Surface Acoustic Wave Phase Velocity Research Articles

Surface acoustic wave in temperature compensated NdCa 4 O(BO 3 ) 3 crystal

A two-port synchronous resonator was used for measurements of surface acoustic wave (SAW) parameters in the Y-plane of NdCa4O(BO3)3 crystal. For YX–5°, YX and YX + 5° orientations, the SAW phase velocity under free surface, electromechanical coupling coefficient, second-order temperature coefficient of frequency and turnover temperature (T O) of about 3481, 3502 and 3503 m/s; 0.68, 0.63 and 0.6%; −37, −32 and −70 ppb/°C2 and 80, 25 and −35 °C, respectively, were obtained. The crystal was assessed as attractive in SAW applications due to temperature compensation and high electromechanical coupling coefficient.

SURFACE-ACOUSTIC-WAVE FIELD AND ACOUSTO-OPTIC INTERACTION IN AlN/128-DEG-ROTATED Y-CUT X-PROPAGATION LiNbO3

The efficiency of guided-wave acousto-optic (AO) interaction in AlN /128-deg-rotated Y-cut X-propagation lithium niobate (128-deg YX- LiNbO 3) structure is analyzed theoretically for the first time by determining the overlap integral between the optical and the surface acoustic wave (SAW) field distribution. The results show that the use of an AlN film can increase the phase velocity of SAW, the electromechanical coupling coefficient and the diffraction efficiency of AO interaction. A maximum of 9.33% for the electromechanical coupling coefficient is obtained when the normalized thickness of AlN film equals 0.09. The diffraction efficiency has a significant improvement when the normalized thickness of AlN film is increased from 0 to 0.05. And, the improvement for the TM polarization is more evident than that for the TE polarization. However, for a well-concentrated optical waveguide, the use of an AlN film reduces the diffraction efficiency of the TM polarization when the SAW frequency is low.

Effect of a pulsed Nd:YAG laser on surface acoustic wave velocity of human dental enamel

The purpose of this study was to evaluate the effect of Nd:YAG laser irradiation on the phase velocity of surface acoustic waves (SAWs) of human enamel. A pulsed Nd:YAG laser at 1064 nm wavelength was used to irradiate the human enamel from extracted human premolars. The output power and repetition rate were 250 mJ and 5 Hz, respectively. The SAW phase velocities before and after laser irradiation were determined using a laser photoacoustic method. The laser-treated enamel surface exhibited a higher velocity value for frequencies higher than 3 MHz. The result of this study suggests that there is an important correlation between the elastic properties of human enamel and the pulsed Nd:YAG laser fluence, which increases the SAW phase velocity, and this may help shed some light on the mechanism of laser treatment in dental research.

Simulation on Effects of Electrical Loading due to Interdigital Transducers in Surface Acoustic Wave Resonator

This paper investigates the effects of electrical loading due to metallic interdigital transducer (IDT) on surface acoustic wave (SAW) velocity in SAW resonators by simulation using FEM in COMSOL Multiphysics. The IDT electrodes fabricated over the piezo-substrate short circuit the parallel electric field associated with SAW under the IDT during wave propagation and affect the SAW phase velocity. The simulation considers a SAW resonator with massless infinite number of IDT fingers on Y–Z cut lithium niobate substrate. The changes in resonance frequency and SAW phase velocity of SAW resonator due to electrical loading are studied for various metallization ratios. The electric field distribution at the surface of piezo-substrate is obtained and it is observed that the short circuit of the electric field due to metallic IDT reduces the SAW phase velocity; consequently, the resonance frequency of the SAW device decreases.

Frequency dependence of laser ultrasonic SAW phase velocities measurements

Advances in the field of laser ultrasonics have opened up new possibilities in applications in many areas. This paper verifies the relationship between phase velocities of different materials, including hard solid and soft solid, and the frequency range of SAW signal. We propose a novel approach that utilizes a low coherence interferometer to detect the laser-induced surface acoustic waves (SAWs). A Nd:YAG focused laser line-source is applied to steel, iron, plastic plates and a 3.5% agar–agar phantom. The generated SAW signals are detected by a time domain low coherence interferometry system. SAW phase velocity dispersion curves were calculated, from which the elasticity of the specimens was evaluated. The relationship between frequency content and phase velocities was analyzed. We show that the experimental results agreed well with those of the theoretical expectations.

A Theoretical study of Propagation of Rayleigh surface waves in functionally graded piezoelectric (FGPM) half-space

This work presents a theoretical study of the propagation behavior of Rayleigh waves in a functionally graded piezoelectric material (FGPM) half-space. The influence of the graded variation of FGPM coefficients on the dispersion curves of Rayleigh waves is investigated for both electrically open and short conditions. The exponential gradient may be applied separately to mechanical and electrical properties. Examples have been given illustrating the use and capabilities of the method based on the recursive stiffness matrix method, in calculating SAW coupling factor (K2) versus crystal orientation, SAW phase velocity for particular frequency range, and field profile variations with depth. The effects of the gradient variation of material constants on the distribution of displacement, stresses and electric potential are presented and discussed in detail. It is note that this paper considers the plane problem of an anisotropic beam which the material composition varies continuously in the direction of the thickness. Some useful discussions and numerical approach are presented to show the significant influence of material inhomogeneity, and adopting a certain value of the inhomogeneity parameter α and applying suitable electric and mechanical loads can optimize the FGPM substrate structures. This will be of particular importance in modern engineering design of high-performance surface acoustic wave (SAW) devices.

Surface Acoustic Wave Propagation in Relaxor-Based Ferroelectric Single Crystals 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 Poled along [011

Surface acoustic wave (SAW) propagation in relaxor-based ferroelectric single crystals 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 (PZN-7%PT) poled along [011]c has been analyzed theoretically. The results show that PZN-7%PT single crystals have excellent SAW properties, such as low phase velocities, very high electromechanical coupling coefficients and small power flow angles. It is also found that the SAW properties strongly depend on the propagation direction and the characteristic curves of SAW phase velocity, and the electromechanical coupling coefficients are symmetric with respect to θ = 90°. Considering all related factors, the X-cut PZN-7%PT single crystal has the best performance. Based on our results, the X-cut PZN-7%PT single crystals poled along [011]c are an excellent candidate for ultra-wide bandwidth low-frequency SAW devices.

Photoacoustic diagnosis of human teeth using interferometric detection scheme

We have investigated the mechanical and acoustic properties of human teeth using the laser generation of surface acoustic wave (SAW) technique. The materials investigated included normal and decayed teeth, which have similar grain sizes and different thicknesses. The tissue responds to the laser-induced stress by thermoelastic expansion. The informative features of this method allow one to determine sample thermal, optical, and acoustical properties that depend on the peculiarities of the sample compositional structure. An interferometric detection experimental scheme is applied for detection generated SAW pulses. The surface displacement curves shape of normal and decayed human teeth are shown. The dispersion curves for SAW pulses were determined by Fourier analysis. The result is an almost linear dependence of SAW velocity on frequency for a normal tooth, the magnitude of the thermoelastic expansion of the normal tooth reaches its peak at 0.344μs, a SAW phase velocity of 2500ms−1 between 0.0008 and 5MHz was determined. For abnormal teeth, the magnitude of thermoelastic expansion of the normal tooth reaches its peak at 1.3μs, the measured velocity was 3225ms−1. Due to the inhomogeneity of abnormal teeth perpendicular to the propagation direction, strong differences in their dispersion curves were obtained. The detection of acoustic waves is the basis of photoacoustic methods, which can be used for diagnostic purposes.

Elastic properties of soft tissue-mimicking phantoms assessed by combined use of laser ultrasonics and low coherence interferometry

Advances in the field of laser ultrasonics have opened up new possibilities in medical applications. This paper evaluates this technique as a method that would allow for rapid characterization of the elastic properties of soft biological tissue. In doing so, we propose a novel approach that utilizes a low coherence interferometer to detect the laser-induced surface acoustic waves (SAW) from the tissue-mimicking phantoms. A Nd:YAG focused laser line-source is applied to one- and two-layer tissue-mimicking agar-agar phantoms, and the generated SAW signals are detected by a time domain low coherence interferometry system. SAW phase velocity dispersion curves are calculated, from which the elasticity of the specimens is evaluated. We show that the experimental results agree well with those of the theoretical expectations. This study is the first report that a laser-generated SAW phase velocity dispersion technique is applied to soft materials. This technique may open a way for laser ultrasonics to detect the mechanical properties of soft tissues, such as skin.

Optimum cut orientation of piezoelectric substrate and propagation direction of SAW for rotation rate sensor

The effect of Coriolis and centrifugal forces on the propagation characteristics of surface acoustic waves (SAW) on a rotating piezoelectric substrate can be utilized for sensing rotation rate. In this paper, the relationship between SAW phase velocity and the rotation rate of the substrate is analyzed theoretically and numerically based on the coupling wave equations on anisotropic piezoelectric substrate with rotation effect. Partial wave theory and surface effective permittivity method are employed. Using LiNbO 3 as an example, some quantitative results of SAW rotation rate sensor, including free and metalized interfaces between substrate and free space in X-cuts, Y-cuts, and Z-cuts, are obtained. Furthermore, by considering comprehensively SAW rotation rate sensitivity with SAW excitation efficiency and beam steering, the optimum cut orientation of piezoelectric substrate and propagation direction of SAW for rotation rate sensor are presented. The research findings can provide theoretical guidance and simulation basis for the experimental research on SAW rotation rate sensor.

Design of Double Mode SAW Filters Using IDT/(100) ZnO/(111) Diamond Structure

Propagation characteristics of surface acoustic waves (SAWs) in interdigital transducers (IDT)/(100) ZnO/diamond structures are investigated in this study using the finite element method. The effects of electrodes on phase velocity, coupling coefficient, and reflectivity of SAWs in the layered structures are illustrated. The extracted coupling-of-mode parameters are then applied to calculate frequency responses of double mode SAW filters using the transmission matrix method. Simulation results show a tailored filter applicable for wideband code division multiple access systems can be achieved.

Surface acoustic wave properties of aluminum oxide films on lithium niobate

Aluminum oxide (Al 2O 3) films have been deposited on lithium niobate (LiNbO 3) substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al 2O 3 films to LiNbO 3 substrates. As Al 2O 3 thin films can sufficiently increase the surface acoustic wave (SAW) velocity, they can be used to improve the performance of the SAW device. The SAW phase velocity in the Al 2O 3/LiNbO 3 structure was found to increase with the insertion of an Al 2O 3 film, which can be attributed to the stiffening effect of the Al 2O 3 layer. The velocity change ratio of SAW was about 4.39% (at 304 MHz) for the Al 2O 3 (9.7 μm)/LiNbO 3 sample. A comparison with other findings in literature reveals that this result is better than what is available from diamond-like carbon/SiC buffer layer/LiNbO 3 structure, whose the velocity change ratio is 2%.

Assessment of langatate material constants and temperature coefficients using SAW delay line measurements

This paper reports on the assessment of langatate (LGT) acoustic material constants and temperature coefficients by surface acoustic wave (SAW) delay line measurements up to 130 degrees C. Based upon a full set of material constants recently reported by the authors, 7 orientations in the LGT plane with Euler angles (90 degrees, 23 degrees, Psi) were identified for testing. Each of the 7 selected orientations exhibited calculated coupling coefficients (K(2)) between 0.2% and 0.75% and also showed a large range of predicted temperature coefficient of delay (TCD) values around room temperature. Additionally, methods for estimating the uncertainty in predicted SAW propagation properties were developed and applied to SAW phase velocity and temperature coefficient of delay calculations. Starting from a purchased LGT boule, the SAW wafers used in this work were aligned, cut, ground, and polished at University of Maine facilities, followed by device fabrication and testing. Using repeated measurements of 2 devices on separate wafers for each of the 7 orientations, the room temperature SAW phase velocities were extracted with a precision of 0.1% and found to be in agreement with the predicted values. The normalized frequency change and the temperature coefficient of delay for all 7 orientations agreed with predictions within the uncertainty of the measurement and the predictions over the entire 120 degrees C temperature range measured. Two orientations, with Euler angles (90 degrees, 23 degrees, 123 degrees) and (90 degrees, 23 degrees, 119 degrees), were found to have high predicted coupling for LGT (K(2) > 0.5%) and were shown experimentally to exhibit temperature compensation in the vicinity of room temperature, with turnover temperatures at 50 and 60 degrees C, respectively.

Effects of conducting layers on surface acoustic wave in AlN films on diamond

The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the coupling coefficient and, thus, broaden the bandwidth of SAW devices. For the Sezawa mode, it is illustrated that using a Ti layer with a layer thickness-to-wavelength ratio of 0.02 the maximum coupling coefficient is 2.546% and the associated SAW phase velocity is 10657 m/s at the AlN films’ thickness-to-wavelength ratio of 0.14. This coupling coefficient is 105% higher than that in the IDT/AlN/diamond structure. The research results can be applied to design SAW devices using diamond based structures in the super high frequency band.

Accelerating Effect of Aluminum Oxide Films on Surface Acoustic Wave on Cystalline Quartz

Aluminum oxide (Al2O3) films have been successfully deposited on stable temperature (ST)-cut quartz substrates by electron beam evaporation without any interlayer to ensure a good adhesion of the Al2O3 films to the quartz substrates. The Al2O3 thin films increase the surface acoustic wave (SAW) velocity sufficiently, and can be used to improve the performance of SAW devices. Both the theoretical and experimental results show that the SAW phase velocity in the Al2O3/quartz structure was increased with the insertion of an Al2O3 film. The increase in SAW velocity with increasing thickness of the Al2O3 film results from the stiffening effect of the Al2O3 layer. The velocity change ratio predicted by the theoretical analysis of the Al2O3 (1.45 µm)/quartz sample was about 4.38% which is slightly larger than the experimental result of 3.28%. These results are better than those published in the literature for a diamond-like carbon/SiC buffer layer/quartz structure with a velocity change ratio of 2.3%.

Preparation of ZnO Thin Film on Diamond-Like Carbon/Si Substrate by RF Magnetron Sputtering for Surface Acoustic Wave Application

Diamond-like carbon (DLC) films have received much attention due to their excellent hardness, chemical inertness, and low surface friction coefficient. But DLC films needed to be combined with one piezoelectric layer such like ZnO or AlN film for surface acoustic wave (SAW) applications. In this paper, we study the effect of DLC thin film fabricated by RF magnetron sputtering on the characteristics of the SAW devices (IDT/ZnO/DLC/Si). The comparison of the phase velocity of the ZnO/DLC/Si layered structure with different thickness of the DLC thin films is discussed. We use a two-step process for the deposition of ZnO film on DLC thin film to enhance the adhesion between them. The full width at half maximum intensity of ZnO(002) orientation obtained is only 0.19° from the X-ray diffraction. The phase velocity of the SAW devices will be increased when the thickness of the DLC thin film is increased. The results show that the characteristics of the SAW devices could be improved by the DLC films in raising the SAW phase velocity.

Brillouin light scattering characterization of the surface acoustic wave velocity in the ZnO/ Si 3N 4 /Si(100) system

The Surface Acoustic Wave (SAW) phase velocity of ZnO thin films has been determined by High Resolution Brillouin Light Scattering Spectroscopy in order to study the influence of an intermediate layer with a set of elastic constants higher than the corresponding ones for ZnO. The study of the system formed by ZnO/ Si 3N 4/Si(100), deposited by reactive magnetron sputtering, shows a SAW phase velocity increment with respect to the ZnO/Si(100) single layer system. Results are discussed in terms of the elasticity theory, which predicts an increase of the acoustic wave phase velocity when an intermediate layer stiffer than the film at the surface is present in the system.

Temperature stability of ZnO thin film SAW device on fused quartz

Surface acoustic wave (SAW) filters for low-frequency (38-65 MHz) applications have been developed using a radio frequency (RF)-magnetron-sputtered ZnO film on fused-quartz substrates. SAW propagation characteristics such as electromechanical coupling coefficient (K/sup 2/), SAW phase velocity (v), insertion loss, and temperature coefficient of delay (TCD) have been measured. The intergidital transducer (IDT)/ZnO/fused-quartz device structure yields almost zero TCD (1 ppm/spl middot//spl deg/C/sup -1/) with 0.316 /spl lambda/ thick ZnO layer (for the device operating at 60 MHz). Alternately, an overlayer of positive TCD material (ZnO itself) has also been deposited on the IDT/ZnO(<0.316 /spl lambda/)/fused-quartz device at a low substrate temperature to reduce the TCD. A modified layered structure consisting of ZnO/IDT/ZnO/fused quartz yields almost zero TCD (-3 ppm/spl middot//spl deg/C/sup -1/) with a 5.3-/spl mu/m-thick ZnO overlayer and a 8.1-/spl mu/m-thick (0.183 /spl lambda/) ZnO bottom layer. Experimentally obtained SAW propagation characteristics have been compared with the theoretical results.

Correlation between adhesion of diamond-like carbon film on LiTaO 3 substrate and SAW velocity

Coating diamond-like carbon (DLC) film to LiTaO 3 substrate is theoretically expected to stiffen the substrate surface so as to accelerate the surface acoustic wave (SAW) at the surface due to its high elastic constant and low mass density. However, it has been reported that DLC film on LiTaO 3 substrate led to a reduction of SAW velocity probably due to poor adhesion between the DLC film and LiTaO 3 substrate. In this study, the adhesion strength between DLC film and LiTaO 3 substrates has been enhanced by introducing a SiO 2 interlayer. Scratch test shows that relatively thick DLC films with an appropriated thickness SiO 2 interlayer exhibit a good adhesion. The increase in SAW velocity correlates with the adhesion strength of the DLC film to the LiTaO 3 substrate, indicating that the adhesion plays an important role of joining the two materials together. In addition, with an improved adhesion, SAW phase velocity in the DLC/SiO 2/LiTaO 3 structure increases with increasing DLC film thickness and with decreasing SiO 2 interlayer thickness.

Applications of piezoelectric ZnO film deposited on diamond-like carbon coated onto Si substrate under fabricated diamond SAW filter

The applications of surface acoustic wave (SAW) devices aim directly at piezoelectric thin films deposited onto amorphous diamond-like carbon (DLC) coated on silicon substrates from target ZnO in this study. Our high-velocity SAW filters are characterized using multi-layer structures of thin films by DLC depositing. However, if propagating velocity of diamond is much higher, then the SAW phase velocity of piezoelectric thin film ZnO deposited on DLC coated onto Si substrate is raised from 2800 to11430 m/s. Consequently, the GHz-band SAW devices could be fabricated using thin films of DLC without sub-micron photolithography technology. We have been also successfully fabricated and demonstrated the diamond-like SAW filters by evaporating interdigital transducers on ZnO thin films with ULSI technology.