Giant magnetoresistance-based eddy-current sensor

TLDR

This paper introduces a GMR‑based eddy‑current technique for detecting surface or near‑surface defects in nonmagnetic metals. The method employs a self‑rectifying GMR sensor integrated on a silicon chip, providing 220 mV/mT sensitivity from dc to 1 MHz, small dimensions, and investigates orientation, liftoff, and excitation effects to enhance spatial resolution. Experiments demonstrate that the probes accurately detect short surface‑breaking cracks and characterize surface and subsurface defects of various sizes and shapes on aluminum specimens.

Abstract

The purpose of this paper is to introduce a new eddy-current testing technique for surface or near-surface defect detection in nonmagnetic metals using giant magnetoresistive (GMR) sensors. It is shown that GMR-based eddy-current probes are able to accurately detect short surface-breaking cracks in conductive materials. The self-rectifying property of the GMR sensor used in this study leads to a simplified signal conditioning circuit, which can be fully integrated on a silicon chip with the GMR sensor. The ability to manufacture probes having small dimensions and high sensitivity (220 mV/mT) to low magnetic fields over a broad frequency range (from dc up to 1 MHz) enhances the spatial resolution of such an eddy-current testing probe. Experimental results obtained by scanning two different probes over a slotted aluminum specimen are presented. General performance characteristics are demonstrated by measurements of surface and subsurface defects of different sizes and geometries. Dependence of the sensor output on orientation, liftoff distance, and excitation intensity is also investigated.