Intensity Modulated Fiber Optic Sensor Research Articles

Fiber Optic Sensor-Based Bearing Defect Detection and Its Usages in Computer Vision

This work focuses on the investigation of surface defects in small bearings. Based on the theory of rough surface scattering and the dual-beam ratio measurement method, fiber optic sensing technology is applied in identifying surface defects in bearings. To facilitate the extraction of features for surface defects in bearings, a sensor probe fiber array with three concentric circles around the central emission is determined. A reflective intensity-modulated fiber optic sensor (FOS) is employed to detect surface defects on bearings. The structural parameters of the FOS are simulated through Matlab, considering the inner/outer diameter, numerical aperture, and axial spacing of the sensor. This work involves designing modulation light source excitation circuits, photoelectric conversion module circuits, pre-amplification differential amplifier circuits, infinite gain bandpass filtering circuits, and window function comparison circuits. This effectively amplifies the defect feature signals and eliminates noise interference. In experiments, the sensor probe is fixed on the support of a micro-displacement measurement platform. By adjusting the distance between the probe and the side surface through rotation, initial tests are conducted using standard roughness samples. The results indicate that installing the sensor probe at a distance of 0.92 mm from the side surface provides better measurement of surface roughness. The oscilloscope waveform reveals that the FOS can identify defects on different bearing surfaces. Furthermore, the bearing surface is divided into sections with engraved text (seal cover part) and without engraved text (inner and outer rings of the bearing). Using computer vision (CV) technology, a FOS detection system is designed, achieving a defect recognition rate of 99% for bearings, in line with the intended design goals.

Intensity-Modulated Fiber-Optic Sensor: A Novel Grid Measurement Unit

This article presents a novel approach to physical-displacement-based power grid measuring via an intensity-modulated fiber-optic sensor (IMFOS). An IMFOS utilizes one fiber to transmit the intensity modulated light from its electro-optic controller to a fiber-optic probe. The power grid voltage and current can induce physical displacements in transducers via the piezoelectric effect and the Lorentz law, respectively, which then result in a distance change between the optical probe and the reflective surface of the transducers. In parallel, multiple fibers are used to collect the reflective light for electro-optic conversion. A National-Instruments-based characterization platform is set up for performance evaluation. The testing result demonstrates that the IMFOS is immune to the inherent dc and low-frequency saturation issues prevalent in conventional potential and current transformers. Finally, the IMFOS is implemented in a universal grid analyzer to illustrate its applicability for phasor estimation in actual power grids.

An intensity-modulated optical fiber sensor with agarose coating for measurement of refractive index

An intensity-modulated optical fiber sensor with agarose coating for measurement of refractive index

Low-cost real-time fiber optic sensor for intrusion detection

PurposeThe purpose of this paper is to introduce a novel intensity-modulated fiber optic sensor for real-time intrusion detection using a fiber-optic microbend sensor and an optical time-domain reflectometer (OTDR).Design/methodology/approachThe proposed system is tested using different scenarios using person/car as intruders. Experiments are conducted in the lab and in the field. In the beginning, the OTDR trace is obtained and recorded as a reference signal without intrusion events. The second step is to capture the OTDR trace with intrusion events in one or multiple sectors. This measured signal is then compared to the reference signal and processed by matrix laboratory to determine the intruded sector. Information of the intrusion is displayed on an interactive screen implemented by Visual basic. The deformer is designed and implemented using SOLIDWORKS three-dimensional computer aided design Software.FindingsThe system is tested for intrusions by performing two experiments. The first experiment is performed for both persons (>50 kg) in the lab and cars in an open field with a car moving at 60 km/h using two optical fiber sectors of lengths 200 and 500 m. For test purposes, the deformer length used in the experiment is 2 m. The used signal processing technique in the first experiment has some limitations and its accuracy is 70% after measuring and recording 100 observations. To overcome these limitations, a second experiment with another technique of signal processing is performed.Research limitations/implicationsThe system can perfectly display consecutive intrusions of the sectors, but in case of simultaneous intrusions of different sectors, which is difficult to take place in real situations, there will be the ambiguity of the number of intruders and the intruded sector. This will be addressed in future work. Suitable and stable laser power is required to get a suitable level of backscattered power. Optimization of the deformer is required to enhance the sensitivity and reliability of the sensor.Practical implicationsThe proposed work enables us to benefit from the ease of implementation and the reduced cost of the intensity-modulated fiber optic sensors because it overcomes the constraints that prevent using the intensity-modulated fiber optic sensors for intrusion detection.Originality/valueThe proposed system is the first time long-range intensity-modulated fiber optic sensor for intrusion detection.

Materials and methods employed in the construction of a multipurpose intensity modulated fiber optic sensor

Abstract The Constitution and the geometry aspects of any sensor is influenced by several factors involved in the assembling of sensor. It is basically influenced by parameter to be measured, method of measuring the measurand, nature of the parameter i.e. weather the parameter is chemical, biological, physical, optical, electrical, magnetic, mechanical or acoustic etc., environment around it, etc. In most of the cases, several sensors are developed, meant to measure a single parameter with maximum achievable sensitivity. In the present paper a fiber optic multipurpose sensor is described, which can be used to measure various physical quantities of liquids with well defined combination at room temperature (30 °C), employing a specific set of materials and methods in the design operation of the sensor. Exploiting all the advantages offered by the fiber optic technology, the sensor was calibrated to measure ultrasonic velocity, refractive index, density, dielectric constant, viscosity, molar volume, acoustic impedance, molar refraction, viscous relaxation time, adiabatic compressibility, free intermolecular length, Gibb’s free energy, absorption coefficient, internal pressure, free volume, mole fraction, concentration, effective mass at room temperature and examined to exhibit superiority in all respects compared to the conventional sensors.

Optical fiber data glove for hand posture capture

Data gloves are widely used for hand posture monitoring in the field of virtual reality interactive technology. In fiber-based data gloves system, fiber Bragg gratings are usually used to monitor the bending of the finger joints, which is characterized by complex and high cost. In recent years, a new type of intensity-modulated optical fiber sensor with a sensitive zone has been developed, which can measure the bending deformation directly. In this paper, a low-cost data glove is developed based on this kind of sensor, which can monitor the posture of the hand. A sensor belt is proposed. The configuration scheme of the sensor and the packaging process of the sensor belt are studied. An untreated fiber which shares the same light source with fiber sensor is introduced as a base signal. Division operation between sensor signal and base signal is done to reduce the measurement error caused by instability of light source. A direction sensor is fixed on the back of the glove to monitor the posture of the palm. The experimental results show that the measurement errors of data glove are π/40 and π/120 respectively when measuring the finger joints and palm pitch, which indicates the effectiveness of proposed data glove.

Wind speed monitoring system based on optical fiber curvature sensor

A new type of intensity-modulated optical fiber sensor with an enhanced sensitivity area has been developed in recent years, which can measure the curvature deformation directly. This paper proposes a wind speed monitoring system based on the optical fiber sensor. The structure of the monitoring system is designed, and the venturi tube is introduced to improve the response of the system to the wind speed. The mechanical structure of monitoring system converts the wind speed into the periodic bending of a cantilever beam. At the same time, the optical fiber curvature sensor is fixed on the cantilever beam. In this way, the wind speed is measured by monitoring the frequency of the periodic signal of the fiber sensor. The mathematical model of the monitoring system is established. The experiments are carried out and the experimental results show that the measurement error and the repeating precision of the wind speed monitoring system are within ±0.65 m/s and ±2.9% respectively, which indicates the effectiveness of the monitoring system.

Reflected Light Intensity-Modulated Continuous Liquid Level Sensor Based on Oblique End Face Coupling Optical Fibers

A light intensity-modulated optical fiber sensor for continuous level measurement is proposed and demonstrated. The sensor is constructed by vertically arranging groups of fibers on the oblique surface which reflects all the incident light when the fibers are in the air but a small proportion of light when the fibers are immersed in the liquid. In order to implement easy modulation and detection, the angle of oblique surface is specially designed to get the maximum intensity modulation according to Fresnel reflection. The fiber groups consist of emitting and receiving fibers, which are tightly fixed to make it easy to detect reflected light based on side coupling effect. The calculation model of the oblique structure and the light path simulation by finite element analysis are used to optimize the oblique angle and prove the feasibility of the sensor. Gradient level experiments and stability tests in the laboratory indicate that the sensor has high sensitivity of 0.21mW/cm, superior resolution and good stability.

MEMS-Based Reflective Intensity-Modulated Fiber-Optic Sensor for Pressure Measurements.

A reflective intensity-modulated fiber-optic sensor based on microelectromechanical systems (MEMS) for pressure measurements is proposed and experimentally demonstrated. The sensor consists of two multimode optical fibers with a spherical end, a quartz tube with dual holes, a silicon sensitive diaphragm, and a high borosilicate glass substrate (HBGS). The integrated sensor has a high sensitivity due to the MEMS technique and the spherical end of the fiber. The results show that the sensor achieves a pressure sensitivity of approximately 0.139 mV/kPa. The temperature coefficient of the proposed sensor is about 0.87 mV/°C over the range of 20 °C to 150 °C. Furthermore, due to the intensity mechanism, the sensor has a relatively simple demodulation system and can respond to high-frequency pressure in real time. The dynamic response of the sensor was verified in a 1 kHz sinusoidal pressure environment at room temperature.

Intensity modulated silver coated glass optical fiber refractive index sensor

Miniature optical fiber sensors with thin films as sensitive elements could open new fields for optical fiber sensor applications. Thin films work as sensitive elements and a transducer to get response and feedback from environments, in which optical fibers act as a signal carrier. A novel Ag coated intensity modulated optical fiber sensor based on refractive index changes using IR and UV-Vis (UV-visible) light sources is proposed. The sensor with an IR light source has higher sensitivity compared to a UV-Vis source. When the refractive index is enhanced to 1.38, the normalized intensity of IR and UV-Vis light diminishes to 0.2 and 0.8, respectively.

Fast response relative humidity clad-modified multimode optical fiber sensor with hydrothermally dimension controlled ZnO nanorods

This work investigates the growth of dense and well-aligned Zinc Oxide (ZnO) nanostructure on multimode optical fiber through low temperature hydrothermal technique and its application as Relative Humidity (RH) sensor. Exponentially decaying evanescent fields were exploited for developing intensity modulated fiber optic sensors. To maximize evanescent fields in the sensing region, a 125µm diameter optical fiber was chemically etched to 28µm. It accordingly gives rise to a significantly enhanced interaction between the device and ambient environment. ZnO nanorods were grown on the 28µm diameter optical fiber with different precursor concentrations and pH values. The nanorods with high density and uniformity were obtained for 0.01M concentration. The developing samples were characterized by X-Ray Diffraction (XRD) pattern, Scanning Electron Microscopy (SEM) and Photoluminescence (PL) spectroscopy. Experimental results revealed a significant increase in the height and width of nanorods by reducing pH, which led to red-shift of the PL peaks. Sensitivity was investigated in two different intervals; lower and higher than 55% RH such that further variation of the output light intensity was observed in the former case. Comparative sensing experiments demonstrated response/recovery time decreased to 2.3s/5.2s for sample with 0.01M concentration. Significant features, such as fast response and recovery time, make the developed device a promising candidate in the deployment of future networks particularly for long-haul telecommunications.

Pulse reference-based compensation technique for intensity-modulated optical fiber sensors

We propose a compensation technique based on pulse reference for intensity-modulated optical fiber sensors that can compensate the power fluctuation of the light source, the change of optical components transmission loss, and the coupler splitting ratio. The theoretical principle of this compensation technique is analyzed and a temperature sensor based on fiber coating-covered optical microfiber is carried out to demonstrate the compensation effect. The system noise is measured to be 0.0005 dB with the temperature sensitivity reaching ?0.063 dB/°C, and the output drift is 0.006 dB in 2 h at room temperature. The output shows a slight variation (0.0061 dB) when the light source and the common light path suffer a 3 dB attenuation fluctuation.

Tip-Clearance Measurement in the First Stage of the Compressor of an Aircraft Engine.

In this article, we report the design of a reflective intensity-modulated optical fiber sensor for blade tip-clearance measurement, and the experimental results for the first stage of a compressor of an aircraft engine operating in real conditions. The tests were performed in a ground test cell, where the engine completed four cycles from idling state to takeoff and back to idling state. During these tests, the rotational speed of the compressor ranged between 7000 and 15,600 rpm. The main component of the sensor is a tetrafurcated bundle of optical fibers, with which the resulting precision of the experimental measurements was 12 µm for a measurement range from 2 to 4 mm. To get this precision the effect of temperature on the optoelectronic components of the sensor was compensated by calibrating the sensor in a climate chamber. A custom-designed MATLAB program was employed to simulate the behavior of the sensor prior to its manufacture.

Intensity-Modulated Optical Fiber Sensor for AC Magnetic Field Detection

An erbium-doped (Er3+) fiber optic laser is proposed for sensing alternated magnetic fields by measuring the laser intensity modulation. The sensor is fabricated using two partially overlapped narrow-band fiber Bragg gratings (FBGs) and a section of doped fiber in a Fabry–Perot configuration. Laser power stability and bandwidth are studied while changing the overlap. A bulk rod of TbDyFe, a magnetostrictive material, is glued to both the FBGs and the laser wavelength and power are modulated according to the magnetic field. Acquisition and processing are done using virtual instrumentation. Results have shown the possibility of detecting 11.18 $\mu \text{T}_{\mathrm {{rms}}}/\surd $ Hz for an alternating magnetic field of 4.17 mT $_{\mathrm {{rms}}}$ .

Study on Signal Processing Technology based on the Reflective Intensity Modulated Fiber Optic Sensor

Study on Signal Processing Technology based on the Reflective Intensity Modulated Fiber Optic Sensor

Optical Fiber Sensors for Aircraft Structural Health Monitoring.

Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

Experimental Study for Improving the Measurement Accuracy of Optical Fiber Sensor

This paper puts forward a double light path deep feedback integrated control compensation plan which is based on the current situation of the reflective intensity modulated fiber optic sensor compensation method. This scheme combines the deep feedback automation control technique with dual light path receiving and common-mode inhibition technique. The probe is designed to coaxial three-layer fiber structure. By experimental verification, this scheme effectively improves light intensity modulation fiber-optic sensor's measuring precision and stability and the error after compensation is less than 0.5%. The effect is Significant.

The Research on Measurement Accuracy of RIM-FOS

There are many factors that can effect on accuracy of reflective intensity-modulated fiber optic sensor (RIM-FOS). Operational object is a major element among them to fiber optic sensor, which is used in measurement of dynamic and static clearance of steam turbine, studied in this topic. For this reason, this letter researches on scattering characteristic of light on surface of medium and distributed function of outline of medium’s surface, and computes and analyzes on their effect on measuring. All of above are benefit to improve accuracy of this kind of sensors.

Pure and Iso-Butyl Methyl Ketone Treated Multi-Walled Carbon Nanotubes for Ethanol and Methanol Vapor Sensing

Multi-walled carbon nanotubes (MWCNTs) coated intensity modulated fiber optic sensor for the detection of ethanol and methanol vapors at room temperature is reported. Pure, 30 and 60 min iso-butyl methyl ketone (IBMK) treated MWCNT were coated on cladding removed polymethyl methacrylate fiber by the dip coating technique. The pure and IBMK treated MWCNT coated fibers were used as sensors. Response of the sensors was studied by measuring the change in output light intensity for different methanol and ethanol vapor concentrations in the range of 0-500 ppm. The 60 min IBMK treated MWCNT coated sensor showed 2 and 3.4 fold increase in the sensitivity for methanol and ethanol vapors at 640 and 630 nm wavelengths light, respectively, compared with the pristine MWCNT coated sensor. Fourier transform infrared spectroscopy confirmed the attachment of C=O functional group in IBMK treated MWCNT. Thermogravimetry results reveal the functionalized nanotubes decomposed at 475 °C after the elimination of attached functional groups. The pristine nanotubes start to decompose at 540 °C. The randomly oriented nanotubes layer of average thickness 1.5 μm on the cladding modified fiber is observed from scanning electron microscope images.

An intensity-modulated optical fiber sensor with concave mirror for measurement of displacement

Two fiber intensity-modulated sensors are investigated and used in number of applications, including those in military, industry, biomedical, and aerospace. A common form of two fiber intensity-modulated optical fiber sensor performs its measurement by making use of a pair of straight optical fibers with a plane reflector. The reflected optical intensity is a function of distance between fiber tips and plane reflector as well as refractive index of the medium. This paper describes an alternative sensing structure with a concave reflector instead of a plane reflector and demonstrates the derivation of the geometric mathematical model for analyzing its sensing characteristics. The mathematical model shows that the blind region is minimized, when the plane reflector is replaced by a concave reflector. Such type of optical sensor can be used where space required for the measurement is the major limitation. Experimental results obtained confirm the model.