Patent GB-1396997-A (GB)
Title: Electromechanical transducdrs and surface wave electrical filters
IPC: H03H9/64
Filed: 1972-05-15
Abstract: 1396997 Surface wave transducers; filters SIEMENS AG 15 May 1972 [6 July 1971 26 Nov 1971 29 Feb 1972] 22654/72 Heading H3U The resonance or bandpass characteristics of acoustic surface wave devices are modified by the provision of transverse protuberances, recesses, or spaced holes in the surface wave supporting substrate. Transducer, Fig. 6.-Electrode fingers 50, 50<SP>1</SP>, 60 at half wavelength spacing are deposited on piezo substrate 22, recesses 30<SP>1</SP>, 40<SP>1</SP> being provided, resulting in the equivalent circuit of Fig. 7 (not shown). By thickening the deposition of the electrode material, fingers 50, 50<SP>1</SP>, 60 may additionally act as protuberances. In Fig. 4 (not shown), the recesses are absent, electrodes (50, 60) acting as protuberances to give the equivalent circuit of Fig. 5 (not shown). Spacings between elements 30<SP>1</SP>, 50 and 40<SP>1</SP>, 50<SP>1</SP> may be equal or otherwise, and the protuberances or recesses may differ in their wave reflecting capacities. A plurality of transducers may be provided in cascade. Instead of recesses, protuberances or lines of holes may be provided. Absorbing material 80 is provided. Several half wavelength spaced pairs of electrodes may be enclosed between recesses 30<SP>1</SP>, 401. Filter, Fig. 1.-The bandpass characteristic is established by means of protuberances such as K 1 -K 3 , recesses such as K 4 -K 7 , or spaced holes K 13  provided in or on a substrate 5 of quartz glass or crystal, or alloy steel, and provided by metal vapour deposition, etching or laser bombardment. Longitudinal protuberances 10, recesses 11, or spaced holes (not shown) provide coupling between spatially separated resonance regions, e.g. R 1 , R 6  or R 2 , R 5  see also the equivalent circuit of Fig. 2 (not shown). Alternatively electrodes 15, 15<SP>1</SP> on a piezo part of substrate 5 may be coupled by leads 16, and possibly a network, or variable capacitor 17, or a single pair of electrodes 15 may be connected to the input or output transducer. The transducer elements 5<SP>1</SP>, 511 on a piezo part of the substrate may take the form of Fig. 4 (not shown), and may be loaded with lumped circuit elements for increased bandwidth. Wedge shaped varnish absorbing layers 6, 7 may be provided or omitted if a low "Q" electrostrictive ceramic substrate is used for the transducers. Frequency divider, or synthesizer, Fig. 3 (not shown). A pair of filters of the above construction, and with distinct bandwidths share a common input transducer (5a) and are mutually decoupled by protuberance, recess, or row of holes (20). A signal may be thus split into two frequency bands, or an arbitrary number of such bands by providing further filters (not shown) on the side of the input transducer remote from the above decoupled pair. Used with input and output functions reversed, the device is a synthesizer. The devices are trimmed by applying further wave disturbing locations on, or providing further holes in, the substrate. The devices are used in carrier frequency systems.