Measurement of small vibrational displacement by SM-LD vibrometer with resonance element

We proposed to enhance a small vibrational displacement of a half light wavelength or less by attaching a thin phosphor bronze plate as a resonance element onto a vibrating body under test. After attaching a 30-Hz or a 90-Hz resonance plate to an air compressor under test, we employed a self-mixing laser diode vibrometer developed by us, and we could confirm the effect of the resonance element.