Measurement of internal defects in aluminum using a nano-granular in-gap magnetic sensor

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机构：

[1] Ozawa, T.

[2] Yabukami, S.

[3] Totsuka, J.

[4] Koyama, S.

[5] Hayasaka, J.

[6] Wako, N.

[7] Arai, K.I.

来源：

Ozawa, T. (ozawa@mail.tohoku-gakuin.ac.jp) | 1600年 / American Institute of Physics Inc.卷 / 117期

关键词：

Techniques for identifying defects in metals are very important in a wide variety of manufacturing areas. The present paper reports an eddy current testing method that employs a nano-granular in-gap magnetic sensor (GIGS) to detect internal defects in aluminum boards. The GIGS consists of a tunnel magnetoresistive film with nanometer sized grains and two yokes. In the presence of an external magnetic field; the nano-granular film exhibits only a small change in resistance due to the tunnel magnetoresistive effect. However; by placing it between two yokes; the magnetic flux can be greatly concentrated; thus increasing the change in resistance. The GIGS is a magnetic-field sensor that exploits this principle to achieve enhanced sensitivity. Moreover; because it has a cross-sectional yolk area of just 80μm×0.5μm; it achieves outstanding spatial resolution. In the present study; it is used in combination with an eddy-current method in order to detect internal defects in aluminum. In this method; an excitation coil is used to apply an AC magnetic field perpendicular to the aluminum surface. This induces eddy currents in the metal; which in turn give rise to an AC magnetic field; which is then measured by the GIGS. The presence of defects in the aluminum distorts the eddy current flow; causing a change in the magnitude and distribution of the magnetic field. Such changes can be detected using the GIGS. In the present study; the proposed method was used to successfully detect indentations with diameters of 5mm on the rear surface of an aluminum plate. © 2015 AIP Publishing LLC;

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