63 research outputs found
Development of fiber grating-based sensing techniques and application in mechanical engineering
Get PDFThis thesis reports my original research on the development and application of fiber grating-based acoustic sensors. This research covers both theoretical and experimental works, which include theoretical modeling of novel sensing schemes, design and fabrication of fiber grating-based sensors, development of a data acquisition system, proof of concept experiment, and application of fiber sensors in the mechanical engineering field. With regard to issues and potential related to the fiber lasers and fiber gratings sensors identified in the research, I propose several schemes and/or techniques to improve overall system performance. Particular focus is given to the enhancement of acoustic sensitivity that is severely limited by the high stiffness of glass fiber. The enhancement was achieved through the fiber grating and system design approaches. This thesis also implements optical fiber sensor technologies into an industrial application of marine structure.
Firstly, I propose and experimentally demonstrate a novel sensitivity enhancement scheme in a composite cavity fiber laser (CCFL) hydrophone. The scheme works based on partial cavity and pre-strained cavity sensing. In this scheme when only one cavity is made responsive and pre-strained, substantial wavelength/phase sensitivity can be attained with regard to the existing single cavity lasers. A CCFL sensing model was developed from multiple reflections theory. From the analysis of the model, the effects of design parameters such as the cavities length ratio, gratings reflectivity and gain toward the sensing performances were identified. The scheme was experimented using in-house fabricated CCFLs in an interferometric-based hydrophone system, and attained an excess sensitivity of 14 dB compared to the standard response, which is in close agreement with the theoretical expectation.
Secondly, I propose and experimentally demonstrate a novel multiple subchannels sensing concept to improve sensitivity (in terms of signal-to-noise ratio) of an intensity-type acoustic sensor interrogated by a broadband source. This scheme was realized using a multiple phase-shifted fiber Bragg grating (MPS-FBG) pair. In this scheme, the collective and simultaneous operation of the subchannels of MPS-FBG multiplies the total acquired signal power change at a particular channel, considerably enhancing sensitivity with regard to the normal FBG. From the intensity-sensing model developed from cross-correlation relations, the effects of FBG design parameters on the sensing performances were identified. Optimum MPS-FBG designs were sought through the transfer matrix analysis. In experiment, substantial sensitivity enhancement was achieved compared to the normal FBG, e.g. 20 dB using 17-phase shifted FBG. The improved sensitivity while retaining the system simplicity would be an attractive option for an economical coarse wavelength division multiplexed acoustic sensing system.
Thirdly, I develop and implement practical fiber grating-based sensor systems for an application in the mechanical engineering field, namely for failure monitoring of marine structures made of E-glass/vinylester composites. Two assessment techniques were implemented in this study: an embedded FBG strain sensor array to provide absolute interlaminar strain; and surface attached FBG acoustic sensors to provide an assessment technique based on the acoustic emission technique. Through the development of the system, a novel embedding procedure of optical fiber strain sensor in curve composites to achieve high survival rate during the vacuum infusion manufacturing process has been proposed. Progressive failure and structural strength of the structure were successfully identified and the result is comparable with those of the commercial piezoelectric sensors.
Throughout the course of this thesis, I have meticulously refined the procedures required for in-house manufacturing and successfully implemented the procedures in manufacturing of complex grating structures presented above. I have developed the required experimental platform including the digital signal processing technique used for data acquisition and demodulation.
I have also developed in-house grating-based devices analysis tools based on the transfer matrix method. The tools have been successfully applied to design and analyze complex gratings and fiber lasers in my experimental research mentioned above, e.g. designing apodized DFBFL and analyzing its performance in terms of the lasing efficiency and the higher order mode threshold
Radiation enhanced sensitivity of temperature and curvature sensor based on Bi/Er Co-doped fibre with ultra-broadband emission
No full textTo accommodate the growing scale and diverse applications of fibre optic sensing networks, a temperature and curvature sensing system suitable for radiation environment is proposed based on Bi/Er co-doped fibre (BEDF) with offset-core and ultra-broadband emission. First, two sections of BEDFs were employed to construct an ultra-broadband light source and a Mach-Zehnder Interferometer (MZI) for the sensing system, respectively. Then, the sensing performance of the MZI was evaluated through simulations and experiment. Especially, the impact of gamma radiation on sensing characteristics was evaluated by comparing MZI sensors based on irradiated and non-irradiated BEDFs. Both simulations and experiment results confirmed that the sensitivity improved due to an increase of the refractive index for the fibre core of BEDF, attributed to radiation-induced refractive index change. The sensing results indicate that for the irradiated BEDF based sensor, the maximum temperature sensitivity at 1592 nm was up to 90 pm/℃ with an increase of 50 %, while the maximum curvature sensitivity at 1550 nm was 5.66 nm/m¯¹ with an increase of 226 %, respectively. Such sensitivity enhancement further demonstrates that 50 kGy gamma ray irradiated BEDF had an increase of effective refractive index of 10¯³ order. Moreover, the proposed MZI sensing system, featuring a broadband near-infrared emission exceeding 500 nm, exhibits great potential for temperature and curvature detection in the Internet of Things (IoT) and ultra-large-scale sensor networks.Zhexu Huang, Yanhua Luo, Jianxiang Wen, Tingyun Wang, Chengbo Mou, Wei Chen, Shuen Wei, Weiwen Zou, Xiaohong Sun, Asrul Izam Azmi, Gang-Ding Pen
Application of fiber grating-based acoustic sensor in progressive failure testing of e-glass/vinylester curve composites
No full textProgressive failure monitoring of E-glass/vinylester curve composites using embedded FBG sensors
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Sensitivity enhancement in composite cavity fiber laser hydrophone
Get PDFWe report an application of composite cavity fiber laser (CCFL) for hydrophone sensitivity enhancement. While most of the sensitivity enhancement methods rely on amplification of acoustic signal by the coating design, our proposed scheme exploits the inherently nonlinear phase condition of the CCFL. A particular point of interest for CCFL hydrophone application is the proposed partial cavity sensing scheme that, when only one cavity is made responsive, a substantial sensitivity enhancement can be achieved. Theoretical analysis shows that this scheme can significantly enhance sensitivity, achieving as high as 40 dB excess to the standard response of a bare fiber. In experiment, this scheme produced a mean responsivity of -41.1 dB re rad Pa-1, representing an improvement in sensitivity by 14 dB compared to the standard response. Evidently, this CCFL sensing scheme provides an additional means for sensitivity improvement in conjunction to the conventional packaging technique
Acoustic partial discharge detection using low-cost pre-amplified piezoelectric transducer and coated optical fiber sensor
No full textFailure monitoring of e-glass/vinylester composites using fiber grating acoustic sensor
Get PDFThis paper reports an application of an optical fiber sensor in a continuous and in situ failure testing of an E-glass/vinylester top hat stiffener (THS). The sensor head was constructed from a compact phase-shifted fiber Bragg grating (PS-FBG). The narrow transmission channel of the PS-FBG is highly sensitive to small perturbation, hence suitable to be used in acoustic emission (AE) assessment technique. The progressive failure of THS was tested under transverse loading to experimentally simulate the actual loading in practice. Our experimental tests have demonstrated, in good agreement with the commercial piezoelectric sensors, that the important failures information of the THS was successfully recorded by the simple intensity-type PS-FBG senso
Air pressure sensor using fiber bragg gratings (FBG as air pressure sensors on generic UTM-LST half model)
Get PDFThis work was performed to investigate the feasibility of using Fiber Bragg Gratings (FBGs) strain sensor in detection of air pressure on aeroplane model known as Generic UTM Half-Model. The FBGs was attached on the surface of the aeroplane model where its position is as near as possible to the location of static conventional pressure sensor. Then, the sensing performance was tested inside UTM Low Speed Tunnel (UTM-LST) with the wind speed set at 30 ms^(-1), 40. ms.^(-1), and 50 ms^(-1). The direction of wind was arranged to be in perpendicular to the FBG and the position of wing model was varied at angle of 0°, 5°, 10°, 15°, and 20°. The measured pressure coefficient, Cp based on Bragg wavelength shift was compared with Static FKPS 30DP Pressure Measuring Module data. The results reveal that the shift in Bragg wavelength was found to increase linearly from angle 0° until 10° and after that the wavelength shift become saturated. The pressure coefficient obtained by FBGs has well agreed with the value obtained by pressure coefficient of pressure sensor module at low angle of attack from 0° to 10°
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