Method of producing an attenuating structure on a surface wave c

Details Method of producing an attenuating structure on a surface wave c Method of producing an attenuating structure on a surface wave c

1997-06-05

1999-05-04

Pascal, Robert

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

333195, 310326, 427493, 427518, 522170, C08F 248, H03H 308

Patent

active

059002867

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Surface wave components, such as, for example, surface wave filters, are electronic components which are used for the signal processing of electromagnetic waves having an information content. In the case of the components used, for example, in radar systems, television sets and video recorders, the electrical pulse or current carrying the signal or the information is converted into mechanical vibrations, so-called surface waves. The acoustic properties of the transducer are influenced by a suitable construction of said transducer, especially by a particular geometrical configuration of the sound-generating transducer surface. As a result, it is possible to modify the acoustic signal in a desired way. For example, the intermediate frequency of approximately 38 MHz is filtered out of the total spectrum of a television or video signal in this way. Surface waves which are not completely converted back into electrical signals again disturb the operation of a surface wave component, as do reflections at component edges or other structures. To attenuate such undesirable surface waves and to reduce edge reflections and echo effects, the surface of the transducer element is predominantly provided in the region of the component edges with an attenuating mass which absorbs the energy of the diverging waves and reduces reflections and echo effects.
Organic materials having a very particular dynamic and mechanical property profile are required to produce such attenuating structures. European reference EP 0 360 037 proposes for this purpose, for example, to use two-component resins which have an epoxide base and which are crosslinkable by base catalysis with carbonic acids and acidic esters. Said two-component resins can be acoustically matched in a desired way and result in the required attenuation, but on the other hand, they present problems in processing. The mixing of the two resin components results in an increased expenditure in the manufacture, resins with limited pot life being obtained. The solvent content of the reactive resins requires a prolonged evaporation and curing procedure in which there is, in addition, the risk that the attenuating structures printed on in a special three-dimensional geometry flow and then no longer have the desired attenuating properties.
European reference EP 0 098 599 A2 proposes using UV-curing acrylic resin mixtures for the attenuating structures of surface wave components and optimizing said mixtures for a high modulus of elasticity and a high density. However, attenuating structures produced and cured in this way exhibit in practice an unduly high brittleness and an unduly low bonding to chip material and transducer material. The structures are produced on a wafer and then separated by sawing. The sawing of attenuating structures required in this process may result in their peeling off and detachment and, consequently, in damage to the entire component.


SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a surface wave component having an acoustically modified attenuating structure which can be produced simply and reliably, which has a low edge reflection and which has a high attenuation for stray signals.
In the invention, a conventional piezoelectric transducer is combined with a novel acoustic attenuating structure which advantageously results in a surface wave component having improved properties. The piezoelectric transducer, which is known per se, essentially comprises a substrate composed of piezoelectric material and transducer electrodes on one surface of the substrate. The transducer electrodes may comprise transmitting and receiving electrodes which are separated from one another by a propagation path for the surface waves. Acoustic attenuating structures are applied to this surface in such a way that transducer electrodes are only partly covered by them and propagation paths are not covered by them.
Since both the outline of the area covered by the attenuating structures and the attenuating structure

REFERENCES:
patent: 4427515 (1984-01-01), Yuhara et al.
patent: 4510410 (1985-04-01), Yuhara et al.
patent: 4977199 (1990-12-01), Koleske et al.
patent: 5242715 (1993-09-01), Schoen et al.
patent: 5328940 (1994-07-01), Zimmer

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