Surface-acoustic-wave reflectors

The technique of reflecting surface acoustic waves by periodic mass loading of the substrate surface is described. Experimental results are presented for a particular microsonic coupler using this interaction.     

Surface-acoustic-wave multiplexing techniques

Two approaches to frequency division multiplexing using SAW devices are described. The first one uses a 9-channel filter array, where the signal combining and splitting is performed using wide-band power splitters. Two of these filter arrays were used in a data link, with data rates up to 7.5 Mbit/s for a total data rate of 67.5 Mbit/s. The second approach uses offset multistrip couplers to channel a wide-band signal into various narrow-band outputs according to frequency. Consequently, this approach exhibits lower insertion loss and is especially suitable for a large number of channels. An 8-channel MSC multiplexer has been constructed with less than 10-dB insertion loss.     

Surface-acoustic-wave frequency-to-voltage converter

A frequency-to-voltage conversion technique is described by using a surface-acoustic-wave delay line with three interdigital transducers, one for input and two for output. Two output signals have a phase difference corresponding to different delay lengths, which are detected as a frequency-to-voltage converted signal via a differential amplifier. The operational principle as a discriminator is reported together with successful experimental results. This type of frequency-to-voltage converter is valid in a number of applications where high frequency is an important consideration.     

Surface-acoustic-wave resonator filters

This paper presents an overview of surface-acoustic-wave (SAW) resonator filter technology. Given the current state of the art, these filters promise reproducible low-loss (≲6 dB) narrow-bandwidth (500 ≲ f/Δf ≲ 50 000) responses in the VHF and UHF ranges. Devices that contain one or a number of sections, each consisting of a resonant cavity between two grating reflectors and an input and output coupling mechanism, are considered. The initial discussion describes the layout, theoretical characteristics, and typical experimental responses of singlesection two-port filters. The subsequent discussion focuses on multisection devices using any of various intercavity coupling techniques. A generalized analysis and design formalism based on wave-scattering theory is reviewed, and experimental results from a number of device prototypes are given. Finally, practical design and fabrication trade-offs and performance ranges are summarized for a number of configurations.     

Surface-acoustic-wave parametric amplifier

Parametric amplification and oscillation of surface acoustic waves has been observed on lithium niobate by varying the stiffness of the surface within a resonator cavity.     

Surface-acoustic-wave frequency-domain limiter

It is shown that, by exploiting the 2-dimensional structure of a SAW substrate to propagate different frequency components over distinct physical paths, the amplitude-limiting process that occurs at high power levels can be made `local? in the frequency domain. One application of such a frequency-domain limiter is to suppress CW interference in spread-spectrum communications.     

Surface-acoustic-wave pulse transducer

Short pulses of surface acoustic waves are launched efficiently by an inline assembly of several finger-pair interdigital transducers, which are connected to successive taps of an electrical delay line, where the electrical time lag between two taps is equal to the acoustic delay between corresponding transducers.     

Surface-acoustic-wave devices for communications

Surface-wave components have demonstrated performance capabilities in the VHF/UHF range which are available with no other filtering technique. The major advantages of the filters are their small size, high reliability, low cost, high Q, good reproducibility, temperature stability, wide dynamic range, and linear phase response, as well as special characteristics relevant to specific applications. Surface-acousticwave (SAW) devices are used for bandpass filtering [1], matched filtering for radar pulse compression [2], [3] or spread-spectrum signal processing [4], delay lines [5], and frequency control elements [3], [6]. Within the context of communication systems' applications, this paper reviews the state of the art for SAW components from high-performance fixed-tuned devices to tunable or programmable filters. Major technological advances discussed include unidirectional SAW filters [7] which eliminate bidirectionality loss and simultaneously suppress in-band spurious responses to achieve an insertion loss below 1 dB with a 0.04-dB peak-to-peak ripple. A novel surface-wave sub-system [8] which offers revolutionary signal processing functions through transform processing is also described.     

Surface-acoustic-wave delay-line controlled low-frequency oscillators

Surface-acoustic-wave delay line is used as the frequency controling element of a low-frequency oscillator, operating at a fundamental frequency of a few kilohertz. Some salient properties of such oscillators are discussed. Initial experimental results indicate that high-frequency stability can be obtained.     

Surface-acoustic-wave devices for signal processing applications

A survey of SAW devices is presented including delay lines, frequency filters, oscillators, matched filters, and Fourier transformers. Application of these devices to signal processing is discussed.     

Surface-acoustic-wave oscillator tuned by magnetoelastic effect

A new technique for achieving frequency modulation with a surface-acoustic-wave delay-line oscillator is reported. A 339MHz s.a.w. delay line has been fabricated on an epitaxial garnet film. A significant phase-velocity shift has been measured as a function of an inplane magnetic field. An s.a.w. oscillator has been implemented with this delay line and its frequency has been controlled by the magnetoelastic effect. A frequency shift of 600kHz (a relative variation of 1.75 × 10-3) has been obtained by changing the biasing magnetic field.     

Surface-acoustic-wave beam shaping with multistrip couplers

A method for tailoring surface-acoustic-wave beam profiles by using strip-length and phase-weighted multistrip couplers is presented. The design of and measurement on a 50 MHz-centre-frequency device is described.     

Surface-acoustic-wave device incorporating conducting Langmuir-Blodgett films

Surface-acoustic-wave (SAW) devices incorporating conducting Langmuir-Blodgett (LB) films are reported for the first time. Excellent characteristics have been obtained using a mixed valence charge tranfer salt of a substituted pyridinium tetracyanoquinodimethane. The control afforded by the deposition technique has enabled the fractional change in surface wave velocity due to the electrical effects to be distinguished from those due to mass loading. The resistivity of the organic surface layer is measured to be 2?cm.     

Surface-acoustic-wave phase shifter using electrical depolarisation

An electrically variable phase shifter employing surface acoustic waves is described that uses electrical depolarisation of a poled PZT ceramic. Phase shifting occurs in a depoling region in which an electric field of variable strength opposes the remanent ferroelectric moment, causing a change in the piezoelectric coupling and surface-wave velocity.     

Surface-acoustic-wave filters employing symmetric phase-weighted transducers

The letter describes a phase-weighting scheme for use in nondispersive surface-acoustic-wave bandpass filters. The advantages of this scheme are enumerated, and the performance of a demonstration filter on ST-quartz is compared with theoretical predictions.     

Surface-acoustic-wave rejection filters using mode conversion/reconversion

The phenomenon of mode conversion/reconversion is considered in terms of filter theory, and the principles applied to a surface-acoustic-wave rejection filter. A rejection peak exceeding 40 dB is obtained with an overall rejection bandwidth of 1%.     

Surface-acoustic-wave guidance produced by ion implantation in quartz

An increase in the surface-acoustic-wave velocity is produced by ion implantation in quartz (y-cut, x-propagating). A 2.5% relative-velocity increase has been measured at 395 MHz, with 100 keV Li+ ions, the flux being 1016 ions/cm2. Slot acoustic waveguides have been realised at about 100 and 400 MHz by these techniques. Horns were used for matching the launched acoustic beams to the guides. An optical probe has been employed for investigating the spatial distribution of the acoustic power. The 100 MHz guide is 148 ?m wide. The guided-power profile along a section of the guide has been measured. The 6 dB beamwidth is about 230 ?m. The 400 MHz guide is 18 ?m wide, and the propagation loss is about 0.75 dB/?s.     

Surface-acoustic-wave oscillators: mode selection and frequency modulation

The letter discusses various aspects of the design and performance of surface-acoustic-wave oscillators, including two proved solutions to the mode-selection problem and a demonstration of the wide frequency-modulation capability.     

Surface-acoustic-wave (SAW) voltage sensor with improved sensitivity

The sensitivity of a surface-acoustic-wave (SAW) voltage sensor can be increased by reducing the thickness of the substrate across which the voltage is applied. Voltage sensitivity of 95 Hz/V has been obtained in a 77-MHz SAW oscillator fabricated on a 71-µm-thick, 728° Y-X LiNbO3substrate.