ASA 125th Meeting Ottawa 1993 May

4pSA9. Simultaneous measurements of in-plane and out-of-plane surface displacements of shell vibrations at several points by an array of miniature laser probe heads.

Ming Yang

Yves H. Berthelot

Jacek Jarzynski

School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332

Experiments are being conducted to measure directly by laser Doppler interferometry the in-plane and out-of-plane components of the surface motion of a vibrating shell simultaneously at several surface points. The proposed design requires three Bragg cells to generate three coherent optical beams with different carrier frequencies. Three 1x4 fiber optic connectors are used to transmit each beam to four surface points. At each point, both the out-of-plane component and one of the in-plane components of the displacement vector are measured. The light scattered by the vibrating surface is Doppler shifted and collected into a large core multimode fiber situated close to the surface and terminated by a photodiode. The signals are acquired and digitized for direct phase demodulation on a computer by means of Hilbert transforms. [Work supported by ONR.]