Nanocrystalline SnO2–TiO2 thin film deposited on base of equilateral prism as an opto-electronic humidity sensor

Present paper reports the synthesis of SnO₂–TiO₂ nanocomposite, its characterization and performance as opto-electronic humidity sensor. Nanocrystalline SnO₂–TiO₂ film was deposited on the base of an equilateral prism using a photo resist spinner and the as prepared film was annealed at 200 °C for 2 h. The crystal structure of the prepared film was investigated using X-ray diffraction (XRD). Minimum crystallite size of the material was found 7 nm. Surface morphology of the film was investigated by Scanning electron microscope (SEM LEO-0430, Cambridge). SEM image shows that the film is porous. Differential scanning calorimetry (DSC) of as synthesized material shows two exothermic peaks at about 40 and 110 °C, respectively which are due to the evaporation of chemical impurities and water. Further the prepared film was investigated through the exposure of humidity and relative humidity (%RH) was measured directly in terms of modulation in the intensity of light recorded on a digital power meter. The maximum sensitivity of sensor was found 4.14 μW/%RH, which is quite significant for sensor fabrication purposes.     

Humidity sensing properties of Ni(OH)2 nanoparticles synthesized via sonochemical method

This work focuses on humidity sensor based Ni(OH)₂ nanoparticles. The sonochemical method was employed to prepare nanoparticles and impedance analysis was used to characterize sensitivity, response, and recovery time of the prepared sensor. The Ni(OH)₂ sensor was found to have high sensitivity and fast response/recovery time to humidity, and its impedance changed approximately two orders of magnitude from about 2.01 MΩ in dry air 20% RH (relative humidity) to 0.0258 MΩ in 90% RH air. Our results demonstrate the potential application of Ni(OH)₂ nanoparticles for fabricating high performance humidity sensors.     

光纤SPR湿敏传感器及其共振光谱特性研究

提出并研制了基于光纤SPR传感探针的新型湿敏传感器。首先研究了光纤SPR传感探针对环境湿度变化的敏感特性,在此基础上提出在光纤SPR传感探针表面增覆不同厚度且具有水分子吸附功能的PVA薄膜来实现环境相对湿度的监测。研究结果表明,增覆双层PVA薄膜的光纤SPR传感探针在高湿区具有较好监测效果,其共振强度对应的相对湿度测量灵敏度达到1.59%/%RH,较光纤SPR探针呈现显著提高。而增覆单层PVA薄膜的光纤SPR传感探针在高湿区共振波长对应的相对湿度监测灵敏度达到2.411nm/%RH。此外所提出的新型光纤SPR湿敏探针在PVA薄膜失效后经过特殊工艺处理仍可重复镀膜使用。     

一种新型高灵敏度光学微环湿度传感器

提出了以聚酰亚胺（PI）为感湿材料的三耦合点单微环新型湿度传感器。外界湿度变化使得聚酰亚胺SOI微环谐振特性发生变化,最终通过谐振波长的漂移量确定湿度值。讨论了不同部位感湿时系统的传感特性,并且选择了最佳湿敏元件。数值模拟结果表明：与传统的单微环传感器相比,新型传感器具有较高灵敏度和测量范围,Through端口的自由频谱范围可提高3倍。三耦合点单微环谐振器整体结构可作为最佳湿敏元件,该传感器在10%RH~80%RH相对湿度范围内,灵敏度可达到0.98 nm/%RH,该结构为制备高灵敏度可集成微型湿度传感器件提供了一定的理论依据。     

基于U型波导耦合单微环结构的高灵敏度湿度传感器

首次提出了一种基于U型波导耦合的新型单微环结构湿度传感器,该传感器以聚酰亚胺(polyimide,P1)作为感湿材料,当外界环境相对湿度变化时,引起感湿部位折射率的相应变化,导致传感器的输出光谱发生漂移。根据传输矩阵法推导U型波导耦合单微环结构的传递函数,重点讨论了不同感湿部位对输出光谱的影响,通过Matlab理论仿真,确定以U型波导耦合单微环结构整体作为最佳感湿部位。当U型波导的两个耦合点间的距离为微环周长的整数倍时,相比于传统的单微环结构,自由光谱范围(FSR)实现加倍。外界相对湿度从10%RH变化到100%RH时,传感器的输出光谱漂移量在0.027～0.191 μm之间变化,灵敏度高达0.001 8 μm/%RH,相比于具有高灵敏度的光纤光栅类湿度传感器,灵敏度提高了10~100倍,实现了在高灵敏度感湿的同时兼顾谐振峰两侧大范围的滤波选频。     

Synthesis and characterization of TiO2 nanotubes for humidity sensing

The highly ordered TiO₂ thin films are prepared by anodic oxidation and calcined at 300, 400, 500 and 600 °C, respectively. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are employed to analyze the structure and the morphology of the TiO₂ films. We design a novel sensor to investigate the humidity sensing behaviours of the samples. The samples calcined at 600 °C show high sensitivity with nearly two orders change in the resistance and short response and recovery time (<190 s) during the relative humidity variation from 11 to 95%.     

光纤布拉格光栅嵌入SMS光纤结构的湿度传感器

提出了一种基于光纤布拉格光栅嵌入单模-多模纤芯-单模(single-mode-multimode fiber core-single mode, SMS)光纤结构的湿度传感器。当环境湿度变化时,SMS光纤结构的干涉光谱会发生漂移,而光纤布拉格光栅对湿度不敏感,其纤芯基模保持不变。因此利用SMS光纤结构对环境湿度的敏感性去调制光纤布拉格光栅纤芯基模,通过检测光纤布拉格光栅纤芯基模的反射能量变化就可以实现湿度测量。数值模拟了SMS光纤结构的内部光场分布规律,理论计算了不同环境折射率时,多模纤芯的长度、直径对SMS光纤结构输出能量耦合系数的影响。理论模拟表明,随着环境折射率变化,SMS光纤结构中传输的纤芯基模的输出能量耦合系数会发生变化。同时制作了传感器样品并对其进行了传感实验研究,实验结果表明多模纤芯长35 mm、纤芯直径为85 μm的传感器在45%～95%RH湿度变化范围内,湿度灵敏度为0.06 dBm·(%RH)-1。在20～80 ℃温度范围内,传感器的温度灵敏度为0.008 nm·℃-1,温度所带来的湿度测量误差为0.047%RH·℃-1。传感器具有制作简单、灵敏度高、反射式能量检测等优点,在湿度测量领域有一定的应用价值。     

Humidity sensing properties of Pd-doped ZnO nanotetrapods

Pd²⁺-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd²⁺-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 °C in air and PdCl₂ was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd²⁺-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl₂. Linear regression algorithm was used for evincing the highly linear behavior of the Pd²⁺-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd²⁺-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (∼74.24324 Hz/%RH (relative humidity)), reproducibility, linearity (R² = −0.98834), short response and recovery time (less than 5 s).     

Photocatalytic degradation of BTEX using W-doped TiO2 immobilized on fiberglass cloth under visible light

W-doped TiO₂ were immobilized on fiberglass cloth (FGC). The catalyst possessed small crystallite sizes with a red-shift on an absorption edge. Good dispersion was observed over the immobilized catalyst. The photocatalytic degradation of gaseous BTEX was conducted in a flow reactor under day-light fluorescent. Parameters including gas flowrate, catalyst loading, initial concentration and relative humidity (%RH) were investigated. The prepared catalysts showed higher efficiency than that of TiO₂ approximately 18, 3, 3 and 2.5× for benzene, toluene, ethylbenzene and o-xylene, respectively. The condition to achieve 100% BTEX removal was found at 20 min/ml, catalyst loading 0.1 mg/cm² and 30% RH.     

串联双微环湿度传感器光谱特性研究

提出了一种基于串联双微环谐振器的新型聚酰亚胺(Polyimide,PI)湿度传感器,采用传输矩阵法和耦合模的理论计算微环谐振器的传递函数,并对比了传统单微环与串联不同半径的双微环的输出光谱特性。外界湿度变化使得聚酰亚胺SOI波导吸收水汽后折射率发生变化,从而引起微环输出光谱发生漂移,通过探测光谱漂移量来测湿度值,得到了串联双微环传感器的灵敏度和测量范围,并且分析了感湿部位不同时谐振器输出光谱特性。理论结果表明：串联不同半径的微环谐振器的自由光谱范围（FSR）要比单微环有所提高,而且串联双微环谐振器整体感湿比单个微环单独感湿的传感性能更优良,可作为最佳的湿敏元件。与传统的单微环传感器相比,串联不同半径的微环结构可提高系统的测量范围和灵敏度,半径为30和50 μm的串联微环谐振器的FSR可达到0.15 μm,传感器测量湿度范围为10%RH～80%RH,灵敏度可达到0.001 7 μm·(%RH)-1。因此串联不同半径的双微环谐振器为制备成本低、结构简单、高灵敏度、可集成的微型湿度传感器件提供一定理论基础。     

Preparation and mechanism investigation of highly sensitive humidity sensor based on Ag/TiO2

In this paper, a high-performance silver-doped titanium dioxide (Ag/TiO₂) humidity sensor was synthesized using a hydrothermal synthesis method for respiratory monitoring. The sensing mechanism was studied by the first principles of density functional theory (DFT). Calculations show that the doping of Ag⁺ ions increases the adsorption energy of TiO₂ to water molecules. Furthermore, the Ti–O bond in TiO₂ is broken due to the doping of Ag⁺ ions, which promotes the generation of Ti³⁺ defects. Experiments show that the doping of Ag⁺ ions can increase the hydroxide groups, Ti³⁺ defects and oxygen vacancies on the surface of TiO₂, thus effectively improving the responsivity, linearity and hysteresis of the TiO₂ humidity sensor. Compared to TiO₂, the resistance of the Ag/TiO₂ (0.5 mM) humidity sensor reaches 4.5 orders of magnitude with a high response of 39707.1, maximum hysteresis rate of 4.6%, response/recovery time of 31 s/15 s and the best linearity in a range of 11%–95% RH. In addition, the Ag/TiO₂ humidity sensor has been successfully used to detect different modes of respiration and determine the respiratory rate under different respiratory states. Significantly, this work demonstrates potential application value in human healthcare and activities monitoring.     

基于光纤锥和纤芯失配的Mach-Zehnder干涉湿度传感器

介绍了一种简单且灵敏度较高的Mach-Zehnder干涉湿度传感器.将单模光纤和多模光纤渐变熔接光纤锥,色散补偿光纤被熔接在两个多模渐变光纤之间,形成了单模光纤-光纤锥-多模渐变光纤-色散补偿光纤-多模渐变光纤-光纤锥-单模光纤结构的传感器.光纤锥起到了增加包层模能量的作用,两个多模渐变光纤节点作为光耦合器,从而形成光纤Mach-Zehnder干涉仪.外界环境湿度的变化,将使得传感器透射谱能量发生变化,通过测量干涉谱波峰峰值能量实现对湿度的测量.实验结果表明干涉谱波峰峰值能量与环境湿度之间存在良好的线性关系.当环境湿度在35%RH—85%RH范围内变化,一段由20 mm色散补偿光纤组成的传感器,其灵敏度为-0.0668 dB/%RH,相关度为0.995.该传感器结构紧凑、尺寸小、制造工艺简单,这使其可以被广泛用于湿度测量.     

A rapid synthesis/growth process producing massive ZnO nanowires for humidity and gas sensing

We report a rapid and simple process to massively synthesize/grow ZnO nanowires capable of manufacturing massive humidity/gas sensors. The process utilizing a chemical solution deposition with an annealing process (heating in vacuum without gas) is capable of producing ZnO nanowires within an hour. Through depositing the ZnO nanowires on the top of a Pt-interdigitated-electrode/SiO₂/Si-Wafer, a humidity/gas-hybrid sensor is fabricated. The humidity sensitivity (i.e., ratio of the electrical resistance of the sensor at 11–95 % relative humidity level) is approximately 10⁴. The response and recovery time with the humidity changing from 11 to 95 % directly and reversely is 6 and 10 s, respectively. The gas sensitivity (i.e., ratio of electrical resistance of the sensor under the air to vaporized ethanol) is increased from 2 to 56 when the concentration of the ethanol is increased from 40 to 600 ppm. Both the response and recovery times are less than 15 s for the gas sensor. These results show the sensor utilizing the nanowires exhibits excellent humidity and gas sensing.     

一种适用于湿度传感的表面等离子微环传感器

提出了一种适用于湿度传感的表面等离子微环传感器。该传感器纵向上采用表面等离子多层波导结构,横向上采用U型微环结构,以聚酰亚胺(polyimide,PI)为感湿材料。根据传输矩阵法推导表面等离子微环传感器结构的传递函数,外界环境的相对湿度变化引起聚酰亚胺的折射率变化,从而多层波导结构的有效折射率发生改变,导致传感器的输出光谱发生漂移。重点分析讨论了多层波导结构的传输特性以及感湿部位折射率的变化对输出光谱的影响。根据计算和仿真得出：当U型波导的两个耦合点间的距离为微环周长的整数倍时,传感器的输出光谱水平漂移量较大,自由光谱范围(FSR)加倍,达到128 nm,当外界环境相对湿度从10%RH变化到100%RH时,漂移量Δλ_m在0.005～0.038 μm之间变化,相比于其他湿度传感器,灵敏度提高了10～50倍,高达0.0005 μm/%RH,并且传输稳定。结果表明：设计的表面等离子微环传感器,灵敏度较好,性能稳定,可以应用于湿度测量,并且实现了在高灵敏度感湿的同时兼顾大范围的滤波选频,为微型光学器件的制备提供了理论基础。     

Design of fiber Bragg grating-based Fabry–Perot sensor for simultaneous measurement of humidity and temperature

A new sensor for simultaneous measurement of humidity and temperature is proposed. The sensor consists of Fabry–Perot cavity formed by two identical uniform fiber Bragg gratings. To make the cavity serves as humidity sensor, moisture sensitive polymer, which is polyimide, is coated on the FBG and on the cavity with different thickness. When the sensor is exposed to the relative humidity change, the polyimide will expand and stretch the fiber and induces strain on the FBG and on the cavity. The induced strain alters the grating period, cavity length and effective refractive index of fiber. The simulation results show that the humidity sensitivity and thermal sensitivity are 1.92 pm/%RH and 8.87 pm/°C, respectively, for polyimide coating thickness of 10 μm on the FBG and 15 μm on the cavity.     

光纤光栅锈蚀传感器在不同湿度下的特性研究

钢结构的锈蚀监测对于钢结构安全的早期预警非常重要.本文提出了一种制备布喇格光纤光栅锈蚀传感器的方法,并研究了该传感器在不同湿度环境下的传感规律.结合磁控溅射和电镀的方法在光栅侧表面制备了Fe-C合金传感膜|利用扫描电子显微镜观察其侧表面形貌|检测在相对湿度60%和99%下中心波长的变化,进而分析该光纤光栅探头在不同湿度下的传感规律.实验和数据分析结果表明:在相对湿度为60%时,锈蚀进程缓慢,随着时间的推移波长呈线性化增加|相对湿度达到99%时光栅光谱出现多峰现象.据此得出:一定湿度条件下,该传感器可监测锈蚀进展|当环境湿度较高（达到99%）时,该传感器可用于锈蚀出现的早期预警.     

基于倏逝波的锥形光纤马赫-曾德尔湿度传感器

提出了一种基于倏逝波原理的光纤马赫-曾德尔湿度传感器,传感器是在2个单模光纤粗锥的传感臂中心通过绝热火焰熔融拉锥处理而成。光由传感器输入端传入,经过第1个粗锥时,将激发出若干高阶模,各模式光传输经过细锥区进入第2个粗锥时被耦合进入传感器输出端。当外界湿度变化时,细锥区倏逝场随之变化,最终导致透射谱能量变化。通过测量透射谱能量变化,可以实现环境湿度传感测量。实验结果表明,在35%~85%RH的湿度变化范围内,透射谱的能量具有相同变化趋势,处于水蒸气吸收峰附近的干涉谷湿度响应灵敏度可达0.157 dBm/%RH,温度交叉灵敏度仅为0.014 %RH/ ℃。该传感器因其制作简单、灵敏度高,温度交叉敏感小等特点,具有很好的应用前景。     

Fiber-optic humidity sensor based on an air-gap long period fiber grating

In this paper, we propose a novel high-sensitivity fiber-optic humidity sensor based on a calcium chloride thin film to be coated on an air-gap long-period grating fabricated (AG-LPG) by combining the fiber side-polishing and fiber etching methods. When the surrounding refractive index of the air-gap long-period grating is changed by a change in humidity, the grating resonant wavelength is considered varied. Experimental results indicate that humidity can be detected by this sensing mechanism and has a high sensitivity of about 1.36 nm/1%RH.     

Hydrogen sensors based on ZnO nanoparticles

Hydrogen sensing characteristics of thick films of nanoparticles (∼35 nm diameter) of ZnO, 3% Co doped ZnO, 1% Pt-impregnated ZnO and 1% Pt-impregnated 3% Co-ZnO have been investigated. The last composition exhibits the highest sensitivity for 10-1000 ppm H₂, reaching values upto 1700 as well as good response and recovery times at 125 °C or lower. The sensor is not affected significantly upto 50% relative humidity.     

基于Nafion-结晶紫传感膜的光纤湿度传感器研究

通过研究基于荧光和可见光吸收的两种湿度传感方法,从数种湿度分子探针中优选出结晶紫为分子识别器,包埋于Nafion溶胶中,制备成基于可见光吸收原理的光纤化学湿度传感膜。该传感膜与电荷耦合二极管阵列检测器等构成的光纤湿度传感器,于640 nm波长处对30%～100%范围内的相对湿度(relative humidity, RH)具有较快的响应时间(＜2 min)、较高的灵敏度(≤5%RH)、选择性和良好的可逆性(RSD≤2.6%)。