Design and fabrication of a Michelson Interferometry based vibration sensor
Design and fabrication of a Michelson Interferometry based vibration sensor
1Shashi Kumari, 1A. Narayan and 1R.P. Sinha
1Department of Physics, Patna University
ABSTRACT Small amplitude vibrations are difficult to measure. Light interferometric methods have a good sensitivity which is of the order of wavelength of light used. This method, in effect, causes very small disturbances in objects under observation. We have fabricated a system that uses Michelson interferometer in which overlapping of two coherent waves produces interference. A Helium-Neon Laser source of 5 mW power is used as the light source. A beam splitter is used to split the light beam into two coherent beams. One beam goes to a fixed mirror and the other goes to a vibrating mirror from which the beam is reflected. These beams are made to recombine. The resultant interference pattern is detected with the help of an indigenously fabricated LDR-based photo-detector assembly for electronically detecting fringe passage. The signals have been displayed with an oscilloscope. In order to produce vibration, one of the mirrors of the interferometer has been fixed to the cone of a speaker. A low frequency oscillation in this mirror produces moving optical fringes which after conversion into electrical signal are displayed by the oscilloscope. Snapshots of the resulting fringes were recorded with a digital camera for further analysis. This system has the sensitivity to detect oscillations of amplitude as small as 3.8 X 10-4 cm. We have tested this apparatus for low frequency sinusoidal vibrations.