Surface Acoustic Wave Waveguides Research Articles

Single-mode and ultra-broadband gigahertz surface acoustic waveguides on AlN-on-SiC substrates

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.

Guiding robust valley-dependent edge states by surface acoustic waves

Recently, the concept of valley pseudospin, labeling quantum states of energy extrema in momentum space, has attracted enormous attention because of its potential as a new type of information carrier. Here, we present surface acoustic wave (SAW) waveguides which utilize and transport valley pseudospins in two-dimensional SAW phononic crystals. In addition to a direct visualization of the valley-dependent modes excited from the corresponding chiral sources, the backscattering suppression of SAW valley-dependent edge modes transport is observed in sharply curved interfaces. By means of band structure engineering, elastic wave energy in the SAW waveguides can be transported with remarkable robustness, which is very promising for new generations of integrated solid-state phononic circuits with great versatility.

Design of tapered SAW waveguide for wavelength‐selective optical switches using weighted acoustooptic interaction

AbstractOptical wavelength‐selectivity in optical switches using waveguide‐type collinear acoustooptic interaction is studied from the viewpoint of sidelobe suppression. It is found that the sidelobe level can be reduced from −9.3 dB to −20 dB by weighting the coupling coefficient over the interaction region. A method to realize the sidelobe suppression by means of modifying the surface acoustic wave (SAW) waveguide is proposed and theoretically analyzed to design the SAW waveguide. A sidelobe suppression at −20 dB is realized with a SAW waveguide of a dense‐flint glass strip whose width and thickness are varied accordingly in the ranges of 700 to 26 µm, and 0.4 to 1.0 µm, respectively, on a Y‐X LiNbO3 substrate. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(1): 36–46, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20251

Design of Tapered SAW Waveguide for Wavelength-Selective Optical Switches using Weighted Acoustooptic Interaction

Optical wavelength-selectivity in optical switches using waveguide-type collinear acoustooptic interaction is studied from the viewpoint of the sidelobe suppression. It is found that the sidelobe level can be reduced from -9.3 dB to -20 dB by weighting the coupling coefficient over the interaction region. A method to realize the sidelobe suppression by means of modifying the surface acoustic wave (SAW) waveguide is proposed and theoretically analyzed to design the SAW waveguide. A sidelobe suppression at -20 dB is realized with a SAW waveguide of a dense-flint glass strip whose width and thickness are varied accordingly in the ranges of 700-26μm, and 0.4-1.0μm, respectively, on a Y-X LiNbO3 substrate.

Analysis of Excitation and Propagation Characteristics of Leaky Modes in Surface Acoustic Wave Waveguides

In this paper, we propose a method of analyzing the excitation and detection of leaky modes in a surface acoustic wave (SAW) waveguide structure. These properties could not be directly evaluated by the conventional scalar potential theory and mode expansion. In the present theory, the SAW excitation and detection are taken into account in the scalar potential theory, and then the SAW signal transfer between input and output ports is estimated in a form of the Fourier transform in the wavenumber domain. Finally, the contribution of each mode is estimated by the residue theorem. This method is effective in estimating the contribution of complete spectra, including leaky modes as well as non-leaky guided modes.

Proton-exchanged Z-cut LiNbO/sub 3/ waveguides for surface acoustic waves

Proton-exchanged (PE) waveguides in Z-cut LiNbO/sub 3/ have been fabricated using benzoic acid. Secondary-ion mass spectrometry (SIMS) measurements show that the distribution of hydrogen in the PE Z-cut LiNbO/sub 3/ samples exhibits a step-like profile with the diffusion constant D/sub 0/ and the activation energy Q of about 2.82/spl times/10/sup 8/ /spl mu/m/sup 2//h and 87.76 kJ/mol, respectively. On the other hand, the important parameters for the design of surface acoustic wave (SAW) devices are measured and discussed. The results show that the phase velocity and electromechanical coupling coefficient decrease with the increase of kd, where k is the wavenumber and d is the waveguide depth. The variation of insertion loss becomes saturated at about kd=0.068 with a maximum increase of about 4/spl sim/5 dB. The temperature coefficient of delay calculated from the frequency change of the output of SAW delay line shows an evident increase in the PE layer. Moreover, the effects of postannealing can result in a restoration of the decreased velocity and an improvement of the insertion loss.

Acoustic-wave-based voltage sensors

Acoustic-wave-based voltage sensors utilizing surface acoustic wave (SAW) delay lines are reviewed. A SAW oscillator that consists of a SAW delay line and an amplifier connected between input and output interdigital transducers (IDTs) can be used as a SAW-based voltage sensor, when a d.c. or a.c. voltage is applied on the SAW propagation path in the piezoelectric substrate. The voltage sensors detect an applied voltage as a fractional change of oscillation frequency. there are two electrode configurations for applying a voltage to the substrates on which the SAW propagates. One is to apply a voltage perpendicular to the surface of the substrate, and the other is to apply it parallel to the surface of the substrate and perpendicular to the propagation direction of the SAW. The former configuration is used in a sensor having a ZnO thin film on Si and a sensor utilizing a Lamb wave, as well as in a sensor utilizing a Rayleigh wave on LiNbO 3 plates, whereas the latter is used in a sensor with SAW waveguides.

Surface acoustic wave microsensors using diffused substrates

Various Y-cut Z-propagating lithium niobate YZ-LiNbO/sub 3/ substrate configurations are investigated to develop efficient ways of confining the wave energy in surface acoustic-wave (SAW) microsensors based on waveguide structure. The core and cladding regions for the SAW waveguide sensors have been titanium in-diffused or out-diffused and in some cases metal overlays have been used. By varying the diffusion conditions, the SAW velocities in these regions can be controlled such that a channeled region with interface wave-reflection is produced while minimizing the wave-velocity-difference between the cladding and the core. >

Proton exchanged waveguides for surface acoustic waves on LiNbO3

For the first time waveguides for surface acoustic waves (SAW) have been fabricated by exchanging Li+ ions with protons on Y-cut LiNbO3 substrates. Different waveguiding structures were investigated. The influence of the proton source dilution, the annealing or the Ti prediffusion on the SAW velocity, and the parameters of the SAW waveguides have been studied.

SAW Propagation Properties in Ta2O5 Strip Waveguide for Waveguide-Type Acousto-Optic Devices

SAW (surface acoustic wave) channel waveguides are expected to improve acousto-optic (A–O) interaction efficiency and integration density in construction. Thin strips of Ta2O5 and Al-coated Ta2O5 showed excellent properties as 3-dimensional SAW waveguides on LiNbO3. Propagation loss in the 100 µm-width Ta2O5 strip was about 1 dB for 40∼100 MHz. Coupling loss of SAW excited by a focused IDT into the waveguide was 2 dB. Stronger field confinement was obtained in a wider frequency range by overlaying thin Al on the Ta2O5 strip than Ta2O5 alone. These waveguides are useful for A–O devices of optical processing and communication.

Finite-Element Analysis of Finite Periodic Waveguides for Surface Acoustic Waves

A numerical approach based on the finite-element method is described for the analysis of finite periodic waveguides for surface acoustic waves. To treat a large structure in which a repetition of complicated components arises, a 'substructure' has been introduced. Numerical examples are presented for the Rayleigh-wave reflection characteristics of groove arrays. The results obtained agree approximately with the experimental results reported by several authors.

Radiation Pattern and Coupling Efficiency of Leaky Waveguide

It is well known that the maximum coupling efficiency of a surface-acoustic-wave (SAW) coupler employing leaky waves is about 81%. But if the coupling strength is varied appropriately, the coupling efficiency is expected to be higher. In this paper the coupling strength suitable for obtaining higher efficiency is given and is numerically examined. As a result, higher coupling efficiency is obtained. Furthermore, the diffraction of radiant waves was considered and the influence on the coupling efficiency was investigated numerically. The relation between coupling efficiency and diffraction of radiant waves from SAW waveguide was analyzed quantitatively.

Erratum: Numerical analysis of two-dimensional piezoelectric waveguides for surface acoustic waves by finite-element method

Erratum: Numerical analysis of two-dimensional piezoelectric waveguides for surface acoustic waves by finite-element method

Numerical analysis of two-dimensional piezoelectric waveguides for surface acoustic waves by finite-element method

A combined approach of the finite-element method and the analytical solutions is described for the analysis of two-dimensional piezoelectric waveguides with semi-infinite media for surface acoustic waves. Agreement between the exact and predicted results is very good.

Microwave Network Analyses of Surface Acoustic Waveguides - I. Flat Overlay Guides

A new approach is described for the systematic analysis of a variety of waveguides for surface acoustic waves on isotropic solids, and explicit results are presented which in most cases are either the only analytical solutions available or ones which furnish superior accuracy. This new approach adapts the techniques of microwave network theory to guided acoustic wave problems, so that many of the powerful methods developed in the context of electromagnetic microwaves can be applied to advantage. These methods utilize transmission lines and equivalent networks which look electrical but are actually purely acous- tic. They furnish physical insight and are particularly helpful to those trained in transmission line theory. The basic elements of this new ap- proach are explained in the paper. Waveguides for acoustic surface waves fall into two classes: overlay guides and topographic guides; the most important ones in each class are treated here. In Paper I, the strip and slot guides are discussed, and in Paper 11, the topographic and overlay rectangular ridge guides are analyzed. For each of the waveguides treated, analytical (not simply numerical) results for the dispersion relations are presented, curves for the dispersion behavior are included, and comparisons with other theories and with measurements (where available) are indicated. I. INTRODUCTION N A PAIR of papers by the present authors (l), (2), the foundation was laid for the systematic application of well- established and proven microwave network techniques to problems involving acoustic waves in isotropic media. This foundation involved the formulation of a rigorous transmission- line formalism for guided acoustic waves. The formalism makes possible, in principle, the derivation of equivalent network rep- resentations for acoustic wave junctions and discontinuities. As an illustration of this new approach, transmission-line representations were derived for the bulk plane-wave modes in isotropic media, and equivalent networks were obtained for a large variety of planar interfaces. With these results, the solution for the modal propagation characteristics of two- dimensional, plane-stratified structures becomes systematic and straightforward, as seen, for example, in (3), (4). Al- though such a method of solution does have the very definite virtues of minimizing the algebra required in the analysis and furnishing physical insight, its full utility and value are not clearly manifested in the context of such two-dimensional problems because the latter can always be solved analytically by classical techniques.