A force transducer based on leakage flux variations

Abstract

A novel construction for a magnetoelastic transducer for sensing tensile or compressive loads is described. The device requires neither coils nor exciting currents, relying instead on the field from a permanent magnet to polarize a magnetostrictive core element. A field intensity sensor, such as a Hall-effect device, detects the leakage flux from the magnet/core combination. Variations in this flux by the stress-dependent bulk moment of the core are used to signal the applied force. The core moment affects the flux both by sourcing an additional field and by altering the operating point of the magnet. The moment in the core is altered by the redistribution of domain orientations by the stress anisotropy. Data from experimental sensors using tubular cores with internal magnets show good linearity and a small hysteresis that can be of either sign. The design allows for the construction of small, low-cost force transducers.