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Proceedings Paper

Comparing dynamic surface tilt with velocity using an LDV
Author(s): Robert A. Bruce
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Paper Abstract

If a laser Doppler vibrometer (LDV) probe beam is normally incident on a resonating metal strip with a mirror-finish, the retro-reflected beam has corresponding dynamic deflections. These lateral beam offsets are proportional to the dynamic surface tilt and can be measured along with the LDV velocity using a separating beam-splitter and a two-dimensional position sensitive detector (PSD). On a thin unbound strip resonating with 'pure mode' deformation, these derivative motions, velocity and tilt, are completely complementary. On a thin unbound plate resonating with 'hybrid mode' deformation, velocity and now two orthogonal tilts are nearly complementary. Maximal tilt has zero velocity, and maximum deformation or velocity has zero tilt. Intermediate values range in complementary fashion except near 'cross-nodes' zones. Here both motion types drop to zero at these cross-node locations. Both velocity and tilt signals are compared simultaneously using a special test fixture. This fixture consists of a stainless steel strip supported on its edges in the center, which can be excited by small speakers at the ends. Two comparison/calibration approaches are demonstrated with a pure 3-0 mode. Significant modal details are also demonstrated by analyzing multiple modes from pulsed excitation, and mapping a 3-1 mode-shape using the combined sensing approaches.

Paper Details

Date Published: 22 June 2004
PDF: 11 pages
Proc. SPIE 5503, Sixth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (22 June 2004); doi: 10.1117/12.579537
Show Author Affiliations
Robert A. Bruce

Published in SPIE Proceedings Vol. 5503:
Sixth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications
Enrico Primo Tomasini, Editor(s)

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