Optical fiber sensors are the most promising technique in monitoring physical and chemical variables of engineering structures. For the brittle material characteristics, a bare sensing fiber is prone to breakage under the shear or torsional action existed in the construction and operation. To guarantee the survival and long-term service of the sensors, the packaging measure is particularly significant. This treatment generates an intermedium layer between the sensing fiber and the monitored structure, which leads to the strain of the host material not entirely transferred to the sensing fiber for a portion of strain loss in the transferring path. To correct the error and improve the measurement accuracy, strain transfer theory is developed to establish the quantitative strain relationship between the sensing fiber and the host material. A state-of-the-art review on strain transfer theory of optical fiber based sensors developed for civil structures is addressed. It aims to demonstrate the advance, the application and the challenge of strain transfer theory and provide scientific guidance for the better understanding of the multi-layered sensing model and the theoretical instruction for the optimum design, calibration and measurement accuracy enhancement of optical fiber sensors.

Keywords: optical fiber sensor, strain transfer theory, measurement accuracy, error modification, optimum design, civil engineering

Dr. Huaping Wang is currently an Associate Professor at School of Civil Engineering and Mechanics, Lanzhou University, China. She received her Bachelor degree (2007) and Master degree (2009) from Wuhan University of Technology, China and her PhD degree (2015) from Dalian University of Technology, China (Lab of academician Jinping Ou, the international famous group in structural health monitoring). She was a visiting scholar at The Hong Kong Polytechnic University between 2015 and 2017 (Prof. Jian-Guo Dai and Chair Prof. Yi-Qing Ni in structural monitoring and control of high-speed railway station based on optical fiber sensors). She worked in National Engineering Laboratory for High-speed Railway Construction of Central South University from 2017 to 2018 (Changjiang Prof. Lizhong Jiang). Her research interests include structural health monitoring, optical fiber-based sensing technology, strain transfer theory, smart sensors and structures in engineering, damage identification, and condition assessment. She has published more than 25 papers in reputed SCI and EI journals. Email: hpwang@lzu.edu.cn; wanghuaping1128@sina.cn.