Detector device and method for distinguishing between fluids having

Abstract

A device and method for distinguishing between different fluids on the basis of their dielectric properties. In an preferred embodiment, the device comprises two substantially parallel conductive surfaces which are positioned on opposite sides of a fluid conduit so as to form a substantially parallel plate capacitor. The first conductive surface is electrically connected through an inductor to a voltage source, and such first conductive surface is also electrically connected to the source electrode of a field-effect transistor. A resonator device is electrically connected between the second conductive surface and the gate electrode of the field-effect transistor. The gate electrode of the field-effect transistor is further electrically connected through a fixed resistance to ground, and the drain electrode of the field-effect transistor is electrically connected directly to ground. The inductance of the inductor is selected such that the resonant frequency of the inductor and the capacitor is substantially the same as the operating frequency of the resonator device when a desired column of fluid is positioned between the two conductive surfaces. In this state, the output voltage of the detector device will oscillate. However, when a column of fluid having significantly different dielectric properties is positioned between the two conductive surfaces, the resonant frequency of the inductor and the capacitor will change, and the output voltage of the detector device will stop oscillating.