Influence of the Frequency Response of Pick-up Coil and the Applied Magnetic Field Strength on the Measurement of Bending Stresses Using the Magnetic Barkhausen Noise Technique

Abstract This work presents an experimental study that evaluates the influence of the frequency response of the Barkhausen Magnetic Noise (RMB) measurement system, as well as the intensity of the applied excitation magnetic field, on the sensitivity of the technique for measuring bending-induced stresses. The experiments were carried out on two samples made of different materials: AISI 1005 steel and AISI 430 steel. The MBN probe was equipped with five pickup coils with different numbers of turns, this being one of the variables that most strongly influences the frequency response of the sensor. The excitation magnetic field was applied at two intensity levels. The acquired signals were analyzed using different approaches, including frequency response profiles, spectrograms, MBN time-domain envelopes, number of voltage pulses in the MBN signal, and RMS values. The results indicate that coils with more than 2000 turns exhibit similar sensitivity levels. Below this threshold, sensitivity is reduced mainly due to a lower signal-to-noise ratio and, consequently, greater susceptibility to electromagnetic interference. Additionally, it was observed that, for AISI 430 steel, the variation in excitation magnetic field intensity between the two applied levels did not influence the sensitivity of the technique for stress measurement. In contrast, for AISI 1005 steel, the sensitivity was higher when a lower excitation magnetic field intensity was used. Finally, the results show how the number of turns installed in the MBN pickup coil significantly influences the performance of the measurement system and provide fundamental information that enables users of the technique to design sensors better suited for a given application.