Torsion Sensor Research Articles

Torsion sensor based on inter-core mode coupling in seven-core fiber.

We proposed a novel torsion sensor based on inter-core mode coupling in seven-core fiber (SCF). The torsion sensor is fabricated by tapering a commercially available SCF spliced with two single mode fibers. Waist diameter and length of the taper structure were experimentally optimized to achieve good transmission spectrum. Based on this structure, the torsion measurement was conducted, and the experimental results demonstrated that the transmission spectrum shows a red shift with the fiber twist. The torsion sensitivity increases with the twisting angle, which can achieve as high as 1.00 nm/°. The direction of wavelength shift was observed to be opposite when twisting the tapered SCF in clockwise and counter-clockwise direction, demonstrating its capability to discriminate the rotation orientation. Moreover, all the measurements were repeated in attempts to confirm its stable performance as well as high accuracy. Mode coupling dynamics and theory of optical anisotropy in twisted fiber are adopted to discuss the sensitivity performance, which agrees well with experimental results. The novel torsion sensor could provide a promising candidate for the applications requiring accurate rotation.

Transmission of dynamic supercoiling in linear and multi-way branched DNAs and its regulation revealed by a fluorescent G-quadruplex torsion sensor.

DNA supercoiling is an important regulator of gene activity. The transmission of transcription-generated supercoiling wave along a DNA helix provides a way for a gene being transcribed to communicate with and regulate its neighboring genes. Currently, the dynamic behavior of supercoiling transmission remains unclear owing to the lack of a suitable tool for detecting the dynamics of supercoiling transmission. In this work, we established a torsion sensor that quantitatively monitors supercoiling transmission in real time in DNA. Using this sensor, we studied the transmission of transcriptionally generated negative supercoiling in linear and multi-way DNA duplexes. We found that transcription-generated dynamic supercoiling not only transmits along linear DNA duplex but also equally diverges at and proceeds through multi-way DNA junctions. We also show that such a process is regulated by DNA–protein interactions and non-canonical DNA structures in the path of supercoiling transmission. These results imply a transcription-coupled mechanism of dynamic supercoiling-mediated intra- and inter-chromosomal signal transduction pathway and their regulation in DNA.

Ionic polymer-metal composite torsional sensor: physics-based modeling and experimental validation

Ionic polymer-metal composites (IPMCs) have intrinsic sensing and actuation properties. Typical IPMC sensors are in the shape of beams and only respond to stimuli acting along beam-bending directions. Rod or tube-shaped IPMCs have been explored as omnidirectional bending actuators or sensors. In this paper, physics-based modeling is studied for a tubular IPMC sensor under pure torsional stimulus. The Poisson–Nernst–Planck model is used to describe the fundamental physics within the IPMC, where it is hypothesized that the anion concentration is coupled to the sum of shear strains induced by the torsional stimulus. Finite element simulation is conducted to solve for the torsional sensing response, where some of the key parameters are identified based on experimental measurements using an artificial neural network. Additional experimental results suggest that the proposed model is able to capture the torsional sensing dynamics for different amplitudes and rates of the torsional stimulus.

Intensity-modulated directional torsion sensor based on in-line optical fiber Mach-Zehnder interferometer.

In this Letter, we demonstrated an intensity-modulated directional torsion sensor based on an in-line Mach-Zehnder interferometer in single-mode fiber. A non-circular symmetric perturbation is created to excite non-circular symmetric cladding mode and then interference with the core mode at the second perturbation. An initial rotation angle is designed between two perturbations for the purpose of discriminating the torsion direction. Both experimental and theoretical results enforce that the spectral peak/dip turns to be the dip/peak when the fiber is twisted from the counter-clockwise to the clockwise direction. Benefiting from the reversal between peak and dip, an intensity-modulated directional torsion sensor is realized in the range from -50 rad/m to 50rad/m with a sensitivity of 45.3%/(rad/cm).

Intensity-demodulated torsion sensor based on thin-core polarization-maintaining fiber.

An intensity-demodulated torsion sensor is designed and realized, which consists of a polarization ring as the sensing part and a section of thin-core polarization-maintaining fiber as the demodulation part. An intensity map of a sinusoidal change can be obtained at some specific wavelengths, and the experimental results correspond to the theoretical analysis well. The maximum sensitivity is about 0.29dB/deg at the wavelength of 1584.6nm, and the minimum sensitivity is about 0.10dB/deg at the wavelength of 1510.2nm. Meanwhile, the temperature characteristic is measured in the experiment. More broadly, the proposed structure can be used in an integrated smart device for loose-screw detection in devices in aeronautics and astronautics.

Highly sensitive torsion sensor based on directional coupling in twisted photonic crystal fiber

We demonstrate a novel torsion sensor based on a twisted photonic crystal fiber with an embedded liquid rod waveguide. Only one resonant dip appears in the transmission spectrum in the range of 1,350–1,650 nm, which is associated with the directional coupling between the core and rod modes. The relative position of the fiber core with respect to the liquid rod waveguide is altered owing to the torsion stress, which changes the phase-matching condition and leads to a resonant-wavelength shift. The helical structure of the liquid rod waveguide can improve the torsion sensitivity of the device and provide an ability to distinguish the rotation direction. The measured torsion sensitivities were as high as ∼203 and ∼208 nm·mm·rad−1 in the clockwise and counterclockwise rotations, respectively.

Passive wireless measurement of tension for overhead transmission line based on surface transverse wave

This study presents a passive wireless surface transverse wave (STW) torsion sensor for an overhead transmission line (OHTL). Two key techniques, namely the design of STW sensing element and clamping structure, were investigated. The relationship between the tension and the frequency shift of the STW resonator was analysed. A numerical analysis on the tension sensitivity and temperature coefficient using different cut types was performed. Results showed that Y − 51° cut quartz, which has a close to zero temperature coefficient of frequency, is a suitable substrate of the STW tension sensors. Other parameters were optimised to obtain a resonator with a Q value of >11,000. Two STW resonators were adopted as sensing element to form a differential structure to reduce the temperature interference. An OHTL clamping and tension transfer mechanical structure was designed, which has an ability of adjusting the tension sensitivity and can be easily installed at any point of OHTL. Moreover, the OHTL tension measurement system was set up and evaluated. Experimental results indicated that the STW tension sensitivity was 24.31 kHz/kN, the non-linearity was 0.26%, and the repeatability error was 0.32%. The OHTL tension measurement method is feasible for practical application.

Torsion, Strain, and Temperature Sensor Based on Helical Long-Period Fiber Gratings

A novel fiber sensor, which enables us to simultaneously measure the torsion, strain, and temperature, is proposed and experimentally demonstrated, which is based on utilization of two successively cascaded helical long-period fiber gratings (TSC-HLPGs). By using the proposed approach, crosstalk effects among temperature, strain, and torsion can totally be discriminated for the first time to the best of our knowledge. Moreover, not only the torsion angle, but also the torsion direction can be determined simultaneously. Accuracies for the resolved temperature, the strain, and the torsion angle are estimated to be ~0.8 °C within the range of 20 °C–100 °C, $\sim 225~\mu \varepsilon $ within the range of 0- $2600~\mu \varepsilon $ , and ~1.2° (corresponding to a torsion responsivity of 3.54 nm/rad/m in our case) within the rotation angle of −360° ~ 360°, respectively.

Highly sensitive torsion sensor with femtosecond laser-induced low birefringence single-mode fiber based Sagnac interferometer.

A highly sensitive optical fiber torsion sensor with femtosecond laser-induced low birefringence SMF-based Sagnac interferometer (SI) is proposed and experimentally demonstrated in this paper. A straight-line waveguide positioned horizontally with respect to the fiber core is inscribed by the femtosecond laser in the cladding of the SMF, which leads to the asymmetry stress distribution in the SMF, and then gives rise to the low birefringence in the SMF. Compared with most of the previous reported SI based torsion sensors, there is no splicing joint in the femtosecond laser-induced low birefringence SMF-based SI, which lowers the transmission loss and makes the SI based torsion sensor more robust simultaneously. The experiment result shows that the proposed torsion sensor exhibits a torsion sensitivity of up to 3.2562 nm/degree, with the high torsion resolution of 0.003 degree. In contrast, the temperature cross-sensitivity and strain cross-sensitivity of the proposed torsion sensor are low, to -0.000055 degree/°C and 0.000013 degree/με, respectively, thus overcoming the cross-sensitivity problem resulting from temperature and strain. Moreover, theoretical analysis are carried out to compare with the experimental results to demonstrate the feasibility and good consistency.

Directional torsion and temperature discrimination based on a multicore fiber with a helical structure.

We propose and experimentally demonstrate a directional torsion sensor based on a Mach-Zehnder interferometer formed in a multicore fiber (MCF) with a ~570-μm-long helical structure (HS). The HS was fabricated into the MCF by simply pre-twisting and then heating with a CO2 laser splicing system. This device shows the capability of directional torsion measurement from -17.094 rad/m to 15.669 rad/m with the sensitivity of ~0.118 nm/(rad/m). Moreover, since the multiple interferences respond differently to torsion and temperature simultaneously, the temperature cross-sensitivity of the proposed sensor can be eliminated effectively. Besides, the sensor owns other merits such as easy fabrication and good mechanical robustness.

Enhanced selfintegration algorithm for fiber torsion sensor based acoustically-induced fiber grating

Mechanical parameter monitoring based on optical mode detection benefits from its low cross sensitivity and inexpensive instrument. The key to improving detection accuracy is to generate high-quality detection light and use efficient algorithms. We present a strain-independent torsion sensor based on acoustically-induced fiber grating (AIFG) in the dual-mode fiber (DMF) and use the enhanced self-integration algorithm to improve the sensing accuracy. By tuning the radio frequency of driving signal, the LP11 mode generated by the AIFG can be exploited to measure the dynamic torsion variations. Without the complex device such as fiber interferometers and photonic crystal fibers (PCFs), the simple structure built by mode converter and charge coupled device (CCD) can track the dynamic variations and has less cross sensitivity of strain along the transmission direction. The AIFG driven by a radio frequency as a mode converter at specific wavelength does not participate in sensing but generates the high-purity LP11 mode that accounts for more than 90% of total power. With the twist from the rotator stage, the DMF keeps rotating and CCD records the spatial distribution of mode profiles. The features of optical mode is enhanced based on matrix analysis and then the relationship between twist angle and mode features is obtained. Based on image processing, the dynamic variation of spatial beam detected by CCD can be easily tracked and quantified. In experiment, the rotation angle can be obtained by calculating the feature value of the optical mode. Our image detection algorithm is specially designed for the optical fiber mode. Compared with traditional image recognition based on feature learning, it is simple and fast because it is needless to use image segmentation and stochastic processing. Through a series of experiments on angle rotation and parallel strain, we verify the correctness of the enhanced self-integration model and analyse the computational uncertainties that influence the stability of experiment. In the 0 to 180 measurement range, the maximum range of measurement error is less than 11%. When the axial strain is between 100 and 1500 , the sensor is strain-independent. Thus, it is verified that the torsion sensor based on AIFG has high sensitivity and can overcome the cross sensitivity of strain along a certain direction. The pertinent results have significant guidance in designing the multi-parameter sensor. The optical mode detection, instead of the traditional spectrum measurement, enables the whole structure to have the potential to be rebuilt by inexpensive devices that work in visible wavelengths.

A polarization-independent torsion sensor based on the near-helical long period fiber grating

A torsion sensor based on the near-helical (NH) long period fiber grating (LPFG) is fabricated by using a high frequency pulsed CO2 laser. Each groove of the NH-LPFG is spirally written in the four sides of a single-mode fiber. The NH-LPFG has a helical periodic vertical index modulation. This is different from the screw-type index modulation of the common helical LPFGs (H-LPFGs) fabricated in a twisted fiber. The torsion and temperature characteristics of the NH-LPFG are experimentally investigated. The temperature sensitivity is about 0.0668 nm/°C. The torsion sensitivity is 0.103 nm/(rad/m) and independent of the polarization state of incident light.

High Sensitive Directional Torsion Sensor Based on a Segmented Long-Period Fiber Grating

A segmented long period fiber grating (LPFG)-based torsion sensor with both high sensitivity and ability to discriminate torsion direction is proposed and experimentally investigated. The sensor is made up of three spatial orthogonal short LPFGs by using a CO2 laser notched method. Experimental results show that the torsion sensitivities can reach −0.54 and 0.33 dB/(rad/m) in dip depth and 0.30 and −0.14 nm/(rad/m) in resonance wavelength for clockwise and counterclockwise, respectively, in a single polarization state. Torsion rate and torsion direction can be measured simultaneously by the sensor. Moreover, the temperature sensitivity of the sensor has been determined as 0.067 nm/°C. Therefore, the proposed segmented-LPFG would have great potential applications in engineering and fiber sensors.

All fiber torsion and displacement sensor based on image detection

We propose an all-fiber-optic sensor for simultaneous rotation and displacement measurement based on elastic-optic effect in a dual mode fiber. LP01 and LP11 modes are both excited in the fiber and are distinguished using wavelength-scanning Spatially and Spectrally resolved imaging technique (S2 Imaging) to accomplish rotation and displacement detection. Mode rotation is characterized by the LP11 mode rotation using elastic-optic theory; a displacement area of 120×120μm is detected and measured by recording the trace of LP01 mode pattern. Balance between the detection range and resolution of the sensor is adjustable by simply changing the fiber length or adjusting the relative position of fiber-end, lens and the CCD camera. Real-time detection at ∼0.5s per measurement speed is achieved, and twist rate and moving velocity can also be measured.

Strain-independent fiber torsion and displacement sensor based on acoustically-induced fiber grating

We present a strain-independent torsion and displacement fiber sensor using acoustically-induced fiber grating (AIFG) in dual-mode fiber (DMF). By tuning the radio frequency of driving signal, LP01 and LP11 modes generated by the AIFG can be exploited to measure the dynamic displacement and torsion variations, respectively. Both the twist angle and the twist direction can be monitored via image detection facility at the end of DMF. Between torsion angles of −80° and 80°, the highest twist sensitivity reaches 15pixel/°. The average displacement sensitivity is 5pixel/µm within the recorded two-dimensional movement of 100um×80um. The stable property of sensor is verified when the strain is varied from 100με to 1500με.

Performance Study of a Torsional Wave Sensor and Cervical Tissue Characterization.

A novel torsional wave sensor designed to characterize mechanical properties of soft tissues is presented in this work. Elastography is a widely used technique since the 1990s to map tissue stiffness. Moreover, quantitative elastography uses the velocity of shear waves to achieve the shear stiffness. This technique exhibits significant limitations caused by the difficulty of the separation between longitudinal and shear waves and the pressure applied while measuring. To overcome these drawbacks, the proposed torsional wave sensor can isolate a pure shear wave, avoiding the possibility of multiple wave interference. It comprises a rotational actuator disk and a piezoceramic receiver ring circumferentially aligned. Both allow the transmission of shear waves that interact with the tissue before being received. Experimental tests are performed using tissue mimicking phantoms and cervical tissues. One contribution is a sensor sensitivity study that has been conducted to evaluate the robustness of the new proposed torsional wave elastography (TWE) technique. The variables object of the study are both the applied pressure and the angle of incidence sensor–phantom. The other contribution consists of a cervical tissue characterization. To this end, three rheological models have fit the experimental data and a static independent testing method has been performed. The proposed methodology permits the reconstruction of the mechanical constants from the propagated shear wave, providing a proof of principle and warranting further studies to confirm the validity of the results.

Highly sensitive torsion sensor based on long period fiber grating fabricated by femtosecond laser pulses

A highly sensitive torsion sensor based on long period fiber grating (LPFG) fabricated by 800nm femtosecond laser pulses is proposed and demonstrated. LPFG with an attenuation depth of ∼14dB is achieved within the wavelength range of 1425–1575nm. The experiment results show that the LP02 and LP03 resonant wavelengths experience red-shift when the twist direction is clockwise while they occur blue-shift in the twist counterclockwise direction as the twist rate increases. However, the LP04 resonant wavelength is always shifted toward shorter wavelength independently of the twist directions and higher twist sensitivity is observed. In addition, the loss peak amplitude of LPFG shows a tendency to decrease with the twist rate increases whether the LPFG is twisted clockwise or counterclockwise. Meanwhile, the resonant wavelength occurs splitting phenomenon in the case of higher twist rate as well as the high order resonant wavelength performs more significantly. Additionally, the sensor shows a twist sensitivity as high as 118.7pm/(rad/m) in the range of −105 to −52.5rad/m and that of 181.7pm/(rad/m) in the range of 52.5–105rad/m.

Torsional Ultrasound Sensor Optimization for Soft Tissue Characterization.

Torsion mechanical waves have the capability to characterize shear stiffness moduli of soft tissue. Under this hypothesis, a computational methodology is proposed to design and optimize a piezoelectrics-based transmitter and receiver to generate and measure the response of torsional ultrasonic waves. The procedure employed is divided into two steps: (i) a finite element method (FEM) is developed to obtain a transmitted and received waveform as well as a resonance frequency of a previous geometry validated with a semi-analytical simplified model and (ii) a probabilistic optimality criteria of the design based on inverse problem from the estimation of robust probability of detection (RPOD) to maximize the detection of the pathology defined in terms of changes of shear stiffness. This study collects different options of design in two separated models, in transmission and contact, respectively. The main contribution of this work describes a framework to establish such as forward, inverse and optimization procedures to choose a set of appropriate parameters of a transducer. This methodological framework may be generalizable for other different applications.

Long period fiber grating based on periodically screw-type distortions for torsion sensing.

A novel long-period fiber grating (LPFG), fabricated by periodically cascading a series of screw-type distortions, is proposed and experimentally demonstrated. These screw-type distortions are induced by twisting the fiber during CO2 laser beam exposure. The resulting LPFG will either be left- or right-hand helical, depending on the twist rate and direction used during fabrication, with a certain frozen shear strain. Due to the independence between grating pitch and twist rate, this type of LPFG could be more flexible than the helical- or chiral-fiber gratings reported previously. During LPFG twisting, the device displays good directional dependence and an enhanced torsion sensitivity of 0.1604 nm/(rad/m), which implies the structure could be an excellent candidate for torsion sensors.

Torsion Sensor with Rotation Direction Discrimination Based on a Pre-twisted In-Fiber Mach–Zehnder Interferometer

We demonstrate a torsion sensor with rotation direction discrimination based on a pre-twisted core-cladding mode Mach–Zehnder interferometer (MZI) fabricated in single mode fiber by twisting the fiber during CO2 laser irradiation to induce a permanent screw-type distortion at the two points of coupling between the core and cladding. The proposed sensor can measure the twist rate with a sensitivity of up to 10.35 nm/(rad/cm) and determine its rotation direction (i.e., clockwise or counterclockwise) simultaneously. Furthermore, the sensitivity of the torsion sensor can be enhanced by increasing the initial shear strain.