Patent ID: 7277012

Claim:
A sensor comprising an ultrasonic transducer, the transducer comprising: a) a transmitter with a stationary acoustic reflector for emitting a broad field ultrasonic radiation; b) a receiver with a matched stationary acoustic reflector for receiving a focused portion of the broad field ultrasonic radiation; and c) means for detecting changes in the focused portion of the broad field ultrasonic radiation, wherein the means for detecting changes in the focused portion of the broad field ultrasonic radiation includes sensor circuit in electrical communication with the receiver and in electrical communication with a load circuit, wherein the sensor circuit opens and closes the load circuit in response to the detected changes in the focused portion of the broad field ultrasonic radiation wherein each of the stationary acoustic reflector and the matched stationary acoustic reflector has a sloped wall, and a plurality of conical cross-sections one arranged around another and positioned in the path of the corresponding transmitter and receiver, respectively.