Novel Acoustic Barkhausen Noise Transducer and its Comparison with Electromagnetic Acoustic Transducer

The analysis of magnetic Barkhausen noise (MBN) has been used to provide information about the stress state and microstructural properties of ferromagnetic materials. Recent work has shown that a technique using acoustic Barkhausen noise (ABN) detection can provide the similar capabilities as traditional MBN along with additional information for defect characterisation and thickness measurement in a single system. Because the detection of ABN using a piezoelectric sensor can be carried out at any point on the material surface, as well as analysing ABN for microstructural characterisation, the interaction of the surface propagating waves with defects can also be analysed and used for defect characterisation, along with frequency analysis for thickness measurement. As with electromagnetic acoustic transducer (EMAT) systems, the ABN technique applies totally different physical principles to traditional ultrasonic methods and couplant is not needed for excitation. The work is carried out through experimental investigations of calibrated steel samples with machined defects using the ABN system, in comparison to readings taken using an EMAT system. Test results show that the ABN technique has potential applications in providing a comprehensive system for material and stress characterisation along with the additional capabilities of defect characterisation and material thickness measurement.