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The paper presents 3D finite element simulation and analysis of Love wave resonator with different guiding layer materials and investigation of the coupled resonance effect with ZnO nanorods on the device surface. Analytical estimation of phase velocity and mass sensitivity of Love wave device with SiO 2 , ZnO, gold, SU-8, and parylene-C as guiding layer materials is performed for comparative analysis. Simulations are carried out to study the variation in electromechanical coupling coefficient, displacement profile and frequency response of the Love wave resonator. SU-8 offers high mass sensitivity of 1044 m 2 /kg while gold layer provides maximum K 2 of 8.6%. In comparison to SiO 2 and ZnO, polymers exhibit sharp rise and fall in K 2 within a narrow range of normalized layer thickness (0.03–0.1). ZnO nanorods of varying height and surface nanorod density are designed over the Love wave resonator with SiO 2 as the waveguiding layer. In the presence of coupled resonance, the nanorods and substrate vibrate in unison causing an increase in average stress and mass sensitivity but leads to decrease in the electromechanical coupling coefficient of the device. Surface nanorod packing density of 25  μ m −2 offers high mass sensitivity of 1304 m 2 /kg that is 20 times greater in comparison to the mass sensitivity of a plain Love wave device. [ABSTRACT FROM AUTHOR]

The spatial three dimensional variation of the polarization ellipse characterizing an elastic movement of the solid particles in the harmonically oscillating ultrasonic fields is studied. Such a variation comes into sight because of the interference of various elastic modes generated during the excitation and/or scattering of acoustic waves by the inhomogeneities located on the solid surface. In order to confirm this effect, an innovative method based on finite element approach is used showing a rule to find the form and orientation of the elastic polarization ellipse in general case. Polarization plane may have an arbitrary orientation in anisotropic crystals. The dispersive parameters of the spatially changeable ellipse of polarization in a substrate with perturbed boundary conditions depend on the polarization and on the relative complex-valued amplitudes of the partial elastic modes which contribute differently to the sum of acoustic fields at every point of analysis. Results of a detailed investigation of the mentioned effects in an interdigital transducer formed by aluminum electrodes on the ST-X cut of quartz substrate are presented. [ABSTRACT FROM AUTHOR]

The measurement of the displacements caused by the propagation of a short pulse of surface acoustic waves on a solid substrate is investigated. A stabilized time-domain differential interferometer is proposed, with the surface acoustic wave (SAW) sample placed outside the interferometer. Experiments are conducted with surface acoustic waves excited by a chirped interdigital transducer on a piezoelectric lithium niobate substrate having an operational bandwidth covering the 200–400 MHz frequency range and producing 10-ns pulses with 36 nm maximum out-of-plane displacement. The interferometric response is compared with a direct electrical measurement obtained with a receiving wide bandwidth interdigital transducer and good correspondence is observed. The effects of varying the path difference of the interferometer and the measurement position on the surface are discussed. Pulse compression along the chirped interdigital transducer is observed experimentally. [ABSTRACT FROM AUTHOR]

A novel structure consisting of a Si plate sandwiched between two ZnO layers is suggested as propagation medium for Quasi Longitudinal (QL) acoustic Lamb waves. Considering a low-dispersive quasi-longitudinal mode as an example, the phase velocity v , electromechanical coupling constant k 2 and mechanical displacements U 1 , U 3 versus plate and ZnO layers thicknesses have been calculated starting from uncoated plate through the same plate with one layer to the plate with two layers onto opposite faces. A remarkable increase in the electromechanical coupling, together with an essential decrease in the vertical displacement U 3 , at the ZnO surface, have been theoretically demonstrated and experimentally verified for definite combinations of the films/plate thicknesses. This property of the structure is attractive for applications to microwave liquid sensors. [ABSTRACT FROM AUTHOR]

In this paper, we examine the significance of the various higher-order effects regarding calculating temperature behavior from a set of material constants and their temperature coefficients. Temperature-induced velocity shifts have been calculated for quartz surface acoustic wave (SAW) resonators and the contributions of different groups of nonlinear material constants (third-order elastic constants (TOE), third-order piezoelectric constants (TOP), third-order dielectric constants (TOD) and electrostrictive constants (EL)) to the temperature-induced velocity shifts have been analyzed. The analytical methodology has been verified through the comparison of experimental and analytical results for quartz resonators. In general, the third-order elastic constants were found to contribute most significantly to the temperature-induced shifts in the SAW velocity. The contributions from the third-order dielectric constants and electrostrictive constants were found to be negligible. For some specific cases, the third-order piezoelectric constants were found to make a significant contribution to the temperature-induced shifts. The significance of each third-order elastic constant as a contributor to the temperature-velocity effect was analyzed by applying a 10% variation to each of the third-order elastic constants separately. Additionally, we have considered the issues arising from the commonly used thermoelastic expansions that provide a good but not exact description of the temperature effects on frequency in piezoelectric resonators as these commonly used expansions do not include the effects of higher-order material constants. [ABSTRACT FROM AUTHOR]

The paper presents the characteristics of vertically polarized surface waves generated in silicon substrate by acoustic coupling of bulk waves excited in a periodically patterned ZnO film on silicon. The finite element simulations are performed on the proposed patterned-ZnO/Si structure and vertically polarized modes in silicon are found to be dominant in the frequency dependent analysis. The generated modes in silicon are concentrated near the surface within a wavelength depth and exhibit surface wave properties. Dispersion curves of phase velocity and coupling coefficient for the surface modes are reported. The results indicate high electromechanical coupling coefficient of 6.4% as well as high phase velocity of 5332 m/s for the surface mode generated in silicon owing to the acoustic coupling of the first order bulk mode in ZnO pattern observed at ZnO height to wavelength ratio of 0.19. [ABSTRACT FROM AUTHOR]

Highlights: [•] 2D COMSOL simulations for CMOS compatible SAW filter were done. [•] We simulated a piezoelectric thin film system consisting of AlN/SiO2/Si(100). [•] Several parameters were calculated like dispersion curves, coupling factor, reflectivity. [•] We could identified the particle displacement for the first two Rayleigh modes. [•] Al-electrodes showing high coupling factors and lowest acoustic reflectivity. [ABSTRACT FROM AUTHOR]

Abstract: The investigations of the propagation of the SAW in the multilayered structures have been of great interest since the combination of the surface acoustic wave (SAW) technology with the microelectromechanical system (MEMS) technology comes true. In this paper, the recursive asymptotic method (RAM) is applied to analysis the propagation of the SAW in the ZnO–SiO2–Si multilayered structure. The influences of the ZnO layer thickness and the SiO2 layer thickness to the phase velocity and the electro-mechanical coupling coefficient for the Rayleigh wave and Love wave are discussed. The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate. In order to prove the theoretical results, a series of Love mode SAW devices based on the ZnO–SiO2–Si multilayered structure is fabricated by micromachining, and their frequency responses are detected. The experimental results are found to be mainly consistent with the theoretical ones except the little larger velocities induced by the residual stresses produced in the fabrication process of the films. The deviation of the experimental results from the theoretical ones is reduced by thermal annealing. [Copyright &y& Elsevier]

Abstract: Highly c-oriented aluminum nitride (AlN) thin piezoelectric films have been grown by pulsed direct-current (DC) magnetron reactive sputter deposition. The films were deposited at room temperature and had a typical full width half maximum (FWHM) value of the (002) rocking curve of around 2°. Resonant devices in thin film plates having surface acoustic wave (SAW) based designs were fabricated by means of low resolution photolithography. The devices were designed to operate with the fast Rayleigh and Lamb modes respectively. Both types of devices exhibited propagation velocities in excess of 10000m/s and sufficient electromechanical couplings. The device measurements illustrate the big potential of these modes for the development of low cost IC compatible electroacoustic devices in the lower GHz range. The basic properties of the modes studied are discussed in a comparative manner. Potential commercial applications are also outlined. [Copyright &y& Elsevier]

We have designed and had manufactured a custom surface acoustic wavefront sensor, using a standard CMOS process. Ultrasound propagating along the surface of an object perturbs the reflection of incident laser light, which has been focused onto the object using a cylindrical lens. These high-frequency angular perturbations of reflected light relate to the amplitude and phase of the ultrasound along a line on the surface of the object, and thus correspond to the acoustic wavefront. The reflected light is imaged onto a custom linear array of split photodiodes; these simultaneously detect the high-frequency perturbations at several discrete points along the line, forming an acoustic wavefront sensor.As well as a description of the device, its role within an adaptive optical scanning acoustic microscope is discussed. The sensor detects the distortions to the acoustic wavefront after it has propagated through an aberrating medium, such as a metal containing grains of random orientation. The information attained may then be used to alter the generation profile of the optical generation source of the acoustic waves, thus reducing the distortion caused by the aberration and increasing the resolution and accuracy of the system as a whole. [Copyright &y& Elsevier]

This article is focused on the analysis of the electroacoustic response of surface acoustic wave (SAW) filters made of aluminium nitride (AlN) thin films on various types of Si wafers. AlN films with (0 0 · 2) orientation were deposited by RF reactive sputtering of an Al target in Ar and N2 admixtures on Si(1 0 0) and (1 1 1) wafers with resistivities ranging between 10 and 2000 Ω cm. The electroacoustic response of SAW filters with an acoustic wavelength of 40 μm was analysed by measuring the Sij parameters with a network analyser. We have determined that the out-of-band loss is directly related to the Si substrate resistivity, varying from 26 dB for 10 Ω cm to 55 dB for 2000 Ω cm. The SAW velocity depends on the orientation of the Si wafer, being approximately 4700 m/s for Si(1 1 1) and 5100 m/s for Si(1 0 0). The electroacoustic responses of the SAW filters were fitted by computations based on a simple circuital model that takes into account parasitic effects such as airborne electromagnetic coupling and conduction through the substrate. This procedure provides accurate values of the electromechanical coupling factor k2 even for devices with poor characteristics. Good quality SAW filters of AlN on high resistivity Si(1 0 0) wafers with k2 larger than 0.12% are demonstrated. [Copyright &y& Elsevier]

In this work we employ additive manufacturing to print a circular array of micropillars on an aluminium slab turning its top surface into a graded index metasurface for surface acoustic waves (SAW). The graded metasurface reproduces a Luneburg lens capable of focusing plane SAWs to a point. The graded index profile is obtained by exploiting the dispersion properties of the metasurface arising from the well-known resonant coupling between the micropillars (0.5 mm diameter and variable length ∼ 3 mm) and the surface waves propagating in the substrate. From the analytical formulation of the metasurface's dispersion curves, a slow phase velocity mode is shown to arise from the hybridisation of the surface wave with the pillar resonance. This is used to compute the radial height profile corresponding to the refractive index given by Luneburg's equation. An initial validation of the lens design, achieved through ray theory, shows that ray trajectories have a strong frequency dependence, meaning that the lens will only work on a narrow band. An ultrasonic experiment at 500 kHz where plane SAWs are generated with a piezoelectric transducer and a laser scanner measures the out of plane displacement on the metasurface, validates the actual lens performance and the manufacturing technique. Finally, comparison between the ray analysis and experimental results offers insight into the behaviour of this type of metasurface especially in the proximity of the acoustic bandgaps and highlights the possibility for acoustic shielding. • Design, modelling and experimental results of a surface acoustic wave Luneburg lens. • Surface acoustic waves are focused to a point by the Luneburg lens. • Additive manufacturing is employed to print the Luneburg lens. • A ray tracing approach models the Luneburg lens behaviour. [ABSTRACT FROM AUTHOR]

• This work piloted the development of thin film GaN-based Acoustic Tweezer (GaNAT). • The vibration of SAW on thin film GaN was quantified. • The numerical study can predict the pressure field and particle trajectories. • GaNAT can manipulate micro-particles and match the numerical results. • The multiphysical properties of GaN improve GaNAT towards integrated electronics. Gallium nitride (GaN) is a compound semiconductor which shows advantages in new functionalities and applications due to its piezoelectric, optoelectronic, and piezo-resistive properties. This study develops a thin film GaN-based acoustic tweezer (GaNAT) using surface acoustic waves (SAWs) and demonstrates its acoustofluidic ability to pattern and manipulate microparticles. Although the piezoelectric performance of the GaNAT is compromised compared with conventional lithium niobate-based SAW devices, the inherited properties of GaN allow higher input powers and superior thermal stability. This study shows for the first time that thin film GaN is suitable for the fabrication of the acoustofluidic devices to manipulate microparticles with excellent performance. Numerical modelling of the acoustic pressure fields and the trajectories of mixtures of microparticles driven by the GaNAT was performed and the results were verified from the experimental studies using samples of polystyrene microspheres. The work has proved the robustness of thin film GaN as a candidate material to develop high-power acoustic tweezers, with the potential of monolithical integration with electronics to offer diverse microsystem applications. [ABSTRACT FROM AUTHOR]

A novel structure consisting of a Si plate sandwiched between two ZnO layers is suggested as propagation medium for Quasi Longitudinal (QL) acoustic Lamb waves. Considering a low-dispersive quasi-longitudinal mode as an example, the phase velocity v, electromechanical coupling constant k 2 and mechanical displacements U 1 , U 3 versus plate and ZnO layers thicknesses have been calculated starting from uncoated plate through the same plate with one layer to the plate with two layers onto opposite faces. A remarkable increase in the electromechanical coupling, together with an essential decrease in the vertical displacement U 3 , at the ZnO surface, have been theoretically demonstrated and experimentally verified for definite combinations of the films/plate thicknesses. This property of the structure is attractive for applications to microwave liquid sensors., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The paper presents the characteristics of vertically polarized surface waves generated in silicon substrate by acoustic coupling of bulk waves excited in a periodically patterned ZnO film on silicon. The finite element simulations are performed on the proposed patterned-ZnO/Si structure and vertically polarized modes in silicon are found to be dominant in the frequency dependent analysis. The generated modes in silicon are concentrated near the surface within a wavelength depth and exhibit surface wave properties. Dispersion curves of phase velocity and coupling coefficient for the surface modes are reported. The results indicate high electromechanical coupling coefficient of 6.4% as well as high phase velocity of 5332 m/s for the surface mode generated in silicon owing to the acoustic coupling of the first order bulk mode in ZnO pattern observed at ZnO height to wavelength ratio of 0.19., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A simulation study of Rayleigh wave devices based on a stacked AlN/SiO₂/Si(100) device was carried out. Dispersion curves with respect to acoustic phase velocity, reflectivity and electromechanical coupling efficiency for tungsten W and aluminium Al electrodes and different layer thicknesses were quantified by 2D FEM COMSOL simulations. Simulated acoustic mode shapes are presented. The impact of these parameters on the observed Rayleigh wave modes was discussed. High coupling factors of 2% and high velocities up to 5000 m/s were obtained by optimizing the AlN/SiO₂ thickness ratio., (Copyright © 2013 Elsevier B.V. All rights reserved.)