Fiber Optic Displacement Sensor Research Articles

Sensitivity of a tapered fiber optic displacement sensor with S-shaped structure

Sensitivity of a tapered fiber optic displacement sensor with S-shaped structure

A New Method to Design Trifurcated Optical Fiber Displacement Sensors

A New Method to Design Trifurcated Optical Fiber Displacement Sensors

Optimizing Algorithm for Existing Fiber-Optic Displacement Sensor Performance.

This paper describes the optimal design of a miniature fiber-optic linear displacement sensor. It is characterized by its ability to measure displacements along a millimetric range with sub-micrometric resolution. The sensor consists of a triangular reflective grating and two fiber-optic probes. The measurement principle of the sensor is presented. The design of the sensor's triangular grating has been geometrically optimized by considering the step angle of the grating to enhance the sensor's resolution. The optimization method revealed a global optimum at which the highest resolution is obtained.

Extended centroid position method in liquid-crystal-based interrogation system for electric-field-modulated Fabry-Perot sensing

A polarized low-coherence interferometer (PLCI) based on a liquid crystal (LC) wedge is designed, and an associated demodulation method encompassing the tunability feature is proposed for tunable, standalone optical sensing. The application of an electric field to the LC material effectively decreases the birefringence value and the related dispersion relation, which in turn enhances the resolution of detection. The effect of the electric field on the demodulation of the cavity length is addressed by the successive determinations of the centroid positions of the PLCI interferograms. Through a comprehensive study of numerical simulations, the effectiveness of the proposed approach is explored relative to the conventional envelope detection methodology. In order to verify this method, an experiment with a Fabry-Perot-based fiber optic displacement sensor is carried out using a 5CB LC wedge-based PLCI setup in the presence of an electric field. The measurement accuracy of the cavity length is found to be 0.74% of full scale, rendering it more precise and robust than the conventional envelope detection method.

Theoretical Modeling of Asymmetrically Inclined Fiber Optic Displacement Sensor: A Blended Approach

ABSTRACT Mathematical modeling of Fiber optic displacement sensor (FODS) is mostly done either by analytical technique or by ray tracing method. This paper is an attempt to blend analytical technique and ray tracing method to get rid of the limitations of these two techniques by superimposing them in such a way so that one gets more efficient, generalized, and accurate mathematical modeling of FODS. Modeling the sensor geometry with asymmetrically inclined fibers is of prime importance. This modeling technique is definitely a new approach to optimize the performance parameters and design of FODS with parallel, symmetric, or asymmetric inclination of fibers.

Demonstration of Improving the Performance of a Fibre Optic Displacement Sensor Using the Optical Harmonic Vernier Effect by Cascading Tapered Optical Single-Mode Fibres

Demonstration of Improving the Performance of a Fibre Optic Displacement Sensor Using the Optical Harmonic Vernier Effect by Cascading Tapered Optical Single-Mode Fibres

Video Motion Magnification and Subpixel Edge Detection-Based Full-Field Dynamic Displacement Measurement

Noncontact measurement techniques in structural dynamics field have progressed significantly in the past few decades. Vision-based measurement techniques are unique in that they have the ability to achieve full-field measurement and possess the typical advantages associated with noncontact measurement techniques. Recently, vision-based techniques have also been applied to streaming of videos for structural dynamic displacement measurement. The most recent trends in vision-based measurements include target tracing, digital image correlation, and target-less approaches. There are, however, some shortcomings of the vision-based techniques such as susceptibilities to image noise, prevailing light conditions, and limit in measurement resolution. To reduce these shortcomings, a method known as video motion magnification (MM) can be used to amplify small structural motions. Using the phase-based motion magnification (PBMM) and subpixel edge detection methods, the full-field dynamic displacements of the structure can be obtained. The deep convolutional long short-term memory (ConvLSTM) network is applied to aid in the selection of the frequency band for magnification in the PBMM algorithm. To achieve higher measurement accuracy, the displacement results with and without MM are combined with the finite impulse response (FIR) filter which can reduce the error caused by the PBMM procedure. In the tests, plastic optical fiber (POF) displacement sensors are introduced and used as reference measurements to compare the dynamic displacement results from the proposed vision-based method. Compared with the measured displacements with POF sensors, the proposed method offers high level of accuracy for full-field displacement measurement.

Ultra-Low Frequency High-Precision Displacement Measurement Based on Dual-Polarization Differential Fiber Heterodyne Interferometer

Picometer displacement measurement in the ultra-low frequency band below 1 Hz is highly demanded in the fields of geophysics and space exploration for the applications of hydrophones, geophones, drag-free space controllers, and so on. In this work, high-precision displacement detection in ultra-low frequency is achieved by proposing and demonstrating a dual-polarization differential fiber heterodyne interferometer. By injecting two orthogonal polarized lights into the dual-polarization differential fiber heterodyne interferometer, two optical interferences can be co-existed in a monolithic interferometer with a fully identical optical fiber path. Through the difference of the two optical interferometric phases, the light source noise and the fiber link noise can be well suppressed. Meanwhile, a pull-push type displacement sensing module is designed to double the displacement sensitivity as well as suppress the common-mode noise derived from the environmental fluctuation. Through the calibration experiment, the displacement sensitivity is obtained as 0.01634(±0.00022) rad/nm, which is consistent with the theoretical calculation. The displacement resolutions of 1.8 pm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at 0.1 Hz and 0.25 pm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at 1 Hz are achieved in the experiment, which is the superior displacement measurement level for this frequency band in the existing optic displacement sensors to our knowledge. The proposed fiber optic displacement sensor with ultra-high resolution in low frequency can be of great use in scientific research and precision engineering.

Assessment of Scattered-Bend Loss in Polymer Optical Fiber (POF) Displacement Sensor

Assessment of Scattered-Bend Loss in Polymer Optical Fiber (POF) Displacement Sensor

Geometric part error and material property profile separation technique of the additively manufactured and post-processed rods.

This paper presents novel surface profilometry for both geometric part error and metallurgical material property distribution measurements of the additively manufactured and post-processed rods. The measurement system, the so-called fiber optic-eddy current sensor, consists of a fiber optic displacement sensor and an eddy current sensor. The electromagnetic coil was wrapped around the probe of the fiber optic displacement sensor. The fiber optic displacement sensor was used to measure the surface profile, and the eddy current sensor was used to measure the change in permeability of the rod under varying electromagnetic excitation conditions. The permeability of the material changes upon exposure to mechanical forces, such as compression or extension and high temperatures. The geometric part error and material property profiles of the rods were successfully extracted by using a reversal method that is conventionally used for spindle error separation. The fiber optic displacement sensor and the eddy current sensor developed in this study have a resolution of 0.286 µm and 0.00359μr, respectively. The proposed method was applied not only to characterize the rods but also to characterize composite rods.

All fiber optic sensor with reference to different reflectors

Light-intensity-modulated displacement sensors are extensively used in numerous applications. Such type of sensors operates by utilizing a pair of adjacent optical fiber—one as transmitter and the other one as receiver. Such displacement sensors have the benefits of higher sensitivity and operating range, because they can efficiently collect more light after a reflectance has occurred. In this brief communication, we report all fiber optic displacement sensor using different reflectors such as plane, convex and concave. The experiment has been performed in the context of different refractive index-based solutions along with a comparative sensing analysis of these sensors. The attained results indicate that concave reflector-based displacement sensor yields the maximum sensitivity as compared to the other reflectors. Further, there has been good corroboration between simulated and observed transmittance. The findings is envisioned to help build more inexpensive displacement sensors with augmented sensitivity.

Optical sensor response towards hydrogen peroxide in low fat and full cream milk

Fiber Optic Displacement Sensor (FODS) categorized as one of the optical sensor based reflective intensity modulation. An intensity based sensor have been widely used in detecting various substances due to their simplicity structures. Generally for sensing principle, a pair of fiber is used to construct FODS which one of optical fiber is the transmitting fiber and another one is receiving fiber. The objective of this current work is to introduce FODS to evaluate the optical response in terms of voltage reading at different concentration of hydrogen peroxide in two different types of milk. A real-time measurement, low cost, stability, high sensitivity and simplicity of design promote a well-developed sensor in providing useful parameters in detecting hydrogen peroxide in milk. Hydrogen peroxide is an adulterated agent added in milk that can harm the consumers. Transmitive optical sensor as a function of displacement technique was developed to study the hydrogen peroxide concentrations in the range of 0 %-10 % as consuming more than 3-10 % of hydrogen peroxide can cause mild allergies reactions, stomach upset and vomiting. The output from the receiving fiber in this designated system was measured in terms of voltage reading through multimeter. The sensor shows outstanding performances of delivering 0.0007 V/% sensitivity for low fat milk and with linearity of >98 %. Whereas, the sensitivity achieved for full cream milk was 0.0005 V/% with a good linearity >97 %. The simplicity and credibility of this system offer a good opportunity in this project and also foods industry applications.

Sensitivity enhanced all-fiber displacement sensor compatible with passive and intracavity system based on Lyot filter

An all-fiber high-sensitivity displacement sensor based on 45°-spliced PM Lyot filter is proposed and its sensing performance is investigated experimentally. The transfer function of PM Lyot filter transmission spectrum is derived by the Jones matrix. It is indicated by the simulation results that the birefringence index and the splicing angle of the PM fiber have obvious influences on the displacement sensitivity and the spectral modulation depth, respectively. According to the relationship between the dips and the displacements, the Lyot-filter based sensing head has a good linearity. The sensitivity of 122.81 pm/μm is finally obtained in the range of 200μm displacement variation and its R square is larger than 0.997. Moreover, the sensing head can be compatible to the intracavity spectroscopy to narrow linewidth and enhance the high signal-to-noise ratio (SNR) so as to realize high-resolution sensing. It is demonstrated experimentally that the sensitivity of the intracavity displacement sensor can be 60 pm/μm with a linewidth narrower than 0.05 nm and a SNR higher than 55 dB. The excellent performance of the proposed sensor compatible with passive and intracavity system not only provides a new approach for optical fiber displacement sensor, but also further expands the application of Lyot filter in the sensing field.

Validation of a torsional balance for thrust measurements of Hall effect and microwave-based space propulsion systems.

A torsional thrust balance has been designed and validated by Surrey Space Centre and Added Value Solutions UK Ltd. in collaboration with the UK Space Agency. The thrust stand has been tested with two electric propulsion (EP) systems operating with xenon: the Halo thruster and the XJET thruster. The first consists of a low-power (<1 kW) Hall effect-based thruster, whose thrust level is between 3 and 20mN, depending on the power of the system. The second is an electron cyclotron resonance thruster whose operative point is in the 0.3-1.5mN thrust range. The thruster is mounted on a titanium rotating beam, whose movement is measured by an optical fiber displacement sensor. The thrusters' direct current electrical connections are routed through room temperature liquid metal pots and microwave power is transmitted via a wireless transfer system, minimizing friction effects. To reduce thermal issues during long thruster operations, the torsional thrust balance is designed with a water-cooling hub around the flex pivot. Noise from the laboratory environment is lessened by using four vibration-dampening spring systems as thrust balance feet. The tests on the two EP systems have shown accurate and repeatable results, demonstrating that the balance can be used to characterize different EP systems in the μN-mN thrust range.

A displacement sensor based on balloon-like optical fiber structure

A modal interferometric fiber-optic displacement sensor based on the balloon-like structure is investigated experimentally. When the bending radius of the balloon-like structure is reduced to 3.0 mm, the displacement sensitivity could reach up to 71.49 nm/mm. Moreover, the evolution process of the transmission spectra in a wide dynamic displacement range exceeding 22 mm is analyzed, which can provide guiding significance for sensor designing. The proposed displacement sensor is extremely low-cost, robust, and compact.

Experimental research on a novel spring-shaped fiber-optic displacement sensor for settlement monitoring

In this paper an innovative spring-shaped fiber-optic displacement sensor (SSFODS) based on optical time domain reflectometer (OTDR) technology with simple construction and cheap cost was proposed for subgrade settlement monitoring. The sensor incorporated a simple spring-shaped fiber bending modulation that increased its sensitivity in bending, light source and detector. The sensing principle between the measured external displacement and bending loss of optical fiber was theoretically explained and its expression was also derived. Sensor calibration was conducted, which showed that the SSFODS was characterized by a large measurement range of 90 mm, minimum displacement resolution of 0.173 mm, maximum hysteresis error of 2.81% and maximum repeatability error of 8.42%, respectively. A soil drainage model test with the SSFODS was performed to study its performance in determining compression deformation of the soil. At last, a simple field monitoring application with two SSFODSs connected in series was conducted and the progressive compaction behavior of the fill slope was accurately captured by two SSFODSs. Additionally, it is possible to connect these SSFODSs in series on one optical link to realize quasi-distributed sensing monitoring. This capability supports a promising application of the sensor in geotechnical engineering for real-time monitoring of the stability of fill slopes, foundation pits and so on.

Review of Fiber Optic Displacement Sensors

Displacement measurements are of significant importance in a variety of critical scientific and engineering fields such as gravitational wave detection, geophysical research, and manufacturing industries. Due to the inherent advantages such as compactness, high sensitivity, and immunity to electromagnetic interference, in recent years, fiber optic sensors have been widely used in an expansive range of sensing applications, ranging from infra-structural health monitoring to chemical and biological sensing. Of particular interest here, fiber optic displacement sensors have gained wide interest and have evolved from basic intensity modulation-based configurations to more advanced structures, such as fiber Bragg grating-based, interferometric configurations, etc. This paper reviews specifically the advanced fiber optic displacement sensing techniques that have been developed in the past two decades. Details regarding the working principle, sensor design, and performance measures of fiber Bragg gratings-based, interferometers-based (including the Fabry-Perot interferometer, the Michelson interferometer, and the multimode interferometer), microwave photonics-based, and surface plasmon resonance-based fiber optic displacement sensors are given. Challenges and perspectives on future research in the development of practical and high-temperature tolerant displacement sensors are also discussed.

Gas-liquid phase-detection and liquid film thickness measurement on a sprayed surface with a two-fluid jet using a fiber-optic probe and laser displacement sensor

The two-fluid jet method, which impacted droplets accelerated by a high-speed air stream, is widely used in cleaning the semiconductor manufacturing process. A wafer must always be covered with a liquid film during the cleaning process because local drying may cause some defects. However, the liquid film thickness formed by the high-speed airflow and droplets and whether a liquid film exists on the impingement surface have not been investigated. In this study, we tried to measure the liquid film thickness using an optical fiber probe and a laser displacement meter. We discuss the return light signal from the optical fiber probe installed on the surface irradiating the two-fluid jet.

A simple and high-resolution POF displacement sensor based on face-coupling method

A Various fiber-optics displacement sensor methods are presented yearly, and a high-resolution displacement sensor with cost-effective and straightforward operation is an essential demand. Here, we present a novel sensor structure for displacement measurement. The design is based on a hole in the one fiber's core, whereas a second fiber is utilized to move inside the hole made on the first fiber. The optical power coupling varies with the distance between the first and second fiber. The drilling length is investigated, and the four sensors are fabricated with different displacement ranges. The results show drilling length influences sensor's range, and the sensor has a nanometer resolution of about 8.647 nm with a sensitivity of 11.56 nW/µm in between 0 µm and 2500 µm. Moreover, a maximum range of 4 mm is achieved. The designed structure could be used not only for displacement, but also for vibration, angle, and pressure sensor.

Error analysis and experimental research of joint fiber-optic displacement sensor based on shear lag model

Landslide displacement monitoring is an efficient method to mitigate casualties and economic losses caused by landslide disasters. In recent years, distributed fiber-optic sensing technology, due to distributed and long-distance advantages, was widely used in subsurface displacement monitoring of landslides. However, existing fiber-optic displacement sensors has a large monitoring error when the landslide has multi-sliding surfaces. Aiming at solving this issue, a new joint fiber-optic displacement sensor which can achieve accurate displacement monitoring, was designed. Its measurement error was analyzed and the feasibility was demonstrated by theory and laboratory experiment. Based on the shear lag model, the error caused by strain transfer was studied by fiber-optic cable pull-out experiment. Finally, the feasibility of the sensor was verified by calibration experiment and soil shear experiment. The results show that the displacement sensor has high sensitivity and accuracy, and can realize distributed displacement monitoring inside the slope with multi-sliding surfaces.