U.S. Philips Corporation

Gerardus Andreas Van Maanen

Cornelis Martinus Van Der Burgt

Nico Valentinus Franssen

Henricus G Kockelmans

An acoustic transducer comprising a transmitter consisting of a plate of piezoelectric ceramic material and a pair of electrodes and an adaptation layer which comprises a receiver consisting of a layer of piezoelectric or ferroelectric polymer material with a pair of electrodes. As a result, optimum operation of the transducer is possible during transmission as well as during reception.

Acoustic transducer

An amplifier comprising a first and a second amplifier element, whose outputs are connected to a load, a difference circuit which comprises a comparator, in which the output signal of the first amplifier element is compated with the input signal thereof to produce a correction signal which is applied to second amplifier element, and a second substantially identical difference circuit which comprises a comparator in which the output signal of the second amplifier element is compared with the input signal thereof to produce a correction signal which is applied to the first amplifier element; a desired signal to be amplified being applied to both amplifier elements. The two amplifier elements, which may be preceded by preamplifiers, take the form of power amplifiers. Because the distortion signals appear at the load as 'common mode' signals, the overall distortion becomes substantially zero in the case of equal attentuation in the two difference circuits. The power amplifiers may be provided with a voltage output as well as a current output.

Amplifier comprising a first and a second amplifier element

For accurate measurements of the sound velocity in liquids, for example water, the propagation delay is measured between an ultrasonic wave which is emitted by a transducer and the wave which returns to the transducer upon reflection. By making the reflector spherical and disposing it at a distance from the transducer which is within 11/2 times the length of the Fresnel region of the emitted acoustic wave, a favorable ratio between the 1 .tau. and the 2 .tau. signal is obtained, which ratio can be further improved when the central portion of the reflector is slightly flattened.

Propagation delay meter

A voltage sensitive trigger circuit with a threshold which must be temperature and supply-voltage independent. To this end, a preamplifier is employed which in itself is not only provided with negative feedback but which also receives a current which is derived from that trigger transistor, which in the quiescent condition is conducting.

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Eindhoven, Netherlands

Gerardus Andreas Van Maanen