Acoustic Emission, being produced when ferromagnetic material is magnetized, is studied. Mainly, A.E. activity, V has been measured in 3% Si-Fe single crystal with various (Bm/Bs) values and frequencies and in 3% Si-Fe polycrystal with various stresses.
Magnetization of ferromagnetic material is alternated by Yoke type magnet. Maximum field intensity and frequency is 7.5 Oe and 100 Hz, respectively. A resonant type A.E. transducer having 30 KHz center frequency is used with a band pass filter (15 KHz - 45 KHz) and total amplification of MAE signal is 80 dB.
From the experimental results, it is found that one burst of MAE is divided into two sub-signal centered at both side of ± Hc on B-H hysteresis loop. Increasing rate of V in case of (Bm/Bs) values over 0.7 is higher than that of (Bm/Bs) values below 0.7. For dependency of frequency, increasing rate of V is divided into three parts, the first 0 Hz - 30 Hz, the second 30 Hz - 60 Hz, and the third 60 Hz - 100 Hz. Increasing rate of V has maximum at the second part, and next at the first part, and minimum at the third part. Two dependences of V on (Bm/Bs) and frequency are nearly consistent with the published results for dependency of number of 180˚ domain wall on (Bm/Bs) and frequency.
It is also observed in 3% Si-Fe polycrystal that 180˚ domain wall spacing decreases with increasing stress and separated 180˚ domains at grain boundaries are joined each other at that of above a certain stress value. For the value of stress 0 to $11.2\times10^6N/m^2$, V increases with increasing stress and above $11.2\times10^6N/m^2$, it decreases with increasing stress.
In conclusion, MAE is produced through magnetomechanical coupling between spin motion of domain wall and internal lattice strain, at the moment of nucleation or annihilation of 180˚ domain wall.