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Sensor Number Minimization in Acoustic Surface-Wave Matched Filters

1971; Institute of Electrical and Electronics Engineers; Volume: 18; Issue: 4 Linguagem: Inglês

10.1109/t-su.1971.29619

2162-1403

Carlo Atzeni,

Advanced MEMS and NEMS Technologies

In tapped ultrasonic surface-wave delay lines for signal matched-filtering the required impulse response is writ- ten onto the surface of a piezoelectric substrate in the form of an interdi@tal array of sensors. The design of the interdig- ita1 array requires the distance between a pair of adjacent sen- sors to be half an acoustic wavelength at the frequency of op- eration, each sensor being a smaller fraction of a wavelength in width. When processing FM signals, the spacing and the width of the sensors must be graded according to the frequency- modulation law. An interdigital array matched to a waveform of mean fre- quency fb and of duration T contains 2fl T sensors. In this paper it is shown how, for narrow-band signals, this number is redundant and can be reduced down to a minimum value, which depends essentially on the signal fractional bandwidth, B/f',. For low fractional bandwidths. a minimum number of about BT sensors is sufficient to synthesize the matched-filter impulse response. The sensor number reduction involves a corresponding increase in sensor spacing and width. which can be a noticeable advantage for the implementation of high-fre- quency devlces. Although the reduction of the sensor number lowers the output signal amplitude, the output signal-to-noise ratio, which is the essential feature in matched-filtering, re- mains unchanged. The criterion for the sensor number minimization is given here in the particular case of a filter matched to a linear FM signal. and experimental results, confirming the theory, are presented.