Doppler effect in flexible and expandable light waveguide and development of new fiber-optic vibration/acoustic sensor

New principle and a geometrical arrangement of an optical fiber for a vibration/acoustic measurement are proposed in the present paper. The sensor is based on a new finding that a frequency of light wave transmitted through a bent optical fiber is shifted by vibration at the bent region. The phenomenon can be explained as Doppler's effect in flexible and expandable light waveguide. Several configurations of the sensor have been designed, and very high sensitivity is achieved in the extremely wide frequency range. Principle, sensor configuration and theoretical sensitivity, measurement system, and some experimental consideration are described in the present paper. The sensor sensitivity was examined experimentally in the low and middle frequency range, and the detectability was confirmed experimentally in the frequency range of acoustic emission signals.