ULTRASONIC TRANSDUCER FOR MEASURING THE TRAVEL TIMES OF ULTRASONIC PULSES IN A GAS
The ultrasonic transducer comprises a piezoelectric radial oscillator (16), preferably of a piezoceramic, fitted with electrodes (18, 20) on both sides. To one side are applied a first and second matching layer (26, 32) the thickness (dA?, dB?) of which is smaller than a quarter of a natural wavelength ($g(l)) of the transducer. Thus no resonance matching is performed here. On the other side of the radial oscillator (16) is secured a damper (36). a needle-pulse voltage (U(t)) is applied to the electrodes (18, 20) by capacitor discharge. The composite action of the radial oscillator (16) and the two matching layers (26, 32) then results in thickness oscillation owing to radial-thickness coupling. The aforementioned natural wavelength ($g(l)) of the transducer is then the one which is produced as a result of natural resonance during thickness oscillation. The first three half-waves (1, 2, 3) of the ultrasonic pulse (I(t)) released on excitation at the most are evaluated.