The present invention relates to a device for use in sensing dielectric changes in a solid, liquid or gas body.
A number of proposals have been made for converting changes in impedance or dielectric into electrical voltage, current or frequency changes. One design described by Marsh in Electronics, 20th Mar. 1967, uses the change in dielectric to control the frequency of an oscillator. The circuit however, is complex and suffers seriously from the effects of stray capacitance, this being particularly pronounced where the circuit is remote from the measuring capacitor, as it usually must be. Other oscillation devices also tend to be fairly insensitive and for similar reasons.
It has also been proposed to use radio frequency voltage sources in balancing circuits. These produce a direct current output, but again problems are encountered with stray capacitance and temperature drift, and these devices accordingly are of low sensitivity.