Showing papers on "Interdigital transducer published in 1989"

Integrated acousto-optic filters and switches

Abstract: of the Disclosure An acousto-optic converter fabricated on x-cut LiNbO3 and having an optical waveguide extending along the y-direction. AD interdigital transducer is oriented at 5° with respect to the y-direction in order to compensate for the acoustic walk-off on such an orientation. Such an integrated acousto-optic converter allows multiple stages of such converters so as to provide for (1) two-stage zero-frequency shifted converters and filters, (2) lasers using an acousto-optic filter as a tuning element, (3) polarization-independent converters in which the modes are divided, separately polarization converted, and recombined according to frequency, (4) and wavelength division multiplexing routing switches capable of simultaneously switching multiple channels.

Electromechanical coupling to Lamb and shear-horizontal modes in piezoelectric plates

Abstract: Recent theoretical studies and experiments have been shown that interdigital transducers can couple strongly to plate modes in piezoelectric materials and in piezoelectric-on-nonpiezoelectric composite membranes. The calculated velocity dispersion and electromechanical coupling factors for plate modes in representative piezoelectric materials are described. The frequency dependence of velocity and electromechanical coupling factors are given, under different metallization conditions, for generalized stiffened-Lamb, pure stiffened-Lamb, and stiffened-shear (shear-horizontal) modes, for various plate orientations in lithium niobate, lithium tantalate, quartz, bismuth germanium oxide, and zinc oxide. For lithium niobate, electromechanical-coupling values as high as 15% are found under narrowband bandpass conditions, and 5% under wideband low-pass conditions. For lithium tantalate, bismuth germanium oxide, coupling values of 0.5, 2, and 4% are obtained. For quartz with its weaker piezoelectricity, the coupling is still made smaller. >

Ultrasonic micromotors

Abstract: Initial work is presented on an ultrasonic micromotor. Small polysilicon blocks were both translated and rotated using traveling flexural waves in thin membranes. The acoustic wavelength was typically 100 mu m. The interdigital transducer voltage was typically 5 V; motion was observed at as low as 1.5 V. The acoustic wave power was about 1 mW. Linear motion quickly moved the blocks off of the 3-mm by 8-mm membrane region, but rotational motion was quite stable. Three possible mechanisms for energy transfer from the acoustic wave to the blocks were examined. Preliminary results in air and in vacuum indicate that a fluid boundary layer is responsible for the energy transfer. >

SAW focusing by circular-arc interdigital transducers on YZ-LiNbO/sub 3/

Abstract: Using the angular spectrum theory and experimental velocity data of surface acoustic waves (SAW) on YZ-LiNbO/sub 3/, the focusing characteristics of a circular-arc interdigital transducer have been demonstrated. The calculated results show that the depth of focus is long and the compressed acoustic beam width is very narrow. The concept of a caustic is shown to be an excellent way of characterizing SAW focusing by a circular-arc interdigital transducer on YZ-LiNbO/sub 3/. Comparison between theoretical and experimental results shows good agreement. >

Surface acoustic wave filter

Abstract: PURPOSE:To obtain a wide pass band by utilizing the longitudinal 2nd order mode having been handled as spurious mode so as to match the frequency. CONSTITUTION:A middle interdigital transducer 2G being one middle set of three-division of an interdigital transducer(IDT) 2 is used as an input transducer, two sets of interdigital transducers 2F, 2H at the left and right side of the interdigital transducer 2G having a nearly equal electrode pair number to each other are connected in parallel and used as output transducers, and the mutual distance L between left and right grating reflectors 3 of the input and output interdigital transducers is selected to be a distance able to accommodate number of electrodes exciting the longitudinal resonance mode in the propagation direction so as to obtain both a longitudinal 0-th order mode and a longitudinal 2nd order mode. Thus, the frequency difference of the resonance frequency between the longitudinal 0-th order mode and the longitudinal 2nd order mode is decreased. Thus, a wide pass band is obtained.

Surface acoustic wave device

Abstract: PURPOSE:To attain high frequency while increasing the sound velocity by forming a diamond thin film to one side of a base. CONSTITUTION:A base 1 is made of a comparatively inexpensive material such as glass, alumina and the diamond thin film 2 is formed on one face of the base 1. The thin film forming technology such as sputtering, vacuum vapor deposition, ion plating, CVD, or ICD is applied to form the diamond thin film 2. An interdigital transducer IDT 3 is formed on the diamond thin film 2 and a piezoelectric thin film 4 is formed to cover the IDT 3. Thus, the diamond is used for the propagation path of the surface acoustic wave in this way, high frequency application of nearly 2.4 times is attained.

A theoretical and experimental study of low-loss SAW filters with interdigitated interdigital transducers

Abstract: A study of low-loss surface-acoustic-wave (SAW) interdigitated interdigital transducer (IIDT) structures is presented. A model based on mixed scattering matrices was used in the analysis. It is shown that the inherent comb frequency response of the IIDT can be smoothed by slanting the transducers in the structure. Alternatively, the combs can be enhanced to produce a compact low-loss feedback element for potential application in multimode oscillators. Experimental verification of the analysis is provided by a 3:2 slanted-finger IIDT filter with a 10% relative bandwidth of 5.9-dB insertion loss, and a comb filter with 13.4-dB insertion loss and comb spacing of about 3 MHz. The measured responses agree quite well with the theory. >

An acoustic plate mode immunosensor

Abstract: A novel acoustic-plate-mode (APM) sensor for sensing antigen-antibody reactions has been developed. The APM sensor utilizes a Z-cut X-propagating lithium niobate (LiNbO/sub 3/) piezoelectric plate in which various types of acoustic waves are excited and received by means of a photolithographically deposited aluminum interdigital transducer (IDT). A judicious choice of the sensor operating frequency results in the selective excitation of an acoustic mode that is highly sensitive to fluid loading of the LiNbO/sub 3/ surface. This mode is then utilized as the sensing element in the sensor. Experiments have been performed using polyclonal antibodies for which the sensor has shown a strong response to the associated antigen. The biokinetics of the antigen-antibody reaction has also been studied. Experimental data compare favorably with theoretical results predicted by an affinity purified human immunoglobulin antibody-antigen model. This model immunosensor also has potentio application in directing various types of viruses such as AIDS (HIV), herpes simplex, and hepatitis. >

An improved model for chirped slanted SAW devices

Abstract: Three improvements for modeling chirped slanted array compressor (SAC) transducer devices are presented. First, the generalized impulse response model for an in-line chirped IDT (interdigital transducer) is applied to individual longitudinal segments of a SAC transducer to obtain transversely distributed source profiles. The inherent simplicity of the coupling-of-mode formalism conveniently encompasses effects of both the chirped transduction and the transducer internal reflections. Second, these source profiles are the driving terms for an accurate propagation model, which calculates the total propagation loss between the transducers by successive applications of Snell's-law refraction and angular-spectrum diffraction, together with an experimentally characterized substrate attenuation. Third, in addition to the static capacitance and subsurface acoustic wave (SAW) conductance, the basic transducer equivalent circuit also includes the SAW susceptance, bulk radiation conductance and susceptance, and a revised parasitic resistive element. The SAW conductance is calculated by integrating the power in the source profiles. This in turn is used to calculate the SAW susceptance and the bulk conductance and susceptance. The combined model and its various elements have been verified by electrical and laser probe measurements. Good agreement with device data, amounting to better than 1 dB in device insertion loss and 0.3 dB in transducer mismatch loss, is reported. >

Surface-acoustic-wave unidirectional transducers using anodic oxidation technology and low-loss filters

Abstract: A new surface-acoustic-wave interdigital transducer (IDT) and unidirectional transducer (UDT) are described. Using a lift-off anodic oxidation method, controllable gaps between electrodes with good insulation can be obtained. Experimental results show good characteristics at 2nd-harmonic operation for a new floating electrode type unidirectional transducer (NG-FEUDT). Also, a low-loss filter of 3.46dB with side-lobe suppression of 40dB at 893 MHz is obtained using the above techniques.

Observation of soliton‐like envelope modulations generated in an anisotropic quartz plate by metallic interdigital transducers

Abstract: It is observed that the bulk acoustic wave radiation from interdigital transducers deposited on a quartz crystal plate is dispersive and nonlinear. Pulse instability, pulse narrowing, and pulse splitting suggestive of soliton behavior are reported for 25–100 ns duration pulses from a transducer with a 17.2 μm spatial period on a Y‐cut, Z‐propagating quartz substrate.

Angular spectrum of waves analysis of SAW filters with dispersive transducers

Abstract: The extended annular-spectrum-of-waves (ASoW) model is applied to the simulation of SAW (surface acoustic wave) devices with dispersive transducers. Both inline and slanted interdigital transducer (IDT) geometries are analyzed. Two extensions of the existing model are presented. The wave propagation between two slanted IDTs is modeled in the ASoW with a three-prism model considering exactly the quadrupole refraction effect at the bus bars between the input and the output IDT. Different velocity dispersions in the bus bars and in the transducers, due to both the electrical loading and the mechanical loading effects, are taken into account. The measurements of two delay lines are compared with the corresponding simulations. Excellent agreement, even at the band edges, is shown. Simulations demonstrate the strong effect of refraction at the bus bars. >

Surface wave interdigital transducer and surface wave filter with symmetric or predeterminable asymmetric transfer characteristic between input and output

Abstract: A surface acoustic wave interdigital transducer of a filter includes split finger electrodes in pairs. To achieve a desired transfer characteristic that is either symmetrical or deliberately asymmetrical, a number of the pairs of the split finger electrodes are replaced by single finger electrodes.

Thin-film induced effects on the stability of SAW devices

Abstract: Measurements show an upward shift on the order of 50 ppm in the resonant frequency of a surface acoustic wave (SAW) resonator, as taken before and after the device is hermetically sealed in vacuum following a certain glass-frit sealing process. The authors analyze some of the thin-film phenomena that are potential sources of the observed frequency shift and that may affect the long-term stability of such devices. Various factors contributing to the shifts include: 1) intrinsic or structural stresses in the bonding layers as well as in the interdigital transducer (IDT) fingers; 2) thermal stresses due to the differences in thermal expansion coefficients of the metallic IDT fingers and the bonding agent (glass frits) from those of quartz; 3) partial oxidation of the IDT fingers and transmission lines during the frit glazing process; and 4) possible metal diffusion into quartz. Quantitative estimates of the contribution of two factors to the total observed frequency shift after a certain glass-frit sealing process are provided. Rough estimates of the frequency shifts due to the oxidized film are made from the dispersion curves for a uniform thin aluminum film and for its oxide film as fully plated on a quartz substrate. It is concluded that the results may provide a way of estimating the magnitude of the intrinsic stress for a given long-term stability of the SAW device. >

Interdigital transducer for surface acoustic wave filter

Abstract: To reduce the frequency bandwidth of an interdigital transducer, acting as an image-impedance connected interdigital transducer in a surface acoustic wave filter with low insertion losses, at least the center-to-center spacing between a first electrode or finger of a first comb, central to the transducer, and a second finger of a second adjacent comb is equal to Rλ 0 /2, where λ 0 is the central wavelength and R is a whole number strictly greater than 1. The center-to-center spacings between the other first and second fingers are at least equal to Rλ 0 /2. An increase in the optimal length of an image-impedance connected interdigital transistor is obtained by reducing the number of active fingers per unit of length. The greater the reduction factor chosen, the narrower will be the frequency band of the transducer.

Saw slanted array correlator (SAC) with separate amplitude compensation channel

Abstract: A SAW slanted array correlator (SAC) comprises a piezoelectric substrate, an input and an output interdigital transducer deposited on the piezoelectric substrate, and a reflective array aligned with the transducers. The input and output transducer are slanted at equal and opposite appropriate angles to each other. The reflective array is disposed on the substrate at an angle the same as the angle of emplacement of the output transducer. The transducers comprise a number of interdigital electrodes with varying periodicity, the periodicity being the same for corresponding portions of the two transducers. The reflective array comprises a number of shorted interdigital electrodes having a periodicity corresponding to the periodicity of the output transducer. The reflective array comprises portion of selected electrodes which are active, partially active or inactive.

An Analysis of Excitation Characteristics of Interdigital Transducers for Surface Acoustic Waves

Abstract: An equivalent network theory and a coupled mode theory are described for the analysis of excitation characteristics of interdigital transducers (IDT) for surface acoustic waves. Circuit parameters of equivalent circuits and coupling and transduction coefficients of coupled mode equations can be theoretically determined by applying the finite-element method to an infinite array corresponding to an electrically shorted or open IDT. Examples are computed for two types of IDTs fabricated on a 128° Y-X LiNbO3 substrate. One is a uniform type of IDT and the other is a single-phase unidirectional transducer utilizing internal floating electrodes.

Light beam deflector

Abstract: A light beam deflector includes an optical waveguide made of a material capable of propagating surface elastic waves therethrough, and n (n≧2) surface elastic wave generating means for generating in the optical waveguide surface elastic waves which travel across the path of a guided wave traveling in the optical wave guide, thereby diffracting and deflecting the guided wave n times and amplifying the deflection of the guided wave caused by the diffraction thereof. Each of the n surface elastic wave generating means comprises an interdigital transducer having electrode fingers spaced at distances that vary stepwise, and a driver for applying an alternating voltage having a continuously varying high frequency to the interdigital transducer. The drivers apply alternating voltages having frequencies shifted from each other to the interdigital transducers, respectively, so that periodic variations in the intensities of the surface elastic waves generated respectively from the interdigital transducers will not amplify each other.

IIDT type SAW filter using acoustic reflection cancel condition with solid IDT

Abstract: The performance of an IIDT (interdigitated interdigital transducer) filter using the acoustic-reflection cancel condition of the solid IDT is investigated for the substrate A1/128 degrees Y-X LiNbO/sub 3/. The acoustic reflection cancel condition is a combination of 2d/ lambda =0.5 and h/ lambda =0.026 in the solid fingers. Near this condition the solid finger width d and thickness h dependence of the acoustic reflection coefficient is calculated by the finite-element method. The solid-finger width needs to be carefully controlled during the etching process, to avoid filter response distortion caused by the acoustic reflection of the IDT and phase velocity difference between the IDT and the propagation area. A new IIDT-type SAW (surface acoustic wave) filter configuration with a reduced number of fingers is proposed. This filter has a low shape factor (the 1 dB-bandwidth to 6-dB bandwidth ratio is 1.1) and a small ripple pass band. >

Idt exciting type 2-port resonator

Abstract: PURPOSE:To obtain a secondary resonator with almost no spurious radiation and resonator filter using the said resonator without increasing insertion loss by constituting input and output IDT electrode capacitors equally so as to apply weighting to an interdigital transducer IDT and connecting them with split in a way of suppressing the second order mode spurious radiation. CONSTITUTION:The IDTs 2, 3 are arranged adjacently on the surface of a piezoelectric substrate 1 of a 2-port SAW resonator, resonators 4, 4' are arranged at both sides of them and COS or COS shape of weighting is applied to the IDTs. The IDTs 2, 3 are split respectively to be IDTs 2', 2'' and 3', 3'' thereby forming new input and output IDTs. In this case, the weighting symmetrical with respect to the center of the IDT is applied to make the electrode capacitance by the IDTs 2', 3' and the electrode capacitance by the IDTs 2'', 3'' equal to each other thereby making the input/output capacitors of the 2-port resonator and the resonator filter employing it equal to each other.

3D electrostatic field analysis of periodic two-dimensional SAW transducers with closed-form formulae

Abstract: A 3-D field analysis method is developed for the analysis of the 2-D charge distribution in surface acoustic wave (SAW) transducers. The method employs a periodic Green's function constructed by superposition of the potential responses of a set of single point sources. A modified inverse-capacitance matrix that describes the whole structure has been established. Discretization has to be performed only in the main period. To obtain a prescribed accuracy, generally only a few periods at the left and at the right side with respect to the main cell have to be included in the analysis. Computational results for interdigital transducer (IDT) structures or YZ-LiNbO/sub 3/ are presented. The influence of bus-bars, floating fingers, and the aperture on the charge distribution is demonstrated. >

Method for manufacturing piezoelectric polymer transducers

Abstract: A piezoelectric transducer of piezoelectric plastic material comprises a body and activated transducer film formed integrally. Electrodes are formed on opposite sides of the film, and a backing material supports the film on one side. The transducer may be formed by molding, applying the electrodes and activating the film by means of a corona discharge.

Apparatus and method for diffracting MSW in a garnet film using SAW

Abstract: A method and apparatus for diffracting magnetostatic waves (MSW) in a garnet film by surface acoustic waves (SAW) so that spectral analysis may be performed on an input microwave signal having a plurality of frequency components. The garnet film, advantageously a YIG film, has a piezoelectric layer of zinc oxide which receives at an interdigital transducer an rf signal to propagate surface acoustic waves (SAW) in the YIG film. The SAW space and time modulates the properties of the YIG film as to diffract magnetostatic waves. A microwave input signal having a plurality of spectral components is supplied to the YIG film, as is a magnetic biasing field, whereby MSW propagates therein. Because of the diffraction of MSW caused by SAW, different spectral components of the microwave signal are obtained at different positions and are output at individual channels.

Iterative method using constrained optimization techniques for second-order effects compensation in SAW filters

Abstract: A novel algorithm for broadband compensation of second-order effects in SAW (surface acoustic wave) filters consisting of one apodized and one unapodized interdigital transducer (IDT) is presented. The method ensures effective compensation of second-order effects even at frequencies close to or equal to zeros of unapodized IDT response. In contrast to earlier methods, inequality constraints are imposed on positions of gaps in apodized IDT. Owing to this feature, this fixed aperture of the IDT can be easily maintained throughout the compensation process. Compensation results are given for a 14 lambda aperture SAW TV-IF filter. >

High density surface acoustic waveguide channelizer

Abstract: A surface acoustic wave device is disclosed which performs frequency channelization in a relatively small volume. The invention utilizes a wide band incline step frequency transducer each step feeding an independent beam width compressor waveguide combination. The waveguides fan out with a wide radius of curvature to contain the wave in off pure mode axis propagation. The output of each waveguide then feeds an independent beam width expander and frequency selector interdigital transducer. The use of the waveguides as a tapping and narrow aperture transport mechanism minimizes defraction, allows the output transducers to be widely separated achieving isolation and permits a larger number of filters per substrate.

Surface acoustic wave device having multilayer structure with reduction in electromagnetic feedthrough

Abstract: Surface acoustic wave device having a multilayer structure comprising a semiconductor substrate (10), an insulating dielectric layer (11) thereon, a set of at least one interdigital input and output transducer (12) deposited thereon, and a piezoelectric layer (13) thereover, in which an electrical input signal is converted in the input transducer and the surface acoustic wave resulting therefrom pro­pagates over the surface and is converted into an electrical output signal in the output transducer. A metal layer (14) which serves to reduce electromagnetic feedthrough between the input and output transducer (12) via the semiconductor substrate (10) is deposited between the semiconductor substrate (10) and the dielectric layer (11) at least at the location of the transducers (12). Said metal layer (14) may also extend over the entire interface between semiconductor substrate (10) and dielectric layer (11).

A Lamb wave electrostatic voltage sensor

Abstract: Lamb-wave electrostatic voltage sensors have been fabricated using planar technology incorporating a standard interdigital transducer (IDT) array (for generation and detection of the Lamb waves) and a capacitative electrode placed on each side of the sensor substrate in the region of wave propagation (for applying the DC potential). The Lamb waves/modes generated for substrate thicknesses of 50, 102, and 254 mu m were identified using theoretical dispersion curves. The modes were of both the antisymmetric and symmetric variety. The electrostatic voltage sensitivity, as measured in a SAW (surface acoustic wave) oscillator configuration, was double that of an equivalent Rayleigh device. Insertion losses, short- and long-term oscillator stability, and oscillator thermal sensitivity are reported. >

New transducer construction for wideband SAW TV IF filters

Abstract: A new construction of an interdigital transducer for a wideband SAW TV IF filter has been developed. When the filter needs wide passband and low shape-factor characteristics, the number of electrodes in the interdigital transducer has to be increased. In that case surface-wave reflection in the transducer causes large ripples in the filter characteristics. In this paper a new type dummy-electrode for suppression of this reflection is described.

Filter zur unterdrueckung von oberflaechen-interferenzen fuer satellitenkommunikations-empfaenger

Abstract: A surface acoustic wave (SAW) filter for suppressing surface to surface interference for a satellite communication receiver comprises two input (IDT1 and IDT2) and one output (IDT3) interdigital transducers constructed and arranged on a common piezoelectric substrate. The widths of the adjacent portions of electrodes and the spaces between the electrodes of the input interdigital transducers are adjusted based upon the principle of a transversal filter so that the frequency response of the input interdigital transducer (IDT1) has a predetermined pass band width and the transducer (IDT2) has a reduced gain in a frequency range which may include an interference signal. A switch SW switches the input signal into either of the transducers IDT1 and IDT2.

SAW device with interdigital transducers at input and output - having reflectors for improved characteristic without increase of chip area

Abstract: The acoustic resonator comprises an input interdigital transducer (3) and an output interdigital transducer (2) on a substrate (1) coated with a sound-absorbing material (4) near its ends to prevent reflection. A reflector (5) returns the acoustic surface wave produced by the h.f. voltage applied to the input interdigital transducer. The reflector is located either side of the input and output transducer, the relative spacing being determined by the wavelength. USE/ADVANTAGE - Microwave filter resonator with improved cut-off characteristic without increase of chip surface area Satellite communication systems.