Wave transmission lines and networks – Coupling networks – Delay lines including elastic surface wave propagation means
Patent
1990-05-09
1992-06-30
Laroche, Eugene R.
Wave transmission lines and networks
Coupling networks
Delay lines including elastic surface wave propagation means
333153, 333194, 310313R, 310313D, H03H 909, H03H 925, H03H 942
Patent
active
051267063
DESCRIPTION:
BRIEF SUMMARY
Surface wave arrangements with converter and/or reflector structures on piezoelectric substrate bodies are sufficiently known.
In order to avoid disturbances caused by surface waves reflected at the edges of the substrate body, it is customary to coat the edges or end faces of the substrate body and the surface regions thereof adjoining these edges with an acoustically inelastic, i.e. damping, material. Such a material serves as a sink for surface waves. Surface waves running into such a sink are absorbed and damped there and, in particular, are not reflected again. This absence of reflection causes the desired surface wave propagation in the manner envisaged.
Although, as seen from the standpoint of the wave propagation, this method yields a result which is satisfactory per se, there are nevertheless disadvantages connected with such a measure. As a rule, material for such a sink is organic material, which is not free from the effect of contamination on the remaining substrate surface. Even slight degrees of contamination of the substrate surface in the region of the envisaged surface wave propagation can, however, lead to very serious disturbances. Such a sink represents a relatively large surface of such an organic material and, on the other hand, this material directly adjoins the surface regions of the substrate body which are to be kept free of contamination.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. Nos. 4,623,855, 4,728,912 and German A-3700789 (British 2,186,456) were cited in the International Bureau preliminary examination report for the corresponding international application. However, none of these disclose a conversion structure which converts the described type of wave generated in order to avoid surface waves reflected by the edges of the substrate, where the distances between adjacent stripes are clearly different from the distances in a known reflecting structure according to the dimensioning rules of this invention.
It is the object of the present invention to find a new measure with which it is possible to avoid the development, possible per se and due to reflection of surface waves at substrate edges, of reflected surface waves in surface regions of the substrate body, where the occurrence of surface waves is not desirable per se.
The present invention is based upon the idea of avoiding, at least if possible, using a sink of organic material, or of at least very considerably reducing the amount of such material known to be employed according to the prior art in order to achieve this effect. The different principal on which the invention is based is, instead of the inelastic disturbance of such surface waves, to provide the elastic disturbance of such waves, but in addition to convert such an undesirable surface wave into a different form. This is preferably the form of a bulk wave. The occurrence of bulk waves is undesirable, and in the case of the present invention measures are taken such that the bulk waves which are intentionally generated have a direction so that they do not disrupt the effective surface-wave propagation region of the converter and/or reflector structures. In particular, for the surface waves which are converted into bulk waves are caused to travel at an angle which is directed away from the substrate surface so that these bulk waves reach the region of the inelastic damping adhesive which secures the substrate body to the support or in the housing.
The reference to this adhesive is only an apparent contradiction to what has been said above concerning the organic material of a sink. For one thing, such an adhesive material joining the substrate body to the support is located exclusively on the back of the substrate body. Virtually the entire adhesive material is covered by this rear surface of the substrate body and by the bearing area in the housing. It is only the extraordinarily narrow edges, and these alone, which are in direct contact with the internal atmosphere of the housing.
However, what has been said above is not a contradiction of the embodiment which i
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Fleischmann Bernd
Riha Gerd
LaRoche Eugene R.
Lee Benny L.
Siemens Aktiengesellschaft
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