Fiber-optic microinterferometer vibration sensor system for monitoring of traffic and traffic induced vibrations of bridges

An electromagnetic immune fiber-optic Extrinsic Fabry-Perot microinterferometer vibration sensor system (EFPI-V) with cantilever type sensing elements is described. Several sensors with low resonance frequency (first bending mode f(1) < 100 Hz) are installed along the edge of a taxiway of Braunschweig airport with separation distances between 15 and 60 m for investigation of ground traffic monitoring via vibrational and noise induced broadband excitation of the resonances. Modified sensors with f(1) greater than or equal to 100 Hz are developed for quantitative low frequency (f < 100 Hz) acceleration measurements. Initial characterization of a 100 Hz - sensor using a capacitive accelerometer as a reference exhibits the expected f(2)-dependence of the amplitude for f < 50 Hz and acceleration amplitudes down to some mg. For the first time to our knowledge field tests with an EFPI-acceleration sensor have been performed for monitoring the traffic induced vibrations of a motorway bridge (EC-project "Smart Structures"). The measured frequency spectra show reasonable agreement with the response of the capacitive accelerometer for f < 50 Hz.