Optical fiber sensors have attracted considerable attention for marine environment and marine structural health monitoring, owing to advantages including resistance to electromagnetic interference, durability under extreme temperature and pressures, light weight, high transmission rate, small size and flexibility. In this paper, the optical fiber sensors employed for marine environment and marine structural health monitoring are summarized for the understanding of their basic sensing principles, and their various sensing applications such as physical parameters, chemical parameters and structural health monitoring. This review paper shows the feasibility of using optical fiber sensing technology for marine application and, due to the aforementioned advantages, it is possible to envisage a widespread use in this research field in the next few years.

Optical fiber sensing for marine environment and marine structural health monitoring: A review

Geologic hazards (geohazards) are naturally occurring or human-activity-induced geologic conditions capable of causing damage or loss of property and/or life. geohazards, such as landslides, surface subsidence, and earthquakes, can seriously affect and threaten life, property, or public safety. geohazards prevention is the application of geologic engineering principles and existing and emerging technologies to reduce, minimize, or prevent the effects of various geologic hazards. Monitoring and early warning are the most common strategies for geohazards prevention. With the development of the Internet of Things (IoT), an emerging new idea is to apply IoT technology to enhance the accuracy and efficiency of monitoring and early warning systems for geohazards prevention. This article aims to present a comprehensive survey of relevant research and technological developments of the IoT applied in geohazards prevention. It first surveys the applications of the IoT in the monitoring and early warning of seven types of common geohazards, including landslides, debris flow, rockfall, surface subsidence, surface collapse, surface cracks, and earthquakes, then investigates the key technologies in geohazards prevention when utilizing the IoT, and finally summarizes the challenges in IoT-based monitoring and early warning systems for geohazards prevention. Moreover, this article also highlights the future directions for employing the IoT for geohazards prevention.

A Survey of Internet of Things (IoT) for Geohazard Prevention: Applications, Technologies, and Challenges

Graphene and its derivatives have become the most explored materials since Novoselov and Geim (Nobel Prize winners for Physics in 2010) achieved its isolation in 2004. The exceptional properties of graphene have attracted the attention of the scientific community from different research fields, generating high impact not only in scientific journals, but also in general-interest newspapers. Optical fibre sensing is one of the many fields that can benefit from the use of these new materials, combining the amazing morphological, chemical, optical and electrical features of graphene with the advantages that optical fibre offers over other sensing strategies. In this document, a review of the current state of the art for optical fibre sensors based on graphene materials is presented.

Optical Fibre Sensors Using Graphene-Based Materials: A Review

Optical fiber sensors are the most promising technique in monitoring physical and chemical variables of civil 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.

Strain transfer theory of industrialized optical fiber-based sensors in civil engineering: A review on measurement accuracy, design and calibration

Vibration sensing is critical to monitor and ultimately preserve the health state of engineering systems. These systems with a large structure are typically working in some harsh environments including strong magnetic fields. However, traditional electrical sensors are difficult to accurately measure the vibration under harsh environments. Besides these instinct advantages of normal fiber optic sensors (FOS) sensors such as compact size, passive sensing, resistance to electromagnetic interference, etc., fiber Bragg grating (FBG) sensors have a capability of distributed sensing based on wavelength demodulation and resistance to light intensity fluctuation and unwanted fiber bending losses. Such merits lead them to be a hot topic in FOS field and excellent candidates for vibration sensing. Three types of FBG-based vibration sensors have been classified based on the difference of vibration-strain coupling way to FBG in this survey, which are pasted FBG-based, axial property of FBG-based and transverse property of FBG-based, respectively. FBG-based vibration sensors' principles and designs have been introduced and discussed. Recent advances in the applications of FBG-based vibration sensors have been investigated. The limitations and prospects of the FBG-based vibration sensing technologies have been analyzed and discussed.

Recent Advances and Tendency in Fiber Bragg Grating-Based Vibration Sensor: A Review

Fiber Bragg grating (FBG) sensor has been considered as a reliable sensor for health monitoring of structural and geotechnical projects. Various types of FBG based sensors have been proposed in past few decades and employed for health monitoring of many geotechnical structures. This paper presents an overview of the recent development and application of FBG based sensors for health monitoring of several key geotechnical structures, including soil nail systems, slopes, and piles. Different sensor design, implementation and packaging methods, advantages and limitations of using FBG based sensors in different projects are reviewed. Comparative analysis of using two mathematical methods for the prediction of ground movement using FBG sensor data are also carried out. The two typical mathematical methods include Finite Difference Method (FDM) and Numerical Integration method (NIM). Possible technical challenges of applying FBG sensors for geotechnical monitoring are discussed.

Lai Ming Gordon Leung

Papers

Application of FBG sensors for geotechnical health monitoring, a review of sensor design, implementation methods and packaging techniques