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 wi th increasing an external field Hex. We call the effect as ''magneto-i nductive (MI) effect.'' This effect sensitively appears in a zero-magn etostrictive wire which is cold drawn and then tension annealed. A mul tivibrator resonance oscillator having oscillation frequencies near 20 0 MHz (180-220 MHz) is constructed using two a-wires and two N channel junction field effect transistors(FET) with some resistors and capaci tors. 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 squa re-root LC at a resonance. Small magnetic field less than several oers teds were linearly detected by adding a bias field to each a-wire. Hig h frequency fields up to the cut-off frequency (around 20 MHz) would b e detected using the MI effect multivibrator, which is effective for n on-contact sensing for a plasma current in a plasma furnace and discha rge current and other high speed electromagnetic phenomena.