A LASER DISPLACEMENT SENSOR USING THE SELF-MIXING EFFECT FOR MODAL-ANALYSIS AND DEFECT DETECTION

A low-cost, simple, noncontact displacement sensor using the self-mixi ng effect inside a cw single-mode laser diode has been developed for m odal analysis and defect detection, The resonance frequencies of thin clamped metallic plates have been determined with a resolution of 0.2 Hz, With such targets, classic spectrum analyzers generate a measureme nt error up to 10% because of the weight of the accelerometer, The fre quency-shift of the fundamental resonance frequency between a standard plate and the same one with a known defect can also be measured, the modal vector associated to this frequency being distorted at the place of the defect.