Linearity of the Faraday-rotation-type ac magnetic-field sensor with a ferrimagnetic or ferromagnetic rotator film

We analyze the linearity and modulation depth of ac magnetic-field sensors or current sensors, using a ferrimagnetic or ferromagnetic film as the Faraday rotator and employing the detection of only the zeroth-order optical diffraction component from the rotator. It is theoretically shown that for this class of sensor the condition of a constant modulation depth and that of a constant ratio error give an identical series of curves for the relationship between Faraday rotation angle Θ and polarizer/analyzer relative angle Φ. We give some numerical examples to demonstrate the usefulness of the result with reference to a rare-earth iron garnet film as the rotator.     

Plastic Optical Fibre Sensors for Environmental Monitoring: Biofouling and Strain Applications

Abstract: Two long-term environmental monitoring plastic optical fibre (POF) sensors are described, using light intensity modulation. An evanescent field biofouling sensor was developed and characterised with sensitivity ±0.007 refractive index units or 0.5% below n  = 1.4 and ±0.002 refractive index units or 0.15% above n  = 1.4. A tapered POF was developed and tested as a strain sensor, which demonstrated a significant proportion of excellent linearity and exhibited good agreement with measured strain values. The POF strain sensor appeared to be well-behaved in that it showed little data scatter and was able to monitor strains up to 1.4% without failure. These two applications clearly demonstrate the potential POF sensors have for cheap, on-line continuous environmental monitoring.     

Study of a fiber optic humidity sensor based on agarose gel

An optical fiber humidity sensor was fabricated using a hydrophilic gel (agarose) deposited on the tapered plastic optical fiber (POF). The sensing element, agarose, can absorb and exude moisture from/to the ambience, thereby altering its refractive index and changing its ability to modulate the intensity of light that propagates through the fiber. Thus, the operating principle of the sensor is based on the intensity modulation technique, which utilizes a tapered POF probe coated with agarose that is sensitive to humidity. The POF, which was fabricated using an etching method, has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 80%, the output voltage of the sensor with agarose gel of 0.5% weight content decreases linearly from 2.24 mV to 1.55 mV. The agarose-based sensor produces a sensitivity of 0.0228 mV/%, with a slope linearity of more than 98.36%. The tapered fiber with agarose gel of 1% weight content produces a sensitivity of 0.0103 mV/% with a slope linearity of more than 94.95% and a limit of detection of 2.635%, while the tapered fiber with agarose gel of 1.5% weight content produces a sensitivity of 0.0079 mV/% with a slope linearity of more than 98.53% and a limit of detection of 6.853%. The fiber with agarose gel of 0.5% weight content shows higher sensitivity compared to that of 1% and 1.5% due to the effect of pore size, which changes with concentration. The results demonstrate that agarose-based optical fiber sensors are both sensitive and efficient for economical and flexible measurements of humidity.     

Faraday-effect optical current sensor with a garnet film/ring core in a transverse configuration

A new scheme of the Faraday effectcurrent sensor of a magnetic ring-core type is reported. With this scheme a uniaxial magnetic garnet film is obliquely inserted into a very narrow gap in the ring core and a probe light beam is passed through the garnet film in the transverse direction to the core. It is experimentally demonstrated that this current sensor shows good sensitivity as well as good isolation from surrounding currents, particularly because of the very narrow core gap allowed. This transverse scheme is much simpler and less expensive than the known longitudinal scheme and can offer a practical optical current sensor of a ring-core type.     

基于电涡流的新型靶式流量计

分析了利用电涡流效应测量靶受力后的位移进行流量检测的原理,并设计了相应的靶结构,构建了具有温度压力补偿的测量系统,最后根据流量标定实验数据,建立了流量传感器的数学模型.试验结果表明,该靶式流量计线性好,灵敏度高,且测量精度优于1%.     

Optical sensors and the salt effect: a dual-transducer approach to acidity determination in a salt-containing concentrated strong acid

A dual-transducer approach has been developed to decompose the optical signals of acid sensors in salt-containing concentrated acid solutions and to give acid and salt concentrations in concentrated LiCl-HCl, CaCl2-HCl, and AICl3-HCl solutions, respectively. The optical acid sensors in this approach are films of porous sol-gel SiO2 or SiO2-Nafion composite doped with low-pKa indicators. A novel linear relationship (dA/dCsalt)cCacid = beta x (dA0/dCacid)Csalt = 0 (A = absorbance of the sensor in a salt-containing HCl solution; A0 = absorbance of the sensor in a salt-free acid solution) was found, and the current approach is based on a set of nonlinear equations derived from this relationship.     

Development of an ordered array of optoelectrochemical individually readable sensors with submicrometer dimensions: application to remote electrochemiluminescence imaging

A novel array of optoelectrochemical submicrometer sensors for remote electrochemiluminescence (ECL) imaging is presented. This device was fabricated by chemical etching of a coherent optical fiber bundle to produce a nanotip array. The surface of the etched bundle was sputter-coated with a thin layer of indium tin oxide in order to create a transparent and electrically conductive surface that is insulated eventually by a new electrophoretic paint except for the apex of the tip. These fabrication steps produced an ordered array of optoelectrochemical sensors with submicrometer dimensions that retains the optical fiber bundle architecture. The electrochemical behavior of the sensor array was independently characterized by cyclic voltammetry and ECL experiments. The steady-state current indicates that the sensors are diffusively independent. This sensor array was further studied with a co-reactant ECL model system, such as Ru(bpy)(3)(2+)/TPrA. We clearly observed an ordered array of individual ECL micrometer spots, which corresponds to the sensor array structure. While the sensors of the array are not individually addressable electrochemically, we could establish that the sensors are optically independent and individually readable. Finally, we show that remote ECL imaging is performed quantitatively through the optoelectrochemical sensor array itself.     

Multiplexing of optical fiber gas sensors with a frequency-modulated continuous-wave technique

We report on the use of a frequency-modulated continuous-wave technique for multiplexing optical fiber gas sensors. The sensor network is of a ladder topology and is interrogated by a tunable laser. The system performance in terms of detection sensitivity and cross talk between sensors was investigated and found to be limited by coherent mixing between signals from different channels. The system performance can be improved significantly by use of appropriate wavelength modulation-scanning coupled with low-pass filtering. Computer simulation shows that an array of 37 acetylene sensors with a detection accuracy of 2000 parts in 10(6) for each sensor may be realized. A two-sensor acetylene detection system was experimentally demonstrated that had a detection sensitivity of 165 parts in 10(6) for 2.5-cm gas cells (or a minimum detectable absorbance of 2.1 x 10(-4)) and a cross talk of -25 dB.     

Simultaneous measurement of current and voltage by use of one bismuth germanate crystal

An optical fiber sensor is presented that allows current and voltage to be measured simultaneously by use of only one block of bismuth germanate crystal. The polarized light from the sensing crystal is split into two light beams: One beam is utilized for current measurement based on the Faraday effect, and the other one is utilized for voltage measurement based on the Pockels effect. Compared with the existing optical sensors that can measure current and voltage simultaneously, this sensor is simple and inexpensive and allows measurement of electric power. The simultaneous measurements of ac electric current from 0.05 to 10 A, voltage from 1 to 235 V, and power from 2 to 1000 W have been achieved with good linear-response characteristics. The input characteristics and measurement uncertainties that are due to the nonlinear error of the sensing system are also discussed.     

Optical Fiber Humidity Sensors Using Nanostructured Coatings of SiO$_{2}$ Nanoparticles

In this paper, a new optical fiber humidity sensor based on superhydrophilic coating is proposed. The electrostatic self-assembly technique has been used to create a nanometric scale surface on the tip of a standard single-mode pigtail. The fabricated sensor has demonstrated a good linearity in the range from 40% to 98% of relative humidity (RH). A variation of 10 dB in reflected optical power is achieved with a response time of only 150 ms. Among other applications, this sensor is intended to be used for monitoring the human breathing, so high dynamic performances are required, specially in the higher RH ranges.     

Electro-optic sensor from high Q resonance between optical D-fiber and slab waveguide

An electro-optic sensor capable of detecting electric fields with a high degree of sensitivity and linearity is fabricated using optical D-fiber. The slab coupled optical sensor utilizes weak coupling and long evanescent interaction with a lithium niobate waveguide. Transmission dips from mode resonances have a linewidth of 0.12 nm and a Q factor of approximately 13,000. These sharp resonances improve device sensitivity and are achieved due to the unique fabrication process possible with D-shaped fibers. The sensor deviates <0.1% from linearity while monitoring fields between 200 V/m and 20 kV/m and promises high sensitivity to fields well beyond that range.     

Giant Magnetoimpedance Current Sensor With Array-Structure Double Probes

We have designed a novel giant magnetoimpedance (GMI) noncontact current sensor with array structure double probes. Unlike previously reported sensors, our sensor's probes consist of many pieces of commercial amorphous ribbons, which are parallel to each other, equidistant, and connected in series, and a permanent magnet provides a bias magnetic field. The double-probe output shows the best sensitivity and linearity at a bias magnetic field of 7.40 Oe. Under this field, the sensor shows sensitivity of 1 V/A in the current range of plusmn3 A, measurement precision of less than 0.15% at room temperature, and good thermal stability in the temperature region between -20degC and 30degC.     

Fiber loop ringdown for physical sensor development: pressure sensor

A new method of developing optical fiber pressure sensors by use of a fiber loop ringdown scheme is described. The fiber loop ringdown system is characterized in terms of the ringdown baseline stability, fiber transmission loss, and fiber refractive index. The overall sensor performance is demonstrated by use of sensing forces applied to the sensor head. The current device can sense pressures in the range of 0 to 9.8 x 10(6) Pa, converted approximately from the applied forces. The sensor's linear response, repeatability, detection sensitivity, measuring dynamic range, and temperature tolerance are explored.     

Brillouin Sensing Cable: Design and Experimental Validation

We report on the design and experimental validation of a distributed Brillouin-based optical fiber sensor embedded into concrete structures for temperature and strain measurement. A composite-made wave-like coating designed by finite-element analysis ensures the sensor is transferring optimally temperature and strain fields from the concrete to the optical fiber, where Brillouin scattering takes place. During all experiments, sensors have been interrogated with a commercially available Brillouin optical time-domain reflectometer unit. First, temperature sensitivity of the Brillouin frequency shift were evaluated in PANDA and SMF28 optical fibers, before wrapping them into the specific sheath for embedment into a 3 m-long reinforced concrete beam. Temperature measurements during concrete beam casting agreed with reference measurements, and showed the significant sensor coating influence. A month later, strain measurements performed during a four-point bending experiment showed promising results: linearity and reliability of measurements were demonstrated, under tensile as well as compressive loadings.     

Mathematical Modeling of Intensity-Modulated Bent-Tip Optical Fiber Displacement Sensors

Intensity-modulated optical fiber displacement sensors have a potential to be used in a number of applications, including those in industry, military, aerospace, and medicine. Compared with other types of optical fiber sensors, intensity-modulated sensors offer distinctive advantages in that they are usually less complex, inexpensive, and less sensitive to thermal-induced strain. They are able to perform accurate contactless sensing while being of a small size and having a wide dynamic range. A common form of the intensity-modulated optical fiber sensor performs its measurement by making use of a pair of straight parallel optical fibers integrated with a moving reflector modulating the reflected optical signal intensity. Although such an optical modulation configuration exhibits good sensing ability, improvement on its performance could still be made to widen the extent of its application areas. This leads to the development of more effective intensity modulation mechanisms utilizing bent-tip optical fibers and a reflector that can either laterally slide or longitudinally move with reference to the central axis of the fibers. This paper describes such alternative sensing structures and demonstrates the derivations of mathematical models proposed for analyzing their sensing characteristics. Based on experimental studies, the models are verified and validated for the analysis of sensitivity and linearity.      

Mechanical stress measurement by an achromatic optical digital speckle pattern interferometry strain sensor with radial in-plane sensitivity: experimental comparison with electrical strain gauges

This paper shows the optical setup of a radial in-plane digital speckle pattern interferometer which uses an axis-symmetrical diffractive optical element (DOE) to obtain double illumination. The application of the DOE gives in-plane sensitivity which only depends on the grating period of the DOE instead of the wavelength of the laser used as illumination source. A compact optical layout was built in order to have a portable optical strain sensor with a circular measurement area of about 5 mm in diameter. In order to compare its performance with electrical strain sensors (strain gauges), mechanical loading was generated by a four-point bending device and simultaneously monitored by the optical strain sensor and by two-element strain gauge rosettes. Several mechanical stress levels were measured showing a good agreement between both sensors. Results showed that the optical sensor could measure applied mechanical strains with a mean uncertainty of about 5% and 4% for the maximum and minimum principal strains, respectively.     

High-basicity determination in mixed water-alcohol solutions by a dual optical sensor approach

The activity of NaOH is known to be significantly affected by the presence of an alcohol in aqueous solutions. A novel linear relationship between (deltaA/deltaC(alcohol)) and C(base) was found in the highly alkaline, mixed H2O-ROH solutions (R = Me, Et, i-Pr). The use of this linear relationship led to a dual-transducer approach to decompose the optical signals of optical base sensors and to give base and alcohol concentrations in concentrated NaOH-H2O-ROH solutions ([OH-] = 0.05-3.6 M). The scope of the new dual-sensor approach was evaluated, and errors in C(base) and C(alcohol) were analyzed. The optical base sensors consist of sol-gel SiO2-ZrO2-organic polymer composites doped with high-pKa indicators. The pKa(s) of the indicators encapsulated in the composite films were determined and found to be affected by the composition of the sol-gel composites. Optical sensors and their uses in multicomponent systems are of intense current interest.( 1-7) In the multicomponent systems, the activity of the analyte and sensor response are often affected by change in ionic strength. For optical sensors that are based on indicator equilibria involving the analyte as their transducing mechanism, such effect is particularly significant. The concentrations of both the analyte and other chemicals affect ionic strength, and the sensor response to concentration of the analyte is thus often indistinguishable from those of other chemicals. An accurate measurement of each component in these multicomponent systems is actively studied. Several approaches have been developed to correct ionic strength in optical sensing for the pH region and solutions of low-to-medium ionic strength. (1-9) We recently reported a dual-transducer approach to measure acid concentrations (2-9 M HCl) in salt-containing, concentrated strong acids such as MClx-HCl (M = Li, Ca, Al) solutions. (10) This approach was shown to reduce the error in C(acid) from, for example,     

Fabrication and Sensing Performance of Smart Composite Structures Using Optical Fibre Sensors

This paper determines the performance of Fibre Bragg Grating (FBG) sensors for strain sensing applications in carbon fibre composite materials. Carbon fibre laminates in either cross-plied or quasiisotropic stacking sequences were fabricated using T300/Hexcel 914 prepregs. The FBG optical sensors were either surface attached, or embedded within laminates. The sensor orientation was aligned either parallel or transverse to the adjacent carbon fibre layers. The composite structures with integrated FBG sensors were subjected to static tensile loading. A scanning fibre Fabry-Perot filter was used to monitor the reflected Bragg wavelengths. The optical sensor embedded between two 90° carbon fibre plies shows a high sensitivity to multi-site cracking formed in the transverse plies. The embedding in 90° plies seems to change the local stress distributions and to become a source of crack initiation. Efficient stress transfer from the host materials to the sensors is dependent upon incorporation methods, the thickness of the adhesive layers, and the location of the sensors.     

Calibration of Multi-Axis MEMS Force Sensors Using the Shape-From-Motion Method

Precise calibration of multi-axis microelectromechanical systems (MEMS) force sensors is difficult for several reasons, including the need to apply many known force vectors at precise orientations at the micro- and nanoNewton (nN) force scales, and the risk of damaging the small, fragile microdevices. To tackle these challenges, this paper introduces the shape-from-motion calibration method. A new design of a two-axis MEMS capacitive force sensor with high linearity and nN resolutions is presented. Structural-electrostatic coupled-field simulations are conducted in order to optimize the sensor design. The designed sensor is calibrated with the shape-from-motion method, the least-squares method as well as the gravity-based method for comparison purposes. Calibration results demonstrate that the shape-from-motion method provides a rapid, practical, and accurate technique for calibrating multi-axis MEMS sensors     

基于分子印迹技术的尿素仿生微传感器

设计了基于分子印迹与电化学微传感器的尿素仿生微传感器,采用MEMS工艺制作集成微型3电极系统,实现了传感器的微型化.通过电化学方法制备了分子印迹聚合物(MIP),印证了分子印迹聚合物的印迹效果.比较了3支传感器的响应曲线,得到了相近的灵敏度,灵敏度在0.10μA/(μmol.L-1)左右,线性度达到了0.95,检测下限为1.00μmol/mL,分析尿素溶液的标准偏差小于5%,达到和接近临床分析要求,为生物传感器向仿生生物传感器发展进行了具有临床意义的尝试.