Curvature Sensitivity Research Articles

Integrated fiber-optic sensor based on inscription of FBG in seven-core fiber for curvature and temperature measurements

An integrated fiber-optic sensor with cross-sensitivity elimination effect is proposed and experimented for simultaneous measurements of curvature and temperature. The sensor structure mainly consists of a section of seven-core fiber (SCF) that fiber Bragg gratings (FBGs) were inscribed in each fiber core by phase-mask technique. Since the FBG in the central-core of SCF is only sensitive to temperature, and others in six outer-cores have same temperature responses and different sensitivity for curvature, the sensor can simultaneously measure temperature and curvature through analyzing the wavelength shifts of central-core FBG and every-two cores of FBG. The experiment results show that the maximum curvature sensitivity reaches 0.39 nm/m−1 in the curvature range of 2.53 m−1–8.62 m−1, and temperature response sensitivity is 9.97 pm/°C, which is consistent with ordinary single-mode FBG in temperature range of 30 °C–70 °C. Furthermore, the verified experiment for simultaneous measurement are performed, the central-core FBG can be used as a temperature calibration during the curvature measurement. The relative errors of curvature and temperature are 2.22 % and 2.58 %, respectively. The SCF-based FBG sensor has the advantages of small dimension, easy fabrication, better repeatability, and potential application values in many fields such as machine structure motion monitoring.

Two-dimensional vector bending sensor based on a hole-assisted three-core fiber coupler.

We demonstrate a two-dimensional vector bending sensor based on a hole-assisted three-core fiber (HATCF) coupler. The sensor is built by splicing a section of HATCF between two single-mode fibers (SMFs). The resonance couplings between the center core and the two suspended cores of the HATCF occur at different wavelengths. Two completely discrete resonance dips are observed. The bending response of the proposed sensor is investigated over a 360° range. The bending curvature and direction can be identified by interrogating the wavelengths of the two resonance dips, and a maximum curvature sensitivity of -50.62 nm/m-1 is achieved at 0° direction. Moreover temperature sensitivity of the sensor is less than -34.9 pm/°C.

Optical Fiber Sensor for Curvature and Temperature Measurement Based on Anti-Resonant Effect Cascaded with Multimode Interference

In this paper, a novel inline optical fiber sensor for curvature and temperature measurement simultaneously has been proposed and demonstrated, which can measure two parameters with very little crosstalk. Two combinational mechanisms of anti-resonant reflecting optical waveguide and inline Mach-Zehnder interference structure are integrated into a 3 mm-long single hole twin suspended core fiber (SHTSCF). The 85 μm hole core gives periodic several dominant resonant wavelengths in the optical transmission spectrum, acting as the anti-resonant reflecting optical waveguide (ARROW). The modes in two suspended cores and the cladding form the comb pattern. Reliable sensor sensitivity can be obtained by effective experiments and demodulation. Through intensity demodulation of the selected dip of Gaussian fitting, the curvature sensitivity can be up to -7.23 dB/m-1. Through tracking the MZI dip for wavelength demodulation, the temperature sensitivity can be up to 28.8 pm/°C. The sensor is simple in structure, compact, and has good response, which can have a bright application in a complex environment.

A fiber sensor for different curvature measurement based on nano-erbium-ytterbium co-doped fiber cascade structure as both source and sensor

A fiber sensing system based on Nano-Erbium-Ytterbium co-doped fiber (Nano-EYDF) is proposed and demonstrated, where it works as both source and sensor. Especially, a fiber curvature sensor based on Mach-Zehnder interferometer is fabricated in a Nano-EYDF, which is a cascaded structure composed of single-mode fiber (SMF), Nano-EYDF and SMF. Based on the principle of evanescent wave coupling, the light transmitted in the SMF core can be coupled into the Nano-EYDF cladding. Therefore, the Nano-EYDF core mode and cladding mode that satisfy the phase matching conditions can couple evanescent waves to form a double-beam interference. When the external environment changes, the interference spectrum will change, so the curvature sensing can be realized by observing the wavelength shift. The experimental results show when the length of the Nano-EYDF is 20 mm and 25 mm, the transmission spectrum of the sensor appears blue shift in the downforce curvature range of 0–1.76 m−1, and the curvature sensitivity is −9.763 nm/m−1 and −12.787 nm/m−1 respectively. In the propulsion curvature range of 0–0.94 m−1, the transmission spectrum exhibits blue shift, and the curvature sensitivity can be up to −9.261 nm/m−1 and −9.411 nm/m−1, respectively. The sensor is easily fabricated and has high sensitivity, and demonstrates good application prospects in curvature measurement fields such as 3D shape reconstruction and geological monitoring.

Surface Curvature Sensor Based on Intracavity Sensing of Fiber Ring Laser

The measurement of surface curvature is of great significance in aerospace, structural health monitoring, energy batteries, etc. In this paper, a fiber-optic surface curvature sensor, based on intracavity sensing of fiber ring laser (FRL), is experimentally demonstrated. A no-core fiber- based filter performs as the sensing head of the FRL sensor. The response between the curvature of the NCF and the output wavelength of the FRL was investigated. In the measurement of curvature, the sensor system showed a narrow 3-dB bandwidth of 0.08 nm, with a high signal-to-noise ratio of about 60 dB. The curvature sensitivities were measured as −0.348 nm/m−1 within 0.2 m−1, and −3.185 nm/m−1 from 0.2 m−1 to 0.475 m−1. The performance of the surface curvature sensor was characterized by parameters, including output stability, temperature cross-sensitivity, and detection limit.

Highly sensitive curvature sensor based on a sandwich multimode fiber Mach-Zehnder interferometer.

A highly sensitive optical fiber Mach-Zehnder interference curvature sensor based on MMF-GIMMF-MMF, which was made by sandwiching the graded-index multimode fiber (GIMMF) between two pieces of very short stepped-index multimode fibers (SIMMFs) spliced with input-single-mode fiber (SMF) and output-SMF, respectively, was proposed. The core diameter of the SIMMFs and GIMMF was 105 µm and 50 µm, respectively, and cladding diameter of them were both 125 µm. The sensing principle of the MMF-GIMMF- MMF sensors and the influences of structure parameters on the interference spectrum characteristics were theoretically analyzed in detail. Experimental results showed that when the length of the GIMMF was short enough (usually ≤ 10 mm), interference spectrum was induced by the interaction between the core modes and the low-order cladding modes due to the special structure of the designed Mach-Zehnder interferometer. Intensity of the interference valleys was highly sensitive to the applied bending but nearly independent of the surrounding temperature, on the contrary, the dip wavelength showed negligible sensitivity to the applied bending but relatively high temperature sensitivity. Thus, a temperature- independent curvature sensor could be realized by tracing the intensity variation of interference valley. In addition, different interference valley exhibited different intensity-based curvature sensitivity, providing more options for curvature sensing applications. Especially, total length of the sensor could be as short as 3 mm with length of GIMMF and SIMMFs only 1mm, the maximum curvature sensitivity could reach up to -78.75 dB/m-1 in the small curvature range of 0-2.36 m-1. Owing to its compact size, easy fabrication, good reproducibility and low cost, the proposed sensor is promising for bending-related high-precision engineering applications.

Femtosecond laser-inscribed off-axis high-order mode long-period grating for independent sensing of curvature and temperature.

We propose and demonstrate a novel curvature and temperature sensor based on an off-axis small-period long-period fiber grating (SP-LPG) which is inscribed in a single mode fiber by a femtosecond laser in one step. The total length of the SP-LPG is only 2.1 mm. The period of the SP-LPG is 30 µm, which is smaller than that of conventional long period fiber gratings. Essentially, the SP-LPG is a high-order mode long period fiber grating. Due to the off-axis structure, the SP-LPG can be used for two-dimensional vector bending sensing. The curvature can be demodulated by the intensity variation of the dips in the transmission spectrum. When the incident light is polarized, the instantaneous curvature sensitivity of the SP-LPG can exceed 20 dB/m-1. Meanwhile, a series of Bragg resonant peaks can be observed in the reflection spectrum, which can be used to monitor the fluctuation of temperature. The transmission dip is insensitive to temperature and the reflection peak is insensitive to curvature, which allows the SP-LPG to measure curvature and temperature independently. The characteristics of high curvature sensitivity, two-dimensional bending direction identification, real-time temperature measurement, and compact structure make the device expected to be applied in the field of structural health monitoring and intelligent robotics.

Highly Sensitive Bending Sensor Based on Multicore Optical Fiber With Diagonal Cores Reflector at the Fiber Tip

A high-sensitivity bending sensor based on multi-core fiber Bragg gratings (MCFBGs) is presented and demonstrated. The bending sensor is based on FBGs fabricated on the symmetric distribution cores of seven-core fiber (SCF), where a 45-degree reflective cone frustum (RCF) is fabricated at the fiber end. The optical paths of two symmetric cores are connected by the 45-degree RCF. The wavelength drifts of the two FBGs on the symmetric cores caused by bending were similar in magnitude and opposite in direction, while the wavelength drifts of the two FBGs caused by temperature were similar in magnitude and direction. Therefore, the influence of temperature change on the curvature measurement can be automatically eliminated, and the bending sensitivity can be doubled by calculating the difference between the reflected wavelengths of the two FBGs. The sensor's spectral responses to the curvature at different bending directions are experimentally investigated. The maximum curvature sensitivity of the sensor is 225.9 pm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , within the curvature range from 0 to 6.9 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> .

Fiber cladding SPR sensor based on V-groove structure

The difficulty with fiber cladding Surface Plasmon Resonance (SPR) sensors lies in coupling the core mode to the cladding mode without removing the cladding. This paper hereby endeavors to demonstrate a fiber cladding SPR sensor based on V-grooves structure by using a CO2 laser. V-grooves are engraved on single-mode fiber, step-index multimode fiber, and graded-index multimode fiber. When the transmitted light reaches the V-grooves structure, the higher-order cladding mode is excited, and a metal film is coated on the 2 cm cladding area after the V-grooves to form fiber cladding SPR sensors. This paper investigates the refractive index and bending sensing of V-groove cladding SPR sensors of single-mode, graded-index multimode, and step-index multimode fibers. The experimental results show that: the refractive index sensitivity of three kinds of sensors is 2811.34 nm/RIU, 1862.33 nm/RIU, and 1418.85 nm/RIU, respectively, and the curvature sensitivity of three types of sensors is 0.42 nm/m−1, 1.03 nm/m−1, and −6.59 nm/m−1, respectively. The proposed sensors in this paper are easy to manufacture, demonstrate quality of high sensitivity, and can be applied extensively.

High sensitivity curvature sensor based on a double-sphere tapered no-core fiber Mach–Zehnder interferometer

A micro-fiber Mach–Zehnder interferometer (MMZI) based on a double-sphere tapered no-core fiber (DST-NCF) for curvature sensing is proposed and experimentally demonstrated. The sensor is composed of the DST-NCF sandwiched to two single-mode fibers (SMF). The DST-NCF is tapered from a double-sphere structure which is fused by no-core fiber (NCF). When light passes through the DST-NCF from SMF, higher-order modes will be excited, which will improve the sensing performance of the MMZI. This proposed structure achieves a significant improvement in curvature sensitivity for the first time by combining the characteristics of NCF, spherical format, and MMZI. When the central waist region is 2.07 mm, the maximum curvature sensitivity of the sensor is −224.64 nm/m−1, which is the highest curvature sensitivity in the MZI structure based on the spherical structure or the NCF as we have known. In addition, the maximum temperature sensitivity is −5.79 pm/℃ in the range of 40 ℃ − 90 ℃. It shows that this sensor has the characteristics of being insensitive to temperature and avoids the cross-sensitivity effect between temperature and curvature.

Research on Vector Bending SPR Sensor Based on V-Groove Fiber

Bending curvature measurement and bending direction identification are very important in the field of mechanical engineering. This study aimed to realize the high sensitivity direction recognition and curvature sensing based on SPR mechanism by a V-groove fiber SPR vector bending sensor. By CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser, multiple evenly spaced V-grooves were fabricated on the step multimode fiber. The V-groove fiber coupled the core mode to the cladding mode. By rotatably coating 50nm gold film on the cladding behind the V-groove area, and splicing with a multimode fiber with larger diameter to receive the light with SPR signal, the fiber SPR sensor was realized. When the sensing probe was concave inward, the V-groove was squeezed, the angle became smaller, and the excited cladding mode changed with it, resulting in the increase of SPR incident angle, the resonance valley blue shifted, and the sensitivity of curvature sensing wavelength is −5.98nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . Similarly, when the sensing probe was convex outward, the angle became larger, resulting in the decrease of SPR incident angle, the resonance valley red shifted, and the sensitivity of curvature sensing wavelength is 1.42nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The proposed V-groove fiber SPR sensor realized the bending curvature measurement and bending direction identification. The manufacturing method is simple and the sensitivity is high, which opens up a new way for application of the SPR technology in bending measurement.

Finite Element Modeling Approaches, Experimentally Assessed, for the Simulation of Guided Wave Propagation in Composites

Today, structural health monitoring (SHM) systems based on guided wave (GW) propagation represent an effective methodology for understating the structural integrity of primary and secondary structures, also made of composite materials. However, the sensitivity to damage detection promoted by these systems can be altered by such factors as the geometry of the monitored parts, as well as the environmental and operational conditions (EOCs). Experimental investigations are fundamental but require a long time period and are costly, especially for tests in real-life scenarios. Experimentally validated simulations can help designers to improve SHM effectiveness due to the possibility of further broadening study on the different geometries, load cases, and material types with less effort. From this point of view, this paper presents two finite element (FE) modeling approaches for the simulation of GW propagation in composite panels. The case study consists of a flat and a curved composite panel. The two approaches herein investigated are based on implicit and explicit finite element analysis (FEA) formulations. The comparison of the predicted measures against the experimental dataset allowed the assessment of the levels of accuracy provided by both modeling approaches with respect to the dispersion curves. Furthermore, to assess the different curvature sensitivities of the proposed numerical and experimental approaches, the extracted dispersion curves for both flat and curved panels were compared.

Membrane curvature regulates the spatial distribution of bulky glycoproteins

The glycocalyx is a shell of heavily glycosylated proteins and lipids distributed on the cell surface of nearly all cell types. Recently, it has been found that bulky transmembrane glycoproteins such as MUC1 can modulate membrane shape by inducing membrane protrusions. In this work, we examine the reciprocal relationship of how membrane shape affects MUC1’s spatial distribution on the cell membrane and its biological significance. By employing nanopatterned surfaces and membrane-sculpting proteins to manipulate membrane curvature, we show that MUC1 avoids positively-curved membranes (membrane invaginations) and accumulates on negatively-curved membranes (membrane protrusions). MUC1’s curvature sensitivity is dependent on the length and the extent of glycosylation of its ectodomain, with large and highly glycosylated forms preferentially staying out of positive curvature. Interestingly, MUC1’s avoidance of positive membrane curvature enables it to escape from endocytosis and being removed from the cell membrane. These findings also suggest that the truncation of MUC1’s ectodomain, often observed in breast and ovarian cancers, may enhance its endocytosis and potentiate its intracellular accumulation and signaling.

Forces of Change: Optical Tweezers in Membrane Remodeling Studies.

Optical tweezers allow precise measurement of forces and distances with piconewton and nanometer precision, and have thus been instrumental in elucidating the mechanistic details of various biological processes. Some examples include the characterization of motor protein activity, studies of protein-DNA interactions, and characterizing protein folding trajectories. The use of optical tweezers (OT) to study membranes is, however, much less abundant. Here, we review biophysical studies of membranes that utilize optical tweezers, with emphasis on various assays that have been developed and their benefits and limitations. First, we discuss assays that employ membrane-coated beads, and overview protein-membrane interactions studies based on manipulation of such beads. We further overview a body of studies that make use of a very powerful experimental tool, the combination of OT, micropipette aspiration, and fluorescence microscopy, that allow detailed studies of membrane curvature generation and sensitivity. Finally, we describe studies focused on membrane fusion and fission. We then summarize the overall progress in the field and outline future directions.

The curvature sensor based on fiber-optic spindle arrays

Three curvature optical fiber sensors inserted with different spindle arrays have been proposed and experimentally demonstrated. The spindle structure is fabricated by a fusion splicer after that prestress was applied to a complete single-mode-fiber (SMF) with coating peeled off, where cladding modes are excited and couple with the core mode. The experimental results show that the curvature sensitivities of these sensors are respectively 24.08 dB/m−1, 28.79 dB/m−1 and −38.40 dB/m−1. With inserted spindles in the array increasing in the same length, the curvature sensitivity is improved by 14.32 dB/m−1. In addition to the advantages of low cost and easy fabrication, the sensors have great value in improving curvature sensitivity.

Curvature sensor based on femtosecond laser-inscribed straight waveguide in FMF

We propose an ingenious method for higher-order mode excitation in few-mode fiber (FMF), in which a femtosecond laser is utilized to inscribe a straight waveguide in FMF. Based on this method, a new-type in-fiber Mach-Zehnder interferometer (MZI) for bending sensing is proposed. The in-fiber MZI is achieved through femtosecond laser directly writing a straight waveguide in a very short section of FMF between two standard single mode fibers. The MZI is caused by the interference between the fundamental mode and the higher-order mode excited in the modified FMF. When the device is bent in specific four orthogonal orientations, the direction of its spectrum shift is different. The device has a large curvature measurement range of 0–10 m−1. The curvature sensitivity can reach 2 nm/m−1 and the temperature sensitivity is as low as 2.34 pm/°C. Moreover, the device has the superiorities of miniature size, simple manufacturing, high reproducibility, low insertion loss and high spectral contrast.

Self-Assembled Highly Sensitive Hybrid Structure Sensor for Vector Curvature and Temperature Measurement

A highly sensitive hybrid structure sensor based on suspended-core fiber (SCF) is proposed for vector curvature and temperature measurement. The sensor is prepared by self-assembly of SCF-based cascaded Fabry-Perot interferometer (cFPI), single-mode fiber (SMF), and fiber Bragg grating (FBG). In view of the asymmetry of the cFPI, theoretical analysis of the beam transmission and spectral characteristics is implemented when the beam is incident from different directions. The two sensing fibers in the triangular distribution sensor will not be located on the neutral plane at the same time, which makes it possible to measure bending in any orientation. The Vernier effect formed by the cFPI enlarges the curvature and temperature sensitivity to −1064.5 pm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and 50.7 pm/°C, respectively, without affecting the measurement range. The spectrum shows the opposite spectral response when the sensor bending direction difference is 180°. The sensor overcomes the bottleneck of bending sensitive blind spots in dual-fiber sensing. In addition, the sensor maintains a smaller size and more flexible preparation, which is conducive to its application in artificial intelligence, medical detection.

A multi-stage ensemble network system to diagnose adolescent idiopathic scoliosis

To develop a deep learning algorithm to automatically evaluate and diagnose scoliosis on full spinal X-ray images. This retrospective study collected full spinal X-ray images (anteroposterior) from four hospital databases from January 1, 2018, to March 31, 2021. The data were divided into training and validation sets. Full spinal X-ray images for external validation were independently collected at one hospital from April 1, 2021, to June 30, 2021. Model effectiveness was validated with a public dataset. Statistical software R was used to analyze the accuracy and sensitivity of the model curvature and anatomical balance parameters and assess interrater consistency. This study included 788 and 185 training and test datasets, respectively. The accuracy and recall of the algorithm model for the Cobb angle, apical vertebrae (AV), upper vertebrae, and lower vertebrae were 89.36%, 85.71%, 77.2%, and 80.24% and 97.35%, 93.38%, 84.11%, and 87.42%, respectively. The symmetric mean absolute percentage error at the Cobb angle was 5.99%, and the automatic measurement time was 1.7 s. The mean absolute error values of the Cobb angle and the distances between the center sacral vertical line and AV and C7 plumb line were 1.07° and 1.12 and 1.38 mm, respectively. Statistical analysis confirmed that the Cobb angle results were in good agreement with the gold standard (interclass coefficients of 0.996, 0.978, and 0.825; p < 0.001). Our deep learning algorithm model had high sensitivity and accuracy for scoliosis, which could help radiologists improve their diagnostic efficiency. •Our deep learning algorithm model had high sensitivity and accuracy for scoliosis, which could help radiologistsimprove their diagnostic efficiency. • Multi-center validation data were used in this study to guarantee the reliability of the research. • Algorithmic model measures 200 times faster than radiologists.

Ring core few-mode fiber sensor for curvature measurement.

An all-fiber Mach-Zehnder interferometer (MZI) using ring core few-mode fiber (RC-FMF) for curvature sensing is proposed and experimentally demonstrated. The MZI was fabricated by splicing a segment of RC-FMF between two pieces of single-mode fiber (SMF). With the benefit of a RC of the central axis of the RC-FMF, the sensor is more sensitive to curvature compared to other fiber sensors based on ordinary SMF or FMF. Curvature measurement can be achieved by monitoring the wavelength shift of interference dips. Experimental results have shown that the sensitivity of curvature sensing can reach up to -4.370nm/m-1, within the range of 1.199-1.549m-1. Also, the temperature sensing characteristics of the sensor are measured, and the maximum temperature sensitivity is 57.6 pm/°C, ranging from 25°C to 45°C. The proposed MZI sensor has excellent potential for curvature measurement of building structural health monitoring, bridge engineering, and more.

High Sensitivity Temperature and Curvature Sensor Based on Mach-Zehnder Interferometer With Tapered Two Peanut-Shaped Structures

A high-sensitivity temperature and curvature microfiber Mach-Zehnder interferometer (MMZI) with two peanut-shaped structures is proposed and demonstrated for the first time. The interferometer consists of a section of microfiber and two peanut-shaped structures. The microfiber can be easily affected by the external environment due to its strong evanescent field on the surface and the peanut-shaped structure is conducive to excite fundamental mode to high-order mode, which is beneficial to realize high-sensitivity sensing detection. The experimental results show that the maximum temperature sensitivity of &#x2212;678.67 pm<inline-formula> <tex-math notation="LaTeX">$/$ </tex-math></inline-formula>&#x00B0;C is obtained in the range of 30 &#x00B0;C to 42 &#x00B0;C, which is the highest temperature sensitivity we have known in the peanut-shaped structure sensor. Furthermore, the sensor is also used for curvature measurements. The curvature sensitivity can be up to &#x2212;79.09 nm<inline-formula> <tex-math notation="LaTeX">$/\text{m}$ </tex-math></inline-formula>^&#x2212;1 from 0.10188 m^&#x2212;1 to 0.20374 m^&#x2212;1. Therefore, the proposed sensor will have good application prospects in the field of biological detection and environment monitoring due to the advantage of high temperature sensitivity.