| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1993: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
(1)Principle : The Doppler beat signal obtained from a self-mixing laser diode (SM-LD) has a sawtooth waveform when the emitted light beam is directly illuminated onto a vibrating loudspeaker surface. Every one wave in the beat signal corresponds to a half wavelength displacement (0.93 mum). Therefore, the digital surface displacement has been successfully counted by adding or subtracting a successive counting pulse train produced from the sharp edge of the each sawtooth in accordance with the positive or negative sign of the velocity, respectively, which is detected by a direction discrimination circuit.
(2) Accuracy : The measured digital displacement amplitude, 10mum-140mum at 200Hz sinusoidal vibration, agreed well with the theoretical value within a few percent erro, when the sawtooth-like waveform is clear and sharp, however, the measured displacement was reduced to 40% - 90% of the theorelical value in accordance with the decrease of the sharpness of the sawtooth.
(3) Measurable Range : The measurable range for vibration frequency and velocity was 7.6Hz-40kHz and 6.7mm/s-163mm/s, respectively. The measurable upper limit of displacement amplitude was 1200mum at 10Hz and 40mum at 500Hz, and the lower limit was around 4mum. In case of an SM-LD with an optical fiber the measurable range was greatly reduced, and the measured displacement was reduced to around 50% of the theoretical value, because the sharpness of the sawtooth was low.
(4) Simultaneous Measurement : Two vibration waveforms at two different points on the loudspeaker were simultaneously measured using two SM-LD's with each optical fiber, and the phase difference between the two vibration waveforms was obtained by an FFT method.
(5) Vibration Measurement of Rain-Drop Repelling Mirror : The displacement amplitude 0.6mum-0.8mum at a resonance frequency 42.97kHz could be measured using an SM-LD without an optical fiber, but could not in case of an SM-LD with a fiber.
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