Torsion Sensor Research Articles

Cross-Sensitivity-Free Highly Sensitive Torsion and Strain Sensor Based on Concatenated DTP-Customizable Helical Fiber Gratings

Cross-Sensitivity-Free Highly Sensitive Torsion and Strain Sensor Based on Concatenated DTP-Customizable Helical Fiber Gratings

High Sensitivity Interference Torsion Sensor Based on Dumbbell Fiber

High Sensitivity Interference Torsion Sensor Based on Dumbbell Fiber

A Fiber-Based Torsion Sensor With Tunable Sensitivity

A Fiber-Based Torsion Sensor With Tunable Sensitivity

Ultra-low bending and temperature crosstalk directional torsion sensor by few-mode fiber based Mach-Zehnder interferometer

In this paper, a few-mode-fiber based in-line Mach-Zehnder interferometer is proposed and completed for directional torsion sensing by core-offset splicing technique. The optimal offset and fiber length for fabrication are gained and the comprehensive tests are conducted in terms of torsion, bending and temperature. The experimental results show that our sensor has obvious intensity variation with the applied shear strain. The torsion sensitivity reaches ∼1.1 dB/(rad/m) in the range from −13.08 rad/m to 13.08 rad/m, but with the wavelength shift of 0.102 nm/(rad/m). In addition, thanks for the tiny bending and temperature responses of −0.055 dB/m−1 and 0.014 dB/℃, the ultra-low cross-sensitivities of 4.7 × 10−2 (rad/m)/m−1 and 1.2 × 10−2 (rad/m)/℃ are gained simultaneously, which dramatically improves the practicality of fiber-optic torsion sensor.

Highly sensitive torsion sensor based on a coupled optoelectronic oscillator incorporating nonlinear polarization rotation.

We propose and demonstrate a new, to the best of our knowledge, technique to implement a high-speed and highly sensitive torsion sensor based on a coupled optoelectronic oscillator (COEO) incorporating nonlinear polarization rotation (NPR). The COEO consists of a mode-locked laser loop and an OEO loop. In the laser loop, the NPR effect effectively induces intensity- and wavelength-dependent loss, which acts as a Lyot birefringent fiber filter. When twisting the polarization-maintaining fiber (PMF), the transmission of the filter varies as well as the laser output wavelength. In the OEO loop, the optical source is provided by the output signal of the mode-locked laser. The variation in the optical carrier wavelength changes the time delay and the oscillation frequency of the OEO loop. The oscillation frequency shift is a linear function of the twist angle. Sensitivities of -60.006 Hz/deg over 360° for a 48 cm PMF and -180.996 Hz/deg over 92° for a 22 cm PMF are achieved.

Fiber specklegram torsion sensor based on residual network

A novel fiber specklegram torsion sensor based on multimode fiber (MMF) is proposed and experimentally demonstrated in this paper. The Residual Network (ResNet) is used to establish the relationship between the changing process of the specklegram and the torsion angle of the MMF. The experimental results indicate that the sensor exhibits the advantages of high accuracy and large measurement range. Within a torsion angle range of 0–360°, the prediction error is within ±2° for 99.1% of the specklegrams in test set. By analyzing the decorrelation process of the specklegrams from different kinds of MMFs, we find that the difference in torsion angle prediction accuracy of different MMFs stems from the decorrelation angle of the specklegram, and the larger decorrelation angle of specklegram holds higher torsion angle sensing accuracy of the trained ResNet. Meanwhile, the difference of the decorrelation angle of specklegram is attributed to the difference of the fiber normalized frequency. This analytical process may be applicable to the analysis of other specklegram based sensing schemes and the selection of dataset for fiber specklegram sensor. The possibility of transfer learning is also investigated to show an improved portability and reusability. In addition, the fiber specklegram torsion sensor owns other merits such as easy fabrication and good robustness, which shows its wide range of potential applications.

High sensitivity vector torsion sensor based on a single Stress-Applying fiber Sagnac interferometer

A vector torsion sensor based on a Single Stress-Applying Fiber (SSAF) Sagnac interferometer is proposed and experimentally demonstrated. Taking use of the high birefringence and structural asymmetry of the SSAF, the spectrum of SSAF based Sagnac interferometer shows both wavelength shift and intensity variation with the change of torsion angle. A torsion sensitivity as high as 53.3 nm/(rad/m) can be achieved by wavelength demodulation and 4.3 dB/(rad/m) by intensity demodulation. In addition, the torsion direction can be also recognized in the torsion angle range from −50° to 50°. The temperature cross sensitivity is 0.03 rad/m/℃ by wavelength demodulation in the temperature range from 20℃ to 38℃. The advantages of high sensitivity, direction recognition, multi-parameter demodulation and simple structure make the sensor great potential in civil engineering, surgical robot and other applications.

Power-Interrogated Torsion and Strain Sensor Based on a Helical Long-Period Fiber Grating Written in a Thinned Four-Mode Fiber

A helical long-period fiber grating (HLPG)-based temperature-insensitive torsion and strain sensor is proposed and experimentally demonstrated, which was realized by using a second-order HLPG written in a thinned four-mode fiber. Simultaneous measurement of the torsion and strain was accomplished by using the power-interrogated scheme, i.e., the torsion- and strain-induced changes in transmission spectrum of two linear regions were especially used as the testing objectives. The maximum torsion sensitivity is 665 pm/(rad/m) under the torsion ranging from -22.4 to 22.4 rad/m and the maximum strain sensitivity is -5.42 pm/με under the strain ranging from 0 to 1588 με, which are about 2-fold and 10-fold higher than those of the conventional long-period fiber grating (LPG)-based fiber sensors, respectively. In addition, the temperature sensitivity of the proposed sensor is ~13.7 pm/°C at a temperature ranging from 20 to 70 °C, which is almost 4-fold lower than that of conventional LPGs.

Torsion and bending loads on a ski-touring boot shell during uphill and downhill skiing

Ski touring is an established winter activity that has experienced a recent increase in popularity. Differently to alpine skiing, skier gains altitude without lifts, thus equipment weight must be minimized. Nevertheless, structural properties of the equipment, such as ski boots, must be adequate to withstand skiing loads. Several studies provided data on flexural stiffness of alpine ski boots in bench and field tests. The present study focused on the torsional properties of ski-touring boots. Indeed, touring bindings design implies a higher torque transmission to the front piece which induces a torsional load throughout the shell. To conduct the study, we prepared a ski-touring boot with strain gage bridges, and we performed bench tests to determine the stiffness of the boot and the bridge sensitivity. We also positioned and calibrated strain gage bridges to measure bending load in the shell and axial load in the ski/walk lever placed between shell and cuff of the boot. Then, we conducted a field test measuring the loads during a ski-touring trip including ascent and descent. Bench tests evidenced linearity of the torsion sensor, and a variation of stiffness depending on dummy leg absence/presence and boot buckle setting. Field tests showed torque ranges of 17 Nm in climbing and of 27 Nm in skiing. Bending moment range on the boot shell was of 150 and 228 Nm, respectively. Maximum force on the ski/walk mechanism reached 570 N. Results could be useful to test ski-touring boot performances and to optimize their design.

Microfiber optomechanical torsion sensor

In this paper, we propose and demonstrate experimentally an optomechanical torsion sensor using a microfiber mechanical resonator. The torsion angle could be obtained by monitoring the resonant frequency shifts of the microfiber resonator. Theoretical and experimental results show that the shift of resonant frequency is non-linear to the torsion angle, and the fundamental mode is more sensitive than other higher modes. The highest sensitivity of the sensor tested in our experiments is 1,687 Hz/degree, and the corresponding resolution of torsion angle is up to 0.0006°, which is 2 orders of magnitude higher than that of the reported fiber-optic torsion sensors. The proposed sensor is a promising candidate for the practical engineering applications.

Temperature insensitive torsion sensor based on ring-core fiber orthogonal core-offset structure

We have proposed a temperature-insensitive fiber-optic torsion sensor based on ring-core fiber (RCF). The sensor is fabricated by orthogonal core-offset splicing between the RCF and single-mode fiber. Due to the core-offset structure, the Mach-Zehnder interference is enhanced, and the torsion sensing is realized. The sensor is fabricated and tested, exhibit high linear torsion sensitivity of −0.2 nm/(rad/m) in the range of 0–28.5599 rad/m and −0.079 nm/(rad/m) in the range of −25.3866–0 rad/m. The torsion increasing and decreasing process proves the good reliability of our sensor. Besides, through the temperature sensing, it is found that our sensors show a low temperature sensitivity of 26.4 pm/°C in the temperature range from 30 °C to 90 °C, which reduces the cross-sensitivity between torsion and temperature. Thus, the sensor can be used in structural conventional health monitoring, biomechanics due to many advantages such as sample size, low-cost and high sensitivity.

Directional Torsion Sensor Based on a Two-Core Fiber with a Helical Structure

A fiber-optic torsion sensor based on a helical two-core fiber (HTCF) is proposed and experimentally demonstrated for simultaneously measuring torsion angle and torsion direction. The sensor consists of a segment of HTCF and two single-mode fibers (SMFs) forming a Mach-Zehnder interferometer (MZI). The helical structure is implemented by pre-twisting a 1 cm long two-core fiber (TCF). The performance of the sensor with pre-twisted angles of 180°, 360°, and 540° is experimentally analyzed. The results show that the sensor can realize the angular measurement and effectively distinguish the torsion direction. It is worth noting that the sensor has maximum sensitivity when the pre-twist angle is 180 degrees. The obtained wavelength sensitivities of torsion and temperature are 0.242 nm/(rad/m) and 32 pm/°C, respectively. The sensor has the advantages of easy fabrication, low cost, compact structure, and high sensitivity, which is expected to yield potential applications in fields where both torsion angle and direction measurements are required.

High-performance vector torsion sensor based on high polarization-dependent in-fiber Mach-Zehnder interferometer.

We propose a high-performance vector torsion sensor based on an in-fiber Mach-Zehnder interferometer (MZI), which consists of a straight waveguide inscribed in the core-cladding boundary of the SMF by a femtosecond laser in only one step. The length of the in-fiber MZI is 5 mm, and the whole fabrication time does not exceed 1 min. The asymmetric structure makes the device have high polarization dependence, and the transmission spectrum shows a strong polarization-dependent dip. Since the polarization state of the input light entering the in-fiber MZI varies with the twist of the fiber, torsion sensing can be achieved by monitoring the polarization-dependent dip. Torsion can be demodulated by both the wavelength and intensity of the dip, and vector torsion sensing can be achieved by setting the appropriate polarization state of the incident light. The torsion sensitivity based on intensity modulation can reach 5763.96 dB/(rad/mm). The response of dip intensity to strain and temperature is weak. Furthermore, the in-fiber MZI retains the fiber coating, so it maintains the robustness of the complete fiber structure.

Highly sensitive torsion sensor based on Mach–Zehnder interference in helical seven-core fiber taper

We propose a high-sensitivity bidirectional torsion sensor using a helical seven-core fiber taper embedded in multimode fiber (MHSTM). Sensors with different taper waists and helical pitches are fabricated, and their transmission spectra are obtained and analyzed. The waist and length of the sandwiched seven-core fiber are finally determined to be 68 µm and 3 mm, respectively. The experimental results show that the clockwise and counterclockwise torsion sensitivities of the proposed sensor are 2.253 nm/(rad/m) and -1.123 nm/(rad/m), respectively. When tapered waist diameter reduces to 48 µm, a superior torsion sensitivity of 5.391 nm/(rad/m) in the range of 0–4.24 nm/(rad/m) is obtained, which is 46 times as large as the traditional helical seven-core fiber structure. In addition, the MHSTM structure is also relatively stable to temperature variations.

Elastomeric Core/Conductive Sheath Fibers for Tensile and Torsional Strain Sensors.

Motion sensing, aimed at detecting and monitoring mechanical deformation, has received significant attention in various industrial and research fields. In particular, fiber-structured mechanical strain sensors with carbon-based materials have emerged as promising alternatives for wearable applications owing to their wearability and adaptability to the human body. Various materials, structures, sensing mechanisms, and fabrication methods have been used to fabricate high-performance fiber strain sensors. Nevertheless, developing multi-modal strain sensors that can monitor multiple deformations remains to be accomplished. This study established core/sheath fiber multi-modal strain sensors using polymer and carbon nanotubes (CNTs). Specifically, a flexible and conductive CNT sheet was wrapped onto the elastomeric core fiber at a certain angle. This wrapping angle allowed the CNTs to mechanically deform under tensile and torsional deformations without fatal structural damage. The CNTs could sense both tensile and torsional strains through reversible structural changes during deformations. The fiber strain sensor exhibited an increase of 124.9% and 9.6% in the resistance during tensile and torsional deformations of 100% and 1250 rad/m, respectively.

Highly Sensitive Torsion Sensor Based on Periodical Helix-Style Long Period Fiber Grating

We demonstrated a periodical helix-style long period fiber grating (HS-LPFG) based torsion sensor with both high sensitivity and the ability to discriminate torsion direction. The proposed structure has asymmetric refractive index modulation in radial and azimuthal directions, which leads to the HS-LPFG being highly sensitive to torsional sensing. Experimental results show that torsion sensitivity is obtained up to 1.65 nm/(rad/m) in the measuring range of -17.952 rad/m to 17.952 rad/m, which is about fifty times higher than that of the conventional LPFG induced by CO2 laser. Moreover, the structure has low crosstalk of 0.037 rad/m/°C and a compact length of 5 mm.

Dynamic response of torsional waves in an anisotropic infinite cylinder with finite thickness

The transference of torsional surface waves in an infinite triclinic cylinder has been investigated. The equation of motion has been expressed in the cylindrical coordinate system, and by the means of the separation of variables, the displacement has been derived in terms of the Bessel function of the first kind and second kind. With the use of suitable boundary conditions, the dispersion equation has been deduced in a closed-form. Particular cases have been derived for monoclinic, orthotropic, transversely isotropic(precisely transtropic), and isotropic medium. The continuum comparision of each one of the cases have been discussed in details. In order to exhibit the present findings, 2D and 3D graphs have been plotted for phase velocity against wave number to study the impact of elastic coefficients and the ratio of radii of the cylinder. In the end, phase velocity for different media has been compared numerically. The study may be useful to construct torsional wave sensors in predicting the extent of damage during an earthquake by means of artificial explosions.

Internet of Things in Sport Training: Application of a Rowing Propulsion Monitoring System

The application of electronics, communication, and telemetry technologies in the field of sport training is a major trend today, specially with the explosion of the Internet of Things (IoT) paradigm. In particular, the rowing sport is one of the disciplines that could benefit from efficient, easy to integrate, and low cost IoT technologies to help analyzing and optimizing the performance of the rowers. However, traditionally monitoring tools in rowing are expensive and very limited. In this work, a rowing propulsion monitoring system for onboard analysis of rower’s key parameters is proposed, based on the development of a low-cost IoT device that combines sensing, global positioning, wireless communication, and data fusion for runtime information processing and monitoring on the boat. A power calculation model during the stroke is also proposed in order to estimate the energetic efficiency of the strokes in relation with the boat velocity. An acceleration sensor on the oar is used to decompose the movement; a torsion sensor to calculate the rower’s strength and energetic values; and navigation data for speed and distance values of the boat. A comprehensive comparative experimentation in a real rowing training scenario is performed, applying the proposed system and considering various rowers. The results show that the device provides a good vision in time of the movement and also very valuable technical information that can be used by rowers and trainers to define specific optimization profiles and improvement targets.

Direction-Discriminating torsion sensor based on optical fiber Mach-Zehnder interferometer

Optical fiber torsion sensors play a pivotal role in artificial intelligence, construction engineering, structural health monitoring and other fields. Research on low cost, simple structures and measurement methods has become a priority for researchers. Here, we propose an intensity-modulated and direction-recognizing torsion sensor based on two mode fiber with a sandwich structure, that serves as a mode interferometer formed by fundamental modes LP01 and second order core modes LP11 excited by means of offset fusion splicing. The capacity of intensity modulation and torsional direction recognition comes from the antisymmetric phase of fiber mode, which makes the sensor work like Marius’ law. The antisymmetric phase of the LP11 mode leads to an asymmetric transmission spectrum, whose direction enables the sensor to distinguish the torsion direction. Peaks and troughs in the measured spectrum interchange when the torsion direction is reversed. The initial angle between two offset directions enables control of the zero-crossing point within in the twisting range. The torsion sensitivity reaches 364%/(rad/cm) with a measurement accuracy of ± 0.22 rad/m.

INVESTIGATION OF THE TEMPERATURE DEPENDENCE OF TFBG WITH TILT ANGLES OF 20 AND 40

Due to advantages such as electromagnetic stability, durability, and high sensitivity, fiber Bragg gratings have found application as sensors of physical quantities. A special place in the line of such devices is occupied by Bragg gratings with tilted strokes (Tilted fiber Bragg grating- TFBG). At the moment, TFBGs are used to estimate the velocity of two-phase flows, to create a torsion sensor, as temperature and deformation sensors, etc. This article examines the possibility of implementing a temperature sensor based on TFBG with an angle of inclination of 2° and 4° inscribed in a single-mode optical fiber. For this purpose, experimental studies of the dependence of the wavelength of the Bragg resonance on temperature have been carried out. The grating period is 540 nm and the length is 10 mm. The temperature ranged from 30 °C to 85 °C in increments of 5 degrees. The results of the experiment are to find a linear dependence of the minimum wavelength of the Bragg resonance λB on the change in ambient temperature.