Failure monitoring of e-glass/vinylester composites using fiber grating acoustic sensor

This 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

Characterization of Erbium Doped Photonic Crystal Fiber

Photonic crystal fibers (PCFs) which exhibit unique and tremendous optical properties have been undergoing quick growth in recent years. Studies on the characteristics of various types of PCFs have been reported. However, characterization on erbium-doped PCF has not previously been investigated. Therefore, in this paper, an erbium-doped core PCF having 7 rings of hexagonal air holes has been modeled. A perfectly matched layer (PML) is modeled within the PCF structure and simulated using Finite Element Method (FEM) using COMSOL software. The PML is optimized by varying the radius and thickness of the layer. Modal properties of the PCF have been investigated in terms of its effective index of the supported fundamental mode, confinement loss and thickness of the perfectly matched layer. This erbium-doped PCF has a confinement loss of 1.0E-6 at 1500 nm and a maximum effective refractive index of 1.476. This paper gathers useful data, which could be used for studying the characteristics of a PCF

Air pressure sensor using fiber bragg gratings (FBG as air pressure sensors on generic UTM-LST half model)

This 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°

Discrete liquid level fiber sensor

A novel simple fiber sensor to sense liquid level is presented. The operation principle is based on the relative Fresnel reflective intensity. The sensor consists of a fiber splitter with the configuration of one input to multiple fiber outputs, i.e. 1×4, 1×8 and 1×12 arrangements that act as a discrete liquid level. A broadband source (BBS) is used as the light source supply. The total reflected power intensity is measured using a power meter. Experimental results show that the power intensity decreases as the level of liquid is increased. The sensor has a simple configuration, low cost, and it can be customized for a wide height measurement range spanning from a few centimeters up to a hundred meters

Droplet-like bent multimode fiber sensor for temperature and refractive index measurement

This work proposes and demonstrates a bent multimode interference (MMI) sensor for refractive index and temperature measurement. The MMI structure was fabricated by successive splicing between single-mode-multimodesingle- mode (SMS) fibers. A droplet-like bent was introduced in the multimode fiber section for excitation of modes into the acrylate coating. The excitation of higher modes into the acrylate coating is particularly interesting due high thermooptic coefficient of acrylate which could improve temperature sensitivity, while evanescent field interaction of modes at the acrylate surface with surrounding material could be used for refractive index sensing. These modes experienced phase changes due to temperature and/or refractive index changes, consequently shift the spectra of the sensor. The sensor structure was simulated using BeamProp software to determine the required bending to excite light into acrylate coating for sensing. In experiment, a 3.5 mm bent sensor demonstrated refractive index sensitivity of 42.41 nm/RIU tested with refractive index between 1.30-1.395. Meanwhile, temperature sensitivity of 1.317nm/°C was attained using 5 mm bent sensor between 25 °C to 35 °C. The low cost and simple sensor structure is desirable in many applications including for detection, diagnosis, and determine of health, safety, environmental, liquid food, and water quality control

Investigation of Michelson interferometer fiber temperature sensor based on single mode-multimode-single mode fiber structure

A simple fiber temperature sensor based on Michelson interferometer is investigated experimentally. The sensor is formed successive splicing of a single mode fiber (SMF) spliced to a short section of multimode fiber (MMF) followed by another SMF, which also known as single mode-multimode-single mode (SMS) structure. Temperature response of three different sensor lengths of 10 mm, 20 mm and 30 mm are experimented with increasing and decreasing temperature. The sensor exhibits good linearity, stability and repeatability for the test range from room temperature to 180 °C. The highest sensitivity is attained by the 10 mm sensor with response ~0.108 nm/°C. Factors that affect sensitivity are discussed and related issues are addressed. This sensor is most suitable for low to intermediate temperature applications

Resolution Improvement in Fabry-Perot Displacement Sensor Based on Fringe Counting Method

This paper presents an improved Fringe Counting Method (FCM) technique in order to enhance the displacement resolution of a Fabry-Perot Displacement Sensor (FPDS). A simulation model of a FPDS based on the improved FCM has been developed and simulated for nanometer displacement range by using MATLAB mathematical software. Unlike conventional FCM that analyzed the number of fringes produced over one time period, the improved FCM analyzed the number of fringes for one largest Free Spectral Range (FSR). In this work, the initial length of Fabry-Perot Interferometer (FPI) cavity has been set at 75 μm due to limitation of the machining precision equipment. For the displacement analysis, the improved FCM technique is used as an algorithm. The research results prove that this FPDS could detect displacement at 10nm resolution over a working range of 40 nm. It showed that the improved FCM technique managed to enhance the capability of the conventional FCM in detecting nanometer displacement.

Investigation of the effect of inlet radius on the response time of a transmission type ozone sensor

The effect of inlet radius of a transmission type optical gas cell on its response time is reported. Six gas cells of varying lengths, and internal radius of 0.32cm were considered at first and then other internal diameters were also investigated afterwards. The effect of inlet radius is easily discernible at all velocities considered; however it is more pronounced at lower flow rates. At a velocity of 16.79cm/s of ozone gas, and for a target sensing time of ≤ 0.5 seconds; we observed that the inlet radius requirements for gas cells of varying lengths and varying internal diameters is not the same for a specific target sensing speed. The length and the internal radius of a gas cell are proportional to its inlet radiu

Fiber optic acoustic sensor based on SMS structure with thin polymer diaphragm for partial discharge detection

This paper proposes a fiber optic acoustic sensor (FOAS) based on a single-mode fiber - multimode fiber - single-mode fiber (SMS) structure attached to a thin polymer film used as a diaphragm. The diaphragm was specially developed to enhance the sensitivity towards the acoustic pressure-wave resulted from the partial discharge (PD) events. The sensitivity and signal-to-noise ratio (SNR) characterizations of the FOAS without and with a thin polymer film were performed. Both time-resolved and phase-resolved partial discharge (PRPD) patterns measurements were carried out in air and oil media. The experiment was conducted with three-electrodes using FOAS in conjunction with the conventional PD measurement as per IEC 60270 standard. The sensor achieved a sensitivity up to −31.21 dBm and −30.8 (0 dBm is defined as 1V/µBar) using broadband and tunable light source, respectively. The discharge characteristics pattern of FOAS was verified with IEC 60270 standard, and the patterns of FOAS resembled IEC 60270 standard. The proposed FOAS was capable for detecting the PD using both broadband and tunable laser lights. The use of the thin polymer film had a significant impact on the acoustic sensitivity. With the simple, low-cost design structure and free from electromagnetic interference, FOAS is found to be suitable as an in-situ sensor for detecting the acoustic signals of partial discharge and can be utilized inside the transformer

Effect of surface roughness on sensitivity of unclad fiber-optic sensors

This work presents the effect of surface roughness's effect on transmission characteristics and the sensitivity of unclad fiber optic sensor (FOS). A total of three samples with different surface roughness were fabricated using the chemical etching technique using different chemical solutions which are 49% hydrofluoric acid (HF), 5:1 Buffered Oxide Etchants (BOE), and 7:1 BOE to analyze the spectrum behavior and the performance of these samples. All samples were fabricated by immersing the 4 cm of sensing zone inside the chemical solution according to the etching rate of that solution. Every sample fabricated will be measured using five different concentrations of glucose which were 5g, 10g, 15g, 20g, and 25g as an experiment medium. From the measurement, the results obtained will be analyzed and the graphs were plotted. The power loss for all solutions were analyzed and the least recorded power loss is 32.49 dB exhibited by FOS fabricated in the 49% HF solution while the best sensitivity in terms of power loss is FOS fabricated in the 5:1 BOE solution with the highest sensitivity of 9.526 dB/g at 5g of glucose concentration