Fiber Optic Displacement Sensor Research Articles

Fiber optic salinity sensor using beam-through technique

A fiber optic displacement sensor is proposed to sense salinity based on different concentration of sodium chloride (NaCl) in de-ionized water using the beam-through technique. The performance of a 594nm and 633nm He–Ne laser as the light source are compared. For a concentration change of sodium chloride from 0 to 12% in de-ionized water, the output voltage increase linearly and the sensitivity is dependent on the displacement position of the receiving fiber from the quartz cell containing the sodium chloride solutions. Measurements taken at higher displacement positions contribute to lower sensitivity with the highest sensitivity of 0.0237mV/% and 0.0412mV/% occurring at the 0mm displacement position for the 594nm and 633nm He–Ne lasers, respectively. Furthermore, a better limit of detection of 1.44% is achieved when the 633nm He–Ne laser is used compared to the 1.28% limit of detection achieved by using the 594nm He–Ne laser. The main novelty of this sensor is that it is contactless and non-destructive which are attractive features for applications involving delicate and hazardous processes.

A comparative evaluation of three hydrophones and a numerical model in high intensity focused ultrasound fields

The pressure fields of two different high intensity focused ultrasound (HIFU) transducers operated in burst mode were measured at acoustical power levels of 25 and 50 W (continuous wave equivalent) with three different hydrophones: A fiber-optic displacement sensor, a commercial HIFU needle hydrophone, and a prototype of a membrane hydrophone with a protective coating against cavitation effects. Additionally, the fields were modeled using a freely available simulations software package. The measured waveforms, the peak pressure profiles, as well as the spatial-peak temporal-average intensities from the different devices and from the modeling are compared and possible reasons for differences are discussed. The results clearly show that reliable pressure measurements in HIFU fields remain a difficult task concerning both the reliability of the measured values and the robustness of the sensors used: Only the fiber-optic hydrophone survived all four exposure regimes and the measured spatial-peak temporal-average intensities varied by a factor of up to 1.5 between the measurements and the modeling and between the measurements among themselves.

Theoretical and experimental studies on coupler based fiber optic displacement sensor with concave mirror

A new fiber optic displacement sensor (FODS) is proposed and demonstrated using a multimode fiber coupler as a sensor probe and a concave mirror as a reflective target. A mathematical model is also developed to investigate the performance of proposed FODS at various coupling ratio, fiber diameter, and surrounding media. Three slopes are obtained for the displacement response where the third slope starts at a displacement position of twice the focal length. The numerical results show that higher performance is attained at lower coupler ratio of 50:50 or smaller core diameter. The results also show that the proposed FODS has a potential application in liquid and gas chemical sensors. The experimental performances are also investigated for the proposed sensor where it is observed that the second peak of the displacement curve is located at exactly two times of the focal length or 20mm.

Transmissive fiber optical displacement sensor using cutting plate

AbstractIntensity modulated transmissive fiber optical displacement sensor is introduced and its performance is investigated.In the experiments, the relative error is 4% and the linearity is higher than 99.2% with source light intensity stable. The relative error is 0.2% with the source light intensity changed at a certainly frequency. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:446–448, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26586

Using a validated transmission model for the optimization of bundled fiber optic displacement sensors

A variety of intensity-modulated optical displacement sensor architectures have been proposed for use in noncontacting sensing applications, with one of the most widely implemented architectures being the bundled displacement sensor. To the best of the authors' knowledge, the arrangement of measurement fibers in previously reported bundled displacement sensors has not been configured with the use of a validated optical transmission model. Such a model has utility in accurately describing the sensor's performance a priori and thereby guides the arrangement of the fibers within the bundle to meet application-specific performance needs. In this paper, a recently validated transmission model is used for these purposes, and an optimization approach that employs a genetic algorithm efficiently explores the design space of the proposed bundle sensor architecture. From the converged output of the optimization routine, a bundled displacement sensor configuration is designed and experimentally tested, offering linear performance with a sensitivity of -0.066 μm(-1) and displacement measurement error of 223 μm over the axial displacement range of 6-8 mm. It is shown that this optimization approach may be generalized to determine optimized bundle configurations that offer high-sensitivity performance, with an acceptable error level, over a variety of axial displacement ranges. This document has been approved by Los Alamos National Laboratory for unlimited public release (LA-UR 11-03413).

Modeling and experimental studies on retro-reflective fiber optic micro-displacement sensor with variable geometrical properties

Fiber optic displacement sensors (FODS) are studied and analyzed by using different configurations (Atsushi and Kohichi, 1996; Faria, 1998; Buchade and Shaligram, 2006) [1,2,6]. Mathematical models developed for these configurations use analytical methods and techniques. It is observed that these models are useful for a specific geometrical arrangement of fibers and reflector and are not useful for any variation in configuration. Hence it is necessary to develop a mathematical model which is independent of configuration of the fiber optic sensors. This paper discusses development of such generalized model which is useful for studying and analyzing any configuration and scenario of fiber optic sensor. The model is expected to be useful in analyzing manufacturing tolerances as well as effects of the geometrical parameters on performance of the sensor.

Environment‐independent liquid level sensing based on fiber‐optic displacement sensors

AbstractA new fiber‐optic liquid‐level sensor (LLS) for continuous monitoring of the liquid level is proposed using a fiber‐optic displacement sensor (FODS). A float is used to measure the level of liquid in the tank and it is connected to the FODS probe to convert the variation of the liquid level into a displacement change. The performance of the LLS is investigated for two different FODSs with a concave and a flat mirror target. With a concave mirror, six measurement slopes within a range of 25 mm are observed with the highest sensitivity of 1.3015 mV/mm. With a flat mirror, two measurement slopes are observed with the highest sensitivity of 1.4533 mV/mm and the longest measurement range of 4.8 mm. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2451–2453, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26358

Characterization of a fiber-optic displacement sensor for measurements in high-intensity focused ultrasound fields

A fiber-optic sensor is presented that is capable of measuring the particle displacement in high-intensity focused ultrasound (HIFU) fields. For this probe, a secondary calibration was performed, and the resulting complex frequency response is discussed. As a first practical application, the setup was used to measure the pressure in the field of a weakly focusing ultrasound transducer. The result is compared with that of a membrane hydrophone measurement. The feasibility of measurements in HIFU fields is demonstrated by means of measurements of the spatial distribution of the peak particle velocity within the focus of a HIFU transducer and of the dependence of the peak values on the acoustical power level.

The Study and Applications on Fiber Bragg Grating (FBG) Monitoring System for Deep and Large Deformed Soft Ground

The fiber Bragg grating (FBG) technology is studied based on the current monitoring status of the highway soft ground settlement, for instance, the low degree of automation, the unsatisfied accuracy of the device, the slow data transmission and the greater measurement errors. The limited measuring range and the difficult situations of the soft ground burying and installing of the fiber optic sensor still need to be addressed. This thesis has analyzed the development of the long range optical fiber displacement sensor as well as its burying techniques which are suitable for soft ground settlement monitoring. Both of them have been successfully applied to De Chang Highway D10 subject. The study also shows that the long range optical fiber displacement sensor is able to meet the requirements of the soft ground monitoring. And data can be accurately monitored by means of real-time or on-line continuously. This is of great significance in pushing forward the development of the fiber optical monitoring technology in the field.

Micro-displacement sensor with multimode fused coupler and concave mirror

Fiber optic displacement sensor is demonstrated using a multimode fused coupler probe and a concave mirror target. It is observed that a focal length of the concave mirror make a significant influence to the displacement response, which illustrates three linear slopes with the second slope peaks at the position that is in vicinity of two times of the focal length. The highest sensitivity of 0.56 mV/mm is obtained with an infinity focal length and it is decreased as the focal length of the concave mirror decreases. The widest linear range of approximately 3.3 mm is observed in the third slope region with focal length of 6.0 mm. The highest linear range obtained with the use of 50:50 coupler.

Theoretical and experimental studies on concave mirror‐based fiber optic displacement sensor

PurposeThe purpose of this paper is to investigate, theoretically and experimentally, a concave mirror‐based fiber optic displacement sensor performance for three‐axes directional measurements.Design/methodology/approachMathematical model is constructed based on spherical mirror properties of the concave mirror and the simulated result is found to be in good agreement with the experimental results.FindingsBoth theoretical and experimental results show that the focal length and radius of the concave mirror make significant influence to the displacement response. In the x‐axes measurement, six linear slopes are obtained with four of them are located in the vicinity of the position, two times of the focal length. The maximum measurement range of about 20 mm is obtained using a focal length of 10 mm. In the y‐ and z‐axes displacement measurements, the linear range increases as the diameter of concave mirror increases. The longest linear range of 8 mm is achieved at mirror radius of 10 mm.Originality/valueThis is the first demonstration of three axes directional displacement measurements using a concave mirror as a target

Long distance fiber-optic displacement sensor based on fiber collimator

A simple fiber-optic displacement sensor based on reflective intensity modulated technology is demonstrated using a fiber collimator. The sensing range is over 30 cm, which is over 100 times that of the conventional fiber-optic displacement sensor based on the normal single-mode fiber. The measured data are fitted into linear equation very well and the values of R-square are more than 0.995. The sensitivity of the device achieves 0.426 dB∕cm over the range of 5-30 cm. By applying the relative technique, the errors resulted from the fluctuation of light source and influences of environment are effectively eliminated, and the stability for wide range measurement can be improved. The simplicity of the design, high dynamic range, stability and the ease of the fabrication make it suitable for applications in industries.

Plastic Optical Fiber Displacement Sensor Based on Dual Cycling Bending

In this study, a high sensitivity and easy fabricated plastic optical fiber (POF) displacement sensor is proposed. A POF specimen subjected to dual cyclic bending is used to improve the sensitivity of the POF displacement sensor. The effects of interval between rollers, relative displacement and number of rollers on the sensitivity of the displacement sensor are analyzed both experimentally and numerically. A good agreement between the experimental measurements and numerical calculations is obtained. The results show that the interval between rollers affects sensitivity most significantly than the other design parameters. Based on the experimental data, a linear equation is derived to estimate the relationship between the power loss and the relative displacement. The difference between the estimated results and the experimental results is found to be less than 8%. The results also show that the proposed POF displacement sensor based on dual cyclic bending can be used to detect displacement accurately.

Fiber Optic Displacement Monitoring in Laboratory Physical Model Testing

For physical models, conventional techniques have difficulties in monitoring internal displacements during laboratory testing. In this paper, based on fiber Bragg grating (FBG) sensing technology, a bar-type fiber optic displacement sensor is developed for small-scale models. When the model deforms due to loading or unloading, the embedded displacement sensor can capture the displacement profile along the bar length using the strain data from quasi-distributed FBGs. Laboratory calibration tests have showed that the displacements measured by the FBG sensing bar are in good agreement with those from conventional displacement transducers. For the physical models of a gravity dam and a cavern group, the FBG sensing bars were successfully installed in predefined holes, together with conventional gauges. During testing, the FBG sensing bars measured the displacement distributions within the models. The fiber optic monitoring results demonstrate the deformation characteristics of surrounding rock masses induced by overloading and underground excavation and indicate the overall stability conditions of these two geo-structures.

Performance comparison between plastic-based fiber bundle and multimode fused coupler as probes in displacement sensors

Fiber optic displacement sensors with bundled and fused coupler fiber probes are being investigated. The effects of axial displacements on the detected output voltages are also investigated for fiber bundle probe sensor. The resolutions obtained are 0.9 and 4.0 μm, for the front and back slopes, respectively. A comparison is made with a commercial plastic based multimode fused coupler which gives a better range of 2.0 mm. This is longer than that achieved by the fiber bundle probe which is only 0.4 mm and has a lower resolution of 34 μm for the case of 50:50 coupling ratio.

Enhanced bundle fiber displacement sensor based on concave mirror

Fiber optic displacement sensor (FODS) is proposed using a concave mirror for enhanced flexibility in sensitivity selection and linear range. The effect of focal length and diameter of the concave mirror on the displacement response is investigated. The experimental and theoretical results show that the second dip of the displacement response is located at distance equivalent to twice of focal length. For the third slopes and above, the sensitivity and the linear range of the sensor are strongly dependent on the focal length and diameter of the mirror. A good agreement between the theory and experimental results are shown. The measurement range as far as 26 mm can be achieved by using a 12 mm focal length concave mirror.

A novel quasi-distributed fibre optic displacement sensor for dynamic measurement

We present a novel technique based on incoherent optical frequency domain reflectometry (OFDR) to measure length changes quasi-distributed between reflection points in optical fibres. The technique enables length changes to be measured with a resolution better than 1 µm and allows for static and dynamic measurement capabilities up to 2 kHz. We demonstrate that dynamic measurements of multiple fibre sections can be conducted independently from each other with high precision. Due to the precise and dynamic measurement capabilities, the proposed sensor system is expected to open new fields of application, especially in the structural-health-monitoring sector. Possible applications are discussed in the paper.

Design and Analysis of a 6-DOF Monolithic Nanopositioning Stage

A 6-DOF monolithic nanopositioning stage is developed for three coordinate measuring machines (CMM) with nanometer resolution. The stage consists of a monolithic flexure hinge mechanism, six piezoelectric actuators and six fiber-optic displacement sensors. A mathematical model of the constraint optimization problem is presented. Based on the solution of the optimization problem, the final design of the 6-DOF stage is also presented. The numerical analysis on static and dynamic behavior of the stage is done by using the finite element method. The experimental results of the performance of the 6-DOF stage are presented.

Estimation of metal surface roughness using fiber optic displacement sensor

A fiber optic displacement sensor is proposed to estimate the roughness of metal surface using the intensity modulation technique. A light beam is launched onto the metal surface via a bundled fiber. The reflected light from the surface is collected and then routed to a silicon detector. The level of roughness for aluminum, stainless steel and copper samples are estimated to be approximately 27, 26, and 20% respectively by fixing the object within the linear range of the sensor. The output voltages are measured as a function of lateral distance to estimate the roughness of the surface.

Determination of the thickness of a transparent plate using a reflective fiber optic displacement sensor

A fiber optic sensor for determining the thickness of a transparent plate (1–2.5 mm) is described based on a fiber optic displacement sensor. The sensor characteristics are found to vary with the change in the thickness of a plate. A theoretical model is proposed and validated with experimental results. The behavior of the sensor is evaluated and analyzed in terms of the numerical aperture and diameter of the fiber.