Magnetic flux leakage detection and eddy current testing is studied more and more by means of sensor chips based on thin film technology. Magnetoresistive sensor chips, for example, are used to measure AC or DC magnetic fields emitted by the device under test. In case of surface cracks detection, the magnetic field sensing elements (e.g. GMR-stripes) must be placed very close to the surface under test. Here we show techniques to achieve distances in the order of 100μm between the sensing elements and the cracks. In addition we demonstrate a high density of GMR elements in a linear array. Both aspects together allow to detect small surface cracks with a high spatial resolution. Alternatively two dimensional microcoil arrays can be implemented in the design. These microcoils can have diameters smaller than 300μm and can have a magnetic core.
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