Non-Contact Displacement Sensors Using Amorphous-Wire Core Multivibrators and Its Application to Mechanocardiograph

Abstract

New con-contact type linear displacement (oscillation) sensors are presented which combine a two amorphous-wire core multivibrator bridge with a small magnet. The nonlinearity of the relationship between magnetic field from the magnet and the distance between the detection point and the magnet is cancelled by utilizing the saturation characteristics of the amorphous-core magnetometer. Linear ranges as large as 8mm have been obtained using a zero-magnetostrictive amorphous wire (made by UNITIKA Co.) of 44mm in diameter on which two 20mm long coils are placed separately. The cut-off frequency is about 4 kHz in the displacement sensor, and the minimum detectable displacement is about 1 μm.
A new sensing technique is developed using these non-contact linear displacement sensors for mechanocardiography for cardio-function diagnosis combined with the electrocardiograph.