THE EFFECTS OF DEMAGNETIZING AND STRAY FIELDS ON MAGNETOACOUSTIC EMISSION

Magnetoacoustic emission (MAE) has been measured from a Ni bar and a m ild steel bar. The magnetizing field was produced by a c-core electrom agnet, which was separated from the specimen surface by a nonmagnetic spacer layer (thickness l(a) In Ni, the MAE profile contains a single peak when l(a) is small. As l(a) increases, a second peak appears and then a third peak, indicating that MAE is not only caused by domain wa ll creation and annihilation, but also by domain wall motion. In the c ase of the mild steel bar, only two peaks are detected, which are incr easingly separated as l(a) increases. The different results between th e two materials can be explained by the different mobility of non-180- degrees domain walls. The present results also indicate that the MAE p rofile obtained from Ni is less sensitive to l(a) than that obtained f rom mild steel. This difference can be explained by considering the re luctance of the magnetic circuit.