Magnetostrictive effect type force (strain) sensor using mutual induction of planar coils

A new structure is proposed for the magnetostrictive effect type force sensors using a pickup head layered with magnetostrictive foil and a pair of planar coils. Mutual coupling between two planar coils is used as a measure of force applied to the magnetostrictive foil glued to a mechanical component. The mutual coupling is governed by force-induced anisotropic permeability at the magnetostrictive foil. In this type of the force sensor, the output voltage is zero when force is zero, and the planar coils with electric wires can be put on and taken off easily because the magnetostrictive foil does not need a current contact. Basic characteristics of the force sensors are examined using Metglas2605SC amorphous foil glued to the side of an aluminum square bar of 15mm × 15mm in cross-section area and a pair of 16-turn planar coils. Sensitivity was 38.4 mV/Nm (1.57 mV/με (ε = 81/1)) at the coil excitation condition of 1 MHz, 60 mA.