The acousto-magnetic effect is a new one discovered recently by the author. It is a physic phenomenon occurred on the surface of the ferromagnetic materials, the domain wall in which make a drift under the action of elastic stress field of the acoustic wave, and a change of the magnetization state will be resulted. If this change occurs on the surface of the sample, it can be tested by means of magnetic field measurement. The related works of the author show that, above acousto-magnetic conversion requires rather strong acoustic field intensity under the demagnetized state, while under certain magnetized state, it is much easier to do and the conversion efficiency much increased.

The sensor, designed according to this character of acousto- magnetic conversion, is composed of a magnetization coil and a testing coil. The former provides a D. C. bias magnetic field, while the latter picks up the change of the magnetic state on the surface of sample. Experimental results show that the sensitivity of this sensor to acoustic wave is very close to that of a piezoelectric sensor. The sensor need not touch to the tested surface and the couplant is not required at all. These are the obvious advantages of this sensor.