High-Resolution Magnetic Sensors for Human–Machine Interfacing

Abstract

Human-machine interfaces (HMIs) translate physiological signals into commands, enabling users to interact intuitively with digital systems. Magnetic sensing has established itself as a particularly attractive HMI modality, enabling non-contact, non-invasive measurement of the faint biomagnetic fields associated with cardiac and muscular electrical activity. Detection is achieved via the magnetoresistive (MR) effect, in which an applied magnetic field induces a measurable change in the electrical resistance of a sensing element, enabling accurate transduction of both the magnitude and direction of the field. Within the family of MR technologies, tunnel magnetoresistive (TMR) sensors stand out. Their architecture comprises two ferromagnetic electrodes separated by an ultrathin insulating tunnel barrier, most commonly magnesium oxide (MgO). The probability of electrons tunneling quantum-mechanically through this barrier, and therefore the junction resistance, is governed by the relative orientation of the electrode magnetizations: a parallel configuration produces low resistance, whereas an antiparallel configuration produces high resistance.