An experimental study on the concrete hydration process using Fabry–Perot fiber optic temperature sensors

This paper describes the contribution of Fabry–Perot (FP) fiber optic temperature sensor to investigate the effects of concrete hydration process. The FP temperature sensor was easily fabricated by controllable chemical etching and adjustable fusion splicing. Detailed optical properties of the sensor were theoretically analyzed and temperature calibration experiments were performed. A sensor with a 90 μm cavity length was demonstrated to have a temperature sensitivity of 0.01 nm/°C and the linearity coefficient of 0.99. Furthermore, the FP sensor was embedded in the concrete structure for sensing the temperature change during the early age of hydration. During the concrete hydration experiments, the measured peak temperatures of the concrete specimens with different water-to-cement (w/c) ratios of 0.4, 0.5 and 0.6 were 51.42 °C, 52.88 °C, and 55.08 °C, respectively, corresponding to final setting times of 13.52 h (w/c = 0.4), 14.16 h (w/c = 0.5) and 15.2 h (w/c = 0.6) after concrete casting. Temperature profiles will be used for concrete hydration heat study, which will help us to have a better understanding of cement hydration behavior.     

一种光纤光栅传感实验仪的可靠性分析

光纤光栅作为一种传感单元可以测试应变、温度和压力等物理量.近年来,可用于光纤光栅信号解调的技术和仪器相继出现,并在不同的场合得到了很好的应用.但由于制造、安装和操作等原因,这些仪器的可靠性问题也开始引起不同程度的关注.仪器的可靠性分析是其设计过程中不可缺少的重要环节之一.以一种基于匹配解调技术的准分布式光纤光栅解调仪为例,介绍了该仪器的基本组成和原理;采用故障树法从机械和光电器件的可能出现的如光纤光栅脆断、螺钉松动和脱焊等故障和失效形式出发,根据光路配置、电路以及机械结构分析了可能的故障模式,计算了可靠性.结论有利于对这类仪器的故障诊断和维护.     

Electrolytic sensor for trace level determination of moisture in gas streams

A thin film platinum electrode-based electrolytic moisture sensor for the measurement of lower concentrations of moisture in gas streams with flow rates lesser than 5 ml/min was designed. The thin film electrode was fabricated with pulsed laser ablation technique and screen printing. The PL-ablated electrode showed deterioration after 80 h of operation. The screen-printed thick film electrode sustained for more than 12 months. The response of the sensor was absolute and so the electrolytic and non-electrolytic currents were deduced. The sensor recovery time from either extreme dry or moist conditions was 70 s. The concentration of trace moisture in an argon cylinder was identified using the present design and the values were found to be 3.97 ± 0.07 ppm at cylinder pressure of 150 kg/cm² and 37.41 ± 0.27 ppm at 30 kg/cm². In addition to the sensitivity up to 1 ppm the present design could detect the sensor failure during operation.     

A bi-material microcantilever temperature sensor based on optical readout

As one of the simplest MEMS sensors, microcantilever can sense temperature faster and more sensitively than traditional thermometers as its small size and low thermal mass. In this paper, an Au/SiNx bi-material microcantilever temperature sensor based on optical readout is presented. The deflection of the cantilever varies with the change of temperature due to the differences in thermal expansion coefficients between gold and silicon nitride. Then, the temperature could be accurately measured by detecting the deflection of the cantilever with optical lever method. By experiments, the theoretical model is verified and the temperature characteristics of the sensor are also determined. With a commercial microcantilever, the temperature resolution of the sensor is tested to be 0.02 K when 25 mm length of optical arm set. By optimizing the microcantilever parameters, the temperature resolution of the sensor could be 0.1 mK. High sensitivity makes it suitable for some special precise temperature measurements.     

Measurement of thermal conductivity of fluid using single and dual wire transient techniques

A modified measurement device to measure thermal conductivity of fluids using transient hot-wire technique has been designed, developed, tested and presented in this paper. The equipment is designed such that the thermal conductivity could be measured using both single wire sensor of different length and dual wire sensor. The sensor, which is also a heater, is a platinum micro-wire of 50 μm diameter. The influence of wire length on the measurement of thermal conductivity of fluids is tested using two single wires of length 50 mm and 100 mm. The thermal conductivity is also measured using a dual hot wire arrangement; which is achieved by placing the 100 mm and 50 mm wires in a Wheatstone bridge with the 100 mm wire as the sensor and 50 mm wire as a compensation wire. The apparatus requires a 100 ml of test fluid to perform the experiment. The testing temperature of the test fluid during the experimentation can be suitably varied by the choice of heat exchange fluid used in the apparatus. Water is chosen as testing fluids for primary standards. When compared to single wires, the thermal conductivity of the fluids measured is consistent with dual-wire method with an uncertainty of ±0.25%.     

Real-time temperature measurement with fiber Bragg sensors in lithium batteries for safety usage

In this work, fiber Bragg grating (FBG) sensors are integrated in lithium batteries to measure temperature variations. In situ calibration of the FBG sensors against a co-located thermocouple shows a linear response. The thermal behavior of lithium batteries is real-time recorded by FBG sensors, during the batteries operation under normal and abnormal conditions. In spite of the small cathode mass and a low current, temperature variations of 0.1 °C are detected. The sensors also exhibit good thermal response to dynamic loading when compared with the thermocouple. The thermal stabilities of four kinds of cathode materials are estimated using FBGs testing results.     

Application of Fabry-Pérot and fiber Bragg grating pressure sensors to simultaneous measurement of liquid level and specific gravity

An approach is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-pressure-sensor system comprising a fiber Bragg grating (FBG) pressure sensor and a Fabry-Pérot (FP) pressure sensor. In the FBG sensor, the pressure is derived from the FBG wavelength shift induced when the sensor is immersed in the liquid. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The advantageous concept of the dual-pressure-sensor system is atmospheric pressure compensation. The experimental results show that the FBG and FP pressure sensors have sensitivities of 0.1495 nm/kPa and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the FBG wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors.     

Added advantages in using a fiber Bragg grating sensor in the determination of early age setting time for cement pastes

A fiber Bragg grating (FBG) sensor was used to monitor the early age curing temperatures of cement paste. Additional advantages in using the sensor were highlighted. The FBG was inscribed by a Continuous Wave 244 nm argon ion laser in the photosensitivity fiber. The fabricated FBG was calibrated from room temperature to 105 °C. In this temperature range, the FBG was found to be good in terms of both the sensitivity and linearity which were around 9 pm/°C and 99.9%, respectively. A host specimen with ratio of Portland cement, sand and water of 800, 500, and 275 ml by volume was used in the experiment. Results showed that the FBG could determine the initial and the final early age setting times. The initial early age setting time for the cement paste was about 5 h and the final early age setting time was about 14 h after casting.     

MEMS magnetometer based on magnetorheological elastomer

To develop a simple and low-cost MEMS magnetometer, a novel sensor based on the magnetostrictive effect of magnetorheological elastomer is proposed. The micromechanical sensor consists of a silicon sensitivity diaphragm embedded with a piezoresistive Wheatstone bridge, and a magnetorheological elastomer layer attached on the sensitivity diaphragm. The interaction between the magnetic field and the elastomer generates a deflection of the sensitivity diaphragm, which changes the piezoresistance and unbalances a Wheatstone bridge. The experimental results show that the sensor has good linearity in the magnetic field range of 0-120 kA/m and the saturation magnetic field is ∼150 kA/m. This simple, low-cost, low-power sensor is easily integrated with electronic circuits using the MEMS processes.     

Novel method for fabrication of polyaniline-CdS sensor for H2S gas detection

In this paper, we report on the performance of a H₂S sensor based on polyaniline-CdS nanocomposites fabricated by a simple spin coating technique. The nanocomposites showed the sensitivity to H₂S gas at room temperature (300 K). The resistance of polyaniline-CdS nanocomposites showed a considerable change when exposed to various concentrations of H₂S. Maximum response up to 48% was achieved for 100 ppm H₂S for PANi-CdS sensor. Depending on the concentration of H₂S, the response time was in the range of 41 and 71 s, whereas the recovery time was in the range of 345-518 s.     

Fabrication and characterization of a new MEMS fluxgate sensor with nanocrystalline magnetic core

This paper presents a new MEMS fluxgate sensor with a Fe-based nanocrystalline ribbon magnetic core and 3D micro-solenoid coils. The excitation coils were placed vertically to the sensing coil on the chip plane. Second harmonic operation principle was adopted in this fluxgate sensor. The total size of the fluxgate sensor was 6.25 mm × 4.85 mm × 120 μm. A simple testing system was established to characterize the fabricated devices. A band pass filter was used to pick up the second harmonic signals in the sensing coils. When excitation rms current of 120 mA and the operational frequency of 200 kHz were selected for the testing of the fabricated devices, the sensitivity of the developed fluxgate sensor was 1005 V/T in the linear range of −500 μT to +500 μT. Due to the combination of the 3D structure coils with the nanocrystalline core, relatively low sensor noise was achieved. The noise power density was 544 pT/Hz^0.5@1 Hz and the noise rms level was 9.68 nT in the frequency range of 25 mHz-10 Hz.     

一步超声法金属化封装FBG的传感特性

为解决传统胶封传感器普遍存在的蠕变、老化问题,本文提出基于一步超声法的光纤光栅表面金属化封装方法。在相同条件下分别对有聚酰亚胺涂覆层和无涂层的两种FBG进行金属化封装,研究了封装后FBG传感器的光谱、热学和力学特性,并利用扫描电子显微镜对其横截面的微观形貌进行了表征。结果表明:封装后有涂覆层FBG的反射光谱无明显畸变、边模抑制比大于10 dB,温度灵敏系数达34.63 pm/℃,应变灵敏系数为1.18 pm/με,应变传递效率达98.5%,线性度达0.999,均优于无涂层的FBG传感器。当温度从14.2℃突变到80℃经过多次冲击试验,发现金属化封装无涂层的FBG的温度增敏结构被破坏,而有涂层的FBG传感器仍保持优异的温度响应特性。SEM图显示,金属合金与有无涂覆层的光纤和金属基底都结合致密。该方法无需对光纤进行表面金属化预处理,操作简单易行,在恶劣环境、超长服役时间的光纤传感应用领域中具有重要的价值。     

Fabrication and characterization of ZnO thin film for hydrogen gas sensing prepared by RF-magnetron sputtering

A ZnO thin film-based gas sensor was fabricated using a SiO₂/Si substrate with an integrated platinum comb-like electrode and heating element. The structural characteristics, morphology, and surface roughness of the as-grown ZnO nanostructure were investigated. The optical properties were examined by UV–vis spectrophotometry. The film revealed the presence of a c-axis oriented (0 0 2) phase of 20.8 nm grain size. The sensor response was tested for hydrogen concentrations of 50, 70, 100, 200, 400, and 500 ppm at operating temperatures ranging from 250 °C to 400 °C. The sensitivity toward 50 and 200 ppm of hydrogen at the optimum operating temperature of 350 °C were about 78% and 98%, respectively. The response was linear within the range of 50–200 ppm of hydrogen concentration. Our results demonstrated the potential application of ZnO nanostructure for fabricating cost-effective and high-performance gas sensors.     

采用在线成型工艺的光纤光栅传感器

为了实现对光纤光栅的温度补偿功能,基于一种新型的热应力温度补偿机制,设计并制造出一种新型的、采用在线成型工艺的光纤光栅温度自补偿应变传感器,该传感器不仅具有温度补偿功能,而且可以实现应变增敏,解决了管式封装胶粘不牢、胶层老化的问题,以及温度补偿的传感器不能测量应变的问题。实验结果表明,在-20℃~40℃的温度变化范围内,传感器实现了良好的温度补偿和应变增敏效果;其中在实验温度范围内,光栅传感器的波长基本保持不变;应变敏感性为1.69pm/,增至原来的1.4倍,与理论计算值吻合的很好。     

Monitoring of sea bed level changes in nearshore regions using fiber optic sensors

This work reports the implementation and test of a pressure optical sensor suitable to measure, in situ, the sea bed level changes in the nearshore regions. The sensor is based on a fiber Bragg grating (FBG) embedded in a polymeric resin block. The increase of the pressure on the top face of the sensor, due to the change of sediments layer height, results in a change of the FBG Bragg wavelength. The sensor response reveals the capacity to discriminate sea bed level changes down to 2.5 cm, under field survey conditions. Finally, the sensor was successfully tested in a field trial survey at Costa da Caparica, Portugal.     

膜片式微型F-P腔光纤压力传感器研究

对基于Fabry-Perot（F-P）干涉仪原理的膜片式微型光纤压力传感器的制作工艺进行了实验研究。在单模光纤端面上直接熔接外径约175μm的毛细石英管,在石英管的另一端制作敏感膜片,从而在光纤端面与膜片内表面之间形成F-P干涉腔。首先采用电弧熔接、切割、腐蚀膜片的方法制作了石英膜片式压力传感器,该传感器在0-3.1MPa压强范围内F-P腔的腔长变化灵敏度为41.09nm/MPa,压强测量分辨率681Pa,并具有很小的温度敏感系数。在30-140℃的温度范围内,温度交差敏感小于1.07KPa/℃。为了克服石英膜片减薄困难的缺点,选用聚合物材料（PSQ）作为压力敏感膜片制作了F-P传感器,室温下在0.1-2.1MPa压强范围内PSQ膜片的F-P腔长变化灵敏度达到 1 886.85nm/MPa,压强测量分辨率达到53Pa。     

Design and implementation of a low-cost multi-channel temperature measurement system for photovoltaic modules

An efficient and low-cost temperature logging system with a 16-channel input was developed for measurements of photovoltaic module temperature. This paper reports the principle of operation, design aspects, as well as the experimentation and performance of the simultaneous temperature measurement of 16 solar cells/modules. The system consists of a 16 channel multiplexer, a 12 bit A/D, a differential amplifier and NTC temperature sensors. The temperature range of the sensor is from −20 °C to 120 °C. The simplistic design requires no large internal memory to store data but incorporates a high degree of sensitivity and dynamic range (according to climate condition), thus the cost of the design remains low and makes it suitable for field applications. The system was successfully tested for the operating temperature of a 40-cell mono crystalline Si photovoltaic module under realistic outdoor conditions during a summer and a winter day. The temperature Instrumentation developed for avoidance of special interface card use enabled the successful collection of data from long distances with negligible level of noise.     

Measurements on room temperature gas sensing properties of CSA doped polyaniline-ZnO nanocomposites

In this paper, we report on the performance of an ammonia gas (NH₃) sensor based on camphor sulfonic acid doped polyaniline-zinc oxide nanocomposites fabricated by a simple spin coating technique. The nanocomposite showed the sensitivity to ammonia gas (NH₃) at room temperature (300 K). Maximum response up to 28.11% was achieved for 100 ppm NH₃. Depending on the concentration of NH₃, the response time was ranged between 22 and 66 s, whereas the recovery time was 256-418 s.     

A new application of functionalized platinum nanoparticles as chemiresistor coating

Chemiresistor sensor based on Pt nanoparticles stabilized with 11-mercaptoundecanoic acid was developed for detection of some volatile organic compounds (VOCs). This sensor was prepared by drop coating technique onto interdigitated microelectrode. This film displayed linear current–voltage (I–V) characteristics and decrease the resistance at room temperature. The chemiresistive sensing properties were measured over a concentration range of 1.4–400 mg L⁻¹ for methanol, ethanol, ethyl acetate and acetone vapors. The results showed good sensitivity to methanol vapors and low detection limits for all examined vapors.     

Measurement of fluid flow rate using nanocomposite silicone rubber sensor

This paper describes the use of an elastic nanocomposite sensor to measure the water flow rate in open and closed hydraulic circuits. A sensor was constructed of multiwalled carbon nanotubes (MWCNTs) dispersed in silicone rubber (SR) and subsequently tested to verify its ability to measure water flow rate. The results reveal that the correlation between the fluid flow rate and the pressure variation across the sensor entails that its electrical resistance can be correlated to the flow rate. The sensor constructed of 2 and 3 wt,% of MWCNTs in SR-based nanocomposite sensors exhibited a low percolation threshold. An electron microscope (HRSEM) was used to characterize the manufactured nanocomposite sensors and confirm the conductive networks. The variation in the electrical resistance of the sensor in terms of both water pressure and flow rate is described. The elastic sensor was calibrated to measure the water flow rate in the range of 0–35 l/min. The results show that an elastic sensor fabricated from MWCNTs dispersed in silicone rubber does exhibit sensitivity to the slight strain levels produced by dynamic water pressure and, as such, can be used to measure flow rate. In addition, the sensor's response to water flow in the presence of bubbles enables pump cavitation monitoring. This paper also investigates the reduction of sensor electrical conductivity in response to water immersion. The findings reveal that the elastic nanocomposite sensor could potentially be used as a liquid sensor to detect water leakage in hydraulic circuits.