SAW Reflection Research Articles

Characterization of surface acoustic wave propagation in multi-layered structures using extended FEM/SDA software

This paper describes the characterization of SAW propagation in layered substrate and overlayered structures. The software based on the finite element method and spectral domain analysis was newly developed and applied to the characterization of SAW propagation under an infinitely-long Al interdigital transducer on a rotated Y-cut LiTaO(3)/sapphire substrate. Because of the finite LiTaO(3) thickness, a series of spurious resonances appears. It is shown that the excitation strength of the spurious resonances changes with frequency as well as the rotation angle, which reflects the frequency and rotation angle dependence of the energy leakage. Next, the analysis was carried out for SAWs propagating in a SiO(2) layer/Al IDT/42 degrees YX-LiTaO(3) structure. It is shown that the influence of the SiO(2) layer is significantly dependent on the location where the SiO(2) layer is deposited. In particular, it is shown that when the SiO(2) layer is deposited only on top of the electrodes, the SAW reflectivity increases compared with when the SiO(2) layer is deposited between and on top of electrodes.

SAW reflection and scattering by electrodes

SAW reflection and scattering by electrodes

Single-Phase Unidirectional Surface Acoustic Wave Transducer Using Cu Electrode

This paper proposes the application of Cu electrodes to surface acoustic wave single-phase unidirectional transducers (SAW SPUDTs). Since SPUDTs require large and widely variable reflectivity obtained by relatively thin electrodes, Cu with large mass density is one of the candidate materials. First, SAW reflection characteristics of a Cu electrode on 128°YX-LiNbO3 were theoretically investigated. It is shown that Cu electrodes offer much larger reflectivity than Al electrodes. In addition, SAW velocity change with electrode width is quite moderate compared with other materials having large mass density such as Au. An SPUDT was fabricated employing Cu electrodes to discuss how effectively SAW reflectivity contributes, for example, to its unidirectionality. As a result, the obtained directivity for the Cu-SPUDT was about 16 dB, which was 10 dB larger than that for an SPUDT employing conventional Al electrodes.

Scattering of SAW at discontinuities: some numerical experiments

In developing models to characterize the metallic-finger step discontinuity in SAW devices on piezoelectric substrates it is important to estimate the SAW reflection coefficients and the effect of other modes at step discontinuities. In the literature perturbation approximations, finite element methods and various phenomenological parameter-fitting using experimental data are among the techniques which have been exploited. In this paper, a nonperturbation approximation method, which attempts to parallel some well-established techniques used in solving electromagnetic waveguide-discontinuity problems, is explored as an alternate numerical procedure for calculating SAW reflections. Implementing such a method requires that the full solution to SAW propagation in the free and in the layered regions be obtained. Thus, for a free-to-metallized discontinuity, the two SAW phase velocities, the total SAW power now in the free region and in the layered region, and the electroacoustic fields, must be calculated. In this paper the reflection problem is formulated as an optimization problem subject to the necessary scattering parameter constraints. Numerical experiments are described, and the results of calculations for reflectivity are compared to perturbation approximations, nonperturbation approximations and the available experimental data for the effects of energy storage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Green's function approach to the reflection behavior of SAW in layered structures

A Green's function method is used to derive expressions for the mechanical part of complex SAW reflection coefficients for layered structures of any material symmetry with transverse perturbations of arbitrary shape and material symmetry. The computed data are in qualitative agreement with published results that have been derived using the variational principle or the perturbation theory. Deviations arise from quite different situations concerning the point of observing the reflected wave.

Non-linear SAW reflection: experimental evidence and NDE applications

Acoustic non-linearity of the interface between solids that are pressed in contact has been experimentally demonstrated to make the principal contribution to the backscattered acoustic field of an incident SAW at high harmonic frequencies. Contact acoustic non-linearity has also been shown to represent a close simulation of non-linear elastic properties of fractured defects in solids, whose non-linear reflection efficiency was found to be the highest Consequently, non-linear SAW backscattering results in the primary detection of various kinds of surface imperfections in solids and has good prospects for the NDE of a wide range of materials with microcontact inhomogeneities.

Theoretical determination of equivalent circuit parameters for reflective SAW metallic gratings

AbstractA theoretical method is described for determining equivalent circuit parameters for metallic gratings on arbitrary piezoelectric substrates. In this paper, to consider an energy storage effect, we adopt the equivalent circuit model proposed by Li et al. The finite‐element method is used to calculate the upper and lower cutoff frequencies of the stop band for metallic gratings of infinite periodic structure, and circuit parameters are determined from these values. Therefore, in this equivalent circuit, all the effects of piezoelectric perturbation, mechanical perturbation, and energy storage are taken into account. To show the validity and usefulness of this approach, for aluminum strips on some useful piezoelectric substrates (LiNbO3, quartz, LiTaO3, Li2B4O7), equivalent circuit parameters for each of the metallic gratings are determined and SAW reflection characteristics are computed. Result show that for the Li2B4O7 substrate, the reflection magnitude per strip is large and the influence of the change of strip thickness on the center frequency shift is small.

Right-Angle Reflection of SAW from an Array of Conducting Strips

Right-Angle Reflection of SAW from an Array of Conducting Strips

Insertion loss and TTE of SAW filter using 3‐transducer configuration

AbstractThe use of a 3‐transducer SAW element configuration gives complete suppression of the triple‐transit effect (TTE) at the frequency at which the external circuit is electrically matched to the central transducer. But when designing such an element as a filter it is necessary to deal with TTE at all frequencies within the filter band. This paper discusses the TTE within the filter band for an element with a 3‐transducer configuration, assuming negligible SAW reflection. The significance of the impedances of the external circuit and the interdigital transducer, the electromechanical coupling coefficient of the substrate and the relation between bandwidth and insertion loss in obtaining 40 dB or better TTE suppression in the main signal is demonstrated. In particular, a TV‐VIF filter with the regular 3‐transducer configuration prepared on a thin‐film ZnO substrate gave 40 dB of TTE suppression in the filter band and had 11 dB insertion loss. A device with a proportional band for use in a TV‐VIF filter was prepared in order to test the theoretical calculation. The TTE and main response signals were separated by means of a pulse modulation set‐up. The TTE frequency response within the filter band was observed directly, and the 3‐transducer configuration was found to be capable of producing the low‐loss filters needed for band design without alteration of commonly‐used design methods, and is an effective method of achieving TTE suppression.

Optical Probing Measurements of Surface Wave Generation and Reflection in Interdigital Transducers on LiNbO3

Surface wave generation and reflection in interdipjtal trans- ducers were studied over a range of frequencies near SAW resonance with light scattering and standard electrical measurement technique. The growth with distance of SAW under both generating and reflecting transducers and the reflection of SAW from transducers, shorted, open, and with SO-S2 loads, were measured directly with optical probing. The ex erirnental data for 25-finger pair transducers on y-z, z-y, x-Z, and 4li-x cuts of lithium niobate supported the predictions of Emtage's transducer model with a phenomenological reflection parameter about twice that predicted by theory.

SAW Reflection from Conducting Strips on LiNbO3

SAW Reflection from Conducting Strips on LiNbO₃

Effect of groove-depth variation on the performance of uniform SAW grooved reflector arrays

Computations of the variation with groove depth of the SAW scattering properties of a uniform shallow-grooved reflector array are reported for an equivalent isotropic elastic substrate representing Y-cut Z-propagating LiNbO3. In agreement with previous qualitative conclusions based on experimental studies of SAW grooved resonators, the present computations indicate the existence of an optimum groove depth yielding maximum array SAW reflectivity. This optimum groove depth is a monotonically decreasing function of the total number N of grooves in the array. Computed optimum groove depths for various fixed values of N are presented.

Reflection of magnetostatic surface wave at a shallow groove on a YIG film

A field theory for the magnetostatic surface wave (MSSW) reflectivity of a single shallow groove etched on top of an epitaxial YIG film is presented. Computed reflection characteristics are obtained for the case in which the grooved YIG film is unmetallized, and compared to corrected results for a metallized geometry. The conditions under which the MSSW reflctivity of a groove is significantly larger than the SAW reflectivity of an equivalent groove on a LiNbO3 substrate are pointed out.

Magnetostatic surface wave reflectivity of a shallow groove on a YIG film

A field theory for the magnetostatic surface wave (MSSW) reflectivity of a single shallow groove etched on top of an epitaxial YIG film is presented. Computed reflection characteristics are obtained for the case in which the surface of the YIG film is metallized after the groove is etched. It is found that the MSSW reflectivity of a groove is significantly larger than the SAW reflectivity of an equivalent groove on a LiNbO3 substrate.

Redeposition: a factor in ion-beam etching topography

The design of high performance SAW resonators and reflection pulse compression filters using grooves as the reflective arrays requires that the profiles of the grooves be rectangular and reproducible. The use of neutralized ion-beam technology has largely been adopted for etching these grooves in quartz and lithium niobate because of the precision and control which can be exercised in its use. The experimental work presented here asserts the major contribution that redeposition makes in the evolution of ion-beam etched topography of amorphous, polycrystalline and crystalline materials in a way which is directly useful to the determination of groove profiles. Data are also presented on the relationship between the incidence angle of the ion beam and the etch rate of some important SAW materials indicating the connection between this function and the etching characteristics of the materials.

SAW reflection and bulk-wave loss characteristics of a groove reflector grating

The reflection and bulk-wave loss characteristics of a SAW reflector grating comprised of shallow grooves are treated using the coupled-mode approach well known in the area of optical gratings. This approach offers the following distinct advantages over the previously reported equivalent network approach: (i) it derives the grating characteristics directly in terms of the material constants of the substrate; (ii) it provides quantitative information on the power loss resulting from bulk-wave radiation; and (iii) it can accommodate changes in groove profile or height among the individual grating elements, making this approach amenable for use in the design of tapered arrays. Computed reflection and bulk-wave loss characteristics of a grating comprised of a varying number of identical trapezoidal grooves are presented.