Barkhausen Noise and Eddy Current Microscopy (BEMI): Microscope Configuration, Probes and Imaging Characteristics

On the basis of the approved nondestructive tsting methods Barkhausen noise measurement and eddy current testing a microscope for both techniques has been built up. With this Barkhausen Noise and Eddy Current Microscope (BEMI) high resolution images of the distribution of the maximum of Barkhausen noise and the eddy current coil impedance can be obtained by scanning a sensor with a precise manipulation unit over a test specimen. The aim is the caracterization of magnetic and mechanical properties of ferromagnetic materials (e.g. thin films). In addition to a suitable manipulation and signal processing system probes with high resolution and high sensitivity are necessary. These probes or sensors strongly affect the measured signals and the imaging characteristics. The frequency-dependent influence of the probe on the transmitted signals can be determined by the transfer function derived from a model of a ferrite ring head respecting the frequency-dependent complex permeability. The head parameters for computing the transfer function were found by measuring the head impedance at several frequencies and fitting the theoretical impedance function to the experimental results to answer the question of the resolution of the microscope the effective width of the sensors were detected by linescans over a ferrite test specimen. In addition there will be shown examples of images obtained by the Barkhausen Noise and Eddy Current Microscope (BEMI) that indicate the range of applications