Patent ID: 7388810

Claim:
A system for measuring distance in a gas or liquid operating medium, comprising: an even number of ultrasonic transmitters, and a single ultrasonic signal receiver, wherein the transmitters are electro-acoustic transmitting piezoelectric transducers and the receiver is an electro-acoustic receiving piezoelectric transducer; the ultrasonic signal transmitters being adapted to transmit ultrasonic signals to a target in the operating medium, each transmitter being driven by a separate pulse source so that the total ultrasonic signal transmitted into the gas or liquid operating medium is a combination of positive and negative signals which form an overall transmitted signal, wherein each of the transmitters and receiver are so spaced apart in a geometrically symmetrical planar array within an acoustically attenuating substrate medium and wherein each of the transmitted ultrasonic signals are so pulse driven in an acoustically symmetrical relationship that opposing ultrasonic positive and negative signals transmitted through the substrate medium by symmetrically opposed transmitters are cancelled at the receiver, and a signal for measuring distance to the target is formed at the receiver by combination of the transmitted signals through the operating medium.