Low-frequency electromagnetic sensing of cracks and inclusions in ferromagnetic materials using magnetoresistive sensors

Alexander R. Perry; Peter V. Czipott; Alan L. Singsaas; William F. Avrin

doi:10.1117/12.339883

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28 January 1999 Low-frequency electromagnetic sensing of cracks and inclusions in ferromagnetic materials using magnetoresistive sensors

Alexander R. Perry, Peter V. Czipott, Alan L. Singsaas, William F. Avrin

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Proceedings Volume 3586, Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware III; (1999) https://doi.org/10.1117/12.339883
Event: Nondestructive Evaluation Techniques for Aging Infrastructures and Manufacturing, 1999, Newport Beach, CA, United States

Abstract

Ultrasonic inspection methods are often used to detect defects in ferrous and non-ferrous metal casting processes. The finite sensor recovery time following emission of the ultrasonic pulse leads to a 'shadow zone', from the surface to a depth of about 1 cm, that cannot be probed by ultrasonics. Conventional eddy current methods, operating at frequencies of several kHz or higher, can only detect surface-breaking flaws. Giant Magneto-REsistive and Anisotropic Magneto-Resistive sensors offer their full performance independently of frequency from 100kHz down to DC. This allows eddy current-based technique to prove ferrous materials deeper than heretofore, and thus to provide coverage through the shadow zone. The work presented here demonstrate the performance and sensitivity that can be achieved. The separation of eddy current and ferromagnetic signals allows the structure to be probed and the material properties to be imaged. We have detected artificial defects in ferrous steel samples to a depth of 1 cm as well as surface flaws smaller than those found by conventional eddy current methods. We also show results of probing a cast and rolled steel sample with real defects, where a band of presumed subsurface ferromagnetic inclusions masks the signal from tight surface cracks.

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Alexander R. Perry, Peter V. Czipott, Alan L. Singsaas, and William F. Avrin "Low-frequency electromagnetic sensing of cracks and inclusions in ferromagnetic materials using magnetoresistive sensors", Proc. SPIE 3586, Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware III, (28 January 1999); https://doi.org/10.1117/12.339883

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