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Breast cancer is one of the most challenging health problems in women worldwide. Early detection and regular breast cancer screening can considerably improve the survival rate. Many advanced imaging technologies are currently being used in the detection of breast malignancy. However, these methods are costly, uncomfortable, and time-consuming. Therefore, in this work, a simple and noninvasive thermographic technique, based on a Fiber Bragg Grating (FBG) thermal sensor array, has been developed to detect breast cancer. Breast tissue is simulated using agar gel phantom, and the heaters are embedded inside the phantom in different locations to mimic the tumors. FBG thermal sensor array is employed to acquire the surface temperature distribution of the simulated breast phantom. Also, modeling of the tissue-mimicking phantom and tumor in COMSOL Multiphysics software is carried out to provide a detailed 3D thermal view of the proposed prototype. Both experimental and simulated results are found to be in agreement and display the same trend as expected. Experimental results show that a temperature variation of ≥0.3°C is detected at the location of the tumor’s presence, which can be easily picked up by FBG interrogators which have sensitivity of ~1 pm, indicating the efficacy of the proposed sensing prototype as a potential screening tool for the diagnosis of breast cancer. [ABSTRACT FROM AUTHOR]

There is a need to develop sensors that can measure vital signs such as pulse rate and blood pressure easily; such vital signs can be calculated by measuring arterial strain. To this end, a new method that uses a plastic fiber Bragg grating (FBG) sensor to measure pulsation strain at human fingertips is proposed herein. Plastic fiber has a smaller Young’s modulus than that of the glass fiber. Under the same applied pressure, the plastic FBG sensor deforms more than the silica glass FBG sensor, and the Bragg wavelength shift length becomes longer, which results in higher detection sensitivity. The pulsation strain of the fingertip was measured by the proposed method based on this characteristic. The most sensitive signal detection point in the fingertip was the measurement point 10 or 15 mm from the distal interphalangeal joint in the fingertip direction. Strain signals with periodic peaks were measured from five participants. From the strain signal measured with the cuff attached to the arm, the peak disappeared when the cuff moved, and it reappeared when the cuff was opened. Therefore, the measured signal waveform changes based on the blood flow condition. The pulse rate calculated from the peak interval of the measured signal showed high correlation with the reference pulse rate, and the measurement accuracy was ±5.5 bpm. It may be possible to calculate the blood pressure and pulse rate from the measurement signal of the pulsation strain of the fingertip obtained using the plastic FBG sensor. [ABSTRACT FROM AUTHOR]

The standard support vector machine (SVM) performs poorly on the identification problem of low velocity impact areas due to its lower accuracy rate. Improving SVM's performance using the bat algorithm (BA) is feasible, but BA has the premature convergence problem. In this study, a hybrid bat algorithm with double mutation operations (DMBA), in which the Cauchy mutation operator and the extremal optimization mutation operator are integrated into BA, is proposed to enhance BA's ability to jump out of the local optima. Then, a novel SVM based on this hybrid BA, which is called SVM_DMBA, is developed to address the identification problem. Compared with the standard SVM and twelve improved SVM methods which are combined with the standard algorithms, advanced algorithms, and bat variants, the significant performance of SVM_DMBA is validated using UCI datasets. Moreover, to identify low velocity impact areas, SVM_DMBA is applied to the low velocity impact localization system based on fiber Bragg grating (FBG) sensors. The statistical results indicate that SVM_DMBA is a significantly effective method for identifying the low velocity impact areas and generates higher identification accuracy than comparative methods. For 64 low velocity impact areas of 30 mm × 30 mm on an aluminium plate, the average identification error obtained by SVM_DMBA is 1.615%.

Most of the dam’s disasters that occurred in the world could be avoided if proper and preventive measures were taken, such as long-term surface or underground monitoring to detect small soil displacements. However, due to the complex operation necessary to monitor underground layer displacements, inclinometers are not used with suitable regularity. To circumvent the logistics of field campaigns necessary in conventional inclinometers, a real-time, remote monitoring system was developed. In this paper, a fiberoptic inclinometer system was designed, consisting of FBGs arrays fixed along a flexible tube to be inserted into conventional boreholes to monitor underground layers displacements. Tests on the bench consisted of applying lateral displacements to curve the tube with the Bragg wavelengths acquired by an FBG interrogator. Then, a specially developed algorithm, applying the Frenet-Serret equations, and the cubic spline interpolation method were used to reconstruct the tube profile. For the first validation of the proposed method, the algorithm was applied to real data obtained in-field by a conventional inclinometer. The results of these tests showed a good agreement between the curve reconstruction and the plotted data of field measurements. The final validation was performed by applying lateral displacements to the instrumented tube and comparing the real tube profile measured by a laser ruler with the calculated profile by the algorithm. The errors found in all tests were less than 1% attesting that the proposed system can be an alternative methodology to the conventional techniques of geotechnical instrumentation, through continuous monitoring with fast response and in real-time, with possible application to quantify the mass movement of soils; movements from earth dams, landfills, and slopes. [ABSTRACT FROM AUTHOR]

The real-time, continuous, beat-to-beat blood pressure (BP) monitoring is vital in clinical scenarios such as operations theatres, ambulances etc. In the present study, a non-invasive BP monitoring methodology based on Fiber Bragg Grating sensors is reported. The design and development of Fiber Bragg Grating based Pulse Monitoring Device (FBGPM) is demonstrated which is capable of acquiring the radial arterial pulse pressure waveform effectively in real time. The Radial Arterial Pulse Pressure Waveform is acquired on beat to beat basis employing developed FBGPM in a clinical environment. Further, the recorded radial arterial pulse pressure waveform is processed to obtain systolic and diastolic BP by utilizing a standard non-invasive BP measurement device as a reference. The BP values obtained through FBGPM are then compared with the BP values obtained through an Intra-Arterial (IA) probe. The FBGPM is a chemically and electrically inert device which makes it an effective candidate for monitoring the real-time BP. The focus of the study is to demonstrate the feasibility of deploying developed FBGPM device in clinical environment to acquire beat-to-beat BP and subsequently compare the present device to the IA probe method of BP acquisition. [ABSTRACT FROM AUTHOR]

Gait analysis is vital from the view of its established capacity as an indicator for neuromuscular disorders. Gait analysis is carried out in order to provide a quantified assessment of human movement which may aid orthopaedic and podiatric fraternity to suggest suitable therapeutic treatment. The proposed study comprises of two wearable non-invasive devices realized using FBG sensors i.e. Knee Angle Measurement Device (KAMD) for dynamic knee angle measurement and Forefoot Load Measurement Device (FLMD) for dynamic measurement of load on the forefoot. In the present study, the assessment of locomotion is illustrated and analyzed utilizing the developed devices without any time synchronization complexity. During locomotion, the swing and the stance phase is analyzed with respect to both knee joint angle and forefoot load which further reveals the complementary nature between them. In addition, FLMD can also be utilized for the evaluation of single and double limb support phases during locomotion. Furthermore, the novel cantilever approach utilized in the FLMD design ensures to acquire the load imparted specifically over the forefoot region which facilitates FLMD to be employed for assessment of other locomotory actions such as landing phase analysis during leaps, climbing stairs, treadmill tests etc. Also, the cantilever approach helps minimize the hysteresis effects on the device. [ABSTRACT FROM AUTHOR]

To predict the dynamic load of space deployable structure, a novel prediction method based on fiber Bragg grating (FBG) sensors and long short-term memory (LSTM) neural network is proposed. The FBG sensors can measure strain values of the structure. The LSTM establishes the relationship between the strain values and load without a complex dynamic model. The LSTM first works in training mode, its input is strain values and output is the load. Then, the LSTM works in the prediction mode, which takes the current strain values as input and uses the trained network model to predict load. The network of LSTM is simple, which can achieve good prediction effect and shorten the running time. To evaluate the effectiveness of the proposed method, numerical simulations and experiments of space deployable structure with single-point input load are employed. The results demonstrate that compared with the method based on traditional neural network, the max error, root mean square error, and consuming the time of the proposed method are reduced by more than 43%, 21%, and 67%, respectively.

This article reports the use of fiber Bragg grating (FBG) sensors for electric machines’ in-service bearing condition monitoring. The proposed method enables simultaneous extraction of thermal and mechanical information on the bearing operational status for health monitoring and fault diagnosis purposes. The work first reports the instrumentation, calibration and the measurements interpretation methods of an FBG array sensor fitted to the drive-end bearing of an operating inverter driven induction motor. Experimental tests are then undertaken on a purpose build test rig to evaluate the proposed in-situ sensing scheme's performance under healthy and faulted bearing conditions. The results demonstrate that the measurements acquired by individual FBG sensors fitted in the bearing architecture contain concurrent thermal and mechanical information, which can be clearly differentiated to enable understanding of the examined motor bearing's thermal only and mechanical only operating conditions. Furthermore the in-situ measurements obtained in fault conditions are shown to contain clearly defined time and frequency domains fault signatures, which can enable unambiguous fault diagnosis and trending. [ABSTRACT FROM AUTHOR]

Weight data of vehicles play an important role in traffic planning, weight enforcement, and pavement condition assessment. In this paper, a weigh-in-motion (WIM) system that functions at both low-speeds and high-speeds in flexible pavements is developed based on in-pavement, three-dimensional glass-fiber-reinforced, polymer-packaged fiber Bragg grating sensors (3D GFRP-FBG). Vehicles passing over the pavement produce strains that the system monitors by measuring the center wavelength changes of the embedded 3D GFRP-FBG sensors. The FBG sensor can estimate the weight of vehicles because of the direct relationship between the loading on the pavement and the strain inside the pavement. A sensitivity study shows that the developed sensor is very sensitive to sensor installation depth, pavement property, and load location. Testing in the field validated that the longitudinal component of the sensor if not corrected by location has a measurement accuracy of 86.3% and 89.5% at 5 mph and 45 mph vehicle speed, respectively. However, the system also has the capability to estimate the location of the loading position, which can enhance the system accuracy to more than 94.5%. [ABSTRACT FROM AUTHOR]

We propose a simple and novel circular diaphragm–micro-stylus based single fiber Bragg grating (FBG) tactile sensor for reading Standard English Grade-1 Braille cells. The surface protrusions on the cells are transduced into strain variations on the FBG sensor, bonded along the line of symmetry of the diaphragm, by a free, vertically moving Micro-Stylus (MS). The tension mode of the diaphragm and the mass of the micro-styli are varied to optimize the sensing properties of the system. The maximum sensitivity of 1.786nm/mm is exhibited by the sensor system with the highest mass of the MS (MS-1; 167mg) in the highest tension mode ($770~\mu \varepsilon $). The repeatability error and resolution of the sensor in the aforementioned configurations are found to be 0.028nm and 559nm respectively. The proposed sensor system displayed good linearity, repeatability, high resolution, and easily adjustable sensitivity in the present scenario. [ABSTRACT FROM AUTHOR]

We are working on the development of a sensor that can calculate various vital signs from the signals measured by installing a Fiber Bragg Grating (FBG) sensor at the pulsation point of a living body. In this paper, the influence of blood flow parameters and sensor installation conditions on the FBG sensor signal was verified using two blood flow simulation models. From the results of our study, the following observations were made. The fluid pressure increases, the wavelength shift of the FBG sensor beca me larger. By contrast, an increase in the viscosity of the fluid was seen to cause a decrease in the displacement length of the Bragg wavelength. Fluid pressure and viscosity were observed to opposite effects on the FBG sensor signal. The Bragg wavelength shift of the FBG sensor was observed to be larger when the installation direction of the FBG sensor was perpendicular to the blood flow direction than in the parallel direction. However, FBG sensor signals with higher signal-to-noise (S/N) ratio were measured at an angle of 75 degrees than at an angle of 90 degrees, which is perpendicular to the blood flow direction. From the above results, the installation condition of the FBG sensor on the measurement signal and the influence of each parameter of blood flow were established. [ABSTRACT FROM AUTHOR]

Human joint kinematics has established its capacity as a vital tool for joint pathology and gait analysis. Range of motion (ROM) of a knee joint performed by flexion and extension is an essential tool to assess the efficacy of surgical interventions or therapeutic assessment. This paper proposes a novel wearable device for dynamic measurement of knee joint angle using fiber Bragg grating (FBG) sensor. The proposed knee angle measurement device (KAMD) can transduce the angular movement between the shin and the thigh into strain variations on a cantilever, which is acquired by the FBG sensor over it. The KAMD is also facilitated with tuneable sensitivity with three modes of high sensitivity mode, medium sensitivity mode, and low sensitivity mode, which can be opted based on application specific resolution and range of measurement. The ROM data obtained from the KAMD are validated against ROM obtained from commercially available Polhemus Sensors. Furthermore, the synchronization of the knee joint movement of both legs during walking along with stance and swing phase is illustrated, which shows the ability of KAMD to perform gait analysis. Employment of KAMDs on both legs eliminating the time synchronization complexity makes the proposed FBG-based KAMD an efficient means to evaluate the knee angle from both legs simultaneously. [ABSTRACT FROM AUTHOR]

Vehicle classification is critical due to its significant use in transportation and pavement management and maintenance. In this paper, a vehicle classification system is developed based on in-pavement 3-D glass fiber-reinforced polymer packaged fiber Bragg grating sensors (3-D GFRP-FBG). When vehicles pass by the pavement, it produces strains, which can be monitored by the center wavelength changes of the embedded 3-D GFRP-FBG sensors. The vehicle’s speed and wheelbase can then be estimated according to the different time a vehicle arrived at the sensor sites and speeds monitored from the wavelength changes of the in-pavement sensors. The vehicle classification system in this paper uses support vector machine learning algorithms to classify vehicles into categories ranging from small vehicles to combination trucks. The field testing results from real traffic show that the developed system can accurately estimate the vehicle classifications with 98.5% of accuracy. [ABSTRACT FROM PUBLISHER]

We demonstrate the feasibility of long-period gratings (LPGs) written in microstructured polymer optical fibers (mPOFs) for detecting and measuring the strain rate and magnitude of engineering structures. We validate and compare the results of our experimental tests to a commercial fiber Bragg grating sensor. The encouraging results open the way to the use of LPG mPOF sensors in structural health monitoring applications. [ABSTRACT FROM PUBLISHER]

Low frequency vibration measurements in composite materials using embedded optical fiber sensors are presented in this paper. The two types of fiber sensors embedded are a polarization maintaining photonic crystal fiber (PM-PCF) polarimetric fiber sensor and a fiber Bragg grating (FBG) sensor. A glass fibre reinforced polymer composite material sample is fabricated with both fiber optic sensors embedded in it. A comparison between the performance of both the PM-PCF polarimetric fiber sensor and the FBG sensor embedded in the composite material is also presented. [ABSTRACT FROM PUBLISHER]

The paper reports results obtained from an unusual situation in structural monitoring - a "test-to-destruction," measuring strain using a series of fiber Bragg gratings (FBGs) sensors on a decommissioned concrete Railway Bridge in Ornskoldsvik, Sweden. The study formed part of the EU "Sustainable Bridges" Project. To undertake the study, FBG-based sensors were chosen and embedded in carbon fiber reinforced polymers (CFRPs) composite rods incorporated into grooves specially created in the concrete structure and interrogated using a compact system based on wavelength-division multiplexing (WDM). Throughout the study, the FBG sensors were continuously monitored, allowing the incremental increases in the strain to be seen and through the yield point of the carbon composite reinforcement. The sensors were able to follow the resulting induced changes in strain of over a range in excess of 4000 muepsiv just prior to failure of the bridge and representing extreme levels of strain for such a mechanical structure. The measurements made with the FBG-based system were found to be in agreement with the changes expected in the structure (together with the embedded reinforcement), produced by the loading applied. The study has demonstrated the successful use of FBG-based technology premounted in "smart" carbon fiber composite reinforcements used in a test of this type on a typical bridge structure of a type found widely across the world. [ABSTRACT FROM PUBLISHER]

A novel fiber Bragg grating (FBG) sensor configuration using three broadband light sources of different wavelength bands for the interrogation of FBG sensors distributed over 75 km of fiber is proposed and demonstrated. Rayleigh backscattering was reduced and a 60-dB effective dynamic range was demonstrated. [ABSTRACT FROM PUBLISHER]

We demonstrate a new method for measuring transverse stress with 10.2-mum spatial resolution in a fiber Bragg grating sensor, without the use of polarization-maintaining fiber, by combining a four-state polarization analysis with a layer-peeling algorithm. Measurements of the externally induced birefringence agree well with predicted values. We also demonstrate that our measurement is insensitive to temperature changes and spatial gradients, making it ideal for nonisothermal applications. [ABSTRACT FROM PUBLISHER]

Lead sensitivity in low-coherence interferometric fiber-optic sensors is a well-known problem. It can lead to a severe degradation in the sensor resolution and accuracy through its effect on the fringe visibility and interferometric phase. These sensitivities have been attributed to birefringence in the various components. In the current work, an analysis of the polarization properties of fiber Bragg grating and tandem-interferometer strain sensors, using Stokes calculus and the Poincare´ sphere, is presented. The responses of these sensors as a function of the birefringence properties of the various components under different illuminating conditions are derived. The predicted responses demonstrate very good agreement with experimentally measured responses. These models provide a clear insight into the evolution of the polarization states through the sensor networks. Methods to overcome the lead sensitivity are discussed and demonstrated, which yield a differential strain measurement accuracy of 18 nε·rms for a fiber Bragg grating sensor. [ABSTRACT FROM PUBLISHER]

A tilt measurement structure and signal detection method is proposed based on a self-demodulated fiber-Bragg grating (FBG) sensor, which consists of a couple of matched FBGs and a cantilever-based pendulum clinometer. Compared by the typical matched FBGs demodulating method, of which a sensing FBG and a demodulating filter FBG is placed separately, both matched FBGs of this tilt sensor are attached on the upper and lower surface of only one single pendulum-type cantilever element for simultaneous sensing and demodulating. So the received light power will change due to the split of the two reflected spectrum of FBGs, which is corresponding to the tilt angle. In addition, the cross-sensitivity effect of the FBG-based sensor is automatically solved due to a differential signal process method. Experimental results indicate the feasibility of the proposed idea. [ABSTRACT FROM PUBLISHER]

A novel time-division-multiplexing fiber Bragg grating (FBG) sensor for multipoint temperature warning sensor is proposed and demonstrated. A multiwavelength pulsed laser based on a multichannel matched FBG is employed. The sensor array consists of multiple uniform FBGs at different positions and with different nominal wavelengths. When the temperature exceeds the threshold at a certain position, the light at the corresponding time slot and wavelength can be detected. The sensor provides a simple and flexible solution to locate the abnormal temperature increase with different tolerable thresholds at different locations. [ABSTRACT FROM PUBLISHER]

A new temperature sensing system, which utilizes a thin-film bandpass filter deposited on an optical fiber end face and dual-wavelength push-pull reflectometry, is proposed. The system has the following advantages over the fiber Bragg grating sensor: it can observe the temperature in a localized small area and it gets rid of microcrack growth caused by stripping of cover coating from a fiber. The feasibility of the system has been verified by simulation. [ABSTRACT FROM PUBLISHER]

In this letter, a demodulation algorithm for fiber Bragg grating (FBG) sensor is presented. The proposed demodulation algorithm evaluates the wavelength shift in the reflected spectrum of an FBG sensor. It computes the cross-correlation between the perturbed spectrum and the undisturbed spectrum. We compare the proposed algorithm with another three reported algorithms and then discuss the experimental results in respect of the reflective index of FBGs and other factors that may influence the sensing resolution. We report strain resolutions of 0.4 and 1.5 muepsiv in high reflective gratings and low reflective gratings, respectively [ABSTRACT FROM PUBLISHER]

A novel fiber Bragg grating (FBG) sensor system for static and dynamic measurements with a wavelength-swept fiber laser is proposed and demonstrated. In this system, both static and dynamic perturbation of each FBG in the sensor arrays can be interrogated simultaneously. The experiments demonstrated the strain resolutions of ∼1 με and 3.4 nε/√Hz at 500 Hz for static and dynamic measurements, respectively. [ABSTRACT FROM PUBLISHER]

A novel fiber Bragg grating (FBG) wavelength demodulation scheme based on a compound interference configuration is introduced. This scheme measures the strain-induced wavelength-shift of the FBG in terms of phase-shift signal. The sensing resolution and sensitivity were demonstrated to be 6.2 nε and 1.59°/με, respectively, which match the theoretical value of 1.61°/με very well. [ABSTRACT FROM PUBLISHER]

In this letter, we describe a very accurate and simple demodulation technique for fiber Bragg grating sensors. The technique is suitable for both single and twin Bragg gratings. A twin grating is composed of two identical gratings located at different positions in the same single-mode fiber. Our demodulation technique evaluates the wavelength position of the reflection spectrum with respect to the spectrum of an undisturbed sensor. To calculate the spectrum shift, it computes the autocorrelation product between the two reflection spectra. The demodulation method, which is very fast, has been tested experimentally with temperature sensors. It gives absolute measurements and provides high accuracy compared to a conventional temperature probe. [ABSTRACT FROM PUBLISHER]

We present, for the first time to our knowledge, experimental evidence showing that superimposed blazed fiber Bragg gratings may be fabricated and used to extend the dynamic range of a grating-based spectrometer. Blazed gratings of 4° and 8° were superimposed in germanosilicate fiber by ultraviolet inscription and used in conjunction with a coated charged-coupled device array to interrogate a wavelength-division-multiplexing sensor array. We show that the system can be used to monitor strain and temperature sensors simultaneously with an employable bandwidth which is extendable to 70 nm. [ABSTRACT FROM PUBLISHER]

We propose and numerically demonstrate a novel technique for estimating the spectral content of the perturbation on a Fiber Bragg grating (FBG) sensor. The system utilizes an FBG array as a wavelength reference for time-stamping the wavelength shift of the sensor. This technique has demonstrated a good agreement between the actual and estimated spectrum. In addition to having the advantage of selecting the operational window of the sensor, it also gives an absolute measurement of the perturbation. [ABSTRACT FROM PUBLISHER]

We propose a novel fiber Bragg grating (FBG) sensor system using a linear-cavity fiber laser scheme with a distributed Raman amplifier as a gain medium. The inhomogeneous broadening property of the distributed Raman amplifier is used for multiwavelength operation. The experiment shows that such a linear-cavity fiber Raman laser can provide a stable output with an optical signal-to-noise ratio over 50 dB even if the FBG is located at a 25-km remote sensing position. The feature of our proposed fiber laser can facilitate a long-distance or a large-scale fiber sensor system and can be easily extended for multipoint sensing applications. [ABSTRACT FROM PUBLISHER]

We report a vertical-pendulum-based fiber Bragg grating tilt sensor, which can detect the magnitude as well as the direction of the inclination from the horizontal direction. The sensor is insensitive to temperature, and preliminary results show that tilt angle accuracy and resolution of better than 0.1° and 0.007° can be easily achieved. [ABSTRACT FROM PUBLISHER]