A superconducting quantum interference device magnetometer system for quantitative analysis and imaging of hidden corrosion activity in aircraft aluminum structures

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Abstract
We have designed and built a magnetic imaging system for quantitative analysis of the rate of ongoing hidden corrosion of aircraftaluminumalloys in planar structures such as intact aircraft lap joints. The system utilizes a superconducting quantum interference device(SQUID) magnetometer that measures the magnetic field associated with corrosion currents. It consists of a three-axis (vector) SQUID differential magnetometer, magnetic, and rf shielding, a computer controlled x-y stage, sample registration, and positioning mechanisms, and data acquisition and analysissoftware. The system is capable of scanning planar samples with dimensions of up to 28 cm square, with a spatial resolution of 2 mm, and a sensitivity of 0.3 pT/Hz1/2 (at 10 Hz). In this article we report the design and technical issues related to this system, outline important data acquisition techniques and criteria for accurate measurements of the rate of corrosion, especially for weakly corroding samples, and present preliminary measurements.