Metal Detection Sensor Utilizing Magneto-Impedance Magnetometer

Abstract

A magnetometer with a longitudinal sensing line using the MI effect was examined experimentally to find an application to replace conventional metal sensors based on an LVDT. A sampling to the second peak signal from the pickup coil on the sensing head with a long, thin soft magnetic ribbon and driven with an ultrashort pulse train with a pulse width of 5~7 ns formed the front end of the metal sensor. Unmatched degaussing and geomagnetic field compensation methods were effective not only to minimize the remnant magnetic field but also to prevent the saturation of the magnetic ribbon and expand the dynamic range. The active noise reduction process reduced the inherent noise to the 1/3 level with a minimum influence on the detection signal. The proposed metal sensor with unmatched degaussing, geomagnetic field compensation, and active noise reduction techniques demonstrated the detection of a 0.2 mm diameter magnetized ferrous ball.