Dynamic analysis of a new fibre Bragg grating accelerometer based on a single diaphragm mechanism

The enthusiasm in converting fibre Bragg grating (FBG) sensors to accelerometers has quicken the pace in scientific research and commercialization activities. On the researchers’ part, the capability of FBG-accelerometer should be numerically and experimentally validated while on commercialized players’ side, size, and sensitivity of the FBG accelerometer is the main key to compete with the existing commercialized sensors. These concerns have initiated this research to normalize the size, measurement range and compatibility of the FBG sensors with the encapsulation methods. Two different sizes and designs of diaphragm-type FBG accelerometers are fabricated where the FBG sensor is attached onto the diaphragm using the embedded encapsulation method. The first design uses titanium as its housing where its diaphragm is made of aluminium with the respective diameter and thickness of 6 mm and 0.03 mm. The second design is fabricated using a 3-D printer (bioplastic PLA/PHA) and its diaphragm is made of stainless steel with diameter and thickness of 30 mm and 0.05 mm, respectively. Computational modal analysis is carried out to determine the dynamic behaviour for both accelerometers and investigate its compatibility with the embedded encapsulation method. Results show that having a large diameter of diaphragm leads to low fundamental frequency while the linear measurement range of FBG accelerometer is narrow and vice versa. Since the first design is tiny and made of titanium, it is more robust but harder to be fabricated and costly compared to the second design, which is made of bioplastic (PLA/PHA). The embedded encapsulation method is difficult to be adapted if a small diameter of diaphragm is used because the FBG sensor is easily broken when it is bent (FBG optic is brittle). Conclusion/implications: In short, the trade-off between size and range of measurement should be considered, as large sizes of diaphragm cause small range of measurements but compatible with embedded encapsulation methods.