Reflective Optical Sensor Research Articles

Research on reflective intensity-modulated fibre optical pressure sensor based on desensitisation of temperature compensation method

Research on reflective intensity-modulated fibre optical pressure sensor based on desensitisation of temperature compensation method

Dual-channel fiber optic current sensor based on carrier-transposed demodulation technique

A dual-channel fiber optic current sensor based on carrier-transposed demodulation technique is proposed and experimentally demonstrated. The system is implemented by adding another sensing channel to a standard reflective fiber optic current sensor, which shares numerous key optical devices without much additional expense. The output properties of the system are theoretically analyzed and numerically investigated to demonstrate the feasibility of independent current measurement at different operating frequencies. And the current sensitivity can be flexibly adjusted by changing the modulation amplitude. Based on the carrier-transposed demodulation technique, the current sensing information of both channels can be obtained independently and the cross-talk between them can be eliminated tactfully. The experimental results demonstrate that the current measurements for both channels are well independent and the channel-to-channel influences is relatively low with the standard deviation of 0.0197 mV and 0.0141 mV, respectively. The proposed scheme provides a promising approach for dual-channel current measurement with the advantages of compactness and simplicity and can be applied in practical applications without much additional cost.

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.

Development and Testing of a Data Capture Device for Use With Clinical Incentive Spirometers: Testing and Usability Study.

The incentive spirometer is a basic and common medical device from which electronic health care data cannot be directly collected. As a result, despite numerous studies investigating clinical use, there remains little consensus on optimal device use and sparse evidence supporting its intended benefits such as prevention of postoperative respiratory complications. The aim of the study is to develop and test an add-on hardware device for data capture of the incentive spirometer. An add-on device was designed, built, and tested using reflective optical sensors to identify the real-time location of the volume piston and flow bobbin of a common incentive spirometer. Investigators manually tested sensor level accuracies and triggering range calibrations using a digital flowmeter. A valid breath classification algorithm was created and tested to determine valid from invalid breath attempts. To assess real-time use, a video game was developed using the incentive spirometer and add-on device as a controller using the Apple iPad. In user testing, sensor locations were captured at an accuracy of 99% (SD 1.4%) for volume and 100% accuracy for flow. Median and average volumes were within 7.5% (SD 6%) of target volume sensor levels, and maximum sensor triggering values seldom exceeded intended sensor levels, showing a good correlation to placement on 2 similar but distinct incentive spirometer designs. The breath classification algorithm displayed a 100% sensitivity and a 99% specificity on user testing, and the device operated as a video game controller in real time without noticeable interference or delay. An effective and reusable add-on device for the incentive spirometer was created to allow the collection of previously inaccessible incentive spirometer data and demonstrate Internet-of-Things use on a common hospital device. This design showed high sensor accuracies and the ability to use data in real-time applications, showing promise in the ability to capture currently inaccessible clinical data. Further use of this device could facilitate improved research into the incentive spirometer to improve adoption, incentivize adherence, and investigate the clinical effectiveness to help guide clinical care.

Reflective Optical Tactile Sensor Based on Fiber Specklegram Analysis With the Capability of Contact Position Identification

A reflective tactile sensing scheme based on fiber specklegram analysis is proposed in this study. The specially designed sensor probe with a reflector inside was 3D printed from elastic material. A section of single mode fiber (SMF) and a section of multimode fiber (MMF) were embedded under the reflector. The light emitted from the SMF is reflected by the reflector and the reflected light illuminates the MMF. At the output facet of the MMF, specklegram is detected by a camera. The reflector consists of two soft mirrors that are perpendicular to each other originally. The contact force on the sensor probe causes the variation of the angle between the two mirrors. The transmission path of the light from SMF to MMF changes accordingly, which results in a changed specklegram. In this way, the zero-mean normalized cross-correlation coefficients of the fiber specklegrams decrease linearly with the increase of contact force. The sensitivity and measurement range of contact force are examined with MMFs of different diameters under two operating wavelengths. The negligible effect of fiber bending on the force sensing was also experimentally confirmed. In addition, the convolutional neural network is used to classify the specklegrams of three contact forces applied at nine positions of the sensor probe, and the average accuracy of classification is 100%, which shows its capability to identify the contact position on the probe. On the whole, the proposed tactile sensor is confirmed with a high sensitivity of force sensing in a proper measurement range and a capability to localize the contact position. The reflective structure also facilitates the integration with robot arm and other intelligent structures.

NonInvasive Glucose Fiber Sensor Based on Self-Imaging Technique: Proof of Concept

This paper proposes a proof of concept for a reflective fiber optic sensor based on multimode interference, designed to measure glucose concentrations in aqueous solutions that mimic the range of glucose concentrations found in human saliva. The sensor is fabricated by splicing a short section of coreless silica fiber into a standard single-mode fiber. By studying the principles of multimode interference and Self-imaging it was developed a sensing head that has a total length of 29.1 mm, approximately equal to the second self-image cycle. This sensing head allowed us to detect low concentrations of glucose (ranging from 0 to 268 mg/dl).

Distribution Network Communication Base on Reflective Fiber Optic Current Sensor

Fiber optic current sensor has been brought into the practical application. The main research trend is to use special fiber or improve the system structure, so as to deal with the unstable operation of fiber optic current sensor, thereby improving the measurement accuracy of current. The working principle of the reflective fiber optic current sensor is analyzed, and the Jones matrix is applied to characterize the optical components of the system. With the analysis of the error source of the sensor, a mathematical model of optical path error is constructed, including the fabrication error, temperature error, and strain error. Under these error analyses, the design scheme of twisted fiber optic current sensor is further proposed. In view of the structure of the traditional reflective fiber optic current sensor, twisted optical fiber is used for the 1/4 wave plate and sensing fiber part, and the constant-rate twisted optical fiber is used to replace the ordinary sensing fiber. The error caused by the linear birefringence in the optical fiber is reduced, the temperature sensitivity is lowered, the anti-stress effect is improved, and the adverse interference by temperature and strain on the sensing optical fiber is eliminated. The developed fiber optic current sensor is utilized for long-term pilot application in low-frequency distribution network communication. In the simulation test, the reflective fiber optic current sensor designed with a twisted fiber optic structure has a measurement accuracy of 0.5, which meets the system requirements. As error factors is added and corresponding compensation modules are introduced, the measurement accuracy is increased to 0.2. In the pilot applications of distribution network, it can provide comprehensive and real-time information support, thus laying the foundation for the communication management of the distribution network.

Simultaneous Measurement of Seawater Temperature and Pressure With Polydimethylsiloxane Packaged Optical Microfiber Coupler Combined Sagnac Loop

In the field of physical oceanography, the temperature and pressure of seawater are important fundamental parameters. In order to realize the simultaneous measurement of the temperature and pressure in seawater, a reflective optical fiber sensor based on polydimethylsiloxane (PDMS)-sealed optical microfiber coupler combined with a sagnac loop (OMCSL) is proposed. Benefiting from the high thermo-optical coefficient and large elasticity of PDMS, and the large-scale swift field transmission characteristics of optical microfiber coupler (OMC), the sensitivity and structural stability of our sensor is largely improved. The response performance of the sensor is further analyzed by numerical simulation calculations and theoretical modeling. Experimental results show that the temperature and pressure sensitivity of the sensor could reach −2.133 nm/°C and 3.416 nm/Mpa, respectively, about one order higher than that of bare fiber OMCSL. Furthermore, via inversely calculating the cross-sensitivity matrix, the temperature and pressure sensing can be demodulated simultaneously, and the average errors of the preliminary experimental settlements are 1.61% and 5.02%, respectively. Due to the merits of compact structure, easy fabrication, high sensitivity, fast response speed and high stability, the basic performance of this dual parametric sensor is comparable to the existing electrical temperature-depth (TD) sensor, which is expected to meet the practical application requirements of marine environmental monitoring and ocean dynamics research.

Reflective Optical Fiber Sensor Based on Dual Fabry Perot Cavities for Simultaneous Measurement of Salinity and Temperature

A reflective optical fiber sensor that is composed of two Fabry Perot cavities is proposed for temperature and salinity measurement. One of the Fabry Perot cavity which is fabricated by offset splicing is exposed to the ambient directly to sense the ambient salinity, the other is employed to compensate for the temperature coupling effect. A thin layer of the gold film is coated on the refractive index change interface, which makes the spectrum quality is no longer limited by the refractive index difference between the two sides of the interface. By applying the frequency division multiplexing (FDM) technique and cavity length demodulation technology, the measurement range is no longer restricted to the free spectrum range (FSR), which can realize salinity measurement in the full measurement range. The proposed sensor can realize the salinity sensitivity better than 50 nm/‰ and temperature sensitivity of 6.85 nm/°C in the cavity length domain. It is promising for salinity measurement application for its merits of low cost, easy fabrication, and long sensing distance.

Novel microsampling system for automated spectrophotometry

To enhance the performance of a conventional pulse width modulation (PWM)-based microsampling system, a novel system was developed by bifurcating a fluidic path and by reusing the conventional components. A micro-metering valve was newly equipped to control the speed of the sample introduction, and a reflective optical sensor was used to detect the arrival of a sample. In addition, an analog logic circuit was designed to minimize the response time of the control system. This approach features precise microsampling, rapid response, and stable operation. To verify the volumetric sampling performance and to understand the operational characteristics, a series of experiments were performed. The results show that the aspirated volume was maintained at about 2.8 microliters and that the aspiration requires less than 0.3 seconds. Moreover, the sample removal operation was performed identical to a conventional PWM-based microsampling system. Because our spectrophotometer is operated automatically, the reduction of the sampling time is highly advantageous to measure many samples. Therefore, the total measurement time may be reduced proportional to the number of samples to be analyzed.

Review of a Custom-Designed Optical Sensing System for Aero-Engine Applications

Fibre bundle-based reflective optical sensors are good candidates for parameter monitorisation in aero engines. Tip clearance is one of those parameters of great concern that is necessary to monitor. Within this optical technology, the evolution experienced by a custom-designed optical sensor is presented from its first configuration up to the fifth one. The performance of the last configuration is compared with those of other two optical sensors that are also based on a fibre bundle design. The comparison has been carried out in an experimental program in a transonic wind tunnel for aero engines. The proven high resolution and sensitivity of the last configuration of the optical sensor opens up the possibility to detect blade defects, cracks, etc. that could otherwise be hard to track.

Differential manometer with reflective optical sensor

For the purpose of the identification and quantification of the plasma effect on gas flow rate in atmospheric pressure discharges there was a strong need for differential manometer for fine and precise measurements which is indifferent on the influence of the charged particles. Therefore, a differential manometer with a completely free membrane has been constructed. Manometer is based on the use of reflective sensor CNY70. The basic request, undisturbed measurement of small value of differential pressure, up to 10 Pa, is realized with satisfying sensitivity and accuracy. Furthermore, different ranges of differential pressures measurable with the constructed instrument have been achieved by use of membranes made of different materials and with different thicknesses. The best linearity showed membranes made of copper and rubber. By means of five different membranes, the complete range of pressures from 1 Pa to 100 kPa is covered with substantial overlap.

Photoplethysmography in postoperative monitoring of deep inferior epigastric perforator (DIEP) free flaps

Objective: Deep inferior epigastric perforator (DIEP) free flaps are widely used as a reconstruction option following mastectomy in breast cancer. During such cases partial tissue necrosis can occur due to the insufficient blood supply to the transplanted tissue site. Therefore, monitoring of flap perfusion and early detection of flap failure is a prerequisite to flap survival. There is a need to develop a non-invasive, easy to use, reproducible and inexpensive monitoring device to assess flap perfusion postoperatively. Approach: A three-wavelength reflective optical sensor and processing system based on the principle of photoplethysmography (PPG) has been developed to investigate blood volumetric changes and estimate free flap blood oxygen saturation continuously and non-invasively in DIEP free flaps in the postoperative period. The system was evaluated in 15 patients undergoing breast reconstructive surgery using DIEP free flap. Main results and Significance: Good quality red, infrared and green PPG signals were obtained in the postoperative period. Initial estimation of blood oxygen saturation values estimated from the free flap PPGs seem to be in broad agreement with the commercial finger pulse oximeter used in this study. This pilot study has demonstrated that PPG has the potential to be used as a monitoring technique in assessing free flap viability.

In-Service Detection and Quantification of Railway Wheel Flat by the Reflective Optical Position Sensor.

Railway wheel tread flat is one of the main faults of railway wheels, which brings great harm to the safety of vehicle operation. In order to detect wheel flats dynamically and quantitatively when trains are running at high speed, a new wheel flat detection system based on the self-developed reflective optical position sensor is demonstrated in this paper. In this system, two sensors were mounted along each rail to measure the wheel-rail impact force of the entire circumference by detecting the displacement of the collimated laser spot. In order to establish a quantitative relationship between the sensor signal and the wheel flat length, a vehicle-track coupling dynamics analysis model was developed using the finite element method and multi-body dynamics method. The effects of train speed, load, wheel flat lengths, as well as the impact positions on impact forces were simulated and evaluated, and the measured data can be normalized according to the simulation results. The system was assessed through simulation and laboratory investigation, and real field tests were conducted to certify its validity and correctness. The system can determine the position of the flat wheel and can realize the quantification of the detected wheel flat, which has extensive application prospects.

Highly-sensitive and reflective glucose sensor based on optical fiber surface plasmon resonance

A reflective optical sensor based on surface plasmon resonance (SPR) was proposed to measure the glucose concentration. The gold film was sputtered on the surface of plastic cladding optical fiber to excite SPR and reflect light at the same time, making the SPR sensor highly sensitive to the variation of surrounding refractive index. Then, glucose oxidase (GOD) was adopted as the sensitive film of glucose and covalently bonded on the gold film. The enzymatic reaction between the GOD and the glucose led to the change of refractive index around the optical fiber sensor, and then cause a shift of the SPR spectrum. Therefore, the glucose concentration could be obtained by monitoring the shift of the resonance wavelength. Experimental results showed that the measurement sensitivity of the SPR sensor could reach 85.4 nm/(mg/mL) (for glucose concentration) with good selectivity and stability, which has great potential application in biomedicine and human health monitoring.

A New Technique for Improving the Estimation of a Reflective Optical Color Sensor

This paper proposes and experimentally demonstrates a novel technique of a precise color estimation by using a low cost reflective optical color sensor. The digital output signal of this sensor is a pulses series with a frequency proportional to the intensity of the incident light. In this sensor, three independent detector output signals with optimized spectral responsiveness allow discrimination between red, green and blue (RGB) light spectral components. The analytical expressions for RGB absorption efficiencies, which detect the color information, have been derived. An experimental set-up has been designed to determine the color difference, involving design of a portable color analyzer with wired and wireless computer interface. The detailed description and implementation of each design element are presented, while a developed algorithm is also discussed. The proposed algorithm apply a linear transformation to realize standardized colorimetric RGB and CIE31-XYZ color space coordinates responses. To that end, a correlation of the sensor outputs is established, a wide band correction matrix in old estimations is replaced by many narrowband correction matrices and the CIE standard curves of wavelengths are extracted and used to select a suitable narrowband correction matrix. Also, the sequential algorithm has been parallelized to reduce the response time in multiple measurement applications which need the big data processing. The experimental results in the vision spectrum confirm the theoretical analysis. Based on the findings of this experiment, the proposed system constitutes a high resolution and low cost solution for various color-sensing applications and colorimetric fields.

Retro-Reflective Fiber Optic Displacement Sensor for Performance Optimization Using Taguchi Method

Fiber optic displacement sensors are widely used in industry. Retro reflective fiber optic displacement sensor consists of parallel fibers with a reflector at a distance. Light is launched into the transmitting fiber which gets reflected by reflector. This reflected light is collected by the receiving fiber. The received light is function of the displacement of the reflector from the fiber end faces. This paper is targeted to obtain a robust design for the fiber optic displacement sensor (FODS) using well known Taguchi method. The design takes care of all noise parameters within constraints of manufacturing tolerances. The statistical data analysis is performed on the simulated results. The larger the better signal to noise quality characteristics is used to find the effect of control parameters in the data analysis. Taguchi analysis suggests dominant parameters, which affects the sensitivity of the FODS and causes immunity to noise. A source fiber inclination angle is chosen as an adjustment parameter. Other control parameters are used for fine tuning of the FODS design for achieving three qualities viz. best robustness, optimized sensitivity and robustness and best sensitivity.

Programming and wiring of a low-cost tachometer

This paper deals with development of a measurement system, which is capable to calculate the rotational speed of a rotor. The unit contains a microcontroller, an infrared reflective optical sensor with resistors. The selection of current limiting resistors of the optical sensor will be discussed in order to set up an electrical circuit. The simulation of the electrical circuit was performed to compare the voltage and current values with the calculated ones. Microcontroller programs were written in C language in order to compute the average frequency or the Root Mean Square (RMS) values of a rotating element. Comparative measurements were also carried out to check the accuracy of the developed system.

Reflective optical fiber sensor based on light polarization modulation for hydrogen sensing

A simple reflective hydrogen-sensing system based on polarization modulation is proposed and experimentally demonstrated. The sensing unit consists of a polarizer, a polarization control, and a sensing head composed of a short segment of polarization-maintaining fiber (PMF) with a Pt-loaded ${{\rm WO}_3}$WO3 coating. When the sensing head is exposed to a hydrogen environment, heat is generated due to the interaction between hydrogen and ${{\rm WO}_3}$WO3 with the help of catalyst Pt in air; then, the local temperature of the PMF increases, which results in the reflection spectrum shift because the light polarization state changes due to the variation of the birefringence coefficient of the PMF. Experimental results show that the system is capable of producing a rapid response to hydrogen with a high sensitivity of $\sim{18.04}\;{\rm nm/}\% $∼18.04nm/% (vol%) within the concentration range of 0–4% (vol%). Additionally, the sensing head has a probe structure with reflective measurement and immunity to humidity. Such features make the sensing system promising in the fields of hydrogen transportation or storage.

Reflective SPR Sensor for Simultaneous Measurement of Nitrate Concentration and Temperature

In this paper, a reflective fiber optic sensor based on surface plasmon resonance (SPR) was proposed to measure nitrate concentration and temperature simultaneously. The sensor adopted reflective structure, and used gold film as metal film for exciting SPR. Then, Cu-nanoparticles/carbon nanotubes composite film was used as sensitive material to measure nitrate concentration, and it was coated on the surface of the gold film by the dip coating method. Finally, polydimethylsiloxane was coated on part of the sensing probe to produce two independent resonance dips in the output spectrum. When the nitrate concentration and temperature changed, the two resonance dips would all move, but with different sensitivities. By monitoring the wavelength shifts of the two dips, the nitrate concentration and temperature could be measured simultaneously with using the dual-wavelength matrix method. Experimental results demonstrated that the measurement sensitivity of the nitrate concentration could reach 3.25 nm/lg[M], and the temperature measurement sensitivity was −2.02 nm/°C. Moreover, the sensor had high-mechanical strength and was easy to package, which could be applied to remote measurement field.