EFFECT OF SWEEP AND BIAS FIELD AMPLITUDES ON THE MAGNETOACOUSTIC EMISSION

Magneto-acoustic emission (MAE) measurements were made on samples of pipeline steel, under different ac sweep and dc bias field conditions. The MAE activity was found to be highly sensitive to these magnetizing parameters. With increasing amplitude of flux density of the ac sweep field, the MAE rms voltage increases initially and finally tends to saturate; with increasing dc bias field flux density the MAE rms voltage shows a peak, exhibiting maximum MAE activity around the upper steep portion of E-H hysteresis curve. Pulse height distribution analysis of the MAE waveforms indicates that at low fields, near the steep portion of the hysteresis curve, MAE is dominated by 90-degrees domain wall motion while at high fields, nearing saturation, an additional mechanism of domain rotation giving rise to MAE is suggested.