Optimum Placement of Long Gauge FBG Sensor in Reinforced Concrete Bridge: A Case Study

In the world today, civil infrastructure plays a major role in the advancement of the modern age. They are huge in scale, complex in their behaviour and create great impact in everyday life. To ensure safety of these structures, assessment of their structural integrity is an important and challenging task. The sole purpose of structural health monitoring is to detect damage in the structures and suggest suitable rehabilitation measures. Various sensors are employed to achieve the task of damage detection and establish a warning system to avoid failure of the structures. For large structures, long-gauge Fibre Bragg Grating (FBG) sensors which are sensitive to the global behaviour, can be suitably used for this purpose. However, health monitoring of a structure with large number of sensors is expensive and hence there is a need to optimize the number of sensors deployed to minimize the cost of the exercise without compromising on performance assessment. For this purpose, several optimization algorithms are available in literature. In this study, the Effective Independence Method (EIM) which optimizes the response of the structure based on modal analysis, is used to derive the Optimum sensor placement (OSP) protocol for a reinforced concrete (RC) bridge-deck in Poland, the geometry of which has been taken from literature. This will enable the placement of 40 long gauge FBG sensors in regions for efficient damage response in the bridge-deck. Further, the optimum orientation of the sensors is further validated with a finite element model of the bridge-deck, where a moving load is applied, and strains are recorded in the sensing fibre in both longitudinal (along length) and transverse (along breadth) alignments. It has been found that long gauge FBG sensors placed in the transverse direction are more efficient in damage detection than when they are placed longitudinally

Long period fiber grating for biosensing: an improved design methodology to enhance add-layer sensitivity

We present our theoretical study on the design of LPFG sensor where its add-layer sensitivity is enhanced. addlayer sensitivity quantifies the sensitivity of the sensor to the changes taking place within few tens of nanometers around the receptor molecules. Two different methodologies: the use of dual overlay layer and tailoring of the intermodal separation between two cladding modes, have been used to enhance the add-layer sensitivity. Using coupled mode analysis we compute several examples to carry out a detailed comparative analysis between the results obtained, focusing on the cladding mode near mode transition.This work was supported by Council of Scientific Research (CSIR), India during the 12th Five Year Plan. Project Nos. ESC-0102 and ESC-0110. The author I. D. Villar thankfully acknowledge the support of the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-78047-R) and the Government of Navarre through the project with reference 2017/PI044

Sensitivity Analysis of Sidelobes of the Lowest Order Cladding Mode of Long Period Fiber Gratings at Turn Around Point

A new methodology to enhance the sensitivity of a long period fiber grating sensor (LPFG) at the Turn Around Point (TAP) is here presented. The LPFG sensor has been fabricated by etching the fiber up to 20.4 mu m, until the sidelobes of dispersed LP0,2 cladding mode appeared near TAP in aqueous medium. The dual peak sensitivity of the sidelobes was found to be 16,044 nm/SRIU (surrounding refractive index units) in the RI range from 1.333 to 1.3335

Discrete cosine harmonic wavelet transform and its application to signal compression and subband spectral estimation using modified group delay

This paper proposes a new harmonic wavelet transform (HWT) based on13; Discrete Cosine Transform (DCTHWT) and its application for signal or image13; compression and subband spectral estimation using Modified Group Delay (MGD).13; Further, the existing DFTHWT has also been explored for image compression. The13; DCTHWT provides better quality decomposed decimated signals, which enable13; improved compression and MGD processing. For signal/image compression, compared13; to the HWT based on DFT (DFTHWT), the DCTHWT reduces the reconstruction error.13; Compared to DFTHWT for the speech signal considered for a compression factor of13; 0.62, the DCTWHT provides a 30% reduction in reconstruction error. For an image, the13; DCTHWT algorithm due to its real nature, is computationally simple and more accurate13; than the DFTHWT. Further compared to Cohen-Daubechies-Feauveau 9/7 biorthogonal13; symmetric wavelet, the DCTHWT, with its computational advantage, gives a better or13; comparable performance. For an image with 6.25% coefficients, the reconstructed13; image by DFTHWT is significantly inferior in appearance to that by DCTHWT which13; is reflected in the error index as its values are 3.0% and 2.65% respectively.13; For spectral estimation, DCTHWT reduces the bias both in frequency13; (frequency resolution) and spectral magnitude. The reduction in magnitude bias in turn13; improves the signal detectability. In DCTHWT, the improvement in frequency13; resolution and the signal detectability is not only due to good quality DCT subband13; signals but also due to their stretching (decimation) in the wavelet transform. The MGD13; reduces the variance while preserving the frequency resolution achieved by DCT and13; decimation. In view of these, the new spectral estimator facilitates a significant13; improvement both in magnitude and frequency bias, variance and signal detection13; ability; compared to those of MGD processing of both DFT and DCT fullband and DFT13; subband signal

A discrete cosine adaptive harmonic wavelet packet and its application to signal compression

A new adaptive Packet algorithm based on Discrete Cosine harmonic wavelet transform (DCHWT), (DCAHWP) has been proposed. This is realized by the Discrete Cosine Harmonic Wavelet transform (DCHTWT) which exploits the good properties of DCT viz., energy compaction (low leakage), frequency resolution and computational simplicity due its real nature, compared to those of DFT and its harmonic wavelet version. Hence the proposed wavelet packet is advantageous both in terms of performance and computational efficiency compared to those of existing DFT harmonic wavelet packet. Further, the new DCAHWP also enjoys the desirable properties of a Harmonic wavelet transform over the time domain WT, viz., built in decimation without any explicit antialiasing filtering and easy interpolation by mere concatenation of different scales in frequency (DCT) domain with out any image rejection filter and with out laborious delay compensation required. Further, the compression by the proposed DCAHWP is much better compared to that by adaptive WP based on Daubechies-2 wavelet (DBAWP). For a compression factor (CF) of 1/8, the ratio of the percentage error energy by proposed DCAHWP to that by DBAWP is about 1/8 and 1/5 for considered 1-D signal and speech signal, respectively. Its compression performance is better than that of DCHWT, both for 1-D and 2-D signals. The improvement is more significant for signals with abrupt changes or images with rapid variations (textures). For compression factor of 1/8, the ratio of the percentage error energy by DCAHWP to that by DCHWT, is about 1/3 and 1/2, for the considered 1-D signal and speech signal, respectively. This factor for an image considered is 2/3 and in particular for a textural image it is 1/5

Introduction to Wavelet Transform- A signal Processing approach

A Signal Processing Approach, has been developed in a simple, logical and directed way. To understand this subject, the background required is physics and mathematics at a junior degree level and the basic knowledge of signals and systems. The ease of understanding has been facilitated by providing all the intermediate steps in a mathematical derivation and physical meaning of the mathematical relations, preserving the rigor and depth of the subject

Over coupled long period grating with enhanced sensitivity to refractive index higher than that of cladding

Response characteristics of over coupled long period gratings to ambient refractive index higher than that of cladding index are investigated. For the first time change in the peak attenuation ~ 670 dB/RIU has been reported

Design optimization of fiber Bragg grating accelerometer for maximum sensitivity

Sensitivity of a cantilever-mass based fiber Bragg grating (FBG) accelerometer can efficiently be tailored by altering the distance between the axis of the FBG sensor to the neutral axis of the cantilever. To accomplish that in general, a backing patch is used to mount the FBG on the cantilever. A numerical method to quantify the influence of the material constant (Young's modulus) of the backing patch and its thickness on the sensitivity is presented in this paper. It is explicitly shown that for a specific patch material there is an optimum thickness for which the sensitivity happens to be the maximum. A good agreement between simulation and experimental results is obtained. Finally, it is demonstrated that a sensitivity similar to 1062 pm/g can be achieved, the enhancement almost by a factor of three as compared to that of the conventional cantilever-mass FBG accelerometer of similar bandwidth. (C) 2013 Elsevier B.V. All rights reserved

Response of strongly over-coupled resonant mode of a long period grating to high refractive index ambiance

Over-coupling of the resonant band of interest has been found to have significant influence on the refractive index sensitivity of long period grating (LPG) for surrounding material having refractive index higher than the cladding material. In this paper we report, for the first time to the best of our knowledge, a quantitative analysis using the concept of radiation mode coupling that elaborates the influence of initial coupling strength on the response of LPG to high refractive index surrounding. The simulated results agree well with those obtained experimentally where it could be shown that that a suitably over-coupled resonant mode of LPG can have a sensitivity similar to 724 dB/RIU in the range of the ambient refractive index which is slightly higher than the cladding where the conventional LPGs have almost no sensitivity

Long-Period Fiber Grating Probe: An Improved Design Suitable for Biosensing

Add-layer sensitivity of long-period fiber grating (LPFG) near mode transition (MT) has been studied in reflection configuration to realize a highly sensitive LPFG-based sensor probe suitable for biosensing. The dependency of the sensitivity on the separation between the resonant cladding modes considered during MT has also been investigated. The separation between two consecutive cladding modes was precisely increased or stretched to a desired value by reducing the cladding diameter. The probe was formed by cleaving the mode stretched LPFG (MSLPFG) through the grating region. The MSLPFG was designed to operate near MT by deposition of electrostatic self-assembled (ESA) polymeric overlay layers on the grating surface. We demonstrate that the polymeric overlay not only increases the sensitivity of the sensor but also eliminates undesirable multiple resonant bands that appear due to the introduction of arbitrary phase while cleaving the grating. Add-layer sensitivity of the MSLPFG sensor probe was obtained and found to be similar to 2.0 nmWL/nmTH with a significantly enhanced peak attenuation of similar to -30 dB around the MT region