Objective The existing FBG vibration sensor has a wide operating frequency band, but it has low sensitivity compared to high-sensitivity vibration sensor. Additionally, the sensor's intrinsic frequency is not high, and there are mutual constraints on the relationship between the working frequency band of the FBG vibration sensor and the measurement sensitivity. Consequently, the extension of the sensor's operating frequency spectrum has significant research value in order to guarantee the high sensitivity of the vibration sensor simultaneously.

Methods The proposed FBG vibration sensor is made up of two FBGs, two integrally molded sensing units, and front and rear end caps (Fig.2), each of which has a tower-shaped mass block, an L-shaped base, and a circular flexible hinge (Fig.1). First, structural mechanics modeling research was used to determine the elements influencing the sensing unit's sensitivity and inherent frequency. To enhance the sensitivity, the mass block was shaped like a rectangle. The sensitivity of the sensing unit was determined by measuring the distance between the FBG and the hinge center. The mass block is designed as a tower to increase the intrinsic frequency by lowering the mass block's center of mass, which expands the operating band of a single sensing unit. The intrinsic frequency of the sensor unit is related to the mass block's moment of inertia, which is related to the distance from the mass block's center of mass to the center of the hinge. The sensing unit is skeletonized with such a way that the resonance peak and the "working area" sensing units complement one another and work together to broaden the working frequency band. Subsequently, the dimensional parameters of the sensor are optimized and expedited by the combined simulation of ANSYS and SolidWorks. To finish the packaging and characterization investigations of the sensor, the packaging system (Fig.6) and the performance test system (Fig.9) were constructed.

Results and Discussions The intrinsic frequency of the sensing units 1 and 2 are 650 Hz and 925 Hz, respectively (Fig.10). The sensor operates in the frequency range of 0 to 1500 Hz (Fig.11), with a sensitivity of better than 410.4 pm/g (Fig.12) and a measurement resolution of 0.16 mg (Fig.13).

Conclusions This article proposes a method of design for a high-sensitivity wide-band FBG vibration sensor based on a hinge complementary structure, providing an innovative approach to the current problem of mutual limits on the operating frequency range and sensitivity of vibration sensors. With its wide working frequency range and outstanding sensitivity, the developed sensor provides a unique technical method for micro-vibration monitoring.