Abstract
Distributed vibration sensing in optical fibers opened entirely new opportunities and penetrated various sectors from security to seismic monitoring. Here, we demonstrate a most simple and robust approach for dynamic strain measurement using wavelength-scanning coherent optical time domain reflectometry (C-OTDR). Our method is based on laser current modulation and Rayleigh backscatter shift correlation. As opposed to common single-wavelength phase demodulation techniques, also the algebraic sign of the strain change is retrieved. This is crucial for the intended applications in structural health monitoring and modal analysis. A linear strain response down to 47.5 pε and strain noise of 100 pε/√Hz is demonstrated for repetition rates in the kHz range. A field application of a vibrating bridge is presented. Our approach provides a cost-effective high-resolution method for structural vibration analysis and geophysical applications.
Highlights
Distributed optical fiber sensors have found a wide range of usage in various sectors, from structural health monitoring (SHM), power grid monitoring, to geotechnical, environmental or chemical applications
The research presented in this paper aims, at the development of a distributed vibration sensing (DVS) approach that enables high-resolution measurement of strain changes including the sign of the strain change
We demonstrated, to our knowledge for the first time, a wavelength-scanning coherent OTDR approach for dynamic strain change measurement
Summary
Distributed optical fiber sensors have found a wide range of usage in various sectors, from structural health monitoring (SHM), power grid monitoring, to geotechnical, environmental or chemical applications. Dynamic and high-resolution strain sensing is achieved by interferometric Rayleigh backscatter approaches These distributed vibration sensing (DVS) techniques, often referred to as distributed acoustic sensing (DAS), are typically based on coherent optical time domain reflectometry (C-OTDR) and have experienced dynamic progress and considerable advances during the last few years in both research and industrial application [1]. Minute changes of the temporal separation of the scatterers, for example due to local strain or temperature variations, can be detected as backscattered power variations The advantages of these interferometric DVS techniques are the high strain sensitivity, the high measurement repetition rate and long distance range. The requirement on the measurement repetition rate is generally lower for structural monitoring applications, but the measurement of the correct strain magnitude as well as the algebraic sign of strain change is generally required This sign-correct measurement is a prerequisite, for example, for distributed deformation sensing and mode shape analysis of vibrating structures. The strain magnitude including the sign, cannot be determined by most of the proposed DVS principles
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