Nondestructive Measurement of Hall Coefficient for Materials Characterization

Abstract

The Hall effect is widely exploited in NDE for measuring unknown weak magnetic fields using a small piece of conducting material of known high Hall coefficient. The Hall effect could be also exploited in NDE for measuring the unknown weak Hall coefficient of conducting materials using a strong applied magnetic field, but such measurements are fraught with difficulties because of the need to cut the specimen into a small piece similar to a Hall sensor, which of course is inherently destructive. This paper tries to answer the question how the need for destructive cutting in order to produce a measurable Hall voltage could be avoided. The underlying problem is that the Hall effect produces a Hall current that is normal to the conduction current but does not directly perturb the electric potential distribution unless the Hall current is intercepted by the boundaries of the specimen. This study investigated the feasibility of using alternating current potential drop techniques for nondestructive Hall coefficient measurement in plates. Specifically, the directional four-point square-electrode configuration is investigated with superimposed external magnetic field. Two methods are suggested to make Hall coefficient measurements in large plates without destructive machining. At low frequencies constraining the bias magnetic field can replace destructively constraining the dimensions of the specimen. At sufficiently high inspection frequencies the magnetic field of the Hall current induces a strong enough Hall electric field that produces measurable potential differences between points lying on the path followed by the Hall current even when it is not intercepted by either the edge of the specimen or the edge of the magnetic field. Both techniques are investigated first analytically to illuminate the underlying physics and then by numerical simulations to make useful quantitative predictions.