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Magnetic Barkhausen noise analysis in the audio frequency range

: Szielasko, K.; Altpeter, I.; Rabung, M.

Suortti-Suominen, T. ; International Association of Barkhausen Noise and Micromagnetic Testing -ICBM-; TH Aachen -RWTH-, Laboratorium für Werkzeugmaschinen und Betriebslehre -WZL-:
7th International Conference on Barkhausen Noise and Micromagnetic Testing 2009. Conference proceedings : July 15 - 16, 2009, Aachen
Vaajakoski: Stresstech, 2009
ISBN: 978-952-672470-6
ISBN: 978-952-672471-3
International Conference on Barkhausen Noise and Micromagnetic Testing (ICBM) <7, 2009, Aachen>
Conference Paper
Fraunhofer IZFP ()
Barkhausen noise; stress; frequency range; filtering; audio ADC; MikroMach

A/D and D/A converters which operate in the audio frequency range are available at low pricing and in small packages today. High signal quality and integrated connectivity make them suitable for use in portable testing equipment. This paper regards the particular characteristics of magnetic Barkhausen noise in the frequency range below 24 kHz which may be preprocessed and digitized using low-cost audio signal processing components.
Practical Barkhausen noise probes include an electromagnetic yoke with U-shaped core and a small pickup coil, located between the pole pieces of the yoke, for the detection of magnetic Barkhausen noise. However, the raw Barkhausen noise signal, which is the voltage induced into the pickup coil, still contains parasitic upper harmonics of the magnetization frequency. The removal of these harmonics is commonly achieved by high-pass filtering, but this procedure requires the cut-off frequency of the filter to be at least 2 or 3 orders of magnitude higher than the magnetization frequency, leaving a wide band of frequencies disregarded. A numerical method for the removal of upper harmonics in the Barkhausen noise signal is presented. By use of this method, the analyzed noise frequency range may start as low as one order of magnitude above the magnetization frequency. In this range, Barkhausen noise can show extraordinarily high stress sensitivity.
As an example of practical testing equipment, a robust device which performs low-frequency Barkhausen noise analysis and other non-destructive magnetic testing methods with audio signal processing hardware is presented.