Proximity detector for hard-to-detect materials

摘要

A proximity detection system for detecting the proximity of conventionally hard-to-detect materials having a complex permittivity and/or a complex permeability is disclosed. The system includes an oscillator for producing an output signal, the oscillator having a transistor with an open and a closed loop gain and a base-emitter junction that rectifies resonant signals at the collector to produce the output signal. The oscillator includes negative feedback including a resistive element coupled to the emitter for reducing the sensitivity of the closed loop gain to variations in the transistor's open loop gain and a capacitive element coupling the resistive element to the collector for stabilizing the frequency of the oscillator. The detection system further includes a sensor coupled to the oscillator for varying the level of the oscillator output signal in response to certain electrical properties of the material. Control means are also included operatively coupled to the oscillator to receive the oscillator output signal and respond to variations of predetermined magnitudes of the amplitudes of the oscillator output signal for detecting the presence or level of the material. The sensor is designed to reposition the polarization orientation of the electric field lines extending therefrom such that the field lines extend a greater distance outwardly from the surface of the sensor.