Novel absolute linear displacement sensor utilizing giant magnetoresistance elements

A novel concept for an absolute linear displacement sensor utilizing giant magnetoresistance elements is introduced. This device is based on the division of a magnetically soft layer of a spin-valve device into two antiparallel magnetic domains. The total resistance of the spin valve varies linearly with displacement of the domain wall because of different resistances of the aligned and antialigned magnetic states of the spin valve. Domain-wall translation is achieved by the use of a magnetic wall ''trap'' generated by permanent magnets. Displacement is thus related directly to the device resistance. Position resolution to date is on the order of 10 mu m over ranges of approximately 2 cm and on the order of a micron over reduced ranges. Magnetic hysteresis yields backlash on the order of tens of microns.