Optical Fiber Sensor for Monitoring the Vibration Modes of a Metallic Plate

In this work, we propose and demonstrate a frequency vibration sensor based on Multimode-Coreless-Multimode (MCM) fiber optic structure to measure the frequency of vibration modes of a metallic plate. To take advantage of the curvature sensitivity of the MCM structure, the device needs to be placed in direct contact with the structure under analysis, the vibration produces periodical changes in the curvature of the fiber that in turns modulate the intensity of the attenuation band of the MCM transmitted spectrum. In order to characterize the response of the sensor, we first measured the vibration frequencies of a loudspeaker in the range of 500 to 12500 Hz observing a percentage relative error less than 0.5 %. Then, the sensor was placed in contact with an aluminum plate of 5 cm x 5 cm x 0.3 cm. It was possible to detect the frequency of several vibration modes of the plate in a very simple way. The curvature-sensitive MCM structure is simple, easy to build, and sturdy, these features make the device a good candidate for measuring mechanical vibrations of an object.