Showing papers on "Surface acoustic wave published in 1971"

Acoustic surface wave filters

Abstract: Acoustic surface waves offer several advantages in the construction of delay lines and filters in the UHF range. In these devices the frequency response is determined by the finger spacing and overlap of the interdigital comb structures used as input and output transducers. Models are developed to describe these devices, and the predictions of these theories are compared with several experimental filters, including band-pass filters and dispersive delay lines.

Normal mode theory for acoustic waves and its application to the interdigital transducer

Abstract: A normal mode expansion for the analysis of acoustic-wave problems is given. The expansion is based on orthogonality relations between the modes of an acoustic wave, and makes it possible to relate the perturbation and propagation constant of a particular mode to the properties of the modes of the unperturbed system, and of the perturbation. The use of the general expansions is then demonstrated by using it to determine a variational expression of an interdigital transducer. The results obtained are very similar to those of Smith, and demonstrate the connection between the crossed-field and series formulations for the transducer impedance.

A normal mode theory for the Rayleigh wave amplifier

Abstract: A Rayleigh acoustic wave traveling on the surface of a semi-infinite piezoelectric medium may be amplified by interaction with drifting carriers in an adjacent semiconductor. The gain and frequency response of this interaction is determined here by using a normal mode expansion of the Rayleigh wave piezoelectric fields. The configuration which uses a thin semiconductor film supported by a semi-infinite dielectric and separated from the piezoelectric by a small air gap is described in detail and the results are expressed in a form that clearly shows the effect of piezoelectric, air gap, and semiconductor parameters. Comparisons with experimental data for the lithium niobate-silicon film configuration show that acoustic gains on the order of 100 dB/cm can be obtained in the frequency range above 0.1 GHz.

Optical Guided Wave Mode Conversion by an Acoustic Surface Wave

Abstract: The experimental observation of efficient (55%) mode conversion of thin‐film optical guided waves by a collinear interaction with a surface acoustic wave is reported. The effects of waveguide dispersion and finite geometry are discussed.

Simple Theory of Acoustic Amplification

Abstract: Carriers moving in a semiconductor can impart gain or loss to an acoustic wave traveling through piezoelectric material. A physical picture of this familliar interaction process is given that applies to piezoelectric semiconductors as well as to layered structures in which acoustic wave and movmg earners are phystcally separated. In any of these systems, an acoustic wave is accompanied by a space charge wave, a sinusoidal pattern of electric charges. Such a charge pattern has a relaxation time that depends strongly on system geometry. It is shown that once the relaxation time is known, gain or loss as a function of frequency, carrier drift velocity, and electromechanical coupling factor can be found by a stmple method based on physical intuition.

Perturbation Theory for Electromagnetic Coupling to Elastic Surface Waves on Piezoelectric Substrates

Abstract: Starting from the fundamental acoustic and electromagnetic field equations an approximate expression is obtained for the perturbation in propagation wavenumber of a surface acoustic wave in a piezoelectric crystal. The source of perturbation is taken to be a surface spaced an air‐gap distance h above the piezoelectric and is described in terms of an electrical impedance. The resulting perturbation is found in terms of the perturbing electrical impedance, an effective dielectric constant for the piezoelectric, the air‐gap spacing h, and a perturbation coupling constant defined in terms of the unperturbed electric potential at the piezoelectric surface and the average acoustic power flow per unit frequency. The theory is applied to the case of a short‐circuit perturbing surface and found to be in excellent agreement with certain numerical results for Y‐cut Z‐propagating LiNbO3 and several cuts of Bi12 GeO20. In the general case of a complex perturbing impedance, such as that exhibited by a semiconductor, the theory indicates that attenuation or gain and dispersion may be introduced by the perturbation, in close agreement with experimental observations.

Signal processing in acoustic surface-wave devices

Abstract: The Rayleigh surface-wave mode propagates on the surface of suitable elastic solids with velocity independent of frequency at about 10-5 times the speed of light and an attenuation of about 1.5 dB for 104 wavelengths. Thus as a delay line it is far more compact, has much less attenuation, and can be much cheaper than electromagnetic delay lines. Piezoelectric elastic solids permit the launching and detection of the waves by electrodes on the surface. Fabrication technology is similar to that used for monolithic semiconductors and amplification is possible by interaction with carriers in a semiconductor surface layer. Parametric interactions can be used to perform convolution of two signals. The feasibility of deflecting and modulating light beams also has been demonstrated. This rapidly developing art can today produce delay lines, filters, pulse compressors and expanders, and pulse-sequence generators and decoders, and in the future may perform convolution, correlation, and light-beam manipulation in small, economical, low-power structures.

Evaluation of Digitally Coded Acoustic Surface-Wave Matched Filters

Abstract: Absfracf-Acoustic surface-wave correlation filters for phaseshift-keyed (phase-coded) waveforms have been characterized. The filters were constructed using a surface-wave tapped-delayline technique that resulted in highly compact devices. Both 7- and &bit Barker sequences have been fabricated on Y-cut LiNbO, for propagation in the Z direction. For purposes of evaluation, 20- and 30-MHz center frequencies were used with information bandwidths of 1.6 and 5.0 MHz, respectively. Measurements of the time and frequency domain responses, sidelobe levels, insertion loss, temperature sensitivity, and noise performance have been made. The results obtained closely follow theoretical predictions. Although some problems exist in the control of reflections and secondary generation of the signal, the feasibility of practical acoustic surfacewave digital filters has been demonstrated.

Wavefront Distortion of Acoustic Surface Waves from Apodized Interdigital Transducers

Abstract: The acoustic surface wave launched by an interdigital transducer is experimentally shown to have a distorted wavefront when the transducer has a varying finger overlap (apodization) and is on a high‐coupling piezoelectric substrate, LiNbO3. Results are shown for different transducer geometries, when an acoustic wave passes under the comb and when the apodized comb itself is driven. One geometry having extra metal fingers significantly reduces the wavefront distortion. The origin of the distortion is a retardation of the wave passing under metal fingers.

Ridge guides for acoustic surface waves

Abstract: A low-velocity flexural mode has been excited on acoustic-surface-wave topographic guides. With structures offering some hope of realisation at high frequencies, very strong confinement of the guided wave is obtained. Q factors in excess of 1000 have been observed on a ring resonator only ten wave lengths in diameter.

Characteristics of Surface-Wave Integratable Filters (Swifs)

Abstract: In the last few years, significant efforts have been made to incorporate integrated circuits in signal processing sections of a television receiver. Attempts to obtain frequency selectivity by using active RC filters have not been too successful.

Sputtered ZnO surface-wave transducers

Abstract: Surface waves have been excited efficiently on fused silica using sputtered ZnO films in conjunction with various transducer arrangements. The results are very promising and have yielded values of K2 up to 0.76%.

Acoustic surface wave device having improved transducer structure

Abstract: An improved transducer structure of the interdigitated electrode type is disclosed. In many microwave acoustic devices it is necessary to convert rf energy to acoustic surface wave energy and vice versa. When the acoustic medium is a piezoelectric substrate, interdigitated electrode transducers are widely employed. When such transducers are amplitude weighted, acoustic wave phase distortion of a serious nature can occur. Such phase distortion is eliminated by the use of an interdigitated transducer having dummy (i.e. non-active) electrodes disposed in the transducer pattern so as to present a substantially uniform metalization density to the propagating acoustic surface wave.

Pulse compression using nonlinear interaction in a surface acoustic wave convolver

Abstract: Nonlinear interaction can be achieved over extended signal path lengths in a surface acoustic wave device. Using such a device variable pulse compression was achieved through the mixing of a chirped acoustic signal and its time inversion.

Parametric acoustic surface wave apparatus

Abstract: Parametric surface acoustic wave apparatus including means for establishing two acoustic surface waves in a piezoelectric medium in a fashion to establish the conditions for parametric interaction so that various functions of signal processing can be carried out including, for example, signal convolution and correlation, time delay and time inversion, amplification, and oscillation.

Acoustic surface wave resonator

Abstract: High Q performance is achieved in an acoustic surface wave resonator by the use of acoustic surface wave reflectors. The resonator input transducer and the reflectors are affixed to the propagation surface of a piezoelectric substrate member by photolithographic process. The input transducer is an interdigital structure having many long interleaving finger members. The reflectors also have long interleaving finger members and are positioned in close parallel relationship to the transducer finger members. The reflectors are electrically terminated by inductances.

A Technique for Precision Measurements of Elastic Surface Wave Properties on Arbitrary Materials

Abstract: A technique is described for determining both the elastic surfce wave velocity and its temperature coefficient. The technique can be used on very small samples and is not restricted to any particular class of materials, such as piezoelectrics. It employs an adaptation of the old method of acoustic wave generation with a dc pulse rather than an rf signal applied to a piezoelectric transducer. The generator and receiver transducers are very small chips, approximating point sources, and at the receiver the vertical component of particle velocity is measured as a function of time enabling one to distinguish clearly between various types of surface modes, e.g., Rayleigh wave, pseudosurface wave, Lamb wave, etc. The technique yields absolute surface wave velocities accurate to 0.2% and is readily adaptable to the use of the sing‐around technique for measuring relative changes in the sound velocity as small as 1 ppm.

Long Delay Lines Employing Surface Acoustic Wave Guidance

Abstract: Folded‐path guided surface wave delay lines offer a significant potential advantage over single‐propagation path delay lines for obtaining very long delay times. Measurements are reported here for a spiral folded‐path delay line employing a gold strip on fused quartz as the guidance structure. A 260 μsec delay was obtained at 20 MHz. The spurious signal was ≥35 dB down and the differential propagation loss was 0.03 dB/μsec. These favorable results indicate that practical long delay lines based on surface acoustic wave guidance techniques are quite feasible and that delay times into the millisecond range are attainable at higher frequencies.

Novel helical‐path surface wave delay line

Abstract: A surface acoustic wave delay line has been constructed on quartz in which the path of the wave is approximately a helix. The line operated at 102 MHz and gave delays up to about 50 μsec at room temperature.

Surface acoustic wave generating system

Abstract: In a surface acoustic wave generating system, a portion of a body of semiconductor material is incorporated in structure having electrical capacitance. The capacitive structure is energized to produce mechanical stress in the body of semiconductor material and thereby generate surface acoustic waves on a surface of the body of semiconductor material. In one embodiment of the invention the capacitive structure comprises one or more p-n junctions formed in the body of semiconductor material and intersecting the surface. In another embodiment the capacitive structure comprises one or more MOS capacitors disposed on the body of semiconductor material.

New high-coupling low-diffraction cut for acoustic surface waves on LiNbO3

Abstract: The existence of a new high-coupling low-diffraction-loss cut for acoustic surface-wave propagation on LiNbO3 has been theoretically predicted and experimentally verified. The propagation direction lies 16½° from the Z axis with the plate normal 16½° from the negative Y axis.

Acoustic surface wave transmission device

Abstract: A surface wave integratable filter includes input and output transducers spaced apart on an acoustic wave propagating medium. The input transducer launches acoustic surface waves along a path in which the wavefronts diverge. Disposed on the medium between the input and output transducers is an acoustic lens formed of a material that exhibits an acoustical refractive index greater than one. The lens acts to change the width of the acoustic wavefront and thereby enables appropriate selection of the physical size of the output transducer so as to obtain desired input and output impedances while securing increased efficiency of interaction at the output transducer.

Grating surface acoustic wave transducer

Abstract: A transducer for exciting and/or detecting surface acoustic waves at both UHF and microwave frequencies in piezoelectric materials comprises a plurality of parallel spaced conductors deposited on the surface of the piezoelectric material.

Switchable acoustic surface wave sequence generator

Abstract: A hybrid combination of surface wave acoustics and semiconductor device technology can be utilized to provide electronically switchable coding techniques for acoustic surface wave signal processing devices.