UHF Multilayer Acoustic Filter.
Final rept. 21 Dec 67-21 Dec 68,
STANFORD RESEARCH INST MENLO PARK CA
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The theoretical design of a multilayer acoustic filter is described. A prototype design that uses a minimum number of gold and aluminum films and cadmium sulphide input and output transducers is analyzed and is found to have a 3-dB bandwidth on the order of one percent and an insertion loss on the order of 20 dB. To overcome this insertion loss a transistor amplifier is added in series with the filter. Analysis of both field-effect and bipolar transistors shows that, if no external tuning or impedance matching is allowed, the bipolar transistor is superior. A method is described for measuring the change in amplitude of an acoustic wave as it is reflected from the end of a sapphire rod that is being coated by a metal film or films. The magnitude of the acoustic losses can be inferred from these data. It was found that at 575 MHz the acoustic Q of gold is on the order of 100, while that of aluminum is on the order of several hundred. The construction and testing of several multilayer acoustic filters is described. None of these filters exhibited the desired transmission response, but one of them showed indications that some coupling to acoustic waves was taking place. RF leakage was found to be a major problem in these devices. The construction of several multilayer acoustic transducers on sapphire delay lines is also discussed, wherein it was found that gold-aluminum bimetallic films alloy at relatively low temperatures. Author
- Electrical and Electronic Equipment