Passive sensor system using ultrasonic energy

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Reference is now made to FIG.
1 which illustrates the ultrasonic sensor system of the present invention.
The system comprises a passive sensor 10 and an external ultrasonic activation and detection system 14.
The sensor 10 is implantable in an ultrasound compatible medium 12, such as the human body, or mountable on an inner wall of an enclosure.
The sensor 10 is any suitable sensor, examples of which are described hereinbelow with respect to FIGS.
2-4, which mechanically vibrates in the presence of an ultrasonic wave, much as a tuning fork vibrates in the presence of a sonic wave.
Therefore, sensor 10 is represented schematically in FIG.
1.
as a tuning fork.
The frequency of vibration of sensor 10 is its current vibration frequency which is a function at least of the physical variable being sensed.
The activation and detection system 14 typically comprises an ultrasonic generator 20, at least one ultrasonic transducer 22, a frequency detector 24 and a data processor 25.
The ultrasonic generator 20 and transducer 22 constitute the activating elements and the transducer 22, the frequency detector 24 and the data processor 25 constitute the detecting elements.
The generator 20, such as the non destructive testing unit, model IIB USDF, manufactured by Balteu Sonatest/Schlumberger of Milton Keynes, England, generates an ultrasonic wave to be transmitted by the ultrasonic transducer 22 to the sensor 10 via the medium 12.
Typically, ultrasonic gel 26, located on an outer edge 28 of medium 12, is utilized to couple the transducer 22 to the medium 12.
Typically, the transmitted ultrasonic wave is composed of a single frequency or a range of frequencies.
The ultrasonic transducer 22, such as one part of the non-destructive testing unit, typically also receives ultrasonic waves from the medium 12.
Some of these waves are reflections of the transmitted wave; others are from sensor 10.
In an alternative embodiment, there are two ultrasonic transducers 22, one for transmitting and one for receiving