrated circuits, which will have a major impact on the physical and mechanical properties of the thin film materials and cause deterioration to the structural strength. In this study, the SAW technique based method is proposed for quantitative and nondestructive measuring the residual stress in the nanostructured films. The method is verified by the experiment measuring the SiO2 films in the thickness range of 100â€"2000 nm. The experimental procedures, including signal excitation, reception and processing, are described in detail. By matching the SAW experimental dispersion curve with the calculated theoretical dispersion curve containing the residual stress, the residual stress of the SiO2 films along [110] and [100] crystallographic orientation of the Si wafer is successfully quantified. The determination results are ranged from âˆ'65.5 to 421.1 MPa and the stress value increases as the film thickness decreases, revealing the residual stress of the SiO2 film is compressive. Meanwhile, the conventional substrate curvature method as a comparison is used to verify the correctness and superiority of the proposed SAW method for the residual stress determination. [ABSTRACT FROM AUTHOR]

As core devices for the smartphone RF front end, surface acoustic wave (SAW) filters are in short supply. The detection of SAW filter parameters refers to the connection between layout design and process production, which is an important part of capacity improvement. This paper devises a method based on image processing to detect SAW filter parameters. We improve the morphological operator to recover an image and identify the number of interdigital transducer (IDT) finger bars under noise conditions. The feature points in the color image are selected to extract the scale. The Canny edge detection effect is enhanced through using an adaptive filter, increasing the gradient operator, bilinear interpolation, and other algorithms. We use a minimum shape to enclose the edges to determine the IDT width and period and apply Fourier transform to verify the detection results. The experimental results show that the number of IDT finger bars is accurately identified. The width and period are exactly the same as the real values at the 10th percentile, and the detection requirements are met. [ABSTRACT FROM AUTHOR]

Surface acoustic waves (SAW) have underpinned many acoustofluidic applications. But the typical straight, full-width interdigital transducers used to generate these waves are problematic. Fresnel diffraction of the propagating SAW causes strong nonuniformity in the wave's amplitude as it propagates across the substrate, leading to flow variations, recirculation, and peculiar wetting phenomena in fluids driven by such waves. These have led to many research projects and publications, but, ultimately, uniform fluid flow from SAW-driven streaming remains elusive. By adopting a form of apodization, the shaping of the IDT, we demonstrate the ability to produce laterally uniform SAW for acoustofluidics. Unlike traditional apodization, which shapes the IDT to produce a desired electrical signal, this new approach—unapodization—instead inverts the governing equations to produce a desired spatial distribution of SAW at a defined position along the propagation direction of the SAW. Theoretical analysis and experiment demonstrate a 50% improvement in the SAW uniformity over a straight IDT for three example unapodized designs, all while maintaining the same frequency, input power, quality factor, and electromechanical coupling. The sole downside is a 50% increase in IDT area to accommodate the unapodization. A design tool is provided with tabulated unapodized IDT configurations. To illustrate the potential of unapodization in acoustofluidics, the irregular dewetting and anomalous flows of a thin fluid film induced by traditional straight IDT SAW devices is shown to become regular and uniform with the adoption of unapodized SAW devices. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) devices offer many benefits in chemistry and biomedicine, enabling precise manipulation of micro-droplets, mixing of liquids by acoustic streaming and pumping of liquids in enclosed channels, while presenting a cost-effective and easy fabrication and integration with electronic devices. In this work, we present microfluidic devices which use graphene-based interdigital transducers (IDTs) to generate SAWs with a frequency of 100 MHz and an amplitude of up to 200 pm, which allow us to manipulate microparticle solutions by acoustic streaming. Due to the negligible mass loading of the piezoelectric surface by graphene, the SAWs generated by these devices have no frequency shift, typically observed when metal IDTs are used. [ABSTRACT FROM AUTHOR]

Acoustofluidics operating at high frequencies usually use surface acoustic waves (SAWs), and those emitted by limited-aperture planar interdigital transducers (IDTs) are prevalent. In such devices, field nonuniformity along the lateral direction is observed by many, but there lacks a study to quantitatively clarifying this effect. Here, by modeling IDTs using dirac-type transfer functions, we examine how field nonuniformity changes at varied aperture length, axial distance, and number of finger pairs of the IDTs. For standing SAW (SSAW) devices, field predictions from numerical analysis are validated through experimental measurements employing laser vibrometry. Finally, particle acoustophoresis is carried out in three SSAW devices, while the results provide some useful implications for future device designs. [ABSTRACT FROM AUTHOR]

Several types of research are performed on flow control and this fact highlights the importance of this topic. Over the last two decades, actuators based on acoustic waves have attracted much attention and have been used in widespread applications from mixing to pumping. This paper reveals the effects of some control parameters such as wave amplitude and wave frequency on the dynamical behavior of a sessile drop in order to change the flow characteristics. For this purpose, the removal of water from surfaces and drop movement against gravity are considered. Flow dynamics is simulated using lattice Boltzmann method. The results show that the drop can be removed from the surface in a short period of time (about one-tenth of the normal time) without moving upstream. In the microgravity condition, the dynamical behaviors of drop are affected by Bond number. There is a critical Bond number, when the Bond number is less than this parameter, drop slides on the wall. In this situation, when the wave amplitude is set to be 2.5 nm, the drop is pinned to the wall. If the wave amplitude is increased, the drop moves against gravity. Also, when the Bond number is greater than its critical value, we only can stop or remove the drop using the SAW. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) sensing systems based on the received signal strength indication (RSSI) detection principle have recently gained considerable research attention because of their distinct advantages and disadvantages. However, the test mode requires constant sweeping, which severely limits the system's dynamic response; to overcome this limitation, an effective solution is to establish a suitable eigenvalue search strategy to replace naive sweeping. To this end, a basis for this process is established in this study. Furthermore, the mechanism of the SAW sensing system based on RSSI detection is analyzed, a system model is established by introducing sequence signal superposition, and the model's validity is verified via experiments. Signal variations at each stage and model errors are analyzed, and the system's timing parameters are optimized. Finally, using the SAW torque sensor, an optimized torque measurement prototype is designed and the system's effectiveness is verified through static torque experiments. A complete model of the measurement system can be simulated through this model; it provides the basis for an eigenvalue search strategy and can act as a simulation model or design basis for other researchers building RSSI-detection-based SAW sensing systems. [ABSTRACT FROM AUTHOR]

Surface acoustic waves (SAWs) have the potential to become the basis for a wide gamut of lab-on-a-chips (LoCs). These mechanical waves are among the most promising physics that can be exploited for fulfilling all the requirements of commercially appealing devices that aim to replace–or help–laboratory facilities. These requirements are low processing cost of the devices, scalable production, controllable physics, large flexibility of tasks to perform, easy device miniaturization. To date, SAWs are among the small set of technologies able to both manipulate and analyze biological liquids with high performance. Therefore, they address the main needs of microfluidics and biosensing. To this purpose, the use of high-frequency SAWs is key. In the ultra-high-frequency regime (UHF, 300 MHz—3 GHz) SAWs exhibit large sensitivities to molecule adsorption and unparalleled fluid manipulation capabilities, together with overall device miniaturization. The UHF-SAW technology is expected to be the realm for the development of complex, reliable, fully automated, high-performance LoCs. In this review, we present the most recent works on UHF-SAWs for microfluidics and biosensing, with a particular focus on the LoC application. We derive the relevant scale laws, useful formulas, fabrication guidelines, current limitations of the technology, and future developments. [ABSTRACT FROM AUTHOR]

Due to their unique advantages, surface acoustic wave (SAW) sensors have attracted various disciplines to carry out thorough research. However, in their wireless applications, their high carrier frequency, low signal-to-noise ratio, and short effective signal length have led to poor signal measurement accuracy and complex detection systems. Using an SAW torque sensor as its objective, this paper describes the proposal and completion of a novel processing system based on compressive sensing (CS). The system was implemented using an analog-to-information conversion module. The module hardware's structural parameters and signal recovery parameters were designed and optimized by simulation. Furthermore, an intervening interpolation method based on support vector machine (SVM) signal secondary information prediction was developed to achieve an effective extension of the observed signal. The method's parameters and the SVM super parameters were optimized by a cuckoo search algorithm. The success rate of the predicted signal secondary information reached more than 94%. The compression ratio of the system reached 5.77‰ while ensuring successful signal frequency recovery. Finally, a torque static calibration experiment was carried out using the system prototype; the results show that the system sensitivity is 1.951 kHz Nm−1, which proves that the scheme and methods are effective. The SAW signal-processing system based on CS combines the advantages of traditional demodulation system solutions with low hardware costs, low data volume, and high interference immunity. This system will prompt some new thoughts about SAW sensor signal detection. [ABSTRACT FROM AUTHOR]

This work investigates the design methodology to obtain large electromechanical coupling factor () and high quality factor (Q) of shear-horizontal surface acoustic wave (SH-SAW) resonators based on the thin-film lithium niobate-on-insulator (LNOI) technology. The guided SH wave can be excited through interdigital transducers and propagate at the very surface of the material stackings. Such a guided SH wave in LN/SiO2 double layer structure is expected to offer high by confining the elastic strain energy in the piezoelectric thin film. To capture the optimum design window for high-performance LNOI SH-SAW devices, the impact of electrode material and its thickness on the dispersive characteristics are intensively investigated by finite element method (FEM). In this study, various one-port resonators with wavelengths from 2.8 μm to 8 μm were fabricated on a LNOI wafer with LN and SiO2 thickness of 0.7 and 2 μm, respectively. The 100 nm thick gold film was chosen as the electrode of the devices, which demonstrate a similar dispersive behavior to the FEM simulation with small discrepancy. Among the measurement results over several tested samples, a high- of 25.5% and Q of 960 was recorded at a resonance frequency of 581 MHz (FOM = = 245), revealing great potential for the application of wide-band frequency selection in telecommunications. [ABSTRACT FROM AUTHOR]

Shear horizontal surface acoustic wave (SH-SAW) sensors have great application potential due to their advantages of easy integration, miniaturization and suitability in liquid environments. In this paper, the finite element method is used to analyse a new SH-SAW micro pressure sensor, in which there are many groove structures along the direction of wave propagation on the delay path. We use the transient response simulation method to calculate and analyse the output voltage signal at the output interdigital transducer and surface average stress at the delay path of this new SH-SAW sensor, and its pressure sensitivity is analysed by uniformly applying an appropriate surface pressure on the resonant beam formed after grooving. The simulation results show that the surface average stress can be enhanced in a certain range of groove depth during the vibration of the groove structure. When the groove depth and width are set to 0.7 μm and 0.5 μm, respectively, the sensitivity of the SH-SAW sensor with a groove structure is four times higher than that of the traditional SH-SAW sensor. The increase of pressure sensitivity is the result of the increase of average stress caused by the groove structure. The new groove structure SH-SAW sensor provides a new basis for research on high-sensitivity micro-pressure sensors and lays a foundation for subsequent device design and manufacture. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that rainbow trapping of spoof acoustic surface waves (SASWs) can be realised by introducing structured defects on a textured closed surface in the subwavelength scale. To analyse the basic mechanism of the trapping of SASWs, we first introduce a defective zigzag groove in a closed surface and illustrate that the SASWs can be effectively trapped in the defect when the frequency exceeds the cut-off frequency of the periodic grooves on both sides. Subsequently, we experimentally demonstrate the spatial–spectral separation effect of SASWs by introducing three defective zigzag grooves with different curl numbers in the closed surface. Finally, we design a structure with gradient defective zigzag grooves to show the rainbow trapping of SASWs and spatial separation of different frequency components at different positions. Our results may have potential applications in miniaturised acoustic devices. [ABSTRACT FROM AUTHOR]

Love mode surface acoustic wave (SAW) devices are very useful for sensing in liquid environments. Earlier work on such devices mainly made use of zinc oxide (ZnO) thin films on silicon (Si) or silicon dioxide (). However, using them for sensing still required protection from contamination from zinc (Zn) in the form of some additional passivation layer. In this work, the objective has been to study an aluminium nitride (AlN)-based multilayer structure that is able to generate SAW Love modes very efficiently. A layer of on top of the AlN layer does the trick. A 3D finite element method simulation analysis of the proposed structure () is accordingly performed, and phase velocities, electromechanical coupling coefficients and frequency shift due to mass loading are simulated as a function of the normalized thicknesses of AlN and films. It is shown that the optimal normalized thickness identified to be = 0.18, = 0.45 with AlN c-axis orientation of and the maximum value of the electromechanical coupling coefficient = 0.58% can be achieved. Even though the value of is comparable to ZnO-based Love mode devices, the phase velocity is 1.5 times higher (5530 m s−1 compared to 3652 m s−1). Equally importantly, it is seen that the frequency shift due to mass loading of deionized water (the AlN-based multilayer Love mode sensor) is much higher for that using the ZnO-based multilayer Love mode sensor. [ABSTRACT FROM AUTHOR]

There is significant current interest in using arrays of interacting nanomagnets as efficient hardware platforms to solve difficult computational problems such as image processing, computer vision or combinatorial optimization. Problem variables are encoded in the magnetization states of the nanomagnets and the array is allowed to relax to the ground state, wherein the magnetic order represents the solution to the problem. This strategy is energy-frugal and ultrafast, since it does not involve software (executing instruction sets), but unfortunately it fails if the system gets stuck in a metastable state from which it cannot escape to the ground state. Here, we demonstrate, in a small system of dipole-coupled 3 × 3 array of magnetostrictive nanomagnets fabricated on a piezoelectric substrate, how the system can be driven out of the metastable state into the ground state with a surface acoustic wave. This process emulates 'simulated annealing', which is a well-known algorithm of finding the optimal solution of a function (representing the ground state) by driving the function out of a sub-optimal solution (representing a metastable state) by following a sequence of steps. [ABSTRACT FROM AUTHOR]

In this study, an ultrasonic method for characterizing thin films based on the dispersion of the first Rayleigh mode is presented. The principle of surface acoustic waves (SAW) generation using a broadband transducer and their detection is detailed. It is shown that over a frequency range between 20 MHz and 125 MHz, SAWs are sensitive to fine deposits and the attenuation is reasonable thus enabling measurements over 20 mm. The Slant Stack transform used to obtain the experimental dispersion curves with excellent signal-to-noise ratios is then presented and analyzed. Finally, four samples of silicon on which gold layers 400 nm, 300 nm, 180 nm, and 50 nm thick had been deposited and characterized. The thicknesses and the elastic parameters of the gold layers and the silicon substrate were obtained from the inversions performed on the experimental dispersion curves. These results show the efficiency of the non-destructive ultrasonic technique associated with a Slant Stack transform before inversion. [ABSTRACT FROM AUTHOR]

The measurement and control of trace moisture is an important procedure to maintain and secure the quality and safety of pipeline systems for natural gas. The natural gas mix typically comprises methane, ethane, propane, some higher hydrocarbons, carbon dioxide and nitrogen. It is too impractical to perform additional calibrations of trace moisture measurement every time the combination of gas components in the natural gas mix is changed. This paper proposes a method to separate and compensate for the effect of the background gas composition from the trace moisture measurement by using two different frequencies in a trace moisture analyzer utilizing a ball surface acoustic wave (SAW) sensor. The experiment was performed by connecting the ball SAW trace moisture sensor to supplies of trace moisture in multiple background gases from the National Physical Laboratory (NPL) Multi-gas, Multi-pressure Standard Humidity Generator, and changing the composition of the background gases including N2, air, CH4, 80% CH4/20% C2H6, and 50% CH4/50% C2H6. At the nominal humidity frost-point values of −70 °C, −50 °C, −40 °C and −30 °C, the deviations due to the change of the background gases were within 1 °C in frost point. [ABSTRACT FROM AUTHOR]

The measurement of trace moisture is important in industry to maintain the quality and yield of products, such as semiconductors, lithium-ion batteries, and organic electroluminescence devices. In the field, on-site calibration of a trace moisture analyzer is required to maintain its reliability. Given these circumstances, we previously developed a ball surface acoustic wave (SAW) sensor using SAW on spherical piezoelectric elements and reported its quick response as its advantage over other trace moisture analyzers. However, the ultimately short response time of less than 1 s has not been verified, and it has not yet been calibrated on-site. In this study, we developed a system for the injection of saturated water vapor to evaluate the quick response of a trace moisture analyzer, and we verified the quick response time of as short as 0.64 s. It is the shortest response time reported so far. In addition, to realize its on-site calibration, we developed a dynamic calibration method, which takes only 10 min, by the injection of saturated water vapor, in contrast to the presently available static calibration method that takes 10 h. Since this system consists of simple components, it can be downsized. Moreover, because it uses a small amount of saturated water vapor as the calibration gas, it is easy to prepare calibration gases in the field and may be applied to on-site calibration. [ABSTRACT FROM AUTHOR]

Nozzleless jetting of droplets with different jetting angles is a crucial requirement for 2D and 3D printing/bioprinting applications, and Rayleigh mode surface acoustic waves (SAWs) could be a potential technique for achieving this purpose. Currently, it is critical to vary the jetting angles of liquid droplets induced by SAWs and control the liquid jet directions. Generally, the direction of the liquid jet induced by SAWs generated from a bulk piezoelectric substrate such as LiNbO3 is along the theoretical Rayleigh angle of ∼22°. In this study, we designed and manufactured thin-film SAW devices by depositing ZnO films on different substrates (including silicon and aluminium) to realize a wide range of jetting angles from ∼16° to 55° using propagating waves generated from one interdigital transducer. We then systematically investigated different factors affecting the jetting angles, including liquid properties, applied SAW power and SAW device resonant frequency. Finally, we proposed various methods using thin-film SAW devices together with different transducer designs for realizing a wide range of jetting angles within the 3D domain. A nozzleless jetting method is proposed using thin-film based surface acoustic wave devices to achieve a wide range of jetting angles for droplets. [ABSTRACT FROM AUTHOR]

Transient electric polarization in single crystalline SrTiO3 (STO) substrates was studied by measuring the transmission of surface acoustic waves (SAWs). We applied a large dc electric field (8 × 106 Vm−1) to interdigital transducers (IDTs) on STO substrates in order to induce local piezoelectricity, which is required to generate and transmit SAWs. The resulting electric polarization and the retention thereof were analyzed as a function of time after the applied electric field was removed, by measuring transient SAW signals. The retained polarization turned out to provide strong electromechanical coupling, comparable to that resulting from the dc-field-induced piezoelectricity. SAW signals were observed for more than 30 h (in absence of an external dc electric field), which is evidence for a long-lasting retention of electric polarization. Remarkably, this polarization was found to be rapidly suppressed as the sample was exposed to visible light. By measuring the transient SAW transmission under illumination with light at different wavelengths, we identified photoconductivity and/or acceleration of oxygen vacancy migration by photon-induced splitting of bound vacancy pairs as the main mechanisms behind this photoresponsive memory effect. [ABSTRACT FROM AUTHOR]

Transient electric polarization in single crystalline SrTiO3 (STO) substrates was studied by measuring the transmission of surface acoustic waves (SAWs). We applied a large dc electric field (8 × 106 Vm−1) to interdigital transducers (IDTs) on STO substrates in order to induce local piezoelectricity, which is required to generate and transmit SAWs. The resulting electric polarization and the retention thereof were analyzed as a function of time after the applied electric field was removed, by measuring transient SAW signals. The retained polarization turned out to provide strong electromechanical coupling, comparable to that resulting from the dc-field-induced piezoelectricity. SAW signals were observed for more than 30 h (in absence of an external dc electric field), which is evidence for a long-lasting retention of electric polarization. Remarkably, this polarization was found to be rapidly suppressed as the sample was exposed to visible light. By measuring the transient SAW transmission under illumination with light at different wavelengths, we identified photoconductivity and/or acceleration of oxygen vacancy migration by photon-induced splitting of bound vacancy pairs as the main mechanisms behind this photoresponsive memory effect. [ABSTRACT FROM AUTHOR]

The explosive growth of wireless communication and the creation of new frequency bands for 5G systems increasingly require surface acoustic wave (SAW) with high operating frequency (i.e. 3–6 GHz) as well as high-temperature stability. In this work, high-frequency and high-temperature stable SAW devices using ZnO/SiO2/SiC layered structures were proposed and reported. SAW characteristics of the Sezawa wave mode, including the phase velocities (Vp), electromechanical coupling coefficients (K2) and temperature coefficient of frequency (TCF), were studied systematically by the finite element method. High-frequency SAW one-port resonators with the resonant frequency ranging from ∼4.5–5.4 GHz were fabricated on the above structures. With SiC substrate providing high velocity and SiO2 interlayer for temperature compensation, a 5.0 GHz and nearly zero TCF of 0.7 ppm °C−1 can be achieved in a SAW device based on ZnO/SiO2/SiC structure. The good performance of these devices demonstrates that the ZnO/SiO2/SiC structure is promising for high-frequency and good temperature-stability SAW device applications. [ABSTRACT FROM AUTHOR]

Voltage induced magnetization dynamics of magnetic thin films is a valuable tool to study anisotropic fields, exchange couplings, magnetization damping and spin pumping mechanism. A particularly well established technique is the ferromagnetic resonance (FMR) generated by the coupling of microwave photons and magnetization eigenmodes in the GHz range. Here we review the basic concepts of the so-called acoustic-FMR (a-FMR) induced by the coupling of surface acoustic waves (SAW) and magnetization of thin films. Interestingly, additional to the benefits of the microwave excited FMR technique, the coupling between SAW and magnetization also offers fertile ground to study magnon-phonon and spin rotation couplings. We describe the in-plane magnetic field angle dependence of the a-FMR by measuring the absorption / transmission of SAW and the attenuation of SAW in the presence of rotational motion of the lattice, and show the consequent generation of spin current by acoustic spin pumping. [ABSTRACT FROM AUTHOR]

One-port magnetic surface acoustic wave (MSAW) resonators are fabricated by stacking multilayered (FeCoSiB/SiO2)n films directly on top of interdigital electrodes. It is shown that the magneto-acoustic response of the MSAW resonators critically depends the hysteresis of ΔE effect. For the magnetic multilayer without induced magnetic anisotropy, the resonance frequency (fR) exhibits a butterfly-like dependence on the external field, therefore, enabling bipolar detection of magnetic field smaller than its coercive field. However, for the magnetic multilayers with induced magnetic anisotropy, butterfly-like or loop-like fR–H curves are measured along the interdigtial electrode fingers or the SAW propagation direction, which can be attributed to the competition between the magnetic field-induced anisotropy and the stress-induced or shape anisotropy. [ABSTRACT FROM AUTHOR]

We numerically and experimentally investigate the phononic loss for superconducting resonators fabricated on a piezoelectric substrate. With the help of finite element method simulations, we calculate the energy loss due to electromechanical conversion into bulk and surface acoustic waves. This sets an upper limit for the resonator internal quality factor Qi. To validate the simulation, we fabricate quarter wavelength coplanar waveguide resonators on GaAs and measure Qi as function of frequency, power and temperature. We observe a linear increase of Qi with frequency, as predicted by the simulations for a constant electromechanical coupling. Additionally, Qi shows a weak power dependence and a negligible temperature dependence around 10 mK, excluding two level systems and non-equilibrium quasiparticles as the main source of losses at that temperature. [ABSTRACT FROM AUTHOR]

Coherent exchange between photons and different matter excitations (like qubits, acoustic surface waves or spins) allows for the entanglement of light and matter and provides a toolbox for performing fundamental quantum physics. On top of that, coherent exchange is a basic ingredient in the majority of quantum information processors. In this work, we develop the theory for coupling between magnetic textures (vortices and skyrmions) stabilized in ferromagnetic nanodiscs and microwave photons generated in a superconducting circuit. Within this theory we show that this hybrid system serves for performing broadband spectroscopy of the magnetic textures. We also discuss the possibility of reaching the strong coupling regime between these texture excitations and a single photon residing in a microwave superconducting cavity. [ABSTRACT FROM AUTHOR]

In this work, we experimentally study the effects of the nitrogen concentration in laser wakefield acceleration of electrons in a gas mixture of hydrogen and nitrogen. A 15 TWpeak power laser pulse is focused to ionize the gas, excite a plasma wave and accelerate electrons up to 230 MeV. We find that at dopant concentrations above 2% the total divergence of the electrons is increased and the high energy electrons are emitted preferentially with an angle of ±6 mrad, leading to a forked spatio-spectral distribution associated to direct laser acceleration (DLA). However, electrons can gain more energy and have a divergence lower than 4 mrad for concentrations below 0.5% and the same laser and plasma conditions. Particle-in-cell simulations show that for dopant concentrations above 2%, the amount of trapped charge is large enough to significantly perturb the plasma wave, reducing the amplitude of the longitudinal wakefield and suppressing other trapping mechanisms. At high concentrations the number of trapped electrons overlapping with the laser fields is increased, which rises the amount of charge affected by DLA. We conclude that the dopant concentration affects the quantity of electrons that experience significant DLA and the beam loading of the plasma wave driven by the laser pulse. These two mechanisms influence the electrons final energy, and thus the dopant concentration should be considered as a factor for the optimization of the electron beam parameters. [ABSTRACT FROM AUTHOR]

ZnO thin film-based surface acoustic wave (SAW) devices were fabricated on Si, glass and polyimide (PI) substrates, and their microfiuidic performances were compared. The Rayleigh and Sezawa mode waves were observed from the ZnO/Si devices, the Rayleigh and Lamb modes from the ZnO/PI, and only the Rayleigh mode from the ZnO/glass devices. The ZnO/Si devices have the best performance with the highest acoustic streaming velocity of about 10 cra/s and the shortest particle concentration time of less than 10 sec. The ZnO/glass SAW devices deliver comparable performances to that on Si substrate, while the ZnO/PI devices perform not as good as the devices on other two types of substrates due to the large acoustic attenuation, but still can deliver a streaming velocity up to 1.0 cm/s and reasonable particle concentration function with a particle concentration time of ~70 sec. Owing to its low cost, easy fabrication and compatible with traditional glass-based biochemical analysis systems, ZnO/glass SAW device is believed to have better potential for lab-on-a-chip application. [ABSTRACT FROM AUTHOR]

In this paper, the sensitivity of the LiNbO3 surface acoustic wave (SAW) based humidity sensors has been enhanced with various nanostructured Ag materials, including thermally evaporated or chemically synthesized, and then thermally annealed ones. The results showed that the humidity sensitivity of the SAW devices increases with the surface roughness (porosity) of the sensing film, and can be further improved when Ag NPs are used. Smooth Ag film deposited by evaporation onto the SAW devices did not change the humidity sensitivity noticeably, but those with chemically deposited high porosity Ag films have a good sensitivity of 80 kHz/75%RH. The SAW sensors with the Ag NPs have the highest sensitivity up to about 800 kHz/75%RH, at least one order of magnitude higher than those reported before. The SAW sensors with Ag nano-particles showed a strong non-linearity, and explained by the different chemisorption capabilities of Ag and LiNbO3 surface. [ABSTRACT FROM AUTHOR]

Dual-mode flexible ZnO/polyimide surface acoustic wave (SAW)-based ultraviolet (UV) light sensors were fabricated and their performance was investigated. UV light sensing measurements showed that the responses of the dual wave modes of the sensors increase with the increase of light intensity and the frequency changes linearly with the change of light intensity. Under a 4.5 mW cm−2�UV light illumination, the resonant frequency of the Rayleigh wave decreased up to ∼43�kHz, while that of the Lamb wave was approximately 76�kHz. The UV light sensitivities for the two resonant modes are 111.3 and 55.8�ppm (mW cm−2)–1, respectively. The resonant frequency, phase angle and amplitude of the two resonant modes exhibited a good repeatability in responding to cyclic change of the UV light, and an excellent stability up to a long duration of UV light exposure. The dual-mode flexible SAW resonators are simple in structure, more accurate in detection, and can be fabricated at low cost are, therefore, very promising for application in flexible sensors and electronics. [ABSTRACT FROM AUTHOR]

We propose to use an acoustic surface wave as a memory for a photon carrying orbital angular momentum. We clarify the physical mechanism that enables the transfer of information, derive the angular momentum selection rule that must be obeyed in the process and show how to optimize the optoacoustic coupling. We theoretically demonstrate that high fidelities can be achieved, using realistic parameters, for the transfer of a coherent optical Laguerre-Gaussian state, associated with large angular momentum, to a mechanical shear mode. Our results add a significant possibility to the ongoing efforts towards the implementation of quantum information processing using photonic orbital angular momentum. [ABSTRACT FROM AUTHOR]

The article focuses on use of wafer-scale flexible surface acoustic wave (SAW) devices which are based on Aluminum Nitride (AIN) / Silicon (Si) structure. The article mentions about growing interest in flexible electronics and the use of metal oxide semiconductors. The article also mentions about micrcoelectromechanical system (MEMS) and Complementary Metal oxide semiconductors (CMOS).

Integrated AlN/SiO2/Si (1 0 0) delay lines for Rayleigh surface acoustic waves (SAWs) with resonant frequencies up to 3.4 GHz were fabricated using a new CMOS compatible concept. Different thicknesses of textured AlN films with wurtzite structure were deposited on tungsten-based interdigital transducers embedded in a SiO2 layer by reactive pulse dc-sputtering at a temperature of 200 °C. Rocking curves of the films indicate c-axis (0 0 0 1) oriented, textured piezoelectric AlN films with a full-width at half-maximum of 1.88°. The determined propagation loss and coupling factor K2 of these SAW devices are 0.07 dB/λ and 0.78%, respectively. Different Rayleigh modes with acoustic velocities up to 5770 m s-1 are observed. By varying the wavelength, number of fingers as well as the length (i.e., the separation between the transducers) of the delay lines, the impact of several physical parameters on the frequency responses (S11, S21) was studied. The influence of the AlN thickness and of the orientation of the delay lines on the silicon (1 0 0) wafers was also investigated. Finite element method simulations were applied to model the resonant frequencies, giving resonant frequencies in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) propagation characteristics in a multilayer structure including a piezoelectric aluminum nitride (AlN) thin film and an epitaxial cubic silicon carbide (3C-SiC) layer on a silicon (Si) substrate are investigated by theoretical calculation in this work. Alternating current (ac) reactive magnetron sputtering was used to deposit highly c-axis-oriented AlN thin films, showing the full width at half maximum (FWHM) of the rocking curve of 1.36° on epitaxial 3C-SiC layers on Si substrates. In addition, conventional two-port SAW devices were fabricated on the AlN/3C-SiC/Si multilayer structure and SAW propagation properties in the multilayer structure were experimentally investigated. The surface wave in the AlN/3C-SiC/Si multilayer structure exhibits a phase velocity of 5528 m s-1 and an electromechanical coupling coefficient of 0.42%. The results demonstrate the potential of AlN thin films grown on epitaxial 3C-SiC layers to create layered SAW devices with higher phase velocities and larger electromechanical coupling coefficients than SAW devices on an AlN/Si multilayer structure. Moreover, the FWHM values of rocking curves of the AlN thin film and 3C-SiC layer remained constant after annealing for 500 h at 540 °C in air atmosphere. Accordingly, the layered SAW devices based on AlN thin films and 3C-SiC layers are applicable to timing and sensing applications in harsh environments [ABSTRACT FROM AUTHOR]

We describe an all-angle negative refraction effect for surface acoustic waves in two-dimensional phononic crystals made of cylindrical pillars assembled in a square lattice and deposited on the surface of a semi-infinite substrate. The convexity of the iso-frequency contours of some branches leads to a negative refraction effect despite the fact that the effective index is not negative. It occurs for the frequency range where the group velocity is never in opposite direction to the phase velocity. In addition, the use of cylindrical pillars acting as acoustic resonant elements on the surface permits us to achieve this phenomenon with a sub-wavelength feature size structure; therefore, the effect of all-angle negative refraction can be shifted down to low frequencies, which is highly desirable for high-resolution superlensing applications. A flat lens for surface acoustic waves has also been designed. It demonstrates the focusing of an acoustic source into an image on the other side of the finite-size structure with an image resolution of (λ/4), which overcomes the Rayleigh diffraction limit. The numerical simulations are based on the efficient finite element method and analyze pillars and the substrate of lithium niobate. [ABSTRACT FROM AUTHOR]

Acousto-electric charge conveyance induced by a surface acoustic wave (SAW) is employed to dissociate photogenerated excitons. Over macroscopic distances, both electrons and holes are injected sequentially into a remotely positioned, isolated and high quality quantum emitter, a self-assembled quantum post. This process is found to be highly efficient and to exhibit improved stability at high acoustic powers when compared to direct optical pumping at the position of the quantum post. These characteristics are attributed to the wide matrix quantum well in which charge conveyance occurs and to the larger number of carriers available for injection in the remote configuration, respectively. The emission of such pumped quantum posts is dominated by recombination of neutral excitons and fully directional when the propagation direction of the SAW and the position of the quantum post are reversed. [ABSTRACT FROM AUTHOR]

An acoustic pressure model of bubble bursting is proposed. An experiment studying the acoustic characteristics of the bursting bubble at the surface of a high-viscosity liquid is reported. It is found that the sudden bursting of a bubble at the high-viscosity liquid surface generates N-shape wave at first, then it transforms into a jet wave. The fundamental frequency of the acoustic signal caused by the bursting bubble decreases linearly as the bubble size increases. The results of the investigation can be used to understand the acoustic characteristics of bubble bursting. [ABSTRACT FROM AUTHOR]