# Dynamic Responses Measured by Optical Fiber Sensor for Structural Health Monitoring
## 1 Introduction
A lumped mass is introduced into the structure due to the incorporation of the sensor. This may alter the structural integrity and dynamic properties of the structure [20]. In contrast, FBG sensors with small size and light weight cannot introduce a notable effect on the vibrational characters of structures. [PERSON] et al. [21] proposed a displacement sensing system using FBG sensor to experimentally measure the dynamic and transient responses of a phononic crystal (PC) beam subjected to impact loading. [PERSON] et al. [20] measured the flow-induced vibrations using fiber-optic grating sensors. [PERSON] and [PERSON] [22] presented a methodology of impact-induced delamination assessment using FBG sensor. [PERSON] et al. [23] investigated the temperature sensitivity of FBG sensors coated with metals during a dynamic cooling process. [PERSON] and [PERSON] [24] presented an interrogation technique based on a wavelength division coupler to detect the wavelength shift of FBG sensor. [PERSON] et al. [25] integrated the FBG and LPFG to form a novel optical fiber sensing system for real-time gas detection. [PERSON] et al. [26] reviewed optical fiber sensing configurations and interrogation techniques including FBG, LPFG, micro-interferometers, multimode interference for refractive index measurement. [PERSON] and [PERSON] [27] investigated the thermal effects on the transmission spectra of LPFGs both theoretically and experimentally. [PERSON] et al. [28] developed a temperature insensitive refractive-index sensor using two concatenated dual-resonance LPFGs. [PERSON] et al. [29] proposed an interrogation method integrated FBG sensor with Mach-Zehnder interferometer for simultaneous measurements of refractive index and temperature. [PERSON] et al. [30] employed the FBG sensor incorporation with Sagnac loop to measure the temperature and refractive index simultaneously. [PERSON] et al. [31] demonstrated real-time monitoring of a dynamic FBG strain sensor for structural health monitoring using a Fourier-domain mode-locked (FDML) fiber laser. [PERSON] et al. [32] measured dynamic strain using two wavelength-matched FBG sensors interrogated with a cascaded LPFG. [PERSON] and [PERSON] [33] used a tunable twin-core fiber as an edge filter to demodulate the FBG sensor for temperature measurement. [PERSON] et al. [34] proposed an interrogation system for FBG sensing based on the InGaAs linear image sensor. Recently, Micro Electro-Mechanical System (MEMS) accelerometers have received a lot of attention for structural health monitoring in civil engineering applications [35]. Such sensors are considered to demonstrate high portability and durability with a limited cost. [PERSON] et al. [36] and [PERSON] et al. [37] presented comparative experimental studies of a cost ratio of MEMS accelerometersin comparison with traditional piezoelectric accelerometers. [PERSON] et al. [38] employed MEMS accelerometers for the dynamic measurements of human body motions. [PERSON] et al. [39] used MEMS accelerometers to monitor the vibration of smart machine rotors. However, the cost of FBG sensors is higher than that of electric strain gauges. Nevertheless, the advantages of FBG, such as immunity to electromagnetic interference, suitability for applications in multiplexed and distributed system, capability for long-distance transmission, and better resolution and sensitivity in comparison with the strain gauge provide an alternative choice for users, in particular for applications in structural health monitoring. In this study, the fiber Bragg grating sensor is integrated with a long-period fiber grating (LPFG) filter and a photodetector to measure the transient and vibration responses of structures subjected to a variety of mechanical testing. The mechanical tests comprised three load scenarios: base excitation by a shaker at resonant frequency, impact loading by a hammer, and shock test on a drop table. The dynamic strain measured by the fiber Bragg grating sensor is validated with the strain gauge.