A method using two delay line oscillators is described for measuring the flow velocity of a liquid. Each of the delay line oscillators is composed of two interdigital transducers on one surface of a piezoelectric plate, and an amplifier. The transducer operates as a sound beam radiator or a detector at a liquid–solid interface. The liquid velocity is estimated from the oscillation frequencies of two delay line oscillators. Experimental results confirming the operation principle of the method are satisfactory for water velocity measurement.
A hydrophone using a liquid delay line oscillator has been developed. The delay line consists of two pairs of interdigital transducers on the same substrate surface and a diaphragm used as a reflecting plate of the sound beam. The interdigital transducer operates as a sound beam radiator or a detector at a liquid-solid interface. The oscillation frequency is dependent upon the sound pressure level applied to the diaphragm. Performances of the hydrophone are described, including sensitivity and its frequency dependence.
A new sound sensor system is proposed by the use of two delay devices with interdigital transducers operating at liquid-solid interface. One of two devices, immersed in water, has a delay time dependent upon the sound pressure level. The variation of the phase difference between two output signals of the delay devices, corresponding to a sound signal in water, is detected as an electrical signal via a phase ½omparating circuit.
An equivalent circuit model analysis of a liquid-loaded interdigital transducer is described. The electric loss related to the complex relative dielectric constant and the electroacoustic conversion efficiency are represented in the form of a function of the specific acoustic impedance (ρv) of the loaded liquid. The conversion efficiency for ultrasound into the liquid is estimated from only the acoustic impedance and the relaxation time of the substrate material, which are obtained relatively easily from the water measurement. The estimated theoretical efficiency is in good agreement with the experimental results for various liquids. These results also coincide with the results from the wave equation for the leaky surface acoustic wave propagation at the solid–liquid boundary.
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