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Cardiac electrophysiology is an effective treatment for atrial fibrillation, in which a long, steerable catheter is inserted into the heart chamber to conduct radio frequency ablation. Magnetic resonance imaging (MRI) can provide enhanced intraoperative monitoring of the ablation progress as well as the localization of catheter position. However, accurate and real-time tracking of the catheter shape and its efficient manipulation under MRI remains challenging. In this article, we designed a shape tracking system that integrates a multicore fiber Bragg grating (FBG) fiber and tracking coils with a standard cardiac catheter. Both the shape and positional tracking of the bendable section could be achieved. A learning-based modeling method is developed for cardiac catheters, which uses FBG-reconstructed three-dimensional curvatures for model initialization. The proposed modeling method was implemented on an MRI-guided robotic platform to achieve feedback control of a cardiac catheter. The shape tracking performance was experimentally verified, demonstrating 2.33° average error for each sensing segment and 1.53 mm positional accuracy at the catheter tip. The feedback control performance was tested by autonomous targeting and path following (average deviation of 0.62 mm) tasks. The overall performance of the integrated robotic system was validated by a pulmonary vein isolation simulator with ex-vivo tissue ablation, which employed a left atrial phantom with pulsatile liquid flow. Catheter tracking and feedback control tests were conducted in an MRI scanner, demonstrating the capability of the proposed system under MRI. [ABSTRACT FROM AUTHOR]

Steerable needles are a promising technology to provide safe deployment of tools through complex anatomy in minimally invasive surgery, including tumor-related diagnoses and therapies. For the 3-D localization of these instruments in soft tissue, fiber Bragg gratings (FBGs) based reconstruction methods have gained in popularity because of the inherent advantages of optical fibers in a clinical setting, such as flexibility, immunity to electromagnetic interference, nontoxicity, and the absence of line-of-sight issues. However, methods proposed thus far focus on shape reconstruction of the steerable needle itself, where accuracy is susceptible to errors in interpolation and curve fitting methods used to estimate the curvature vectors along the needle. In this study, we propose reconstructing the shape of the path created by the steerable needle tip based on the follow-the-leader nature of many of its variants. By assuming that the path made by the tip is equivalent to the shape of the needle, this novel approach paves the way for shape reconstruction through a single set of FBGs at the needle tip, which provides curvature information about every section of the path during navigation. We propose a Kalman-filter-based sensor fusion method to update the curvature information about the sections as they are continually estimated during the insertion process. The proposed method is validated through simulation, in vitro and ex vivo experiments employing a programmable bevel-tip steerable needle (PBN). The results show clinically acceptable accuracy, with 2.87-mm mean PBN tip position error, and a standard deviation of 1.63 mm for a 120-mm 3-D insertion. [ABSTRACT FROM AUTHOR]

Minimally invasive surgical procedures have become the preferable option, as the recovery period and the risk of infections are significantly lower than traditional surgeries. However, the main challenge in using flexible tools for minimal surgical interventions is the lack of precise feedback on their shape and tip position inside the patient's body. Shape sensors based on fiber Bragg gratings (FBGs) can provide accurate shape information depending on their design. One of the most common configurations in FBG-based shape sensors is to attach three single-mode optical fibers with arrays of FBGs in a triangular fashion around a substrate. Usually, the selected substrates dominate the bending stiffness of the sensor probe, as they have a larger diameter and show less flexibility compared to the optical fibers. Although sensors with this configuration can accurately estimate the shape, they cannot be implemented in flexible endoscopes where large deflections are expected. This paper investigates the shape sensor's performance when using a superelastic substrate with a small diameter instead of a substrate with dominating bending stiffness. A generalized model is also designed for characterizing this type of flexible FBG-based shape sensor. Moreover, we evaluated the sensor in single and multi-bend deformations using two shape reconstruction methods. [ABSTRACT FROM AUTHOR]

Fiber Bragg gratings (FBGs) are a potential alternative to piezoelectric ultrasound sensors for applications that demand high sensitivity and immunity to electromagnetic interference (EMI). However, limited data exist on the quantitative performance characterization of FBG sensors in the MHz frequency range relevant to biomedical ultrasound. In this work, we evaluated an FBG to detect MHz-frequency ultrasound and tested the feasibility of measuring passive cavitation signals nucleated using a commercial contrast agent (SonoVue). The sensitivity, repeatability, and linearity of the measurements were assessed for ultrasound measurements at 1, 5, and 10 MHz. The bandwidth of the FBG sensor was measured and compared to that of a calibrated needle hydrophone. The FBG showed a sensitivity of 0.99, 0.769, and 0.818 V/MPa for 1, 5, and 10 MHz ultrasound, respectively. The sensor also exhibited linear response ($0.975\leq {R}$ -Squared ≤ 0.996) and good repeatability with a coefficient of variation (CV) less than 5.5%. A 2-MHz focused transducer was used to insonify SonoVue microbubbles at a peak negative pressure of 175 kPa and passive cavitation emissions were measured, in which subharmonic and ultraharmonic spectral peaks were observed. These results demonstrate the potential of FBGs for MHz-range ultrasound applications, including passive cavitation detection (PCD). [ABSTRACT FROM AUTHOR]

This article presents a dexterous robotic system for autonomous debridement of osteolytic bone lesions in confined spaces. The proposed system is distinguished from the state-of-the-art orthopedics systems because it combines a rigid-link robot with a continuum manipulator (CM) that enhances reach in difficult-to-access spaces often encountered in surgery. The CM is equipped with flexible debriding instruments and fiber Bragg grating sensors. The surgeon plans on the patient’s preoperative computed tomography and the robotic system performs the task autonomously under the surgeon’s supervision. An optimization-based controller generates control commands on the fly to execute the task while satisfying physical and safety constraints. The system design and controller are discussed and extensive simulation, phantom and human cadaver experiments are carried out to evaluate the performance, workspace, and dexterity in confined spaces. Mean and standard deviation of target placement are 0.5 and 0.18 mm, and the robotic system covers 91% of the workspace behind an acetabular implant in treatment of hip osteolysis, compared to the 54% that is achieved by conventional rigid tools. [ABSTRACT FROM AUTHOR]

The multinode multibaseline interferometric synthetic aperture radar measurement system is the future development trend in the field of aviation remote sensing. The deformation error between the nodes directly affects the position and orientation error compensation of the load at the node, and the baseline length error directly affects the interferometric phase error compensation. Aiming at the particularity of the wing structure, a structural deformation measurement and baseline measurement method based on the strain mode is proposed. The fiber Bragg grating sensor is used to acquire the strain of each measuring point on the wing in real time, and the deformation of the wing is accurately measured by the modal superposition method, thereby realizing the high-precision measurement of the baseline between the nodes. The measurement result of the dual total station is the benchmark, and the validation of the method was carried out on the existing test system in the laboratory. Under static conditions, the experimental test results show that the wing deformation measurement accuracy is better than 1 mm, and the baseline measurement accuracy is better than 0.5 mm. [ABSTRACT FROM AUTHOR]

Retinal microsurgery requires precise manipulation of delicate tissue in the interior of the eye. Force sensing instruments can provide surgeons the imperceptible force information, thereby improving the safety of retinal microsurgery. Previous force sensing microneedles have demonstrated robust performance in transverse force measurement. However, in some surgical operations such as puncturing the vessel, the axial force sensing function is critical. In this article, we present a three degrees of freedom force sensing microneedle based on fiber Bragg grating (FBG) sensors. A novel configuration of the FBG sensors is arranged to detect the transverse and axial forces. Three optical fibers with dual FBGs are longitudinally attached along the outside surface of a Nitinol tube. Benefiting from the novel configuration of the FBG sensors, a hollow channel can be used to pass through injection catheter. A new force calculation algorithm was developed to decouple the transverse forces and axial forces. Experimental results demonstrate the proposed force calculation algorithm can achieve a resolution of 0.124 and 0.74 mN for transverse forces and axial forces, respectively. Validation and temperature compensation experiments show the force sensor can provide consistent and accurate measurement of 3-D forces within 35–37 °C temperature variation. [ABSTRACT FROM AUTHOR]

Tube internal erosion, which corresponds to its wall thinning process, is one of the major safety concerns for tubes. Many sensing technologies have been developed to detect a tube wall thinning process. Among them, fiber Bragg grating (FBG) sensors are the most popular ones due to their precise measurement properties. Most of the current works focus on how to design different types of FBG sensors according to certain physical laws and only test their sensors in controlled laboratory conditions. However, in practice, an industrial system usually suffers from harsh and dynamic environmental conditions, and FBG signals are affected by many unpredictable factors. Consequently, the FBG signals have more fluctuations and are polluted by noises. Hence, the signals no longer directly follow the assumed physical laws and their proposed thinning detection mechanisms no longer work. Targeting at this, this article develops a data-driven model for FBG signal feature extraction and tube wall thickness monitoring using data analytic techniques. In particular, we develop a spatiotemporal model to describe dynamic FBG signals and extract features related to thickness. By taking physical law as guideline, we trace the relationship between the extracted features and the tube wall thickness, based on which we construct an online statistical monitoring scheme for tube wall thinning process. We use both laboratory test and field trial experiment to demonstrate the efficacy and efficiency of the proposed scheme. Note to Practitioners—This article is motivated by the real industrial needs of inner erosion detection of tubes in harsh environment. Most of the current research works focus on designing various sensing apparatuses based on fiber Bragg grating (FBG) sensors for nondestructive erosion detection. These apparatuses prove to be able to collect signals reflecting tube wall thickness in static and controllable laboratory environment qualitatively. However, in reality, the industrial environment, which is impacted by many changing factors, is dynamic and uncontrollable. Consequently, the signals collected by these FBG apparatuses would have larger variations that mask the signals related to thickness. Furthermore, current methods have neither mentioned how to process their collected data to capture the unnoticeably slow but accumulative erosion information efficiently nor constructed online monitoring algorithms to detect the tube wall thinning process based on the collected signals quantitatively. Built upon their apparatuses but targeting at their unsolved challenges, we propose a novel data-driven approach for FBG signal analysis that can remove the environmental influence and extract features only related to tube wall thickness, and using the extracted features, we construct a statistical process control scheme to monitor tube wall thickness and detect erosion in real time efficiently. [ABSTRACT FROM AUTHOR]

The genetic algorithm (GA) method is used to demodulate the strain distribution of fiber Bragg grating (FBG), which improves the residual stress measurement accuracy of the tube in the hole-drilling method. The accuracy of the method is verified by simulation and experiment. Compared with the traditional peak demodulation, the residual stress error is reduced from 10%–20% to 0%–5% by GA. The results show that the use of the GA method can effectively improve the accuracy of residual stress measurement of the tube based on FBG, which promotes the application of FBG in the measurement of residual stress in special-shaped components and expands the range of FBG residual stress measurement. [ABSTRACT FROM AUTHOR]

The integration of robotics into retinal microsurgery leads to a reduction in surgeon perception of tool-to-tissue interaction forces. This blunting of human tactile sensory input, which is due to the inflexible mass and large inertia of the robotic arm as compared to the milli-Newton scale of the interaction forces and fragile tissues during ophthalmic surgery, identifies a potential iatrogenic risk during robotic eye surgery. In this paper, we aim to evaluate two variants of an adaptive force control scheme implemented on the Steady-Hand Eye Robot (SHER) that are intended to mitigate the risk of unsafe scleral forces. The present study enrolled ten retina fellows and ophthalmology residents into a simulated procedure, which simply asked the trainees to follow retinal vessels in a model retina surgery environment. For this purpose, we have developed a force-sensing (equipped with Fiber Bragg Grating (FBG)) instrument to attach to the robot. A piezo-actuated linear stage for creating random lateral motions to the eyeball phantom has been provided to simulate disturbances during surgery. The SHER and all of its dependencies were set up in an operating room in the Wilmer Eye Institute at the Johns Hopkins Hospital. The clinicians conducted robot-assisted experiments with the adaptive controls incorporated as well as freehand manipulations. The results indicate that the Adaptive Norm Control (ANC) method, is able to maintain scleral forces at predetermined safe levels better than even freehand manipulations. Novice clinicians in robot training however, subjectively preferred freehand maneuvers over robotic manipulations. Clinician preferences once highly skilled with the robot is not assessed in this study. [ABSTRACT FROM AUTHOR]

Force sensing is highly desirable in minimally invasive medical applications, since this feature shows great potential for reducing tissue damage and enhancing manipulation safety. However, embedding force sensors in medical devices is challenging and costly. This article explores the possibility to use shape sensing as a measure to extract force information. In this work, a model-based approach that allows simultaneous shape and force sensing is proposed. Shape information is reconstructed employing a multicore fiber with fiber Bragg grating sensors spaced over the fiber length. This fiber is capable of distributed 3D shape sensing. It is shown how by making use of extended Kalman filter and a mechanics model of the flexible instrument, it becomes possible to estimate both the magnitudes and locations of externally applied forces. Experiments were carried out to validate the proposed method for both one and two external forces applied at arbitrary locations in different directions on a flexible instrument. Results show that one-directional force magnitude and location can be estimated with an average error of 23.08 mN (15.39%) and 11.06 mm (6.51%), respectively. For two-directional forces, results of the load near the base show an average error of 52.01 mN (30.59%) for the magnitude and 29.24 mm (17.20%) for the location. For the load applied simultaneously near the tip, the mean magnitude error is 16.79 mN (11.19%) and the average location error is 10.18 mm (5.99%). The force sensing algorithm can run in real time with an approximate frequency of 59 Hz. In these experiments, it can be observed that the force-sensing accuracy, which depends on the sensitivity of the shape of flexible instruments with respect to the external force, can vary drastically in function of the force application point and force direction. [ABSTRACT FROM AUTHOR]

Objective: Design and evaluate a miniature triaxial fiber optic sensor which is integrated into the confined space at the tip of a flexible ureteroscope to measure the contact force during ureteroscopy. Methods: A notched flexure of multilayer continuous beams is deliberately designed to modulate the sensor sensitivity to axial stiffness but not to lateral bending and torsion, and to avoid the crosstalk between axial and lateral forces. Its structure parameters are optimized by the finite element method to meet the needs of miniaturization and performance. A linear decoupled model based on the singular value decomposition algorithm is proposed to accurately compute the forces from the wavelength shifts of fiber Bragg grating. Results: Experimental results show that in the axial direction the sensor has a range of 0-4 N with a resolution of 0.014 N, and in the lateral direction it has a resolution of 0.011 N within the range of -2 N to 2 N, and is able to provide accurate measurement with an error of less than 2%. Conclusion: Primary tests show the excellent competence of the sensor to measure the interactive force at the ureteroscope tip and to discriminate objects, validating its reliability and robustness. [ABSTRACT FROM AUTHOR]

Fiber Bragg gratings (FBGs)-based temperature sensors present numerous advantages such as small packaging, fast acquisition rate, and accuracy for structural health-monitoring applications in nuclear environments. Among the various classes of FBGs, Type I FBGs are inscribed with a UV continuous or pulsed laser on a photosensitive fiber or with femtosecond laser even in nonphotosensitive fibers. These gratings, however, cannot survive at temperatures exceeding 400 °C. Regenerated FBG (RFBG) gratings, instead, are derivative from type I grating: when a high thermal treatment (> 650 °C) is applied after the inscription on a prehydrogenated fiber, a new grating (RFBG) appears with different thermal properties. It withstands temperatures as high as 1000 °C, opening the way to new application fields such as the temperature monitoring of the nuclear reactor cores. This work investigates the radiation response of RFBGs originated from type I seed FBGs inscribed with an argon laser (244 nm) in two different fibers (SMF-28e fiber or in a B/Ge co-doped fiber), loaded with either H2 or D2 before the inscription to enhance the fiber photosensitivity. Regeneration was achieved at 650 °C or 900 °C depending on the fiber type. After this, the RFBGs were irradiated under 40-keV X-rays at two different dose rates [1 Gy(SiO2)/s or 10 Gy/s] and at two temperatures of irradiation—25 °C or 250 °C. At room-temperature (RT) irradiation, a Bragg Wavelength Shift (BWS) of about 35 pm was observed for the SMF-28e and more than 130 pm for the B/Ge fiber at 400-kGy dose, and the combined temperature and radiation constraints reveal that the RFBGs are radiation-tolerant. Indeed, no BWS is observed anymore, at the highest temperature of irradiation. [ABSTRACT FROM AUTHOR]

There is an increasing interest in the use of surface plasmon resonance tilted fiber Bragg grating (SPR-TFBG) as a sensor for various chemical applications. Signal demodulation is an important process for extracting useful parameters from the unique optical spectra for an accurate measurement. In this work, we proposed a global-based estimator for SPR-TFBG based on a spectral subtraction approach. The estimator is generated based on the root sum squared (RSS) error of the spectral intensity difference between the tested spectrum and the reference spectrum. In the comparison with the other established methods, the proposed method has the lowest standard deviation, the maximum absolute deviation, the finest measurement resolution, and the fastest processing speed. Besides, the proposed method is immune to the interference of white noise in the transmission spectra and capable of producing a high-quality signal with the lowest noise level. [ABSTRACT FROM AUTHOR]

An $\alpha $ -power refractive index profile circular core fiber Bragg grating (FBG) sensor has been numerically and experimentally analyzed for the first time. In the experiment, 40% concentrated hydrofluoric acid (HF) has been used to fabricate an etched FBG (e-FBG) sensor with variable cladding thickness. The proposed study can also be demonstrating the marginal tuning capability of Bragg wavelength shift by deeply etched cladding process. The target of this article is to analyze the $\alpha $ -power refractive index profile e-FBG sensor. For this purpose, a transfer matrix method (TMM) has been devised to analyze the complicated double-clad waveguide structure, while grating is taken along the length of fiber core. In this article, three samples have been fabricated and analyzed with various etched cladding thicknesses, i.e., 6, 8, and $10~\mu \text{m}$ , which give significant change in the refractive index sensitivity. Experimental results of sensitivity analysis have been matched closely with the numerical one. The estimated maximum sensitivity of the developed $\alpha $ -power e-FBG sensor has been found $\approx 35$ nm/refractive index unit (RIU). Also, this value is equivalent to the minimum change in the refractive index of $\leq 10^{-5}$. It has been found that the Bragg wavelength can be tuned marginally as a result of reducing the cladding diameter. It has been noticed that the tuning range can be substantially improved by the deep etching process along with $\alpha $ -power refractive index profile FBG and found to be $4.5 \,\times \, 10^{-3}$ RIU at optimum cladding diameter. [ABSTRACT FROM AUTHOR]

A refractometer based on an etched fiber Bragg gratings (EFBGs) sensor has been developed for monitoring beer fermentation in real time. The sensor was calibrated using synthetic solutions composed of water, maltose, and ethanol with alcohol by volume (ABV) ranging from 4.0% to 12.0% and Brix (sugar content) varying from 5% to 25%. Calibration results showed that the EFBG sensor responds with high sensitivity even to minor density variations less than 0.5 Brix ± 0.03 Brix in a quasi-linear monotonic fashion with respect to sugar and ethanol concentration, which allowed fitting an empirical model with good adherence to experimental data (low model variance) and with well-defined parameters (parameters covariance matrix with elements exhibiting small absolute values). Finally, the developed sensor was tested in a typical fermentation scenario. A rigorous material balance framework was established to relate the fit calibration model to actual density and alcohol content in real time, which is of assistance for process control strategies. As the proposed sensor can be fit in fermentation vessels for real-time (online) fermentation monitoring, it becomes a technological improvement to traditional offline measurements in terms of both biosafety and process control. [ABSTRACT FROM AUTHOR]

The existing slope safety monitoring studies mainly focus on long-term monitoring of slowly evolving horizontal deformations. However, during the practical applications, sudden deformations may also lead to landslides due to the natural and man-made trigger factors. This article first proposes a reusable and distributed fiber Bragg grating (FBG) inclinometer for simultaneous measurement of horizontal deformation and vibration induced by sudden deformation, providing more extensive monitoring for slopes. The proposed inclinometer utilizes ten FBG tilt sensors in series as measuring elements, which are characterized by easy installation and removal, thus making them reusable and eliminating excessive waste. A signal decomposition method is presented for splitting the coupled signal of the tilt sensor into two parts: the inclination angle signal and the vibration signal. The inclination angle signals can be converted to distributed horizontal deformation through a cumulative algorithm. And the vibration intensity can be inferred from the vibration signal. The measuring principle, structure design, and calibration experiment of the inclinometer were present in detail. A distributed horizontal deformation generating device with high precision was specially developed to simulate the internal deformation of slope. Verification experiments further validated the feasibility of the proposed inclinometer for simultaneous measurement of horizontal deformation and vibration induced by sudden deformation. [ABSTRACT FROM AUTHOR]

In this article, we propose a temperature-based proportional–integral–derivative (PID) controlling algorithm using highly dense fiber Bragg grating (FBG) arrays for laser ablation (LA) of ex vivo pancreatic tissues. Custom-made highly dense FBG arrays with a spatial resolution of 1.2 mm were fabricated with the femtosecond point-by-point writing technology and optimized for LA applications. In order to obtain proper PID gain values, finite element method-based iterative simulation of different PID gains was performed. Then, the proposed algorithm, with numerically derived PID gains, was experimentally validated. In the experiments, the point temperature was controlled at different distances from the laser fiber tip (6.0, 7.2, 8.4, and 10.8 mm). The obtained results report robust controlling and correlation between controlled distance and the resulting area of ablation. The results of the work encourage further investigation of FBG array application for LA control. [ABSTRACT FROM AUTHOR]

A fiber ring cavity laser temperature sensor is presented and demonstrated. The sensor probe consists of a fiber Bragg grating (FBG) and a heterostructure based on polymer-coated no-core fiber (NCF), and this probe also functions as a wavelength-selective component in the fiber laser system. There are multimode interference and antiresonance effects in the NCF coated with high refractive index polymer. Embedding this sensing head into an Er-doped fiber ring cavity laser system is helpful to improve the spectral quality and the detection limit (DL). The passband peak position of the heterostructure filter and FBG filter varies with the temperature, which leads to the corresponding shift in the output laser wavelengths. Experimental investigation achieves a maximum sensitivity of −3.155 nm/°C in the temperature range from −4 °C to 47 °C, and the DL is calculated as 0.005 °C. It should be noted that there are several measurement intervals in this temperature range, which can be distinguished by the cascaded FBG to obtain the accurate temperature value. Moreover, the sensor with a smaller NCF diameter has a higher temperature sensitivity. The proposed sensor can meet the actual demands of mesoscale ocean phenomena and microregion temperature detection in seawater, and it provides references for improving the sensing capability of optical methods in ocean detection and other practical application. [ABSTRACT FROM AUTHOR]

The strain- and temperature-sensing characteristics of fiber ring laser (FRL) sensors are studied comprehensively. The reflected sensing head, made up of spheroidal Fabry–Perot interferometer (FPI) concatenated with fiber Bragg grating (FBG), is inserted in the cavity of FRL acting as the laser intensity modulator and wavelength selector. The laser intensity is sensitive to temperature change while insensitive to strain, making the dual-parameter demodulation realizable without multivariate matrix by detecting the laser wavelength shift and the laser intensity variation, for the first time in our best knowledge. The comparable sensitivities of 1 pm/ $\mu \varepsilon $ and 24.9 pm/°C are detected in experiment for strain and temperature, respectively, with low detection limit (DL) of 0.87 $\mu \varepsilon $ and 0.035 °C, high $Q$ factor of 1140 and 7.07 $\times \,\,10^{5}$. The high intensity and narrow linewidth of the sensor make it potentially great for application in long-distance sensing systems. [ABSTRACT FROM AUTHOR]

Micrometeoroid and orbital debris (MMOD) can cause serious impact damage to long-term on-orbit spacecraft. MMOD impact detection and location are essential to improve the safety and reliability of the on-orbit spacecraft. In this article, a combined artificial neural network (ANN) and Mahalanobis distance method for MMOD impact detection and location based on fiber Bragg grating (FBG) sensor network is proposed. The inputs of the proposed ANN are the Mahalanobis distances determined by the wavelength changes of the FBG sensors at impact points and reference points. A finite element model is developed to explore the relationship between the Mahalanobis distance and the actual distance, which proved to be nonlinear based on the finite element simulation results of MMOD impacts. Four FBG sensors were installed on the back of the test board and sampled at a frequency of 100 Hz using a four-channel FBG demodulator. A total of 360 impact experiments were carried out on this experiment system. The average location error of the proposed method is 0.89 cm, which is 39% and 31% lower compared with the Mahalanobis distance discriminant analysis method and the ANN method, respectively. The combined ANN and Mahalanobis distance method reduces the location errors and has higher accuracy of position prediction. [ABSTRACT FROM AUTHOR]

Collaborative robots equipped with multicomponent force-sensing systems at the human–robot–environment interaction interface provides competitive advantages, such as collaboration, flexibility, and reliability. Most wrist force sensors use the cross-beam structures with electrical strain gauge measurement technologies. This article proposes an approach to develop a new ultrathin three-axis fiber Bragg grating (FBG) force sensor. First, an appropriate elastomer with embedded floating beams in ultrathin dimensions to measure three-axis force is designed using a finite-element method (FEM). A temperature-compensated extreme learning machine (TC-ELM) network is proposed to achieve the characteristics of low coupling and temperature compensation (TC). Calibration and experiment on the UR5 robot are conducted, and results illustrate that the highest sensitivity of the sensor can reach 34.07 pm/N, the repetition error is less than 5%, and the maximum coupling error is less than 0.21%. The maximum temperature drift after compensation is less than 20 pm. The proposed sensor has identical output as a commercial sensor and performs well in dynamic loading and unloading operations. Finally, comparison results from commercial and academic alternatives demonstrate the interest of the proposed approach to develop high-performance and integrated force-sensing solutions. [ABSTRACT FROM AUTHOR]

Fiber Bragg grating (FBG) acceleration sensor is an important branch of FBG application and has irreplaceable advantages compared with an electronic accelerometer. An FBG acceleration sensor with high sensitivity and high natural frequency is designed. This sensor adopts a double cantilever structure to sense the vibration perpendicular to the axis. Compared with a single cantilever structure, the natural frequency is increased without reducing the sensing length. Through the above structure design and material selection, the sensor shows a high natural frequency of 8658 Hz and its sensitivity is 0.44 pm/g. After the photoelectric demodulation is used, the sensitivity is 52 mV/g and the linearity is 0.998. Through the experiment and simulation analysis, the sensor performs good anti-interference in the transverse direction and temperature compensation in the process of vibration measurement. The system is very small due to the use of light intensity demodulation technology, which is conducive to application and integration in actual measurement scenarios. [ABSTRACT FROM AUTHOR]

This article reports on the first demonstration of in situ, real-time dosimetry realized with an enhanced backscattering optical fiber, and a high-resolution optical backscattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular, the difficult evaluation of not only the actual X-ray dose that is accumulated on the target volume but also the distribution profile of the ionizing radiation beam. Overall, the research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling, and remote interrogation. The experiments have been conducted by evaluating the spatial profile of radiation-induced spectral shift of the Rayleigh backscattering along an optical fiber exposed to X-rays. The sensing element is a section of specialty optical fiber whose Rayleigh backscattering signature changes under ionizing radiation. The specialty fiber is designed to exhibit an enhanced backscattering, in order to overcome the poor sensitivity to radiation of standard optical fibers that are normally, used in telecommunications. The enhanced sensitivity is achieved by doping the core with either aluminum or magnesium nanoparticles, and two different fibers have been fabricated and tested. The experimental results show the capability of real time detection of the radiation profile from high-dose rates (700 Gy/min) to low-dose rates (2 Gy/min). Moreover, different sensing mechanisms and responses to high- and low-dose rates are evidenced. A comparison with a quasi-distributed sensing system based on an array of fiber Bragg gratings (FBGs) is discussed, highlighting the superior performance of the backscattering approach in terms of sensitivity and spatial resolution, whereas the array of FBGs exhibits an advantage in terms of sampling speed. [ABSTRACT FROM AUTHOR]

A new fiber Bragg grating (FBG) sensor that can measure temperature, vibration, and strain is proposed in this article. The structure of this sensor is designed and optimized via theoretical analysis and the finite-element method (FEM). With an innovatively designed L-shaped cantilever (LSC), this designed sensor can better balance the vibration measurement sensitivity and the resonant frequency. The strain measurement structure is designed as a hollow square so that the reaction force of the sensor for the measured object is only $2.76\times 10^{-3}$ N/ $\mu \varepsilon $ , which ensures that the strain distribution of the measured object is not affected. The designed sensor can significantly amplify the measured strain with a measurement sensitivity (5.44 pm/ $\mu \varepsilon$) that is four times greater than that of the bare FBGs. This article uses single-mode FBGs inscribed by a femtosecond laser (FS-FBG) to make the sensors, and the sensing performance is analyzed. The results show that this FS-FBG-based sensor can withstand temperatures up to 1100 °C. [ABSTRACT FROM AUTHOR]

We report, for the first time, the development of a rectangular fiber with two cores consisting of different refractive indices for the discrimination of temperature effects during strain or curvature measurements using fiber Bragg gratings written in a single segment of fiber. Two cores with a diameter of $8~\mu \text{m}$ and a rectangular cladding with dimensions of $120\,\,\mu \text{m} \times 255\,\,\mu \text{m}$ permit convenient splicing to conventional single-mode fiber and support easy identification of the orientation of the fiber. When placed in the desired orientation, each core of the two-core rectangular fiber experiences a different spectral shift in the presence of applied strain or curvature. The sensitivities of the two cores are 0.87 and 1.08 pm/ $\mu \varepsilon $ for strain, 126 and −128 pm/m−1 for curvature, and 10.05 and 10.40 pm/°C for temperature, respectively. In addition, the flat cladding structure of the fiber provides a large physical contact area between the sensing fiber and the substrate than a circular fiber and allows better strain coupling between the object and the fiber. [ABSTRACT FROM AUTHOR]

In this article, we present a vibration measurement system based on low-frequency cantilever-based fiber Bragg grating accelerometers (CFAs) for a suspension bridge. Each accelerometer has an end-loaded cantilever beam, specifically tailored to achieve a uniform sensitivity for a frequency range of 0–4 Hz, a suitable detection range for the vibration analysis. In the field test, seven CFAs were installed at specific positions along the deck of a 110-m-long suspension bridge for synchronous multipoint vibration measurements. The reflection spectra of the CFA array were recorded and processed using the pseudo-high-resolution scheme to improve the signal quality and measurement accuracy. Three natural vibration frequencies: 1.15, 1.54, and 3.17 Hz have been identified from the measurement. Following that, the acquired time-domain signals were processed by a digital bandpass filter to retrieve the waveform at each natural frequency to determine the corresponding mode shapes. The results are in agreement with the phase difference between the frequency domain signal for each natural frequency. This investigation has shown the feasibility of the proposed measurement system for determining the mode shapes and dynamic frequency analysis of a suspension bridge. It is a potential method for structural health monitoring for other similar civil structures. [ABSTRACT FROM AUTHOR]

A flare system in oil platform is a combustion stack used to burn off excess gases that cannot be processed and gases that have to be eliminated in emergency shutdown to avoid the risk of explosion. Gas flow measurement in flares is still considered challenging because the measurement has to attend many specific demands, quite different from any other flow measurement application. For these types of measurements, many sensor technologies are available; however, they are all very expensive, and only a few ones can attend all demands. The objective of this article is to present a flow rate sensor based on fiber Bragg grating (FBG), cross correlation, and heatwave travel time techniques. The system was developed with inexpensive components and is little intrusive, capable of attaining the rangeability of the flare demand and independent of gas composition, pressure, and temperature. [ABSTRACT FROM AUTHOR]

The strain in a gasoline direct injector was measured during a single injection process by using a fiber Bragg grating sensor installed along the axis of the injector stem in different operating pressure conditions. A fast FBG interrogator, based on linear transmission filters and direct detection, permits to measure dynamic strain up to 240 MHz frequency with a detection limit of 1.1 μϵ and a dynamic strain resolution of 20.2 nϵ/√Hz. The FBG sensor was first calibrated for an internal pressure ranging from 50 to 250 bar and an energizing duration of 5ms; the FBG sensor allows to measure the static internal pressure of the injector inlet, which is linearly dependent on the FBG static strain, as well as the dynamic strain during the opening/spray/closing processes induced by pressure fluctuations, mechanical vibrations and the impact forces related to the injector needle bounces. The fast FBG interrogator, has been first validated by comparison with commercial interrogators, and then used to detect fast transients. The measured FBG strain variation provides important information on the dynamic behavior of the injector during the spray, confirmed by the analysis of the spray injection performed through a High Speed Video camera. The static and dynamic measurements demonstrate the effectiveness of the FBG sensors technology for monitoring the behavior of the injector and controlling the engine performance and emissions. [ABSTRACT FROM AUTHOR]

In this article, we present a fiber Bragg grating (FBG) based 6-D force/torque (F/T) sensor that can be mounted on robot joints for the detection of comprehensive F/T information. The sensor is designed based on a new concept of multilayer measurement in which the elastic structure is divided into four layers. A single optical fiber inscribed with 12 FBGs is symmetrically attached to the elastic structure to sense F/T-induced strains by means of differential measurements. Because of the mechanical decoupling function of the structure and the reasonable arrangement of the FBG sensing elements, the designed sensor possesses a great advantage of low cross coupling compared with the existing 6-D F/T sensors, which simplifies the calibration and maintenance of the sensor. Calibration experiments demonstrate high resolutions of 7.8 N·mm, 7.2 N·mm, 15.8 N·mm, 0.0067 N, 0.0066 N, and 0.0825 N within the range of ±1.56 N·m, ±1.56 N·m, ±1.56 N·m, ±10 N, ±10 N, and ±25 N for the detection of Mx, My, Mz, Fx, Fy, and Fz, respectively. Dynamic performances of the designed sensor have been evaluated in comparison with a commercial F/T sensor. [ABSTRACT FROM AUTHOR]

The current challenge in the field of thermo-ablative treatments of tumors is to achieve a balance between complete destruction of malignant cells and safeguarding of the surrounding healthy tissue. Blood perfusion plays a key role for thermal ablation success, especially in the case of highly vascularized organs like liver. This work aims at monitoring the temperature within perfused swine liver undergoing laser ablation (LA). Temperature was measured through seven arrays of Fiber Bragg Grating sensors (FBGs) around the laser applicator. To mimic reality, blood perfusion within the ex-vivo liver was simulated using artificial vessels. The influence of blood perfusion on LA was carried out by comparing the temperature profiles in two different spatial configurations of vessels and fibers. The proposed setup permitted to accurately measure the heat propagation in real-time with a temperature resolution of 0.1 °C and to observe a relevant tissue cooling near to the vessel up to 65%. [ABSTRACT FROM AUTHOR]

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]

A study on the design, framework, experimental arrangement, data acquisition, and subsequent analysis of cold crack detection using fiber Bragg grating (FBG) sensors during welding is presented. Cold crack induced acoustic emission (AE) events are detected by multiple FBG sensor configurations and using a commercial FBG AE interrogation system. The crack locations are theoretically predicted using a method of linear localization based on the differences in the time of arrival of the AE events at different FBG sensors. The approach is experimentally validated by employing packaged and unpackaged FBG sensor arrays in a welding experiment with gas tungsten arc welding on ultrahigh toughness high hardness armor steel. Frequency analysis of the AE events is also carried out to understand the cold crack characteristics. The weld region of the steel plate is diced into 1-mm cross-sectional pieces, and the positions of the cold cracks are identified using scanning electron microscope imaging and then cross correlated with the measured AE events, and thereby confirming the correct identification of cold crack location using the FBG sensing method. [ABSTRACT FROM AUTHOR]

Precise measurement of temperature is vital in a variety of industries and basic sciences. Numerous techniques have been proposed for temperature measurement, such as fiber Bragg gratings and Fabry–Perot interferometers. Despite several important accomplishments, such optical thermometers are still limited in their performances. Two major limitations are the low operational temperature and the paradox between a large dynamic range and a high resolution. Here, we propose a fiber-optic thermometer based on fiber-tip microspherical Fizeau interferometer made from high temperature-resistant material. The sensor is fabricated by inserting a section of single-mode fiber into a spherical microcavity to form a Fizeau interferometer. Thanks to the thermo-optic effect and thermal expansion effect, the variation of ambient temperature modifies the refractive index and the interferometric length of the microcavity, and then a corresponding change in the interferometric spectrum can be observed. The demodulation method is based on the combination measurement of interferometric fringe shift and free spectral range variation, which is capable of providing high resolution and wide dynamic range. Experimental results show that by using a simple wavelength tracking demodulation method, a sensitivity of 22 pm/°C with a high resolution and a dynamic range over 1000 °C can be achieved. Since the sensor is of small size, it exhibits fast response and recovery time which mean it can monitor ambient temperature variation in real time. Additionally, the structure is robust and compact which makes the technology an interesting alternative to conventional thermometers for temperature measurement. [ABSTRACT FROM AUTHOR]

This article addresses the analysis and design of a high-resolution and temperature-insensitive inclination sensor using fiber Bragg grating (FBG). The sensor uses a pendulum-based structure with FBG attached to its cantilever arm. Initially, strain analysis of the proposed inclination sensor is carried out using the finite-element method (FEM) to optimize the structure and materials for its fabrication. Experimental analysis is carried out on the inclination sensors by varying the inclination angle, and its results are compared with the FEM-based results. The shift in Bragg wavelength of FBG due to the generated strain at the cantilever arm is observed on optical interrogator. To measure the subpicometer wavelength shift with enhanced resolution and lower uncertainty, eigen decomposition of the reflection spectrum using Karhunen–Loève transform (KLT) is implemented. The range of measurement of tilt angle is found to be 0°–3° with a resolution of 0.0008°. The satisfactory linearity of the measured angle versus true angle, excellent repeatability, and very high resolution validates the feasibility of the proposed inclination sensor. [ABSTRACT FROM AUTHOR]

The operation of the Ytterbium (Yb)-doped silica fiber laser is investigated under high temperature gradients generated by various cryogenic materials. A continuous-wave (CW) double-clad single-mode fiber laser working at 1082.51 nm with a linewidth (FWHM) of 0.16 nm and an average power of 10 W was used to study the effect of cooling rate on its output characteristics such as signal power, efficiency, central wavelength and spectral bandwidth. The cooling process is performed along the gain fiber using a cryogenic bath, while the cryo-coolants don’t touch other laser components such as fiber Bragg gratings (FBGs), combiners and optical couplers. A series of rigorous experiments are carried out at room temperature - RT (22.5 °C) and cryo-states when the gain fiber is immersed in different coolants i.e., dry-ice ethylene-glycol - DIEG slurry (−29 °C), dry-ice debris (−58 °C) and liquid nitrogen - LN2 (−189.2 °C) with various pump powers ranging 2.9 – 16.5 W. The gain fiber of 10 m long demonstrates a 36 % power efficiency at LN2 against 66.4 % at RT. The signal power as well as the laser efficiency linearly reduces with temperature drop as to the linewidth undergoes a lucid spectral narrowing accompanying blue shift, mainly owing to the notable temperature response of the absorption / emission cross-section, broadening mechanisms and thermal population as well as energy level schemes, including sublevel and hyperfine structures of the transition accordingly. [ABSTRACT FROM AUTHOR]

In this article, we proposed a laser hot needle for liver tissue tract ablation. The proposed laser hot needle is powered by a 4500-nm-diode laser incorporated with a closed-loop control system that comprises of a uniform fiber Bragg grating (FBG) temperature sensor and a computer. Based on the real-time feedback input from the FBG temperature sensor, the laser power is regulated by a proportional–integral–derivative (PID) control system to control the needle temperature. In the characterization test, a chirped grating-based distributed temperature sensor is employed for measuring the tissue temperature profile in the ex vivo bovine liver tissue during the ablation. A histological test is conducted to study the impact of tract ablation to the cellular structures of treated tissue and tissue coagulation. In a tract ablation test, a ~50-mm × ~ 6-mm (length × width) thermal denaturation zone has been created on ex vivo bovine liver tissue with the laser hot needle at 150 °C. [ABSTRACT FROM AUTHOR]

Distributed sensing plays an important role in many industrial applications. Sensor arrays consisting of identical ultraweak fiber Bragg gratings can be applied to such scenarios by monitoring the optical spectral response of the sensors. Yet, the spatial resolution, the sampling speed, and the supported number of sensors in the array are mostly determined by the interrogation scheme. While dual-optical frequency comb techniques had been successfully demonstrated as a high-resolution spectroscopic technique in metrology, it had been beyond the reach of industrial sensing applications because of its high complexity and costs. It is proposed and demonstrated here that, enabled by a simple fiber-optic, dual-comb spectroscopy setup consisting of a fiber laser without frequency stabilization, interrogation of an ultraweak fiber sensor array can be realized. High spatial and spectral resolution as well as kilohertz interrogation speed is achieved in both static and dynamic measurements. It is expected that our depth-resolved dual-comb scheme can measure hundreds of sensors response in less than 1 ms. It is also flexible to deal with targets closely spaced or farther apart from each other. This shows the potential of applying dual-comb spectroscopy to more and more industrial application areas. [ABSTRACT FROM AUTHOR]

Micro-electric discharge machining (micro-EDM) is the most considerable micro-manufacturing process used to engineer miniaturized features on any high temperature resistive hard material. The machining parameters of micro-EDM are very stochastic in nature. The spark gap measure acts as a vital parameter that correlates with other process parameters for enhancement of the material removal rate (MRR) in micro-EDM. The real-time actual measurement of the spark gap between the electrodes is highly challenging and is limited due to the small gap measure. This article is about the development of a novel sensing technique for spark gap measurement, based on a fiber Bragg grating (FBG) sensor. The sensing system is developed on a cantilever structure bonded with the FBG sensor, for performing accurate spark gap measurements with the displacement measurement of the tool electrode. The deflection on the cantilever during spark gap generation is translated into strain variations, as monitored by the FBG bonded over it. Experimental trials are conducted on the micro-EDM setup with the cantilever beam-based displacement sensing with a sensitivity of $10~\mu \text{m}$ /pm. Real-time spark gap data obtained by FBG are in the range of 1.1–18.6 $\mu \text{m}$ and are validated against a precision measuring instrument. This sensing technology employed for micro-EDM spark gap measurement establishes a novel technique in the micro-machining field and formulates a smart system. [ABSTRACT FROM AUTHOR]

The radiation-resistance of different types of gratings, such as types I-UV, II-IR, and III, was investigated at −120 °C up to the accumulated dose of 100 kGy(SiO2). The grating temperature sensitivity was evaluated from room temperature down to −120 °C, before and after irradiation. We demonstrated no radiation effect on the temperature sensitivity at the accumulated dose of 100 kGy. This article is a preliminary one to explore the best candidate among the grating types for their integration in low-temperature applications and shows that the performances of both type II-IR and type III FBGs written in the F-doped fiber are not influenced by X-rays at −120 °C up to a dose of 100 kGy. [ABSTRACT FROM AUTHOR]

This article reports a miniature, high-resolution fiber Bragg grating (FBG)-based triaxial force sensor to detect the catheter tip–tissue interaction forces. This sensor counts on a delicate three-dimensional-printed flexure comprising a cylinder with an inner elliptical cavity for detecting lateral forces and a hybrid elastomer to enhance axial elasticity for improving z-directional force sensitivity. Four suspended optical fibers inscribed with FBG each are deployed inside the flexure. Such configurations are designed to maximize the decoupling among three force components, achieve temperature compensation, and raise the sensor's robustness under biofluid-filled environments. The sensor characterization results indicate a high resolution of 0.52 and 0.64 mN for both lateral forces within –0.8 to 0.8 N and 0.63 mN for axial direction force within 0–0.8 N. Validation with dynamic loadings along different azimuth angles shows that the sensor can provide a high-accuracy measurement of three force components with an rms error of less than 3.00%. Temperature-induced errors for force detection are considerably alleviated, showing less than 6.5% in the range of 25 °C–50 °C. Ex vivo experiments on a swine heart further validate the performances of the designed sensor. [ABSTRACT FROM AUTHOR]

The temperature distribution on the gas-insulated line (GIL) spacer affects surface charge accumulation. However, the spacer temperature distribution is hard to measure because the conventional electric sensors are large dimensions, hard to multiplex, and sensitive to electromagnetic interference (EMI). In this article, a distributed temperature measurement system of GIL spacer based on the optical frequency domain reflectometry (OFDR) was developed to solve the problems. In this system, ultraweak fiber Bragg grating (FBG) was adopted to replace single-mode fiber due to its higher signal-to-noise ratio. The demodulation method was described for compensating the nonlinear frequency tuning errors induced by the unstable tunable laser. In addition, the relationship between the spacer temperature and the wavelength shift was determined in the calibration experiment. Moreover, the temperature distribution on a 126-kV GIL spacer was measured by the proposed OFDR system. The data processing method for 3-D surface temperature on cone-type spacer was also introduced. High-resolution temperature distribution on the spacer surface was successfully obtained using OFDR system, which is unable to accomplish with the conventional electric temperature sensor. [ABSTRACT FROM AUTHOR]

This article demonstrates a photonic-based wideband true-time delay (TTD) beamforming network employing a raised cosine apodized linearly chirped fiber Bragg grating (FBG) of varying lengths, such as $50\,\,{\times \,\,10^{-3}}$ m, $45\,\,{\times \,\,10^{-3}}$ m, $40\,\,{\times \,\,10^{-3}}$ m, and $35\,\,{\times \,\, 10^{-3}}$ m, and different chirp parameters $25\,\,{\times \,\, 10^{-9}}$ m, $35\,\,{\times \,\, 10^{-9}}$ m, $6\,\,{\times \,\, 10^{-8}}$ m, and $8{\,\,\times \,\,10^{-8}}$ m. The proposed scheme can be used as variable TTD lines having a much lower ripple factor compared with the previously studied apodized linearly CFBG for controlling the radiation angle of phased-array antenna (PAA), i.e., the main lobe radiated by the PAA can be steered squint-free from 0° to ±36.8° suitable for continuous beam forming at microwave frequencies 8–12 GHz extended up to Ku-band. To the best of our knowledge, this is the first experimental demonstration that shows the impact of tuning wavelength on delay change due to raised cosine apodized CFBG in the RF signal fed to the respective element of the antenna array. Four sets of $1\times4$ PAAs have been fabricated with the required electrical parameters, such as reflection coefficient ($S_{11}$), voltage standing wave ratio, gain, far-field radiation pattern, and so on, to show the photonic feed idea. In addition, FBG’s having raised cosine apodization function is fabricated in our collaborative laboratory. [ABSTRACT FROM AUTHOR]

Based on the analysis and research of the existing intelligent bolt technology, this article proposes a smart bolt based on fiber Bragg grating sensing technology. The bolt design process was systematically introduced, and the physical model of the three-point fixed anti-tail fiber sloshing was given, as well as the corresponding simulation and experimental comparison. The ability to monitor the looseness of the smart bolts was also tested and installed as a smart unit in the fiber-optic smart grid system for monitoring and testing. The wire dancing simulation test machine was used to simulate various practical application conditions, and the effective monitoring performance of the intelligent bolt was verified. [ABSTRACT FROM AUTHOR]

This paper presents a disposable fiber Bragg grating (FBG) based tridirectional force/torque sensor mountable at the end of the tip of the aspiration instruments for detecting instrument–tissue interaction force/torque. The sensor utilizes an inexpensive three-dimensional (3-D) printed elastomer with an annular diaphragm, which is sensitive to axial force (Fz) and torques (Mx and My). Four suspended optical fibers inscribed with an FBG each have been fixed on two ends of the elastomer to simultaneously sense and decouple force/torque-induced diaphragm deformation. The associated sensing theoretical model and force-torque decoupling principle with temperature compensation have been derived. Calibration experiments demonstrate a high resolution of 8.8 mN within the range of 0–2 N for the axial force detection. Dynamic performances of the designed sensor have been evaluated in comparison with the commercial force sensor. The average relative errors of force/torque components are less than 4.4% of full-scale range. The maximum temperature drift-caused errors of the force/torque components within the range of 30 °C–45 °C are –0.1340 N, 0.0084 N·mm, and 0.0300 N·mm, respectively. In vivo experiments on a cadaver head have been performed to further validate the feasibility and effectiveness of the designed sensor for real-time monitoring of the interaction force. [ABSTRACT FROM AUTHOR]

Real-time cutting force measurement is significantly important to monitor tool condition and machining process. Although commercial dynamometers are available for a range of machining applications, there is a lack of multipoint and low-cost measuring methods suitable for detecting cutting forces in harsh machining environments. In this paper, a smart cutting tool integrated with optical fiber sensors is first presented for cutting force measurements in turning. Fiber Bragg grating (FBG) sensors are employed to acquire cutting force information on cutting tools. Compared with the electrical and piezoelectric sensors, the proposed smart cutting tool has unique advantages such as electromagnetic interference immunity, explosion proof, ability to measure multiple cutting forces in the same and simplified data acquisition device with along-distance signal transmission, and enabling it to work in harsh machining environments. In addition, the proposed smart tool brings little effect on the structure and characteristics of machine tools due to FBGs’ small size and light weight. This paper investigates the operating principle of the sensory cutting tool theoretically and validates it using finite-element simulations. A prototype of the proposed device was developed and tested. Static calibration, dynamic identification experiment, and comparative cutting tests were conducted to evaluate its performances. The experimental results have shown that the cutting forces acquired by the developed smart tool are in good agreements with the results obtained by the reference commercial dynamometer. The proposed smart cutting tool has the potential to provide a new solution to the real-time measurement and monitoring of multipoint cutting forces in turning processes. [ABSTRACT FROM AUTHOR]

An optical fiber anemometer based on the Pitot-static tube is reported. The device was fabricated in a 3-D printer, and the pressure difference was assessed by means of a latex rubber diaphragm with a mounted fiber Bragg grating probe, so the membrane deflection is obtained in terms of the fiber curvature. The sensor characteristics were first obtained by the simulation in order to determine the correlation between the Bragg wavelength shifts and the airflow speed. Next, the device was experimentally evaluated in a wind tunnel, allowing for the assessment of a 20–36-m/s dynamic range, with 24.9-pm/(m/s) maximum sensitivity and 0.04-m/s resolution. Finally, the system was tested on the measurement of cyclic airflow speeds for predicting the applied speed according to the calibration curve, yielding reproducible results with an average error of 0.98 m/s, which is comparable to other reported sensors based on more complex designs and interrogation setups. [ABSTRACT FROM AUTHOR]

Fiber optics is the elective technology for sensing temperatures in harsh environments. Among the possible exploitable working principles, fiber Bragg gratings (FBGs) are the most widespread implementation for their excellent balance between system complexity and performance. However, despite they are well known and established, so far, metrological investigations have been limited to cases in which the sensor is used in uniform temperature conditions. This paper analyzes the response of commercial FBGs employed as temperature sensors in applications that imply large temperature gradients, such as in laser-based thermal treatments of solid tumors. A theoretical model of the sensor is implemented first and then used to evaluate its response in nonuniform temperature distributions. The model results are experimentally validated by means of a liver phantom and comparisons between different grating configurations, such as single or multiplexed with different lengths, are made. [ABSTRACT FROM AUTHOR]

This article measures the strain response of quasi-isotropic strand at 77 K when subjected to uniaxial tensile loads by using extensometer sensor and simultaneously verifies the possibility of utilizing Fiber Bragg grating (FBG) sensor for the same measurements. Through matching the measured data from the two sensors, strain sensitivity of FBG sensor is calibrated and fitted to be 1.21 pm/μϵ. In elastic deformation region, the stress–strain curve of the strand captured by FBG sensor coincides well with that from the extensometer sensor, but the range it could reach is only 0.31% strain (ϵtens ∼0.31%) due to the limitation of the elongation. Through fitting the stress–strain curve obtained by the extensometer, elastic modulus 115.5 GPa and yield stress 471 MPa of the strand are, respectively, determined. Then, depending on the measured stress–strain results and the equation on critical current as a function of tensile strain, critical stress of the strand is estimated to be 464 MPa. Furthermore, a three-dimensional finite element method model of the strand established by Comsol software is employed to understand the testing results. [ABSTRACT FROM AUTHOR]

In this article, we present a novel stochastic algorithm called simultaneous sensor calibration and deformation estimation (SCADE) to address the problem of modeling deformation behavior of a generic continuum manipulator (CM) in free and obstructed environments. In SCADE, using a novel mathematical formulation, we introduce a priori model-independent filtering algorithm to fuse the continuous and inaccurate measurements of an embedded sensor (e.g., magnetic or piezoelectric sensors) with an intermittent but accurate data of an external imaging system (e.g., optical trackers or cameras). The main motivation of this article is the crucial need of obtaining an accurate shape/position estimation of a CM utilized in a surgical intervention. In these robotic procedures, the CM is typically equipped with an embedded sensing unit (ESU) while an external imaging modality (e.g., ultrasound or a fluoroscopy machine) is also available in the surgical site. The results of two different set of prior experiments in free and obstructed environments were used to evaluate the efficacy of SCADE algorithm. The experiments were performed with a CM specifically designed for orthopaedic interventions equipped with an inaccurate Fiber Bragg Grating (FBG) ESU and overhead camera. The results demonstrated the successful performance of the SCADE algorithm in simultaneous estimation of unknown deformation behavior of the utilized unmodeled CM together with realizing the time-varying drift of the poor-calibrated FBG sensing unit. Moreover, the results showed the phenomenal out-performance of the SCADE algorithm in estimation of the CM's tip position as compared to FBG-based position estimations. [ABSTRACT FROM AUTHOR]