Quick response field sensor using 200 MHz amorphous MI element FET multivibrator resonance oscillator

A circumferential flux change in an amorphous wire due to a high frequency wire current induces an inductive AC voltage e/sub L/ between both ends of the wire. An amplitude of e/sub L/ decreases with increasing an external field Hex. This is called the magnetoinductive (MI) effect. This effect appears in a zero-magnetostrictive wire which is cold drawn and then tension annealed. A multivibrator resonance oscillator having oscillation frequencies near 200 MHz is constructed using two a-wires and two N channel junction field effect transistors with some resistors and capacitors. Small magnetic fields less than several oersteds are 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.<>