Abstract
A first-order gradiometer-type MI sensor that can reduce environmental magnetic noise without a magnetic shield was developed. The noise spectral density of this sensor is 20 pT/Hz1/2 at 1–30 Hz, which is as good as a commercial fluxgate sensor, and the noise at 60 Hz relating to the power source line is reduced. We detected SUS304 austenitic stainless steel balls with the developed MI gradiometer to simulate a system for detecting metallic contaminants using the MI sensor. The variation of magnetic field with moving SUS304 balls corresponds to the theoretical value obtained for the model of a steel ball. This MI sensor without a magnetic shield system provides a compact and simple method of detecting metallic contaminants.
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