U.S. Philips Corporation

Richard Stevens

Richard F Mitchell

Philip D White

Eileen Read

David E Penna

David W Parker

Martin Redwood

Frederick Warren Smith

Ronald George Pratt

Alojzy Karr

In an acoustic wave device having a pair of spaced apart reflectors forming a resonant cavity, each reflector consists of an array of parallel reflective elements. At least one of the reflectors is weighted not by simple withdrawal of reflecting elements from a nominal uniform array but instead by substituting reflective elements of the uniform array with elements providing both net-zero reflection at required positions and also at least partial compensation for the velocity perturbation which would be produced by such simple withdrawal. Such weighting may be used to suppress the side lobes of the reflector response and hence improve the stopband performance of the acoustic wave device and, for example, a coupled resonator filter in which that device is incorporated.

Acoustic wave devices

An acoustic wave resonator device comprises a substrate carrying a pair of spaced apart reflectors forming a resonant cavity that supports only three adjacent distinct resonant mode frequencies. An interdigital transducer is disposed on the substrate between the reflectors and includes an array of electrodes symmetrically arranged relative to a central point of the cavity to form a plurality of electrode pairs with the electrodes of each pair equally spaced on opposite sides of the central point. The central point of the cavity coincides with a node or an anti-node of the standing wave. If the two electrodes of each electrode pair are connected to the same terminal then the transducer has zero net coupling with one set of alternate modes of the cavity, whereas if said two electrodes are connected to opposite terminals then the transducer has zero net coupling with the other set of alternate modes.

A length weighted interdigital transducer has .lambda./2 spaced electrodes within the overlap region. Outside the overlap region, the overlapping .lambda./2 spaced electrodes are connected to the bus bars by pairs of .lambda./4 spaced electrodes and extra 'dummy' pairs of .lambda./4 spaced electrodes are also connected to the bus bars. The .lambda./2 spaced electrodes give a good manufacturing yield, and the .lambda./4 spaced pairs of electrodes and pairs of dummy electrodes provide compensation for wavefront distortion combined with low 'interactions.'

Acoustic surface wave devices

In acoustic surface wave devices the bottom of the substrate is provided with a plurality of discrete recesses to attenuate and/or scatter bulk waves.

Diced substrate S.A.W. device for bulk wave attenuation

An acoustic surface wave device comprising a monocrystalline body of piezoelectric material having a launching and receiving transducer applied to a planar ASW propagation surface. The piezoelectric material and the orientation of the propagation surface and the axial propagation direction relative to the crystal axes are selected to provide zero piezoelectric coupling between the transducers and a longitudinal axial bulk wave and that one of the two shear axial bulk waves that has substantially no component of particle motion perpendicular to said propagation surface. A method of manufacturing the aforesaid ASW device is also disclosed.

An acoustic surface wave filter comprising a monocrystalline wafer of bismuth silicon oxide having a special orientation of the ASW propagation surface and the interdigital transducers relative to the crystal plane whereby pick-up of undesired bulk waves is reduced.

Acoustic surface-wave devices using mono crystalline bismuth silicon

An acoustic surface wave device comprises a launching transducer and a receiving transducer coupled to one surface of a piezoelectric substrate and including means for suppressing spurious signals developed in the receiving transducer due to acoustic surface waves reflected from the ends of the substrate. In one embodiment the electrodes of both transducers are staggered a quarter wavelength at the mid point of their apertures so that waves received direct from the launching transducer arrive in phase at the receiving transducer whereas end reflected waves arrive in antiphase over the two halves of the receiving transducer aperture.

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Copthorne, United Kingdom

Richard Stevens