A Solution to TMR-EMT Blind Spots Based on Biaxial TMR

Electromagnetic tomography based on tunneling magnetoresistance (TMR-EMT) is a new type of electrical tomography technology. In contrast to the traditional EMT that uses the magnetic flux obtained from the coil to reconstruct the electrical conductivity distribution in the region of interest (ROI), the TMR-EMT reconstructs the magnetic permeability distribution in the ROI by the boundary magnetic induction intensity in the direction of the sensitive axis of the uniaxial TMR (Uni-TMR). However, the Uni-TMR measurements are influenced by the direction of boundary magnetic induction intensity at the Uni-TMR location; when the direction is orthogonal to the sensitive axis direction, the Uni-TMR cannot measure the boundary magnetic induction intensity, and such locations are named TMR-EMT blind spots in this article. The blind spots will exacerbate the ill-condition of inverse problem solving of TMR-EMT and even lead to failure of imaging. Aiming at the problem of TMR-EMT blind spots, this article proposes a solution to measure the boundary magnetic induction intensity using biaxial TMR (Bi-TMR). The Bi-TMR consists of two Uni-TMRs, whose sensitive axis directions are orthogonal to each other. The Bi-TMR measurement is obtained by squaring the sum of the squares of these two Uni-TMR measurements, which is unaffected by the boundary magnetic induction intensity direction. Simulation and experimental results show that this solution does not have the blind spots and can obtain complete boundary magnetic induction intensity in plane.