Design of an FBG-Based Tension Sensor With High Sensitivity and Linearity for Cable-Driven Continuum Robots

Fiber Bragg gratings are widely used in electrical equipment monitoring, structural health monitoring, power system fault monitoring and other actual detection occasions due to the unique advantages of anti-electromagnetic interference, low fusion loss, high sensitivity, small size, and easy distributed measurement. Fiber grating has been widely used in actual detection occasions such as electrical equipment monitoring, structural health monitoring, and power system fault monitoring. The temperature measurement of the motor based on fiber grating sensing technology not only has strong anti-electromagnetic interference ability, but also can realize multi-point distributed temperature measurement. The research of fiber grating temperature measurement system for intelligent electrical equipment is of great significance. This article mainly studies the optical fiber grating temperature measurement system of intelligent electrical equipment. This paper designs the temperature measurement system architecture, including data acquisition layer, data monitoring layer and remote monitoring layer. Complete the system design from two aspects: hardware design and software design. In the hardware part, the functions of the temperature sensor module transmission system, signal demodulation system, PLC and host computer are analyzed. Use FTM3501 fiber temperature converter is used to realize the automatic electrical fiber grating. Experimental results show that the thermometer has alarm and display analysis functions. The measurement uncertainty is analyzed, and the uncertainty of the calibration result of the fiber Bragg grating temperature sensor is 0.0725 °C; the fault judgment time of the system in this paper does not exceed 4.73 s, while the fault judgment time of the control group is more than 4.73 s. Compared with the control group, it has a faster fault accuracy speed. The system has high measurement accuracy and good stability, can be applied to actual temperature measurement systems, and has certain practical value.

PDMS-based liquid-core optical fiber fluorescence pressure sensor

Abstract. Optical fiber is a material that can transport light signals, so resulting useful for data transmission and sensing applications. Fiber Bragg Gratings (FBG) are a specific type of optical sensors that can measure parameters like temperature, strain, and vibration. The PhD program focuses on developing a sensing and monitoring strategy for aerospace systems using FBG sensors networks. The study will include material selection, optical fiber manufacturing, sensors packaging and integration, calibration and interrogation techniques and smart logics development for acquiring and controlling phenomena affecting the equipment under test. Some experimental activities have already been conducted to analyse thermal and mechanical sensing and to define a reliable methodology for integrating sensors into various systems. During the tests, FBGs were found to have high accuracy and sensitivity for thermal variations, mechanical strain and short-term thermal transients. The crucial role of bounding technique was also enhanced. Additionally, more complex tests have been conducted for sensor more realistic systems, both for space and aeronautic environments. The results gained in this first period are positive and encouraging, suggesting further developments during PhD program.

Fiber Bragg grating (FBG) sensors are excellent transducers for ultrasonic signal detection in structural health monitoring (SHM) application. While the FBG sensors are typically bonded directly on the surface of a structure to collect signals, one of the major challenges arises from demodulating relevant information from the low amplitude signal. The authors have experimentally demonstrated that the ultrasonic wave detection sensitivity of FBG sensors can be increased by bonding optical fiber away from the FBG location. This configuration is referred to here as remote bonding. However the mechanism causing this phenomenon has not been explored. In this work, we simulate the previous experimental work through a transient analysis based on the finite element method, and the output FBG response is calculated through the transfer matrix method. We first model an optical fiber bonded on the surface of an aluminum plate with an adhesive. The consistent input signal is excited to the plate, which is detected by the directly and remotely-bonded FBGs. The effect of the presence of the adhesive around the FBG is investigated by analyzing strain and displacement along the length of the FBGs at the locations of direct and remote bonding cases, and the consequent output FBG responses. The result demonstrates that the sensitivity difference between the direct and remote bonding cases is originated from shear lag effect due to adhesive.

Underwater vehicles are capable of diving thousands of feet below the water's surface. At these depths, extreme pressures are exerted over every square inch of the hull. As with most current sophisticated structural designs, modern submarines are designed with the use of finite element methods (FEM). Despite the demonstrated accuracy of FEM, the safety of the vessel and crew can only be ensured through extensive structural testing prior to certification and deployment of the submarine for use. However, structural strain measurements under these high hydrostatic pressures are difficult to obtain because of the need for waterproofing, potentially long data transmission distances through water, and the large number of desired sensors. Systems Planning and Analysis, Inc. (SPA) recently planned, installed, and tested a fiber Bragg grating (FBG) strain sensor system with a total of 97 sensors to validate FEM predictions of a new submarine design undergoing American Bureau of Shipping (ABS) certification testing. Fiber optic triaxial, biaxial, and uniaxial gages were selected based on the FEM analysis. FBGs were placed on six optical fibers with two fibers (33 sensors) mounted internally to the hull and four fibers mounted externally. Testing was performed by lowering the submarine to the design depth and recording strain measurements. The optical sensor signals were transmitted directly to the surface and interrogated by top-side electro-optical instrumentation through over 2000 feet of armored fiber optic cable. The measured temperature-compensated strain values were compared to the FEM predicted strain values with a high degree of correlation. To the author's knowledge, this successful test represents the first time that FBG sensors have been used during the certification testing of a submarine design and to validate FEM analysis on a large-scale, marine structure

Nuclear ground state properties including mass, charge radii, spins and moments can be determined by applying atomic physics techniques such as Penning-trap based mass spectrometry and laser spectroscopy. The MATS and LaSpec setups at the low-energy beamline at FAIR will allow us to extend the knowledge of these properties further into the region far from stability. The mass and its inherent connection with the nuclear binding energy is a fundamental property of a nuclide, a unique “fingerprint”. Thus, precise mass values are important for a variety of applications, ranging from nuclear-structure studies like the investigation of shell closures and the onset of deformation, tests of nuclear mass models and mass formulas, to tests of the weak interaction and of the Standard Model. The required relative accuracy ranges from 10−5 to below 10−8 for radionuclides, which most often have half-lives well below 1 s. Substantial progress in Penning trap mass spectrometry has made this method a prime choice for precision measurements on rare isotopes. The technique has the potential to provide high accuracy and sensitivity even for very short-lived nuclides. Furthermore, ion traps can be used for precision decay studies and offer advantages over existing methods. With MATS (Precision Measurements of very short-lived nuclei using an A_dvanced Trapping System for highly-charged ions) at FAIR we aim to apply several techniques to very short-lived radionuclides: High-accuracy mass measurements, in-trap conversion electron and alpha spectroscopy, and trap-assisted spectroscopy. The experimental setup of MATS is a unique combination of an electron beam ion trap for charge breeding, ion traps for beam preparation, and a high-precision Penning trap system for mass measurements and decay studies. For the mass measurements, MATS offers both a high accuracy and a high sensitivity. A relative mass uncertainty of 10−9 can be reached by employing highly-charged ions and a non-destructive Fourier-Transform Ion-Cyclotron-Resonance (FT-ICR) detection technique on single stored ions. This accuracy limit is important for fundamental interaction tests, but also allows for the study of the fine structure of the nuclear mass surface with unprecedented accuracy, whenever required. The use of the FT-ICR technique provides true single ion sensitivity. This is essential to access isotopes that are produced with minimum rates which are very often the most interesting ones. Instead of pushing for highest accuracy, the high charge state of the ions can also be used to reduce the storage time of the ions, hence making measurements on even shorter-lived isotopes possible. Decay studies in ion traps will become possible with MATS. Novel spectroscopic tools for in-trap high-resolution conversion-electron and charged-particle spectroscopy from carrier-free sources will be developed, aiming e.g. at the measurements of quadrupole moments and E0 strengths. With the possibility of both high-accuracy mass measurements of the shortest-lived isotopes and decay studies, the high sensitivity and accuracy potential of MATS is ideally suited for the study of very exotic nuclides that will only be produced at the FAIR facility.Laser spectroscopy of radioactive isotopes and isomers is an efficient and model-independent approach for the determination of nuclear ground and isomeric state properties. Hyperfine structures and isotope shifts in electronic transitions exhibit readily accessible information on the nuclear spin, magnetic dipole and electric quadrupole moments as well as root-mean-square charge radii. The dependencies of the hyperfine splitting and isotope shift on the nuclear moments and mean square nuclear charge radii are well known and the theoretical framework for the extraction of nuclear parameters is well established. These extracted parameters provide fundamental information on the structure of nuclei at the limits of stability. Vital information on both bulk and valence nuclear properties are derived and an exceptional sensitivity to changes in nuclear deformation is achieved. Laser spectroscopy provides the only mechanism for such studies in exotic systems and uniquely facilitates these studies in a model-independent manner.The accuracy of laser-spectroscopic-determined nuclear properties is very high. Requirements concerning production rates are moderate; collinear spectroscopy has been performed with production rates as few as 100 ions per second and laser-desorption resonance ionization mass spectroscopy (combined with β-delayed neutron detection) has been achieved with rates of only a few atoms per second.This Technical Design Report describes a new Penning trap mass spectrometry setup as well as a number of complementary experimental devices for laser spectroscopy, which will provide a complete system with respect to the physics and isotopes that can be studied. Since MATS and LaSpec require high-quality low-energy beams, the two collaborations have a common beamline to stop the radioactive beam of in-flight produced isotopes and prepare them in a suitable way for transfer to the MATS and LaSpec setups, respectively.

Due to the advantages of small size, high sensitivity and strong anti-interference ability, optical fiber sensors are widely used in gas detection. Meanwhile, concentration and humidity detection based on optical fiber sensing are paramount technologies in the field of gas sensing. However, how to solve the issue of cross sensitivity of concentration and humidity of optical fiber gas sensors and realize synchronous detection of two parameters are current common challenges. In this study, taking carbon dioxide as an example, a detection method based on double fiber Bragg grating (FBG) string is proposed to measure carbon dioxide concentration and air humidity simultaneously. Here, a pair of FBGs are welded in series on an optical fiber after being filled with special materials. Using the control variable method, the performance parameters of the sensor can be determined through calculation. The experimental results demonstrate that the gas concentration sensitivity is 0.5952 pm/ppm in the range of 0 ppm~2250 ppm. In the range of 25%~65%, the air humidity sensitivity is 28.62 pm/RH. Moreover, it is less affected by temperature and has satisfactory repeatability and reproducibility. The sensor realizes high sensitivity and low crosstalk measurement of concentration and humidity and can be applied to the simultaneous detection of carbon dioxide concentration and air humidity in specific confined space.

Fiber Bragg grating (FBG) sensors are excellent transducers for collecting ultrasonic wave signals for structural health monitoring (SHM). Typically, FBG sensors are directly bonded to the surface of a structure to detect signals. Unfortunately, demodulating relevant information from the collected signal demands a high signal-to-noise ratio because the structural ultrasonic waves have low amplitudes. Our previous experimental work demonstrated that the optical fiber could be bonded at a distance away from the FBG location, referred to here as remote bonding. This remote bonding technique increased the output signal amplitude compared to the direct bonding case, however the mechanism causing the increase was not explored. In this work, we simulate the previous experimental work through transient analysis based on the finite element method, and the output FBG response is calculated through the transfer matrix method. The model is first constructed without an adhesive to assume an ideal bonding condition, investigating the difference in excitation signal coherence along the FBG length between the two bonding configurations. A second model is constructed with an adhesive to investigate the effect of the presence of the adhesive around the FBG. The results demonstrate that the amplitude increase is originated not from the excitation signal coherence, but from the shear lag effect which causes immature signal amplitude development in the direct bonding case compared to the remote bonding case. The results also indicate that depending on the adhesive properties the surface-bonded optical fiber manifests varying resonant frequency, therefore resulting in a peak amplitude response when the input excitation frequency is matched. This work provides beneficial reference for selecting adhesive and calibrating sensing system for maximum ultrasonic detection sensitivity using the FBG sensor.

Cable-driven continuum robots are widely used for endoluminal intervention because of their dexterity and shape conforming steerability. However, body contact between the continuum robot and its surrounding anatomy is unavoidable, which imposes a potential safety risk, including vessel wall damage or even perforation. This paper presents an approach for body contact estimation of continuum robots with tension-profile sensing of actuation fibers. First, tension-sensing optical fibers with multiple inscribed fiber Bragg grating (FBG) sensors are used for both actuation and in-situ sensing of the continuum robot. Second, a beam theory-based mechanical model considering segmental differences, multiple fiber interactions and external force interactions is established, followed by robust estimation of contact positions and forces. Finally, detailed simulations are conducted to validate the accuracy and effectiveness of the proposed method. Experiments on a notched continuum robot are carried out, and the results show that the proposed approach can effectively recover in-situ segmental actuation forces without the need of explicit modeling of the friction between the fibers and guiding channels. The method enables the estimation of the number of contact points, as well as contact positions and contact forces along the body of the continuum robot.

Optical fibres (OF) with inscribed arrays of fibre Bragg gratings (AFBG) are interesting for different types of fibre devices such as a fibre sensors and fibre lasers and optical signal management. The most advanced method of manufacturing such AFBG is to write them directly in-line during the fibre drawing process. This gives the possibility of making a huge number of fibre Bragg gratings (FBG) in a single OF. The parameters of these AFBG could be constant or variable along the OF length. We present results of an investigation AFBG produced during fibre drawing process. Typical parameters of such AFBG are: working wavelength into 1550 nm band, spectral width 0.2mm (3dB level), reflective contrast (excess to Rayleigh backscattering level) up to 45 dB. We use polymer or aluminum as AFBG coating. AFBG can be written either in single or multi core preforms. OF with fibre Bragg gratings A(FBG) arrays written over a long length and in-line metal coating have been made for the first time. The optical parameters of the FBG arrays are tested by the optical frequency domain reflectometer method in a wide temperature range, demonstrating no degradation in reflection at heating up to 600C for a fibre with Al coating. Moreover, array of metal coated FBG can not be erased thermally. The mechanical strength of the developed fibre is practically the same as for “ordinary” OF with similar coating, showing the absence of the influence of FBG writing process on fibre strength. Some possibilities of the developed AFBG use in advanced sensor systems with special resolution about 10 mm, Brillouin random fibre laser with linewidth less 40 kHz are considered.

The field of communications has been revolutionized by the advent of optical fiber. Optical fiber now connects most of the world carrying a vast amount of information through a very limited physical medium. To the materials engineer, optical fiber technology has stimulated interest in a new type of micro-sensor application, where the size, weight, and the ability to integrate the sensor into a material structure play a major role. Areas of interest currently include materials characterization, cure monitoring, and structural health monitoring. The fiber Bragg grating (FBG) is such a sensor technology, creating an optical strain gauge within the core of an optical fiber through the use of a wavelength specific filter. As the FBG experiences induced strain along its major axis, its light signal indicates the amount of strain with great accuracy and sensitivity. In FBG applications, where loading may occur in all directions, complex changes take place in the FBG signal. As these changes impact the usefulness of the FBG as a strain sensor, this thesis endeavors to study and demonstrate the effect of transverse load on the FBG structure. A review of the basics of optical fiber fabrication, light transmission, and optical fiber sensor technology is presented first, followed by a detailed discussion of the FBG's manufacturing and operation. The crux of the thesis is presented with the results of experiments conducted to characterize the FBG signal in both unloaded and transversely loaded configurations. Polarization and wavelength based experiments and analyses are conducted to detect changes in the FBG signal. The results of the study are used to propose cause and effect relationships between transverse loading, its effect on the material properties of the FBG, and changes in the FBG signal.

This work presents a fiber Bragg grating (FBG) wide-range tilt sensor based on a cam structure. Two FBGs are fixed on a specially-designed sensor shell. When one FBG is stretched by the rotating cam driven by tilt, the other FBG moves along a standard semicircle with a constant radius, and compensates for temperature variations of the stretched FBG. By detecting the difference of the central wavelength shifts of two FBGs, variations of the tilt angle can be measured. The detailed mechanical structure design and measurement theory of the sensor is presented, and the sensor prototype is discussed. Testing results of comprehensive performance show that there is a good linear relationship between the tilt angle and the central wavelength of the FBG over three intervals from -90° to 90°. The repeatability and creep resistance of the FBG tilt sensor are good, the measuring accuracy is 1.516°, and the measuring resolution is 0.003°. The measurement range is much larger than comparable existing sensors, and it avoids cross-sensitivity between temperature and strain for FBG. The sensitivity of the sensor can be easily adjusted by changing the outline of the cam, or the length of the optical fiber between two fixed points.

This study investigates the influence of lay-up and load direction on embedded optical fiber Bragg gratings (FBGs) used as strain sensors. FBGs have shown great promise for application to structural health monitoring with advantages of small size and cylindrical geometry readily allowing for embedment within fiber reinforced composites. Characterization of the embedded FBGs is necessary to develop a rugged and reliable strain sensor. This paper specifically explores the effects of loading direction on the FBG strain outputs. A well behaved baseline case is established with results for gratings loaded parallel to the optical fiber direction while embedded parallel to the adjacent structural fibers in a quasi-isotropic composite. Results and analysis are also presented for a case involving a composite fabricated with the optical and structural fibers parallel to each other but perpendicular to the loading direction. Extremely good results are obtained relating FBG strain measurements with that of surface mounted resistance strain gauges.

A certain value, a method to analyze bending sensing rules of long-period fiber grating (LPFG) according to bending curvature, grating length and grating period was reported, based on coupled-mode theory and perturbation approximation. The transmission spectra of the bended LPFG split when the bending curvature reaches a certain value. The two resonant wavelengths of the splitting peaks change conically with the bending curvature and inversely with grating period, but are independent on grating length. The LPFG written on the B-Ge co-doping single-mode fiber proves the above conclusion. The two resonant wavelengths of the splitting peaks change conically with the bending curvature consist of fiber grating strain sensor. It has following characteristic. Firstly, resonant wavelength transforms into the frequency shift through the electro-optical heterodyne, may cause the ordinary optics wave length survey to transform as the electricity frequency survey, improve the detection and resolution gain five or more orders of magnitude. Secondly, the two split resonant peak wavelength difference frequency is possible to obtain the higher examination sensitivity. Thirdly, use the differential motion structure to eliminate the environment disturbance. Fourthly, transmission peak sensor is suitable to consist of the small array sensor. After a resonant wavelength heterodyne photoelectric conversion for the frequency change, can make an ordinary optical wavelength into electricity to detect the frequency of detection, so that detection and resolution gain through more than five orders of magnitude. 2, the two split resonant peak wavelength difference frequency of changes in detection sensitivity can be higher. 3 Differential structure suitable for the elimination of environmental interference. 4 transmission peaks constitute a sensor suitable for small size of the sensor array. The above characteristic is suitable to constitute the new optical fiber array hydrophone. Many long period fiber grating through elastic carrier curving in appropriate fixed angle, after the seal, uses as the optical fiber hydrophone array. Array works not only in space division multiplexing way, but also work in the wavelength division multiplying and the multiplying active status. The different bending strain may cause the fiber grating bias at the different wave length, can use the optical fiber phase-shift diffraction grating separate the wave length. Detector's connection optical fiber length to different sensor is different, therefore the signal arrives at different time, is advantageous to the multiplying time sampling. The use of photoelectric heterodyne method of long-period gratings on the transmission spectrum of detection not only has high sensitivity but also eliminates polarization effects Two split peaks due to resonant wavelength changes with the bending curvature of the relationship was quadratic curve relationship, the use of photoelectric heterodyne detection frequency, the frequency range up to 1012Hz, the frequency resolution of 10Hz. By LPFG right, photovoltaic devices and microwave heterodyne frequency meter combination can solve the interferometric fiber-optic hydrophone polarization effects and the problem of inadequate resolution, consisting of long-period grating fiber-optic hydrophone size is very small, very convenient to install. In addition the use of long-period fiber grating (LPFG), can constitute an earthquake, bridge monitoring, fatigue testing of aircraft and other important sensor, with wide applications.

In order to realize the non-destructive and real-time dynamic stress monitoring method of the construction machinery surface in complex and harsh environments, a fiber Bragg grating (FBG) stress sensor packaging method based on magnetron sputtering technology is proposed. Two packaging methods of complete embedding (the capillary copper tube embedded in the entire grating area) and two sides embedding (capillary copper tube nested at both ends of the grating area) are studied. The sensitization effect of the sensor is analyzed from the perspective of theory and finite element, and the results are consistent. The physical sensors are made, and temperature, stress, and comparison experiments are carried out. Simulation and experiment show that the FBG sensor improves the sensitivity by about 7.5% under this model. The temperature experiment shows that the temperature feedback correlation coefficient R2 of the second package structure reaches 0.99948, which shows good linearity in the range of 30 ℃80 ℃; the stress experiment correlation coefficient R2 also reaches 0.99924, and the sensitivity is 6.14 pm/MPa. The accuracy of demodulation system reaches 0.05 MPa, it can demodulate stress quickly and accurately. Comparative experiments show that the monitoring system composed of grating demodulator has higher accuracy than the monitoring system composed of strain gauges, and maximum deviation value smaller 59.8%. The packaging structure of metallization method of embedded capillary copper tube combined with organic glue fixed is simple, high sensitivity, and precision, can meet the needs of large-scale construction machinery surface non-destructive real-time health monitoring.