Piezoelectric elements show the maximum displacement and thus the optimum transmission performance at the series resonance frequency, but the maximum receiving voltage sensitivity occurs at the parallel resonance frequency which is higher as a series resonance frequency. Therefore if the piezoelectric element is operated at its series resonance so that it emits ultrasonic waves with maximum efficiency it can receive the echo response only with a poor sensitivity. For the alternative usage of the piezoelectric transducer as transmitter and receiver a matching of the series and parallel resonance frequencies is required. It is the object of the present work to provide a nontraditional (without /spl lambda//4 matching layer or additional inductances) method of matching so that the ultrasonic transducer has optimal transmission and reception characteristics with the same operating frequency.
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