Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1993-09-28
1995-05-09
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310313D, 310326, 333151, H01L 4108
Patent
active
054143217
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-wave arrangement which has interdigital transducers and, possibly, further structures on the surface of a piezoelectric substrate. The interdigital transducers are used to convert electrical signals into acoustic surface waves, and vice versa. Further structures can be resonator structures, reflector structures or even conversion structures, as are known from WO 89/02675.
2. Description of the Related Art
Acoustic waves, which are designated by the general term "surface waves" and are Rayleigh waves, Bleustein waves, surface-skimming bulk waves and the like, run on or in the surface or in the region close to the surface of the respective substrate body. Apart from aperture effects and diffraction effects, such acoustic waves run in a direction which is designated as the main wave propagation direction, having wave fronts which are transverse to this direction and are in a straight line corresponding to the transducers, the opposing direction also being included. Specifically, such acoustic waves are transmitted from an interdigital transducer in the direction and the opposing direction as the main wave propagation direction, unless this transducer is not specifically constructed as a unidirectional transducer.
The substrate body of such a surface-wave arrangement is a platelet, which is normally elongated, is rectangular or whose narrow sides are inclined with respect to the longitudinal edges of the platelet. Such an inclined direction makes it possible for acoustic waves which strike against this end edge of the platelet and run in the main wave propagation direction to be reflected back on this edge in a direction other than the main wave propagation direction. However, it is in general normal instead of this or in addition to this to fit a so-called sump on or to the substrate platelet in the region of a relevant end edge of the substrate platelet. The material of such a sump has the property of absorbing waves of the surface-wave arrangement which pass into the region of this sump, that is to say no longer allowing them to pass back into the structures which are fitted on the substrate surface.
From the documents GB-A-2,048,010, EP-0,057,598 and DE-B-2,738,192, it is known for the outer border of a spot of absorbent material which is fitted on the substrate surface to be given a specific shape, for example as a large-area triangle having a zig-zag edge or some other irregular shape. Another shape (DE-B-2,738,192, FIGS. 4, 5 and 6) is that having a sawtooth shape. If such a sawtooth-shaped edge faces the wave, total reflection effects are thus precluded (which occur in the case of the invention which is still to be described). A sawtooth shape along the rearward edge with respect thereto would be virtually insignificant, even if said edge were to satisfy the angle conditions for total reflection, since the wave is essentially already attenuated to virtually zero, anyway, at this location.
Such materials for acoustic absorption are plastics and the like which are crosslinked with solvents and whose evaporations continuously change the electrical characteristics of a surface-wave arrangement, even over a lengthy time. When the arrangement is in a closed housing, such a material is highly disadvantageous for high-quality arrangements.
Proposals have thus been made, specifically as cases for acoustic waves, to produce incisions, of arranged angle, in the arrangement in the material of the rearside of the substrate platelet (DE-B-2,450,831) or to cut angled notches into the edges of the substrate (DE-A-2,131,614). For a surface-wave arrangement having a piezoelectric layer on a non-piezoelectric substrate, JP-A-60-256214 proposes that the edge of this piezoelectric layer be allowed to run in a zig-zag. Apart from their small effectiveness, such measures are relatively costly.
A method which is very effective even without absorbent plastic and without incisions into the substrate material is specified in the doc
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patent: 3872410 (1975-03-01), Zucker
patent: 3956647 (1976-05-01), Mitchell et al.
patent: 4139791 (1979-02-01), Yamada et al.
patent: 4188596 (1980-02-01), Miura
patent: 4354129 (1982-10-01), Ieki
patent: 4426595 (1984-01-01), Kawaura et al.
Anemogiannis Kimon
Schropp Isidor
Visintini Giuliano
Budd Mark O.
Siemens Aktiengesellschaft
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