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In this paper, an optical fiber sensor based density sensor is proposed and demonstrated experimentally. The sensor is formed by fiber Bragg grating (FBG) sensor. The proposed sensor design is very simple and versatile for density measurements of liquids. The FBG strain sensor has one end mounted to a 3D printed rigid support, and the other end connected to a 3D manufactured clamp in this sensor design. A metal ball is suspended from this clamp by a non-stretchable cord. When it is completely immersed in liquid, the liquid buoyancy force acts on it. As a result, the strain in FBG varies depending on the force applied to the ball. This results in a wavelength shift in the FBG sensor. The proposed sensor design is tested for four distinct liquids, including water, gasoline, engine oil, and acetone, and the measured density values for each were tabulated. We estimated the density of water by varying the temperature and adding salt. Based on the measurements, the sensitivity of the sensor is 2.584 $\text{pm}/\text{Kg}/\text{m}^3$ when the temperature of liquid changes and $3.375\times 10^{-2}$ $\text{pm}/\text{Kg}/\text{m}^3$ when density varied by adding salt to the liquid is reported.

The fiber Bragg grating sensor is widely used in strain monitoring of large metal structure and trend to replace the resistance strain gauge due to its advantages of strong stability, high measurement accuracy, multiple points measuring, strong environmental suitability and long transmission distance. The temperature-induced strain, which can have the same order of magnitudes as the mechanically-induced strain, will cause great errors in the strain monitoring. Therefore, the temperature compensation for the sensors is essential to guarantee the measurement accuracy. The existing theoretical models and experiment platforms for analyzing the temperature compensation are established by assuming that the testing temperature is constant. However, the surrounding temperature of some large metal structure is not stable, and the effect of temperature change cannot be neglected. This paper aims to establish an analytic model and an experiment platform to compare the temperature compensation of the fiber bragg grating sensor and the resistance strain gauge. The superiority of the temperature compensation for the fiber bragg grating sensor is verified. The result provides theoretical support for choosing the fiber bragg grating sensor in the long-time strain monitoring.

Fiber Bragg gratings (FBG) are ideal sensors for temperature, strain or vibration sensing applications with their advantages over conventional electronics sensor systems. In this paper, two different FBG sensor interrogation schemes based on broadband ASE source and tunable EDFRL source are demonstrated and compared. With both interrogator configurations, the response of the FBG sensor to temperature change is found to be linear and the sensitivities are measured as 11 pm/°C and 10.5 pm/°C, respectively. The experimental results have revealed that the optical power reflected from the FBG sensor is almost 20 dB higher with tunable EDFRL source than broadband ASE source. Thus, an interrogation method with tunable EDFRL can be suitable for remote, quasi-distributed sensor applications requiring high output power and OSNR.

For subway safety, it is important to monitor the convergence deformation of shield tunnels in the long term. However, traditional monitoring methods are constrained by high cost and technical diff...

An experimental investigation on square and circular high-strength concrete short columns confined with aramid fiber-reinforced polymer (AFRP) sheets was conducted in this study. Fiber Bragg grating sensors have been applied successfully in monitoring of the strains of the AFRP-confined square and circular concrete columns. The experimental results demonstrate that two types of axial force-strain curves were observed depending on the form of the column. Results show fiber Bragg grating sensors have good repeatability and the ultimate load of the circular concrete column is larger than that of the square concrete column. The interlaminar strains of AFRP and high-strength concrete have also been attained. It helps to analyze the constraint effect of the concrete column and compute the ultimate load of the square and circular concrete column.

In this paper, an improved technique for a centralized fault monitoring and detection in Gigabitcapable Passive Optical Network using fiber Bragg grating sensor is proposed. The technique detects fault once it occurs at the vulnerable locations in the fiber optic distribution link by the proposed Fiber Bragg Grating devices. The scheme uses an amplified Erbium Doped Fiber Amplifier monitoring signal in the C-band and a uniform Fiber Bragg Grating with different Bragg wavelengths and reflectivities as the branch identifiers in the network. The reflected signal from the optical sensor is analyzed at the Optical Line Terminal in the Central Office by an Optical Spectrum Analyzer to determine the branch with rupture in the network. The simulated result obtained shows that the system can monitor and detect a fault in the Feeder Fiber link, up to 20 km at optical power received of −44 dBm. The scheme is capable of detecting a fault in the various optical distribution network at the remote node in the customer’s end, at minimum optical power received of −58 dBm with negligible effects on data signal transmission.

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 $30\,\,\text {mm}\times 30\,\,\text {mm}$ on an aluminium plate, the average identification error obtained by SVM_DMBA is 1.615%.

In this paper, we have proposed a bragg grating based sensor to monitor health of civil structures at distinct temperatures. We have considered increased number of gratings with suitable refractive index to enhance sensitivity of fiber bragg grating sensor. Analysis of Bragg wavelength with respect to load and temperature is successfully studied. The simulation results reveal that when independently strain (50 units per simulation) and temperature (25 ℃) are increased uniformly, a linear shift in Bragg wavelength 0.064 nm and 0.347 nm is observed, respectively. Similarly, when both strain and temperature are increased (ε = 50 & T= 25 ℃) concurrently, a directly proportional relation is found in bragg wavelength (0.403 nm). The results verify the enhanced performance of as-proposed sensor, employing it could be potentially used in civil, bio-medical and military domains.

Recent demand for using FBG as a pressure sensor in a different industrial application makes several types of research to be conducted to enhance the pressure sensitivity. This paper demonstrates a combination method to enhance pressure sensitivity. Firstly, in this work FBG with polymer fiber named perfluorinated monomer (CYTOP) was used with specific parameters. Secondly, this FBG was covered by a patch of thin polymer material. However, the strain, temperature, and pressure sensitivity were recorded and compared with bare silica FBG. The temperature effect was reduced by using the cascade FBG technique. By applying force on the grating and changing of refractive index; the Bragg wavelength was shifting, making the CYTOP FBG responds more efficiently than silica FBG. This responsivity was leading to an improvement in pressure sensitivity. Experimental results illustrate that the enhanced CYTOP FBG based pressure sensor achieves pressure sensitivity up to 93.5 pm/KPs with a resolution of 0.005 KPa, which was 1500 times higher than bare FBG. The advanced CYTOP FBG based pressure sensor can be functionalized in a technical application for instance, structural health monitoring, pressure of oil wells application, explosion wave, and prevention of erosion.

The observation and estimation of deep crustal stress state is a key and difficult problem in in-situ stress measurement. The borehole wall strain gauge based on the overcoring stress relieving method is one of the main methods of in-situ stress measurement. In this paper, a strain sensing array based on FBG is designed by using the main structure of the classical hollow inclusion cell, and its layout scheme on the hollow inclusion is studied. According to the layout scheme, the in-situ stress inversion algorithm of hole-wall strain to stress is deduced; then, the triaxial loading and unloading experiment platform is built, and the calibration experiment of FBG strain sensor is designed; Finally, Abaqus finite element software is used to simulate the in-situ stress measurement process of the overcoring stress relieving. The FBG strain values of each measurement direction before and after the overcoring process are extracted, and the stress inversion equation is used to carry out the stress inversion. Through the comparison of the inversion results, it is proved that the FBG strain sensor group is feasible and reliable. The quasi-distributed FBG sensor module designed in this paper can invert the three-dimensional in-situ stress by measuring the hole-wall strain, which lays a theoretical and experimental foundation for the development and application of FBG hole wall strain gauge. It fairly makes up for the deficiency of the existing hole-wall strain gauge based on resistance strain gauge, provides direct and accurate observation way for hole wall strain measurement, and has important practical value for the development of in-situ stress measurement technology.

This study proposed a new fiber Bragg grating-based smart ring for monitoring body joint postures occurred at elbow joint and knee joint positions. A single-mode fiber Bragg grating sensor was embedded into a 3D printed ring for sensing occurred deformation of the ring. The raw material used for fabricating the smart ring was polylactic acid, which was found to have the advantages of being flexible in nature and having ease of fabrication using fused deposition modeling method. The fabrication process of the fiber Bragg grating smart ring was characterized by the advantages of ease of handling, quick prototyping, high resolution, low cost, and time-saving. Bare fiber Bragg grating sensors were successfully embedded into hot printed polylactic acid material during the fused deposition modeling process, even the printing temperature of the printing nozzle exceeded 200℃. Two new smart wearable rings were fabricated and used to monitor systematic bend motion of elbow joint and knee joint. The measurement sensitivities of the two smart rings mounted at the elbow joint and knee joint were 0.0056 nm/° and 0.0276 nm/°, respectively. The corresponding maximum measurement angle within current calibration tests were 90° and 100°, respectively. The method of using both fiber Bragg grating and fused deposition modeling for sensor design can be extended for the fabrication of other sensors such as temperature sensors, strain sensors, pressure sensors, stress sensors, displacement sensors, and tilt sensors.

In this work, we report a fiber Bragg grating (FBG) sensing system for a real-time temperature monitoring during a high-intensity focused ultrasound (HIFU) treatment of breast fibroadenoma. Temperature monitoring of the HIFU procedure within the treated area contributes to a successful outcome of a thermal ablation procedure by providing a valid feedback to the clinician. The unique characteristics of the FBG sensors make them a valid alternative to traditional sensing techniques for a variety of biomedical applications, including thermotherapies. The experiments were conducted on ex vivo breast fibroadenoma tissues. Results confirm that proposed setup is able to perform multipoint temperature measurements and to distinguish between consecutive ultrasound pulses.

In this paper we investigate the performance of a Fiber Bragg Grating (FBG) as a strain-optic and temperature sensor, using the Coupled Mode Theory (CMT) and the Transfer Matrix Method (TMM), through numerical simulation in an interrogation system with Single-Mode Fiber (SMF) and Photonic Crystal Fiber (PCF). Parameters such as sensitivity, bandwidth, peak power, peak wavelength and side-lobes power, were analyzed through the Bragg wavelength change depending on the simultaneous variation of strain and temperature. The FBG sensor proposed suffered thermal variation 25 °C to 200 °C and of strain of 0 μs to 1000 μs, excellent linearity was obtained for the variation of the Bragg wavelength with differences of 0.7 nm for each 50 °C and 0.245 nm for each 200.

Graphical abstract, Highlights • FBGET is novel, non-invasive, and easy to mount eye tracking methodology. • FBGET can be utilized as a point of care device. • FBGs are electrically and chemically inert, hence suitable for biomedical sensing. • FBGET tracks both eyes simultaneously eliminating time synchronization complexity. • FBGET can facilitate diagnosis of ophthalmological/neurological disorders., Eye movement evaluation is vital for diagnosis of various ophthalmological and neurological disorders. The present study proposes a novel, noninvasive, wearable device to acquire the eye movement based on a Fiber Bragg Grating (FBG) Sensor. The proposed Fiber Bragg Grating Eye Tracker (FBGET) can capture the displacement of the eyeball during its movements in the form of strain variations on a cantilever. The muscular displacement generated by the eyeball over the lower eyelid, by its swiveling action while moving the gaze on a target object, is converted into strain variations on a cantilever. The developed FBGET is investigated for dynamic tracking of the eye-gaze movement for various actions of the eye such as fixations, saccades and main sequence. This approach was validated by recording the eye movement using the developed FBGET as well as conventional camera-based eye tracker methodology simultaneously. The experimental results demonstrate the feasibility and the real-time applicability of the proposed FBGET as an eye tracking device. In conclusion, the present study illustrates a novel methodology involving displacement of lower eyelid for eye tracking application along with the employment of FBG sensors to carry out the same. The proposed FBGET can be utilized in both clinical and hospital environment for diagnostic purposes owing to its advantages of wear-ability and ease of implementation making it a point of care device.

In response to the difficulty of weak detection of early bearing damage, resonance demodulation technology and the principle of fiber Bragg grating sensing strain were combined to design a fiber Bragg grating generalized resonance sensor, which can extract the weak pulse signal of weak detection of early bearing’s early damage from rolling bearing. First, a principle of resonance dynamics of second-order mechanical systems based on fiber Bragg grating and generalized resonance principles is proposed. Second, the basic structure of the sensor is designed. Then, ANSYS finite element simulation is used to analyze the natural frequency of the sensor. Finally, the natural frequency value of the sensor was obtained through experiments. The experimental results of proof-of-principle show that the experimental results are consistent with the theoretical predictions. The theoretical model is accurate, which verifies the feasibility of the sensor.

Additive manufacturing (AM) is a name for techniques applied for constructing three-dimensional (3D) objects in a layer-by-layer process. Such methods can be applied for a variety of materials, like ceramics, polymers, and metals. It results in wide applicability of AM elements in many industrial branches, e.g. energetic, medicine or aerospace. Fiber Bragg grating (FBG) sensors due to their small dimensions and high chemical durability can be embedded into different material types. The goal of the paper is to analyze an influence of FBG sensors embedded into an AM polymeric samples on the polymeric structure durability. The samples will be manufactured using multi-jet printing method. The method was chosen due to its high accuracy of printed polymeric elements and the possibility of manufacturing products with complex shapes. The analyzes will be related to tensile strength determination of the samples with embedded FBG sensors. The comparisons will be performed for the samples without sensors and with sensors after manufacturing and after temperature treatment.

In this paper, we demonstrate characterization of chirp fiber Bragg grating (CFBG) sensor using a hot-tip probe method for determination of physical length (i.e. position) and the corresponding reflected wavelength within the CFBG spectrum. This calibration of CFBG plays an important role in various applications such as high-speed velocity sensor, detonation velocity measurement etc. This scheme provides the relationship between CFBG length and reflected wavelengths which is the principle on which a CFBG functions as a sensor for velocity estimation.

We experimentally demonstrate the visualization of ultrasonic wave propagation in a metallic plate using a surface-bonded fiber Bragg grating sensor and non-contact excitation of the desired guided mode.

We demonstrate a self-referencing FBG sensor for damage detection. The sensor compensates for changing environmental conditions by measuring the reference and distorted signal simultaneously and uses traveling acoustic waves in optical fibers.

The present in vitro study proposes a novel (to the best of our knowledge) methodology employing a fiber Bragg grating sensor for the evaluation of pulp chamber temperature increase during the polymerization of the composite resin induced by the light-curing process. A fiber Bragg grating temperature sensor (FBGTS) has been developed in view of its ease of insertion into the pulp chamber with minimal widening of the pulpal canal. The temperature increase in the pulpal chamber during the polymerization of the composite resin by light curing has been characterized with varying depths of cavities of 1 mm, 1.5 mm, and 2 mm employing FBGTS. Also, the increase in temperature of the pulpal chamber during the polymerization of the composite resin has been studied with variants of the light-curing device. The obtained results are expected to be an indicator towards the potential hazard caused by heat induced pulpal injuries during the polymerization of composite resins using a light-curing device.

Recently, it has become necessary to develop a monitoring technology that combines an FBG (fiber Bragg grating) sensor as a means for continuously monitoring whether the reinforcing effect of an FRP (fiber-reinforced polymer) is maintained on FRP-reinforced structural members. However, most existing research focuses on the insertion of FBG sensors into bar-shaped FRPs, and there is a lack of studies that analyze the details for an FRP strip combined with FBG sensors. In this regard, this paper seeks to develop a reinforcement for an NSM (near-surface-mounted) retrofit in which an optical fiber with an FBG sensor is combined with FRP strips. For this, a series of experiments were performed to find the adhesive strength of optical fiber-epoxy-FRP interfaces, the tensile strength of the FBG sensor part of optical fiber with a reflection lattice, and the sensing performance depending on the adhesion length between the optical fiber and the FRP strips. As a result of the study, the adhesion length not less than 20 mm in one direction from the center, with a total adhesion length of 40 mm, needs to be secured when the optical fiber with an FBG is attached and fixed between the two FRP strips with epoxy. In addition, it is expected that the proposed model can be used to properly predict the strain transfer of an FRP strip with a fiber optic sensor and can also be utilized when determining optimum dimensions.

This study's objective was to propose the use of textile braiding manufacturing methods, thus facilitating the application of the high precision and accurate measurability of optical fiber Bragg grating sensors to various structures.The purpose of this study was to Combine 3d braid processing with the optical Bragg grating sensor's accurate metrology. Out of limits of the sensor's epoxy attachment methods, the textile braiding method can make applicable scope diversify. The braiding processing is capable of designing a 3D fabric module processing, multiple objective mechanical fiber arrangement, and material characteristics. Optical stress-strain response conditions were explored through the optimization of design elements between the Bragg grating sensor and braiding. For this study, Bragg grating sensors were located 75% apart from the fiber center. The sensor core structure is helical of 1.54 pitch. A polyurethane synthetic yarn was braided together with the sensor on the Weaving machine core part in a braiding.Prototyping results, a negative Poisson's ratio makes curled the braided Bragg grating sensor. The number of polyurethan string yarns has been conducted the role of wrap angle in braiding. The 12 strands condition showed an increase in double stress-strain response rate at a Poisson ratio of 1.3%, and 16 strands condition was found to affect the sensor with noise at a Poisson ratio of 1.5%. This study can suggest applying braid processing of the Bragg grating sensor, which is expected to create and develop a new monitoring sensor.

The deployment of the differential form of Golay coding in TDM-FBG sensor is proposed and simulated. The spatial resolution associated to 20 cm was successfully achieved. Furthermore, the coding gain of 6 dB was achieved at Golay code length of 64 bits during 0 and 1500 μstrain applications.

We have proposed and experimentally demonstrated a plasmonic tilted fiber Bragg grating (TFBG) biosensor for labelfree detection of small biomolecule S-adenosyl-L-homocysteine (AdoHcy) in different concentrations. The biosensor is designed as a reflective probe type with a 50-nm-thick gold film coating over the fiber surface of an 18° TFBG, together with a surface functionalization with protein lysine methyltransferase Set7 working as bio-detector. The sensor is fabricated without any destruction of fiber structural integrity, thereby ensuring the stability and reproducibility. The experimental results demonstrated that our biosensor can detect biomolecule AdoHcy with concentration as low as 1 nM. We have also measured AdoHcy in different concentrations, including 0.01, 0.1 and 10 nM, and the results indicated that as the AdoHcy concentration increases, the association ratio between AdoHcy and Set7 arises correspondingly, agreeing with the theory.

Rock strains detection is one of the principal ways to monitor geohazards. Classic strainmeters are cumbersome, hard to install and very expensive. Opto-electronics devices based on fiber Bragg grating technology allow to realize strainmeters with high sensitivity, low-cost, small volume and high performance.We present the long term result of continuous soil strain monitoring on the Etna mount by a three-axial fiber Bragg grating sensor. The sensor has been developed in the framework of European Project MED-SUV (MEDiterranean SUpersite Volcanos). The installation site is a 8.5 meters deep borehole at a distance of about 7 km South-West from the summit craters of the Etna mount, at an elevation of about 1740 meters. This kind of sensor has a resolution better than 100 nanostrains on a daily timescale. Despite it is only a prototype, the sensor has worked for four years with a duty-cycle higher than 90% detecting both fast event, as earthquakes, and slow event, as epochal rocks strain behavior.

Traffic volume studies are conducted to determine the number, movements, and classifications of roadway vehicles at a given location and period. Typically, there are two methods for conducting traffic volume studies: manual and automatic counting. When manual counting is used, a person records the traffic volume on the site or alternatively from video recordings and this estimate can have a large margin of error. Automatic counting is based on measurement technologies, including pneumatic road tubes, inductive loops, infrared, microwave Doppler/radar, passive acoustic, video image detection, and Bluetooth devices. However, they are costly to install and have various limitations, such as high maintenance cost, availability of power source, and dependence on surrounding environment. Currently, weigh-in-motion (WIM) technology has become popular for automatic vehicle counting. In this paper, a three-dimensional glass fiber-reinforced polymer packaged fiber Bragg grating sensor (3-D GFRP-FBG) is introduced for in-pavement vehicle counting. The 3D GFRP-FBG sensor was installed on I-94 freeway, at MnROAD facility, Minnesota. When a vehicle passes over the road, the pavement produces strain signals that are picked up by wavelength changes. These strain peaks can be tracked to achieve vehicle counting. The sensors were laid out 9 feet from the road centerline with 16 feet distance between them to detect all the vehicles travelling on the right side of the road. The feasibility tests show the ability of the sensors to detect vehicles from small cars to semi tractor-trailer. For a 250-second period, the sensor detected 23 vehicles, with a total of 69 axles.

Optical sensors based on fiber Bragg gratings have become an important type of sensing element for strain measurements. In this study, fiber Bragg grating strain sensors and corresponding reference temperature sensors were integrated into a pantograph strip. The results of an online test indicated that the temperature of the pantograph strip impacting the strain measurement reaches about 80 ℃ while the vehicle was running. In addition, Fourier analysis showed that the energies of the temperature measurement signals dominated the relatively low-frequency band (less than 0.02 Hz), whereas the strain signals prevailed in the relatively high-frequency band. Thus, a novel method based on a digital filtering technique was proposed for temperature compensation in fiber Bragg grating sensor systems for monitoring the conditions in electrified pantograph–catenary systems. A Butterworth high-pass filter was designed to reject the temperature-related signal component with a stopband and to capture the real strain in the passband in frequency domain. To achieve this filtering, the cutoff frequencies and the filter order were calculated adaptively according to the frequency-domain characteristics of the measured temperature signal. With the designed filter, the temperature effect to the strain signals can be eliminated so that the strain can be estimated accurately. In comparison with the traditional temperature compensation technique, the proposed method is more effective in terms of estimating the real strain of the pantograph strip in practical applications. Compensated by the proposed method, the time-domain and frequency-domain analyses of the contact force denote the frequencies corresponding to the support span, and the dropper can be distinguished. Further, the first-order (4 Hz) and second-order (8.3 Hz) natural frequencies of the pantograph are visible in the measurements from catenary sections, which demonstrates the sufficiency and rationality of the proposed temperature compensation method for fiber Bragg grating sensor systems.

The intelligent measurement-based technology of Fibre Bragg Grating (FBG) sensor was proposed for establishing a wireless sensing network of airport asphalt pavement for structural information moni...

Distributed optical fiber strain sensing significantly increases the number of sensing points compared with fiber Bragg grating sensor, which makes it an excellent candidate for shape sensing. Theoretical analysis indicates that the spatial resolution of strain measurement is crucial to the performance of shape sensing, so a shape sensor based on differential pulse-width-pair Brillouin optical time-domain analysis is proposed to improve the spatial resolution and shape sensing performance. The sensing fiber is attached on the both sides of a steel strip substrate, which enables the measurement of Brillouin frequency shifts (BFSs) of both the sides to suppress temperature crosstalk. In the experiment, first, the dependence of BFS variation on the curvature of the fiber is measured, the result of which agrees well with theory. Then the reconstruction of three shapes are demonstrated, the spatial resolution of which is 10 cm.

A method for the continuous detection of heart rate (HR) in signals acquired from patients using a sensor mat comprising a nine-element array of fiber Bragg gratings during routine magnetic resonance imaging (MRI) procedures is proposed. The method is based on a deep learning neural network model, which learned from signals acquired from 153 MRI patients. In addition, signals from 343 MRI patients were used for result verification. The proposed method provides automatic continuous extraction of HR with the root mean square error of 2.67 bpm, and the limits of agreement were -4.98–5.45 bpm relative to the reference HR.

To solve the problem that the curvature information of the large flexible rocket body affects the attitude control of the rocket body, a shape reconstruction method based on optical fiber strain sensing is proposed in this paper, which can measure the bow deformation and vibration state of the rocket in real time as the input data for adjusting the attitude control of the rocket. In this scheme, the dynamics of flexible rocket can be solved stably and quickly. In order to verify the reconstruction method, the beam model was used as the experimental analysis object, and the vibration information such as deformation of the beam model was identified through the strain value measured by fiber Bragg grating (FBG) sensors. The results show that the deformation reconstruction method can well restore the deformation and rotation angle of the beam system and has good stability and real-time performance. This method can provide a theoretical basis for the real-time deformation calculation and high-precision attitude control of future flexible launch vehicle.

Fiber Bragg grating (FBG) is also widely used to detect the heart because it can be received in the form of pressure that results in changes in strain. FBG was chosen because it has a high sensitivity to strain. Heart rate detection can be done in several ways such as using a telescope, but using FBG has a high degree of accuracy and is sensitive to strain. Heart detection is still developing because of the serious problem with human life behavior so that efforts are needed to find other ways to more easily detect the heart. Currently, heart detection can be done without having to go to the hospital, such as by using a cellphone, watch, and others. This study aims to design and measure changes in the output power of FBG and to analyze the effect of strain change on FBG by loudspeaker vibration. The Bragg wavelengths used are 1310 nm and 1550 nm with a power of 1 mW as a diode laser source and the output is measured by an optical power meter. The highest change in output power at a wavelength of 1310 nm Bragg is equal to 0.471 μW, while at a wavelength of 1550 nm it is equal to 0.032 μW. The highest shift of the Bragg wavelength is at the Bragg 1310 nm wavelength, which is 0.598 nm, while the Bragg wavelength of 1550 nm is 0.552 nm. The highest change in strain was at 1310 nm Bragg wavelength valued at 576.186 με, while at 1550 nm Bragg wavelength was 432.113 με. This shows that the response at the Bragg wavelength of 1310 nm is more sensitive than the Bragg wavelength of 1550 nm.

Highlights • GO/Au/FBG sensor is fabricated to diagnosis the COVID-19 virus via patient saliva. • Sensor considerably responses to patient saliva having different virus concentration. • Deviation of wavelength and amplitude from healthy saliva identify the disease level., Monitoring the COVID-19 virus through patients’ saliva is a favorable non-invasive specimen for diagnosis and infection control. In this study, salivary samples of COVID-19 patients collected from 6 patients with the median age of 58.5 years, ranging from 34 to 72 years (2 females and 4 males) were analyzed using an Au/fiber Bragg grating (FBG) probe decorated with GO. The probe measures the prevalence of positivity in saliva and the association between the virus density and changes to sensing elements. When the probe is immersed in patients’ saliva, deviation of the detected light wavelength and intensity from healthy saliva indicate the presence of the virus and confirms infection. For a patient in the hyperinflammatory phase of desease, who has virus density of 1.2 × 108 copies/mL in saliva, the maximum wavelength shift and intensity changes after 1600 s were shown to be 1.12 nm and 2.01 dB, respectively. While for a patient in the early infection phase with 1.6 × 103 copies/mL, these values were 0.98 nm and 1.32 dB. The precise and highly sensitive FBG probe proposed in this study was found a reliable tool for quick detection of the COVID-19 virus within 10 s after exposure to patients’ saliva in any stage of the disease.

The sensitivity of Fiber Bragg Gratings (FBGs) to the variation of a specific parameter can be improved by choosing a suitable coating material. This paper explores the possibility of measuring the concentration of Ethanol in aqueous solutions by using poly (methyl methacrylate) (PMMA) as coating material of a single-mode FBG. The basic measurement principle relies in the absorption of liquid Ethanol which produces controlled swallowing of the coating, straining the underneath Bragg grating. The PMMA coating was deposited on the FBG by means of a specifically designed dip coating test bench, able to accurately control the thickness of the applied layer. Metrological performances of the developed PMMA-coated FBG Ethanol sensor have been assessed for Ethanol concentrations in the range of 0-38 % in distilled water at 25 °C constant temperature. The prototype shows good repeatability and better sensitivity when compared to an uncoated FBG, especially at low Ethanol concentrations. The dynamic behavior of the sensor (which depends on the kinetics of the absorption mechanism) has been assessed as well, showing a response time of about 290 s, while the recovery time (660 s) was almost twice.

In this article, a new closed-form apodization expression, which describes the light propagation in fiber Bragg grating sensor (FBGS) according to the design setting of the sensor application, is developed and presented. The main goal of the proposed approach is to optimize the FBGS apodization to enhance the reflected power as long as side lobes are kept in a low level. For this purpose, the coupled mode equations (CME) method has been used with the new apodization formula to customize the light propagation in the FBGS. The new apodization algorithm is processed based on side lobe level (SLL) and full width at half maximum (FWHM) of the FBGS grating spectrum. Further, the developed method has been compared with other apodization profiles presented by other authors. All results show very satisfactory performance of the proposed method.

The authors wish to make the following erratum to this paper [...]

A novel technique to achieve real-time and high-precision interrogation of a linearly chirped fiber Bragg (LCFBG) grating sensor array based on dispersive time delay and optical pulse compression is proposed and experimentally demonstrated. In the proposed system, an ultra-short optical pulse is launched into an LCFBG sensor array consisting of 𝑁 identical LCFBGs, to produce 𝑁 reflected pulses with their time delay changes corresponding to the strain or temperature changes. The reflected pulses are sent to another LCFBG having an opposite dispersion coefficient to achieve optical pulse compression to improve the measurement accuracy. A proof-of-concept experiment is demonstrated. A 2×3 LCFBG sensor array using six identical LCFBGs is implemented, and the performance is evaluated experimentally. The sensing speed can be as high as 48.6 MHz, and the sensing accuracy can be as high as 0.26 με for strain and 0.045°C for temperature.

Prolonged seated works are responsible of awkward poses (e.g., excessive neck forward flexion) and job stressful conditions. Musculoskeletal disorders in the cervical spine region are common in computer workers who are often affected by neck pain. Neck pain has a high prevalence amongst the general population (from 42% to 69%). Reduction of workers productivity, absence from work and utilization of health care services worsen the socioeconomic burden associated to neck pain. Early evaluation of postural mistakes and changes in vital signs associated to job stress may be beneficial to reduce the incidence of neck pain. To reach this aim, wearable systems based on different sensing technologies have been developed. In the last decades, smart systems based on fiber Bragg grating sensors (FBGs) have been extensively used for instrumenting wearables. The present work aimed at preliminary assessing the capability of an FBG-based smart system in detecting single-plane neck movements associated to poor postural habits and respiratory frequency changes associated to stressful working conditions. Results confirmed the system capability in detecting flexion/extension movements in the sagittal plane and its good accuracy in monitoring respiratory frequency during computer work.

Wavelength variation of fiber Bragg grating sensor is caused by strain and temperature. We propose a method to discriminate between these two parameters by measuring full width half maxima at different strain and temperature values.