Title page for ETD etd-09092012-164037


Type of Document Dissertation
Author Wang, Yunmiao
Author's Email Address kathy618@vt.edu
URN etd-09092012-164037
Title A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings
Degree PhD
Department Engineering
Advisory Committee
Advisor Name Title
Wang, Anbo Committee Chair
Pickrell, Gary R. Committee Member
Poon, Ting-Chung Committee Member
Safaai-Jazi, Ahmad Committee Member
Xu, Yong Committee Member
Keywords
  • Structure health monitoring
  • Quasi-distributed sensing
  • Optical fiber sensor
  • Multiplexing
  • Fiber Bragg gratings
Date of Defense 2012-08-28
Availability restricted
Abstract
Structural health monitoring (SHM) has become a strong national interest because of the need of reliable and accurate damage detection methods for aerospace, civil and mechanical engineering infrastructure. Health monitoring of these structures usually requires the sensors to have such features as large area coverage, maintenance free or minimum maintenance, ultra-low cost per measurement point, and capability of operation in harsh environments. Fiber Bragg grating (FBG) has attracted considerable interest for this application because of its compactness, electromagnetic immunity, and excellent multiplexing capability. Several FBG multiplexing techniques have been developed to increase the multiplexing number and further reduce the unit cost. To the author’s best knowledge, the current demonstrated maximum multiplexing number are 800 FBG sensors in a single array using optical frequency domain reflectometry (OFDR), whose maximum fiber span is limited by the coherence length of light source.

In this work, we proposed and demonstrated a wavelength-scanning time-division multiplexing (WSTDM) of 1000 ultra-weak FBGs for distributed temperature sensing. In comparison with the OFDR method, the WSTDM method distinguishes the sensors by different time delays, and its maximum operation distance, which is limited by the transmission loss of the fiber, can be as high as tens of kilometers. The strong multiplexing capability and low crosstalk of the ultra-weak FBG sensors was investigated through both theoretical analysis and experiment. An automated FBG fabrication system was developed for fast FBG fabrication. With this WSTDM method, we multiplexed 1000 ultra-weak FBGs for distributed temperature sensing. Besides the demonstrated temperature measurement, the reported method can also be applied to measure other parameters, such as strain, pressure.

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