A low-cost high-frequency plastic optical fiber vibrometer

Abstract

A low-cost optical sensing system to measure vibrations up to high frequencies (40 kHz) is presented and validated with experiments. The developed system uses a sensing head made with plastic optical fibers to illuminate the vibrating surface and collect the reflected light; a non-demanding data processing is used to measure the amplitude and frequency of the vibration and to compensate the reflectivity of the vibrating surface. Preliminary measurements, performed on vibrating targets with different surface reflectivity have been performed to assess the performance of the system.

Dynamic strain measurement system with fiber Bragg gratings and noise mitigation techniques

“…The measurement clearly shows a resonance peak around 7.6 Hz, while the noise floor is almost 15 dB lower. This result is in good agreement with the similar measurement performed with another non-contact plastic optical fiber (POF) vibrometer developed in our lab [23,24]. In this case, the sensing principle relies on the measurement of the light launched by a POF and reflected from the vibrating surface followed and compensation of the target reflectivity.…”

“…In this case, the sensing principle relies on the measurement of the light launched by a POF and reflected from the vibrating surface followed and compensation of the target reflectivity. From the data in figure 9 of [23], the peak frequency estimated through FFT is 7.8 Hz; by comparing these results, the effectiveness of signal processing comes out: while the POF sensor exhibits a peak/floor ratio of about 10 dB and a wrinkled spectral response that makes it hard to unambiguously detect the peak position, the proposed FBG sensor achieves a better SNR and a clearer spectral response. In the last experiment, we tested the capability of the presented system to work under worst-case conditions, i.e.…”

“…Spectrum of vibration recorded with the FBG sensor on a vibrating wall perturbed by the air conditioning system. See figure9of[23] for the analogous measurement with a plastic fiber vibrometer developed in our labs.…”