Abstract
A novel multipoint fiber loop ringdown (FLRD) strain sensing system using frequency-shifted interferometry (FSI) is proposed and experimentally validated. Compared to conventional multipoint FLRD techniques, this scheme measures the decay rate of the continuous wave (CW) light in the space domain and thus greatly reduces the cost without the requirement of expensive devices. A serial dual-point strain sensing system was experimentally constructed and a biconical tapered multimode fiber (MMF) as the sensor head was used for obtaining the large measuring range. By applying different strains on the sensor heads through translation stages, a linear response between strain and additional loss induced by strain sensor was obtained, and the static strain sensitivities of 0.13676 dB/mε and 0.19665 dB/mε were achieved, corresponding to the detection limit of 0.0123 dB and 0.0360 dB, respectively. Moreover, a large measuring range of approximately 6 mε was achieved for both strain sensors. The experimental results indicate that our proposed method offers a promising multipoint strain sensor which has the advantages of low cost, a simple sensing structure and a large measuring range.
Highlights
For the past decades, multipoint fiber-optic strain sensors have played an increasingly significant role in structural health monitoring due to the advantages of low cost, high sensitivity, large multiplexing capability, immunity to electromagnetic fields and robustness in hazardous environments [1,2,3,4].A variety of multipoint fiber-optic strains sensing techniques have been developed, including time-division multiplexing (TDM) [5], wavelength division multiplexing (WDM) [6] and the frequency-modulated continuous-wave (FMCW) technique [7]
In the TDM scheme, in order to distinguish each strain sensor, a fast optical switch is needed to extract only one pulse from the pulse trains reflected by the fiber Bragg grating (FBG) array
The measurement time will increase as the number of strain sensors increases, that is to say, the measurement points are limited by the measurement time in the TDM scheme
Summary
Multipoint fiber-optic strain sensors have played an increasingly significant role in structural health monitoring due to the advantages of low cost, high sensitivity, large multiplexing capability, immunity to electromagnetic fields and robustness in hazardous environments [1,2,3,4]. Compared with FLRD schemes, FSI-FLRD technique uses a CW laser source, slow detector and low-speed data acquisition to observe the ringdown signal [17], which greatly reduces the cost. It measures the changes in the decay rate of the CW light in the space domain instead of the decay rate of an optical pulse in the time domain. A cost-effective multipoint strain sensing system with a large measuring range based on FSI-FLRD was proposed. The experimental results showed that the proposed sensing system was capable of performing multipoint strain measurements with a large measuring range, good linear responses, simple sensing structures and low costs
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