Noncontact torsional wave transduction in a rotating shaft using oblique magnetostrictive strips

A noncontact method to generate and measure torsional waves in rotating shafts by a set of magnetostrictive patches and a solenoid is proposed. The main issues in the present wave experiment are how to generate torsional waves having sufficient power and how not to interfere with shaft rotational motion. Magnetostrictive patches are bonded obliquely to the shaft axis for pure torsional wave generation and an arrayed patch configuration is employed for sufficient power generation and frequency localization. For uninterrupted shaft rotation, a solenoid encircling a rotating shaft wirelessly supplies or detects the ac magnetic field in the patches. The validity and performance of the proposed wave transduction method were checked by several experiments. An application of this method to the detection of a circumferential crack in a rotating shaft is also presented.