Interferometric sensor for measuring the vibrations of mechanical structures

Conventional vibration sensors imply necessarily a mechanical contact with the piece tested, so they cannot be used on light structures excited at high frequency, such as turbomachine blades. It is to meet this difficulty that the study of an interferometric sensors without material contact was undertaken. After analyzing the difficulties pertaining to interference in diffuse light (speckle phenomenon) and the means to remedy them, the paper describes the instrument and its operation. Some experimental results are presented, in particular those concerning a torsion-excited blade and a helicopter main transmitting gear.