Characteristics Of Surface Acoustic Waves Research Articles

Surface acoustic wave digital microfluidics with surface wettability gradient.

This paper reports a digital microfluidic technology that combines surface wettability gradient and surface acoustic waves. The technology enables selection of the driven object, facilitating reactions among multiple droplets and improving the precision of droplet control. Octagonal patterns with a wetting gradient and orthogonally distributed interdigital transducers were created on the surface of a LiNbO3 wafer by photolithography. Leveraging the propagation characteristics of surface acoustic waves on different wetting models, the latter serve as a switch for microfluidic motion, successfully achieving selection of the driven object and demonstrating sequential reactions among multiple droplets. Also, under the excitation of standing surface acoustic waves, droplets on the wetting gradient surface move slightly in the direction of wetting gradient descent, significantly enhancing the positional accuracy of the droplets to the micrometer level. With the advantages of surface acoustic wave digital microfluidics, this technology addresses the challenges of multi-droplet digital manipulation and improved droplet positional accuracy.

Quantitative detection of crack depth in V-groove weld using laser-generated surface acoustic waves

Thick-walled structures are widely used in kinds of high-end equipment. As the most conventional method adopted to manufacture large-scale structures, multi-pass butt-welds are one of the most critical areas prone to defects. In this paper, we focus on the quantitative detection of crack depth in a V-groove weld using laser-generated surface acoustic waves. A two-dimensional finite-element method with Q345 steel is adopted to reveal the complicated propagation characteristics of laser-generated surface acoustic waves with surface cracks. The displacement fields are discussed to show the wave transmission, reflection, and mode-conversion phenomena. The main propagating wave modes—P, R, R′, R′r, and R′t waved—are distinguished with the help of the out-of-plane displacement under different crack depths in the time domain. It is found that R′r can be used to locate the cracks and R′t can be used to quantify the depth of the cracks.

Finite element analysis on the propagation characteristics of laser-generated surface acoustic wave in V-groove weld

Thick-walled structures, such as marine engineering and rail transportation, are widely used in modern society. V-groove welding is a common welding method in thick structures. At the same time, the V-groove weld is also the area of a thick-walled structure in which defects are most easily formed. Laser-generated surface acoustic waves are a promising non-destructive testing method in most fields. This study examined the propagation characteristics of laser-generated surface acoustic waves in a V-groove weld. A two-dimensional finite element model with Q345 steel was constructed. A thermoelastic mechanism was adopted to generate the wave. The temperature and displacement fields were analyzed in detail. The results showed that wave transmission, reflection, and mode conversion are generated with an R wave at the junction, and the dispersion phenomenon of the R wave occurred in the welded area.

Analysis of propagation characteristics of Rayleigh surface acoustic waves on Yb0.33Al0.67N piezoelectric films/high-velocity substrates

Piezoelectricity of YbAlN films has recently been shown to be almost as high as that of ScAlN films. YbAlN film surface acoustic wave (SAW) resonators are expected to have a high coupling factor. We theoretically investigated the propagation characteristics of first-mode Rayleigh SAWs (RSAWs) on Yb0.33Al0.67N film/high-velocity Si, sapphire, AlN, SiC, BN, and diamond substrates. The first-mode RSAWs on the YbAlN layered structures had high coupling factors, higher than those on ScAlN layered structures. An enhancement of the effective coupling factor of the first-mode RSAWs was observed in polarity inverted YbAlN film/BN or diamond substrate structures.

Surface Acoustic Waves in Z-Sections of Piezoelectric Monocrystals of Hexagonal Syngony

A new statement of the problem on the calculation of kinematic and dynamic characteristics of surface acoustic waves in piezoelectric monocrystals is proposed. A procedure for solving the above problem is also proposed with due regard for the existence of electric field scattering on the crystal surface not covered with electrodes and the vortex component of electric field in the general case. The procedure for mathematical description of surface acoustic waves at zero approximation is shown using an example of Z-section of monocrystals of hexagonal syngony. The system of eigenfunctions is built and eigenvalues are determined of the uniform boundary problem for the case of plain deformed state. The general solutions obtained for a particular case of isotropy of elastic properties of deformable solid body are reduced to the generally known definitions of the Rayleigh surface waves. The surface acoustic waves in Z-sections of ZnO and CdS monocrystals similar to the Rayleigh wave in isotropic elastic half-space are shown to exist in a narrow near-surface region, while taking into account the spread of electromagnetic field outside the limits of monocrystal on surfaces that are not covered with electrodes, and the vortex part of the electric field component made it possible to establish the fact that the vertical component of the shift vector of material particles had the maximum value at the depth of (0.15–0.2)λ rather than on the very surface of crystal. A similar peculiarity of Rayleigh waves is typical also for isotropic samples. The presence of local extremum (within 7%) is typical for the vertical component of shift vector in near-surface region having thickness 0.25λ. While penetrating inside the piezoelectric at the depth of more than 2.5 wavelength, the shift levels of material particles decrease by more than one order of magnitude.

An analytically based computer model for evaluating effective elastic properties of nitride nanowire-polymer compositions using laser-generated surface acoustic waves

The investigation of physical and mechanical properties of nitride nanowires (NWs) is a topical field of modern nanotechnological research due to a wide range of promising applications. Normally, the NWs are embedded in a host polymer (e.g., hydrogen silsesquioxane – HSQ), and it becomes necessary to determine the effective properties of polymer-NW compositions rather than of separate wires. The central idea of the present research is the evaluation of the effective elastic moduli of the anisotropic composite HSQ-NW material via the minimization of the goal function that specifies the discrepancy between the measured and calculated characteristics of laser-generated surface acoustic waves. The experimental data are obtained on the basis of transient grating spectroscopy while the theoretical dispersion curves are calculated using the analytically based computer model for elastic guided wave excitation and propagation in multilayered elastic anisotropic half-spaces. The numerical examples illustrate the validation of the developed computer model against the experimental data acquired for sandwich microstructures with known elastic moduli as well as demonstrate the restoration of the latter in the case of HSQ-NW compositions with unknown mechanical properties.

High coupling and highly stable leaky surface acoustic waves on LiTaO3 thin plate bonded to quartz substrate

The propagation properties and resonance characteristics of leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) on a LiTaO3 (LT) thin plate bonded to an AT-cut quartz substrate were investigated experimentally. For the LSAWs and LLSAWs, the bonded structures of 36°Y-cut X-propagating LT (36°YX-LT)/AT-cut 90°X-propagating quartz (AT90°X-quartz) and X-cut 31°Y-propagating LT (X31°Y-LT)/AT-cut 45°X-propagating quartz (AT45°X-quartz) were fabricated, respectively. For the LSAW on 36°YX-LT/AT90°X-quartz, the electromechanical coupling factor (K2) of 11.1% was obtained at an LT thin-plate thickness of 0.25 wavelength, whereas K2 for a single LT substrate was measured to be 5.7%. For the LLSAW on X31°Y-LT/AT45°X-quartz, K2 increased from 2.8% for the single LT substrate to 7.2% at an LT thin-plate thickness of 0.14 wavelength. Furthermore, K2 of approximately 12% and the temperature coefficient of frequency (TCF) of 0 ppm/°C were theoretically obtained simultaneously for the LSAW on 36°YX-LT/AT-cut 90°X-quartz at a certain thin-plate thickness.

Characteristics of surface acoustic waves in (11 $$\bar 2$$ 2 ¯ 0)ZnO film/R-sapphire substrate structures

(11\(\bar 2\) 0)ZnO film/R-sapphire substrate structure is promising for high frequency acoustic wave devices. The propagation characteristics of SAWs, including the Rayleigh waves along [0001] direction and Love waves along [1ī00] direction, are investigated by using 3 dimensional finite element method (3D-FEM). The phase velocity (v p), electromechanical coupling coefficient (k 2), temperature coefficient of frequency (TCF) and reflection coefficient (r) of Rayleigh wave and Love wave devices are theoretically analyzed. Furthermore, the influences of ZnO films with different crystal orientation on SAW properties are also investigated. The results show that the 1st Rayleigh wave has an exceedingly large k 2 of 4.95% in (90°, 90°, 0°) (11\(\bar 2\) 0)ZnO film/R-sapphire substrate associated with a phase velocity of 5300 m/s; and the 0th Love wave in (0°, 90°, 0°) (11\(\bar 2\) 0)ZnO film/R-sapphire substrate has a maximum k 2 of 3.86% associated with a phase velocity of 3400 m/s. And (11\(\bar 2\) 0)ZnO film/R-sapphire substrate structures can be used to design temperature-compensated and wide-band SAW devices. All of the results indicate that the performances of SAW devices can be optimized by suitably selecting ZnO films with different thickness and crystal orientations deposited on R-sapphire substrates.

Love waves in layered flexoelectric structures

In this paper, the flexoelectric effect on Love waves propagating in a structure with a nanoscale piezoelectric guiding layer deposited on an isotropic elastic substrate is analytically investigated. Transcendental complex dispersion equations are obtained and solved numerically which are corresponding to the electrically open and short conditions at the free surface. A detailed discussion about the dispersion relations of the fundamental mode is subsequently presented. The results indicate that flexoelectricity has a substantial effect on Love wave propagation. The presence of flexoelectricity leads to a complex phase velocity with a negative/positive imaginary part, which means Love waves attenuate/grow over time. In addition, the phase velocity dispersion relations depend greatly on the thickness and flexoelectric coefficients of the guiding layer. The current work is the first attempt to explore the flexoelectric effect on the propagation characteristics of surface acoustic waves (SAWs). And the results would be beneficial to achieve a better performance of SAW devices.

Propagations of Rayleigh and Love waves in ZnO films/glass substrates analyzed by three-dimensional finite element method**Project supported by the National Natural Science Foundation of China (Grant No. 11304160), the Natural Science Foundation of Jiangsu Provincial Higher Education Institutions, China (Grant No. 13KJB140008), and the Foundation of Nanjing University of Posts and Telecommunications, China (Grant No. NY213018).

Propagation characteristics of surface acoustic waves (SAWs) in ZnO films/glass substrates are theoretically investigated by the three-dimensional (3D) finite element method. At first, for ZnO films/glass substrates, the simulation results confirm that the Rayleigh waves along the [0001] direction and Love waves along the direction are successfully excited in the multilayered structures. Next, the crystal orientations of the ZnO films are rotated, and the influences of ZnO films with different crystal orientations on SAW characterizations, including the phase velocity, electromechanical coupling coefficient, and temperature coefficient of frequency, are investigated. The results show that at appropriate , Rayleigh wave has a maximum k2 of 2.4% in (90°, 56.5°, 0°) ZnO film/glass substrate structure; Love wave has a maximum k2 of 3.81% in (56°, 90°, 0°) ZnO film/glass substrate structure. Meantime, for Rayleigh wave and Love wave devices, zero temperature coefficient of frequency (TCF) can be achieved at appropriate ratio of film thickness to SAW wavelength. These results show that SAW devices with higher k2 or lower TCF can be fabricated by flexibly selecting the crystal orientations of ZnO films on glass substrates.

Suppression of Rayleigh wave spurious signal in ultra-wideband surface acoustic wave devices employing 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals

The propagation characteristics of surface acoustic waves (SAWs) on rotated Y-cut X-propagating 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMN-33%PT) substrate are theoretically analyzed. It is shown that besides the existence of a shear horizontal (SH) SAW with ultrahigh electromechanical coupling factor K2, a Rayleigh SAW also exists causing strong spurious response. The calculated results showed that the spurious Rayleigh SAW can be sufficiently suppressed by properly selecting electrode and its thickness with optimized rotating angle while maintaining large K2 of SH SAW. The fractional -3 dB bandwidth of 47% is achievable for the ladder type filter constructed by Au IDT/48oYX-PMN-33%PT resonators.

Determination of Mechanical Properties of Battery Films from Acoustic Measurements

Measuring the mechanical properties of lithium-ion battery films, such as thickness and elasticity, is important for predicting and improving homogeneity of the film and performance of the battery. Problems with film heterogeneity could be identified and addressed early on through accurate, non-destructive inspection of the electrode as it is being manufactured. There are several techniques currently used to measure the mechanical characteristics of films, including nanoindentation and laser-induced surface acoustic waves (SAW). However, their use for analyzing battery electrodes is fairly limited. This research investigates the use of acoustic measurements as an alternative means of non-destructive quality control that could be adapted for on-line use. Mechanical properties of thin films, including elastic modulus and thickness, have been determined using SAW [1,2]. Additionally, acoustic time-of-flight measurements have been taken on complete battery cells to find the state of charge [3]. Here we report on our efforts to measure mechanical properties with SAW. A film under tension is excited to produce a wave. This wave is measured at multiple points along the film to determine the speed of the wave. Because wave dispersion is based on properties such as elasticity and density, we can calculate mechanical properties of the film from the wave speed measurements. Preliminary results indicate that acoustic tests can demonstrate observable differences between films with different properties, and that changes in the stiffness of the film (such as what happens during the drying process for battery films) can also be detected as a difference in wave speed.

Propagation characteristics of laser-generated surface acoustic waves in composite plate with gradient changes of near-surface viscous moduli

Taking into account the gradient change of the near-surface viscous property, we develop a finite element model of laser-generated surface acoustic wave in composite plate. The propagation characteristics of the surface acoustic wave in the composite plate are studied in detail, and the influences of the near-surface viscous modulus, thickness, and Lam constant on the attenuation characteristics of the surface acoustic wave are discussed. In addition, the propagation characteristics of the surface acoustic wave are verified by the theoretical calculations of the dispersion and attenuation curves. The results show that the near-surface viscous modulus and thickness are related to the attenuations of the surface shear wave and the Rayleigh wave, but have no influence on the propagation velocity. Furthermore, the imaginary part of the Lam constant has great influence on the attenuations of the surface shear wave and the Rayleigh wave, whereas the imaginary part of has no effect on the attenuation characteristics of the two waves, which indicates that the attenuation of the surface acoustic wave is related to the near-surface shear viscous modulus. The study gives theoretical basis for evaluating the near-surface mechanical properties of the composite plates by the laser ultrasound technique. Besides, it provides a feasible way to study the surface micro-cracks on the composite plates.

FEM simulation of Rayleigh waves for SAW devices based on ZnO/AlN/Si

In this study, the propagation characteristics of surface acoustic waves (SAWs) in ZnO/Si and ZnO/AlN/Si structures are investigated. The phase velocity, the coupling coefficient and the temperature coefficient of frequency (TCF) of the first two modes of SAWs for the ZnO/Si structure are numerically analyzed and compared to experimental data. The results show that a large coupling coefficient of 3.5% associated with a phase velocity of 4600m/s and a TCF of −42.8ppm/°C are obtained in mode 1. Close agreement is achieved between the numerical and experimental results.Inserting an AlN layer between the ZnO and Si layers is shown to increase the performance of the SAW resonator. The simulation results indicate that for mode 0, a temperature compensation of 0ppm/°C and high velocities of up to 4600m/s are obtained by optimizing the AlN/ZnO thickness ratio. These results demonstrate that the ZnO/AlN/Si structure can be used to design wide-band and temperature-compensated SAW devices.

Frequency Domain Characteristics of Laser Surface Acoustic Waves in Healthy Incisor and Initial Dental Caries

Since the dental structure and the mechanical parameters of dental hard tissues would affect the propagation features of ultrasonic waves, laser ultrasonic nondestructive evaluation (NDE) technique can be used to assess human teeth. With the application of an expansion Laguerre polynomial technique, surface acoustic waves (SAW) in human incisors are calculated, and the effects of inhomogeneous elastic properties of enamel and initial dental caries on SAW are also discussed. An experimental setup to generate and detect SAW in incisor by noncontact and nondestructive manner is established. A focused laser line source is used to generate broadband SAW, which is detected by laser Dopple vibrometer on healthy incisor and initial dental carious, respectively. The results demonstrate that some dental parameters such as dental structures and initial dental carious can affect the phase velocities of laser induced SAW. Laser ultrasonic NDE methods have the potential for evaluation of human teeth in vivo. [doi:10.2320/matertrans.I-M2014815]

Characteristics of surface acoustic waves excited by (1120) ZnO films deposited on R-sapphire substrates.

(1120)-textured ZnO films are deposited on Rsapphire substrate by RF magnetron sputtering and the effects of deposition conditions on ZnO films are investigated. The chemical compositions of the ZnO films are characterized by X-ray photoelectron spectroscopy and the results indicate that the ratio of latticed oxygen to zinc increases with increasing of oxygen concentration in the sputtering gas, which demonstrates the improvement of crystal structures in ZnO films. To investigate the characteristics of surface acoustic waves excited by the (1120)-textured ZnO films, SAW delay lines based on layered structures of (1120) ZnO film/R-sapphire substrate are fabricated, in which Rayleigh and Love modes are excited along the (0001)- and (1100)-directions of the ZnO films, respectively. The phase velocities and electromechanical coupling factors of both wave modes are characterized as functions of the film-thickness-to-wavelength ratio. The acoustic properties of the layered structures are calculated using the transfer matrix method. The experimental and theoretical results are in good agreement with each other.

A study of SH-SAW propagation in cubic piezomagnetics for utilization in smart materials

This theoretical investigation provides characteristics of shear-horizontal surface acoustic waves (SH-SAWs) in piezomagnetic cubic monocrystals. The wave characteristics for various cubic piezomagnetics such as Alfenol, Terfenol-D, Metglas, NiFe2O4, etc., with the coefficient of magnetomechanical coupling (CMMC) and are studied. Knowledge of properties of cubic piezomagnetics is beneficial to the design of smart devices, sensors, and actuators, as well as applications in non-destructive testing. Also, the obtained results allow us to choose apt materials to constitute piezomagnetic/piezoelectric laminate composites in the microwave technology.

Surface acoustic wave characteristics of a (100) ZnO/(100) AlN/diamond structure

Propagation characteristics of surface acoustic waves (SAWs) in the (100) ZnO/interdigital transducer (IDT)/(100) AlN/diamond structure are investigated in this study. The temperature coefficient of delay (TCD), the phase velocity, and the coupling coefficient of the first three modes of SAWs for different thicknesses of (100) ZnO and (100) AlN are theoretically analyzed. Results show that the second mode (Sezawa mode) exhibits the largest coupling coefficient. In the second mode, the largest coupling coefficient of 6.05% associated with a phase velocity of 6234m/s and a TCD of 20.9ppm/°C can be found; for a zero TCD case, a large coupling coefficient of 5.35% associated with a phase velocity of 6460m/s can be obtained. Those coupling coefficients and phase velocities are better than the ones in the IDT/(100) ZnO/diamond structure that possesses a large positive TCD. Simulation results indicate that the (100) ZnO/IDT/(100) AlN/diamond structure exhibits a high phase velocity, a large coupling coefficient, and a small TCD, which can be used to design the wideband and temperature-compensated SAW devices for gigahertz-band applications.

Propagation characteristics of surface acoustic waves in single-electron transport devices and the electrical measurement

We focused on investigating the propagation characteristics of surface acoustic waves (SAWs) in SAW-based single-electron-transport (SAW/SET) devices. SAW/SET devices operating in the gigahertz frequency range were fabricated on a GaAs/Al(x)Ga(1-x)As heterostructure. The transmittance and reflection performances of SAW/SET devices were obtained via the electrical measurement. Modeling based on coupling-of-modes theory was introduced to analyze SAW/ SET devices. Based on this model, many second-order effects such as propagation loss and the mechanical and electrical loadings caused by electrode perturbation of the surface were taken into account. Multiple-transit reflections of SAWs were also contained in the calculation. The calculated transmittance and reflection performances were in good agreement with the measured data. Furthermore, we proposed four interference types which could satisfactorily explain the periodic oscillations presented in the acoustoelectric current versus frequency characteristics.

Theoretical analysis of ultrahigh electromechanical coupling surface acoustic wave propagation in Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals

The propagation characteristics of surface acoustic waves (SAWs) on the Y-cut X-propagating Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) substrate are theoretically analyzed. The results indicate the existence of a shear horizontal (SH)-type SAW with an ultrahigh electromechanical coupling factor K2. Different metal layers (Au, Al, and Cu) were examined as the electrode material. With gold, the maximum K2 for the SH SAW reaches 72.6%, while it is smaller (69.7%) for Al or Cu. There also exists a Rayleigh SAW causing the spurious response. It is shown that the response can be suppressed sufficiently by properly adjusting the thickness of the metal layer. This feature is very attractive for the realization of ultrawideband SAW filters. Variation of SAW properties with the substrate rotating angle θ was also investigated. The result indicates that θ = 0° is the best due to the relatively larger K2 for SH SAW and lower value for Rayleigh spurious response.