QUICK RESPONSE FIELD SENSOR USING 200MHZ AMORPHOUS MI ELEMENT FET MULTIVIBRATOR RESONANCE OSCILLATOR

A circumferential flux change in an amorphous wire (a-wire,for short) due to a high frequency wire current induces an inductive AC voltage e, between both ends of the wire. And an amplitude of e(L) decreases with increasing an external field Hex. We call the effect as ''magneto-inductive (MI) effect.'' This effect sensitively appears in a zero-magnetostrictive wire which is cold drawn and then tension annealed. A multivibrator resonance oscillator having oscillation frequencies near 200 MHz (180-220 MHz) is constructed using two a-wires and two N channel junction field effect transistors(FET) with some resistors and capacitors. An inductance L of the a-wire and a capacitor C appeared between the source and the drain decide a oscillation frequency of 1/2pi square-root LC at a resonance. Small magnetic field less than several oersteds were linearly detected by adding a bias field to each a-wire. High frequency fields up to the cut-off frequency (around 20 MHz) would be detected using the MI effect multivibrator, which is effective for non-contact sensing for a plasma current in a plasma furnace and discharge current and other high speed electromagnetic phenomena.