A Wide-Range Displacement Sensor Based on Plastic Fiber Macro-Bend Coupling

Development of a dual point humidity sensor using POF based on twisted fiber structure

The humidity has often been measured through a single point sensor. Where, the humidity could be varied at different locations as well as depending on environmental conditions. The present paper developed the dual point humidity measuring sensor by using a polymer optical fiber (POF) based on a single illuminating fiber. The sensor's basic structure is to twist two fibers and bend them at a certain radius. However, the dual point sensor is developed through the cascading of twisted micro bend (TMB-1 and TMB-2). The twisting of fibers couples the light from one fiber to another fiber through the side coupling method. An increase in the humidity level leads to a change in the reflective index, which helps to get variation in coupled light intensity. To measure the humidity, the dual point sensors are placed into the control humidity chamber at two random positions. The power reading variation is significantly linear when the humidity level increases from 30 to 80%. The sensor has a fast response of about 1 s and a recovery time of about 4 s. Furthermore, the chemical coating is applied to improve the sensor's sensitivity. Between 30 and 80% range of humidity, the both sensors of dual point TMB-1 and TMB-2 have appropriate sensitivity and detection limits, which is about 680.8 nW/% and 763.9 nW/% and 1.37% and 1.98%, respectively. To measure the humidity at variable positions, the present dual points humidity sensor is well-stable, easy, and straightforward, which uses a less expensive method.

Marker-Based Structural Displacement Measurement Models with Camera Movement Error Correction Using Image Matching and Anomaly Detection

To prevent collapse accidents at construction sites, the marker-based displacement measurement method was developed. However, it has difficulty in obtaining accurate measurements at long distances (>50 m) in an outdoor environment because of camera movements. To overcome this problem, marker-based structural displacement measurement models using image matching and anomaly detection were designed in this study. Then, the performance of each model in terms of camera movement error correction was verified through comparison with that of a conventional model. The results show that the systematic errors due to camera movements (<1.7°) were corrected. The detection rate of markers with displacement reached 95%, and the probability that the error size would be less than 10 mm was ≥ 95% with a 95% confidence interval at a distance of more than 100 m. Moreover, the normalized mean square error was less than 0.1. The models developed in this study can measure the pure displacement of an object without the systematic errors caused by camera movements. Furthermore, these models can be used to measure the displacements of distant structures using closed-circuit television cameras and markers in an outdoor environment with high accuracy.

All-fiber optic displacement sensing system for an Ilizarov transverse tibial bone transport device

A single-mode-multimode-single-mode (SMS) optical fiber-based displacement sensing system mounted on an Ilizarov transverse tibial bone transport device for microcirculation reconstruction is reported. Wide-range displacement is approximated as a uniform extension of a spring that is connected to an SMS optical fiber structure acting as the displacement sensor and allowing full displacement characterization. Transmission spectrum changes are measured, providing a displacement range of 24 mm with a sensitivity of $ - {55.42}\;{\rm pm/mm}$-55.42pm/mm and a resolution of 45.2 µm. The experimental results are characterized using a polynomial response curve for measuring the displacement due to transverse distraction of the Ilizarov device. The SMS fiber interrogation system is based on a macrobending fiber edge filter-based ratiometric measurement system. The use of SMS fibers together with the macrobending fiber-based interrogation system eliminates the influence of temperature on the displacement measurement. The implementation of the all-fiber sensing system of this investigation has uniquely facilitated a smart clinical device with a wide displacement range as well as operating in real-time monitoring when attached to the Ilizarov transverse tibial bone transport device. It also means that this fiber-optic sensing device can be made more cost-effective, simpler in construction, and more versatile while providing a high degree of measurement accuracy and resolution.

Multimode-interference-effect-based all-fiber displacement sensing system for an orthopedic Ilizarov apparatus device

The paper describes a multimode-interference-effect-based single-mode-multimode-single-mode (SMS) fiber optic sensing system for wide-range displacement monitoring on an Ilizarov orthopedic external fixation device. Displacement measurement is implemented as the uniform extension of a spring, which is connected to an SMS optical fiber displacement sensor, allowing full displacement characterization. SMS fiber structures are used together with a macrobending-fiber-based interrogation system to measure temperature perturbation and hence eliminate its effect on the displacement measurement. Transmission spectra are measured, achieving a displacement measurement range of 110 mm with maximum sensitivity of -53  pm/mm and a resolution of 500 μm. The all-fiber sensing system has facilitated a clinical device with a wide displacement range operating in real-time when attached to the Ilizarov apparatus.

Simultaneous measurement of displacement and temperature using a PMF-based dual Mach-Zehnder interferometer

A dual Mach-Zehnder interferometer (MZI) based on polarization-maintaining fiber (PMF) is described for simultaneous measurement of displacement and temperature. Two orthogonal polarization components of a beam are simultaneously transmitted in the interferometer. The sensing configuration contains a short PMF section, a lens, and a mirror. The lens can transmit the slow polarization component and reflect the fast polarization component. Each polarization component exhibits a unique phase shift in response to changes in displacement and temperature, forming a dual MZI. Experimental results show that the resolutions of displacement and temperature are 60 pm and 2×10^-3°C, respectively, and measurement ranges of displacement and temperature can reach 20 cm and 70°C. The experimental result demonstrates that there is no crosstalk between displacement and temperature, and high repeatability is demonstrated experimentally. This sensor allows multiparameter measurement, high resolution, wide measurement range, and good repeatability, conferring good application potential.

Non-contact temperature-independent random-displacement sensor using two fiber Bragg gratings

We present a full-range displacement sensor system using two fiber Bragg gratings (FBGs). The magnetic-scale-combined FBGs allow the exploration of random position. The sinusoidal function variations are displayed by two detectors with a phase difference of 90 deg, and the optimal magnetic gap is explored through numerical simulations. The feasibility of the method is demonstrated in experiments that show the sinusoidal relation between center wavelength shifts with the linear displacement. Results showed that the amplitudes of the tensile-compressive load were 446.1 μϵ and 434.7 μϵ, respectively, with linearity of 0.998 and 0.999 at 1.5 mm between the detector and the magnetic scale. These results demonstrate that the sensors can realize non-contact, temperature-independent and full-range measurement.

An Optical Interferometric Triaxial Displacement Sensor for Structural Health Monitoring: Characterization of Sliding and Debonding for a Delamination Process

This paper presents an extrinsic Fabry–Perot interferometer-based optical fiber sensor (EFPI) for measuring three-dimensional (3D) displacements, including interfacial sliding and debonding during delamination. The idea employs three spatially arranged EFPIs as the sensing elements. In our sensor, the three EFPIs are formed by three endfaces of three optical fibers and their corresponding inclined mirrors. Two coincident roof-like metallic structures are used to support the three fibers and the three mirrors, respectively. Our sensor was calibrated and then used to monitor interfacial sliding and debonding between a long square brick of mortar and its support structure (i.e., a steel base plate) during the drying/curing process. This robust and easy-to-manufacture triaxial EFPI-based 3D displacement sensor has great potential in structural health monitoring, the construction industry, oil well monitoring, and geotechnology.

A Cost-Effective Relative Humidity Sensor Based on Side Coupling Induction Technology

A intensity-modulated optical fiber relative humidity (RH) sensor based on the side coupling induction technology (SCIT) is presented and experimentally demonstrated. The agarose gel and the twisted macro-bend coupling structure are first combined for RH sensing applications. The refractive index (RI) of the agarose gel increases with the increase of the RH and is in linear proportion from 20 to 80%RH. The side coupling power, which changes directly with the RI of the agarose gel, can strip the source noise from the sensor signal and improve the signal to noise ratio substantially. The experiment results show that the sensitivity of the proposed sensor increases while the bend radius decreases. When the bend radius is 8 mm, the sensor has a linear response from 40% to 80% RH with the sensitivity of 4.23 nW/% and the limit of detection of 0.70%. A higher sensitivity of 12.49 nW/% is achieved when RH raises from 80% to 90% and the limit of detection decreases to 0.55%. Furthermore, the proposed sensor is a low-cost solution, offering advantages of good reversibility, fast response time, and compensable temperature dependence.