A high sensitive fiber Bragg grating strain sensor with automatic temperature compensation

A high sensitive fiber Bragg grating (FBG) strain sensor with automatic temperature compensation is demonstrated. FBG is axially linked with a stick and their free ends are fixed to the measured object. When the measured strain changes, the stick does not change in length, but the FBG does. When the temperature changes, the stick changes in length to pull the FBG to realize temperature compensation. In experiments, 1.45 times strain sensitivity of bare FBG with temperature compensation of less than 0.1 nm Bragg wavelength drift over 100 ◦C shift is achieved

Use of FBG sensors for SHM in aerospace structures

This paper details some significant findings on the use of the fiber Bragg grating (FBG) sensors for structural health monitoring (SHM) in aerospace fiber reinforced polymer (FRP) structures. A diminutive sensor provides a capability of imbedding inside FRP structures to monitor vital locations of damage. Some practical problems associated with the implementation of FBG based SHM systems in the aerospace FRP structures such as the difficulty of embedding FBG sensors during the manufacturing process and interrelation of distortion to FBG spectra due to internal damage, and other independent effects will be thoroughly studied. An innovative method to interpret FBG signals for identifying damage inside the structures will also be discussed

Interferometric time division FBG interrogator and multiplexer with static, dynamic, and absolute wavelength measurement capabilities

We report on the design and preliminary testing of an interferometric interrogator capable of large-scale time-division multiplexing of FBG sensors. The scheme employs a passive algorithm for phase demodulation, allowing changes in FBG sensor reflected wavelengths to be calculated instantaneously upon arrival, and incorporates a technique for identification of initial absolute sensor wavelengths in order to overcome the measurement ambiguity associated with interferometric schemes. The proposed system will allow for high-speed interrogation of large-scale FBG sensor arrays with interferometric resolution and the capability for dynamic, static, and absolute FBG wavelength measurement

Encapsulation of FBG sensor into the PDMS and its effect on spectral and temperature characteristics

Fiber Bragg Grating (FBG) is the most distributed type of fiber-optic sensors. FBGs are primarily sensitive to the effects of temperature and deformation. By employing different transformation techniques, it is possible to use FBG to monitor any physical quantity. To use them as parts of sensor applications, it is essential to encapsulate FBGs to achieve their maximum protection against external effects and damage. Another reason to encapsulate is increasing of sensitivity to the measured quantity. Polydimethylsiloxane (PDMS) encapsulation appears to be an interesting alternative due to convenient temperature and flexibility of the elastomer. This article describes an experimental proposal of FBG PDMS encapsulation process, also providing an analysis of the FBG spectral characteristics and temperature sensitivity, both influenced by high temperature and the process of polydimethylsiloxane curing itself. As for the PDMS type, Sylgard 184 was employed. Encapsulation consisted of several steps: allocation of FBG to PDMS in its liquid state, curing PDMS at the temperature of 80°C ± 5 %, and a 50-minute relaxation necessary to stabilize a Bragg wavelength. A broadband light source and an optical spectrum analyzer were both used to monitor the parameters during the processes of curing and relaxation. Presented results imply that such a method of encapsulation does not have any influence on the structure or functionality of the FBG. At the same time, a fourfold increase of temperature sensitivity was monitored when compared to a bare FBG

Response Fibre Bragg Grating (FBG) strain sensors embedded at different locations through the thickness around a delamination in a composite lamina

A few FBG strain sensors were embedded at a vicinity of delamination of a laminated composite plate. Reflected spectra of FBG sensors which located in the same layer as the delamination and one layer above the delamination were investigated in order to understand the change of the reflected spectra due to stress concentrations at the delamination. The reflected waveforms of sensors were broadened with the increase of loading, as expected. A considerable difference in the response of two sensors was observed during both uniaxial and flexural loading. These differences show that the FBG sensors are capable of capturing the precise nature of the delamination under various loading conditions. Further, these observations provide evidence of the feasibility of using FBG sensor responses obtained from various locations allows the location of the delamination to be determined. This paper details some new and interesting findings of the use of spectral shapes and strain measurements from embedded FBG sensors in damage detection

High-sensitivity Fiber Bragg grating temperature sensor at high temperature

A method of making full use of the durable strain which fiber Bragg grating (FBG) can undertake is presented, which hugely improves the sensitivities of FBG temperature sensors at high temperature. When a sensor is manufactured at room temperature, its FBG should be given a pre-relaxing length according to the temperature it is asked to measure; once the temperature rise to the asked one, its FBG starts to be stretched and it starts to work with high sensitivity. The relationship between the pre-relaxing length and the working temperature is analyzed. In experiments, when the pre-relaxing lengths are 0.2mm、0.5mm、0.6mm, the working temperatures rise 25℃、50℃、61℃, respectively, and the sensitivities are almost the same (675pm/℃). The facts that the experimental results agree well with the theoretical analyses verify this method’s validity

Photonic realization of the relativistic Kronig-Penney model and relativistic Tamm surface states

Photonic analogues of the relativistic Kronig-Penney model and of relativistic surface Tamm states are proposed for light propagation in fibre Bragg gratings (FBGs) with phase defects. A periodic sequence of phase slips in the FBG realizes the relativistic Kronig-Penney model, the band structure of which being mapped into the spectral response of the FBG. For the semi-infinite FBG Tamm surface states can appear and can be visualized as narrow resonance peaks in the transmission spectrum of the grating

Comments on the European Commission’s Draft Proposal for a Council Regulation on the Law Applicable to Non-Contractual Obligations (Hamburg Group for Private International Law)

ROYAL INSTITUE OF TECHNOLOGY Abstract Laser Physics Group Department of Applied Physics SA104X Degree Project in Engineering Physics, First Cycle Fiber Bragg Gratings in Temperature and Strain Sensors by Ilian Haggmark Supervisor: Michael Fokine A Fiber Bragg Grating (FBG) is a periodic variation of the refractive index in an optic ber. It works as a wavelength selective lter and is used in several dierent applications such as telecommunication and sensor technology. Fiber sensors are based on a simple principle; the ber is aected by strain, temperature etc. due to which the selection of wavelengths in the FBG change. With an optical spectrum analyzer the changes in wavelength reection can be observed and converted to the physical quantity measured. In this thesis the properties of FBGs used in temperature and strain sensors are tested. Experiments to improve the precision of the sensors by embedding FBGs in metal are also carried out.KUNGLIGA TEKNISKA HOGSKOLAN Sammanfattning Laserfysikgruppen Institutionen for Tillampad Fysik SA104X Examensarbete inom Teknisk Fysik, Grundniva Fiberbraggitter i Temperatur- och Spanningssensorer av Ilian Haggmark Handledare: Michael Fokine Ett berbraggitter (FBG) ar en periodisk variation av brytningsindex i en optisk ber. FBG fungerar som ett vaglangdsselektivt lter och har era olika tillampningar inom bland annat telekomunikation och sensorerteknik. Fibersensorer bygger pa en enkel princip; bern paverkas av temperatur, spanning m.m. och da forandras ltreringen av vaglangder i FBG. Med en optisk spektrumanalysator kan forandringar i vaglangd registreras och konverteras till den storhet som mats. In detta examensarbete testas de egenskaper hos FBG som utnyttjas i temperatur- och spanningssensorer. Experiment for att forbattra precisionen hos sensorerna genom att gjuta in FBG i metall utfors ocksa

Impacts of different concentrations of spent carbide waste on the growth and yield of maize (Zea mays linn,.) And groundnut (Arachis hypogea linn.)

The impacts of different concentrations of spent carbide waste on the growth and yield of Zea mays Linn. (maize) and Arachis hypogea Linn. (groundnut) were studied at the screen house, Botanic garden, University of Port Harcourt, Nigeria. The crops were planted in carbide waste concentrations of 40g, 80g, 120g, and 160g per 2,8 kg of soil alongside a control in bags of height 20.5cm. Results indicated that carbide waste had significant (p=0.05) adverse affects on plant height, fresh weight and dry weight yield of the two crops (maize and groundnut) especially at 120g and 160g carbide waste concentrations. Results also showed that Zea mays experienced highest yield in total fresh weight (3.59±0.11), shoot dry weight (0.99±0.02), and total dry weight (1.33±0.06) at 80g carbide waste; while Arachis hypogea showed highest yield in total fresh weight (4.53±1.2), shoot dry weight (1.32±0.1), root dry weight (0.32±0.02), and total dry weight (1.64±0.01) in 40g carbide waste. These values were significantly (p=0.05) higher than their respective controls. Shoot-root ratios of the two crops and the soil pH were found to increase with increasing carbide waste concentrations. It therefore, means that these two crops can tolerate carbide waste pollutant at low concentrations but the phytotoxicity of this waste was high at higher concentrations

The association of fasting blood glucose (FBG) and waist circumference in northern adults in Iran: A population based study

Objectives: The aim of this study was to evaluate the association between Fasting Blood Glucose (FBG) level and Waist Circumference (WC) in men and women among 25-65 years old people in the north of Iran.Material and methods: This was a cross-sectional and analytical research gender that carried out on the 1797 subjects (941 males and 856 females) between 25-65 years old using multistage cluster sampling technique. FBG was measured in the morning after a 12-hour fast and was determined by using laboratory kits (enzymatic methods) and spectrophotometry technique. Central obesity was defined based on World Health Organization criteria: waist circumference ≥102 cm and ≥88 cm in men and women, respectively. The SPSS.16 software was used for statistical analysis.Results: As whole, the mean of FBG in women (98.3 ± 40.1 mg/dl) was higher than in men (94.6 ± 32.2 mg/dl). Also, the mean of WC in men 4.5 cm was lower than in women. In men, the mean of FBG statistically differs between normal and central obese subjects both in 35-45 year-age group (P = 0.001) and in 45-55 year-age group (P = 0.042). As whole, in men, the FBG level increased up 2.82 mg/dl in each 10 cm of WC with the highest rate in 35-45 year-age group. In totally, in women, the FBG level increased up 3.48 mg/dl in each 10 cm of WC and in 25-35 year-age group and it was higher than in other age groups. In men, the regression coefficients were constant with age increasing while in women it was decreased. Constant trend in men and decreasing trend in women with age was shown between FBG and WC. The cut-off point of WC for detecting of diabetes obtained 89 cm and 107 cm in men and women, respectively.Conclusion: The positive correlation was seen between WC and FBG level and it was declined with age in women. Cut-off point for detecting of diabetes in men was less than in women. WC is useable as a predictor of type 2 diabetes mellitus risk among adults in the north of Iran. © 2014 Veghari et al.; licensee BioMed Central Ltd