面向结构健康监测的压电传感器综述

压电传感器在结构健康监测方面的应用日益广泛。大型工程结构、混凝土结构及微电子构件的损伤监测与智能传感为其提供了广阔的应用平台。压电薄膜与涂层制备工艺不断革新,使压电传感器性能逐步优化,从而开拓了更广阔的应用领域与前景。结合国内外的研究热点和现状,简述了压电传感的动态监测原理,综合概述了外贴式压电传感、埋入式压电传感及表面涂覆式压电传感在结构智能监测中的研究进展,其中针对不同制备工艺,分别阐述了不同表面涂覆式压电传感器的应用研究,归纳并总结了3种传感器的优缺点及表面涂覆式压电传感器的制备工艺,最后展望了未来的应用前景和发展方向。     

Multiscale Humidity Visualization by Environmentally Sensitive Fluorescent Molecular Rotors

Building humidity sensors possessing the features of diverse‐configuration compatibility, and capability of measurement of spatial and temporal humidity gradients is of great interest for highly integrated electronics and wearable monitoring systems. Herein, a visual sensing approach based on fluorescent imaging is presented, by assembling aggregation‐induced‐emission (AIE)‐active molecular rotors into a moisture‐captured network; the resulting AIE humidity sensors are compatible with diverse applications, having tunable geometries and desirable architectures. The invisible information of relative humidity (RH) is transformed into different fluorescence colors that enable direct observation by the naked eyes based on the twisted intramolecular charge‐transfer effect of the AIE‐active molecular rotors. The resulting AIE humidity sensors show excellent performance in terms of good sensitivity, precise quantitative measurement, high spatial–temporal resolution, and fast response/recovery time. Their multiscale applications, such as regional environmental RH detection, internal humidity mapping, and sensitive human‐body humidity sensing are demonstrated. The proposed humidity visualization strategy may provide a new insight to develop humidity sensors for various applications.     

气体中痕量水蒸气测量技术进展

气体中水蒸气含量测量在工业生产和科研领域发挥至关重要的作用。随着许多工业生产和科研领域对气体水分含量更加严格的测试要求,对于气体中水蒸气含量测量灵敏度的要求也越来越高。目前测量nmol/mol痕量水分的仪器方法有可调谐二极管激光吸收光谱法、光腔衰荡光谱法、大气压离子质谱仪法;达到这个痕量水平的传感器类测量技术有石英晶体微天平法、冷镜露点法、阻容法、电解法。针对这些测量方法的优缺点以及今后的发展趋势进行了论述分析,通过克服测量过程中的干扰因素,可在一定的程度上提高痕量水含量的测量准确性,对促进痕量水含量准确测量技术的发展有所裨益。     

Comparison of three humidity sensors for a pulmonary functiondiagnosis microsystem

Three capacitive humidity sensors developed for a portable clinical application are presented and compared. The first structures consist of interdigitated electrodes covered by a polyimide sensitive layer. The second structures have the same geometry but include a benzocyclobutene sensitive layer and a heating. resistor. The third structure has been developed with a new geometry, with the electrodes being stacked. Humidity measurement results are presented, in particular sensor response time in absorption that must be very small (less than 500 ms). The influence of the heating on the response time is described. In conclusion, the three sensors are compared and the most suitable structure for our application is indicated. Although polyimide has been widely used for realization of capacitive humidity sensors, we demonstrate here that it is not the best sensitive material for our application     

A novel integrated acoustic gas and temperature sensor

Acoustic temperature sensors have the advantages of a high-resolution frequency output and ease of integration with other acoustic sensors but require hermetic packaging to prevent sensor contamination. Surface-skimming bulk-wave (SSBW) devices have been found to be much less sensitive to surface contamination than other acoustic devices, and although their temperature response has been studied extensively, they have not been studied specifically as temperature sensors. Surface acoustic wave (SAW) based chemical sensors requiring temperature measurement or control are susceptible to temperature measurement error because the temperature cannot be measured in the same location as the chemical sensor. The objectives of this work were to examine the temperature characteristics and performance of a SSBW temperature sensor when integrated with a SAW condensation and humidity sensor in a novel design. The SSBW temperature sensor had over an order of magnitude less sensitivity to condensation and water uptake in certain polyimide films than an integrated SAW gas sensor indicating that this design is practical for sensing films in the delay path where film thickness is carefully considered.     

Evanescent Field Fiber-Optic Sensors for Humidity Monitoring Based on Nanocoatings

The transmitted optical power of two different fiber optic based structures when a nanofilm is being deposited onto them is experimentally studied. The technique used to build the nanofilms is Electrostatic Self Assembly (ESA), which has been widely reported in the literature. For the shake of comprehensibility, the comparative analysis of this phenomenon is accomplished for a particular sensing measure, humidity. The two structures selected towards development of practical humidity evanescent field sensors are hollow core fibers and tapered optical fibers. Some preliminary experimental studies of depositing humidity sensitive thin films and demonstrating their feasibility are presented. Depending on the working point selected, up to 10dB of variation in the optical output power is obtained when the environmental humidity changes. Both configurations exhibit similar dynamic behavior and response times shorter than 300msec, making these evanescent field sensors good candidates to monitor human breathing     

露点温度传感器发展趋势综述

介绍了目前露点温度传感器领域的研究现状,阐述了光学式、谐振式、电学式、热学式、重量式、化学式露点温度传感器的原理及构造,指出光学式露点温度传感器测量精度极高,其中冷镜式露点仪可作为湿度计量标准;谐振式露点温度传感器具有体积小、成本低、响应时间短、灵敏度高、可靠性好的特点;电学式露点温度传感器灵敏度高、功耗小,便于实现小型化、集成化;重量法是准确度最高的湿度绝对测量方法;化学法常用来测量低湿环境下的有机混合气体。探讨了露点温度传感器在环境监测、工业制造、医疗诊断等领域的应用情况,指出未来露点温度传感器将会向高精度、高稳定性、高响应的方向发展,且应用范围将进一步拓展,以满足极端环境下的测量需求。     

炭纤维水泥石压敏传感器的温湿度补偿方法

介绍了适合混凝土结构局部压应力、 压应变状态监测的嵌入式炭纤维水泥石压敏传感器的概念及其传感原理, 并研究了环境温度和湿度两个因素对炭纤维水泥石压敏传感器零点输出的影响; 同时从传感器电路设计角度探讨了温度、 湿度的补偿方法及其在结构中的应用方式。研究表明: 炭纤维水泥石压敏传感器的零点输出对环境温度、 湿度的变化比较敏感, 温度、 湿度的最大影响分别约为6%和200%; 对炭纤维水泥石压敏传感器采用"测试-补偿"对耦设置构成的补偿电路可以消除因环境温度、 湿度以及极化作用产生的噪声信号对传感器零点输出的影响。      

Highly Sensitive Humidity Sensor Using Pd/Porous GaAs Schottky Contact

This paper investigates the suitability of porous GaAs as a semiconductor material for sensing humidity. The authors have developed two types of sensors based on Pd/porous GaAs and Pd/GaAs Schottky contacts for humidity measurements. It was found that the porosity on GaAs wafer promoted the sensing properties of the contact used as highly sensitive humidity sensor toward different amounts of relative humidity operated at room temperature. On the contrary, the Pd/GaAs sample operated at room temperature exhibited negligible sensitivity to relative humidity. The advantages of using porous GaAs for Schottky humidity sensor are the following: high sensitivity, low response time, and insignificant dependence on temperature. Current-voltage (I-V) characteristics of the Pd/porous GaAs Schottky humidity sensor exhibited a saturation current value of 8.5times10^-10 A under dry condition (5% relative humidity). This was increased to 7.0times10^-9 A when submitted to a relative humidity of 25%. The saturation current was further increased considerably to 3.0times10^-7 A as the relative humidity was increased to 95%. This is more than two orders of magnitude increase in saturation current compared to dry condition. A parameter called humidity sensitivity was defined using the current value at a fixed forward voltage of 0.2 V to present the sensitivity of the sensor. Response times are reported to discuss the adsorption and desorption characteristics of the device. Pd/porous GaAs sensor operated at room temperature showed a fast response time of 2 s and a sensitivity value of 93.5% in the presence of 25% relative humidity. Furthermore, the influence of increase in relative humidity as well as heating effects on the responsivity of the sensor is described. Scanning electron microscopy analysis of the Pd/porous GaAs sample exhibited highly porous structures     

Modeling optical microfiber loops for seawater sensing

Based on resonant and waveguiding properties of optical microfiber loops, we theoretically investigated silica microfiber loop resonators (MLRs) for refractive index (RI) and salinity sensing of seawater. Dependences of sensitivity and detection limit on probing wavelength, fiber diameter, and ring diameter are calculated with typical parameters of seawater. Our results show that the sensitivity of MLRs increases with the increasing wavelength and the decreasing diameter of the microfiber. Bending loss and absorption loss are both important factors to determine the detection limit. By optimizing the parameters of the sensing system, RI sensitivity and salinity detection limit can reach 10(-6) RI units (RIU) and 10(-2) ‰ (10 ppm), respectively. The model presented here may be helpful for developing microscale fiber sensors for seawater detection with high sensitivity, low detection limit, and miniaturized sizes.     

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.      

Thin plasma-polymerized layers of hexamethyldisiloxane for humidity sensor development

The response of resistive-type sensors based on thin hexamethyldisiloxane layers to relative humidity (RH) was evaluated. Humidity sensitive layers were plasma polymerized at low frequency glow discharge using a capacitively coupled parallel plate reactor. The sensor design comprises the absorbing layer deposited on clean glass substrate with comb-shape aluminum electrodes (interdigitated structure). The change in electrical impedance of the sensing film was monitored as the device was exposed to humidity. The variation of the plasma-polymerization parameters resulted in different humidity sensing properties which could be correlated to the results of Fourier transform infrared spectroscopy (FTIR). The deposited films exhibited a detectable response to RH ranging from 30 to 95% with low hysteresis, good reproducibility and stability in long-term use. Films with a greater thickness showed a significant decrease in the humidity sensing capability. FTIR analysis revealed the presence of SiH bonding groups, which are frequently linked to the film density. The increase in the plasma discharge power induced also a significant decrease in the diffusion process of water vapor inside the sensitive layer bulk.     

Slow-wave structures-based method of measurements

A novel electromagnetic measurement method is described from the physical point of view. Based on the application of slow-wave structures, this method combines the advantages of relatively high and relatively low frequency bands. Concentration of an electromagnetic field, caused by wave deceleration, leads to a significant increase in sensitivity. The main parameters and characteristics of the sensitive elements, built as sections of slow-wave structures, are considered in this paper. It is shown that the electric and magnetic fields split in the transverse direction in sensors based on coupled slow-wave structures. This leads to an additional increase in sensitivity. Some examples of practical slow-wave structure-based measurement methods are also presented.     

一种基于光纤F-P腔的石墨烯谐振式压力传感器

谐振式传感器具有良好的重复性、分辨率和稳定性,全光纤谐振式微型传感器则集合了微纳结构与光纤传感特性两者的优点。石墨烯作为近年来发现的一种新型材料,具有良好的热学和力学特性,可以作为谐振式传感器中的敏感元件。本文提出了一种基于光纤F-P结构的石墨烯谐振式压力传感器,其兼具微机械传感器和光纤谐振器的优点,具有较高的谐振频率,在测量压力的实验中展现出良好的性能,压力灵敏度最高可达2. 93Hz/Pa,具有重要的应用价值。     

电极结构对高分子电阻型湿度传感器性能的影响

本文以聚苯乙烯磺酸钠为湿敏材料,制备了以金叉指电极为基底的高分子电阻型湿度传感器。研究了电极基片材料和叉指电极构型对传感器湿敏响应特性的影响。研究表明,采用多孔结构的基片材料可降低传感器电阻,增强湿敏膜与基片的结合能力从而提高传感器的稳定性;叉指电极构型对传感器的电阻大小有一定影响,增加电极中心线间距离使传感器的稳定性提高。     

Intracore fiber bragg gratings for strain measurement in embedded composite structures

An intracore Bragg grating written on a photosensitive fiber core is used for strain measurement in composite specimens under load. The strain information is directly related to the absolute change in the Bragg-reflected wavelength. Fiber Bragg grating (FBG) sensors (fibers with intracore gratings) are thus sensitive to strain that is caused by changes in temperature as well as to load-induced changes. Thus these sensors can be made to be independent of source intensity variations and losses. FBG sensors used for load-induced strain sensing in composite structures and the effects of temperature on them are discussed. A detailed account of the use of such embedded structures as self-monitoring nondestructive testing devices is given.     

石墨烯纳机电谐振式传感器研究进展

石墨烯是一种新型的二维纳米材料,因独特的电学和力学性质而备受关注。近年来,一系列针对石墨烯谐振特性及其应用的研究得到广泛开展,已显示出石墨烯在谐振式纳机电传感器领域巨大的应用潜力。简要描述了石墨烯优异的物理性能和目前主要的几种石墨烯制备工艺现状,重点介绍了近期石墨谐振器的实验、理论研究以及石墨烯谐振器在压力、加速度和质量等物理量传感器方面的应用进展,其中主要围绕石墨烯谐振敏感结构、敏感机理和研究方法等方面进行评述,并分析了石墨烯谐振式传感器研发所面临的挑战和发展前景。     

Hydrophobic ionic liquid-in-polymer composites for ultrafast,linear response and highly sensitive humidity sensing

Traditional ionic liquids are sensitive to humidity but with long response time and nonlinear response.Pure liquid-state ionic liquids are usually hard for dehydration which have ultralong response time for humidity sensing.The immobilization of ionic liquids provide a possible way for high performance humidity sensing.Hydrophobic materials and structures also promised faster response in humidity sensing,because of easier desorption of water.In this work,we prepared flexible humidity sensitive composites based on hydrophobic ionic liquid and polymer.The combination of hydrophobic ionic liquid with hydrophobic polymer realized linear response,high sensitivity with low hysteresis to humidity.By adjusting the ratio of ionic liquid,not only the impedance but also the hydrophobicity of composite could be modulated,which had a significant influence on the humidity sensing performance.The morphology and microstructure of the material also affected its interaction with water molecules.Due to the diverse processing methods of polymer,highly transparent film fabricated by spinning-coating and nanofibrous membrane fabricated by electrospinning could be prepared and exhibited different response time,which could be used for different application scenarios.Especially,the fibrous membrane made with electrospinning method showed an ultrafast response and could distinguish up to 120 Hz humidity change,due to its fibrous structure with high specific surface area.The humidity sensors with ultrafast,linear response and high sensitivity showed potential applications in human respiratory monitoring and flexible non-contact switch.To better show the multifunction of ionic liquid-polymer composite,as a proof of concept,we fabricated an integrated humidity sensitive color change device by utilizing lower ionic liquid content composite for sensing in the humidity sensing module and higher ionic liquid content composite as the electrolyte in the electrochromic module.     

Optical Microresonators for Sensing and Transduction: A Materials Perspective

Optical microresonators confine light to a particular microscale trajectory, are exquisitely sensitive to their microenvironment, and offer convenient readout of their optical properties. Taken together, this is an immensely attractive combination that makes optical microresonators highly effective as sensors and transducers. Meanwhile, advances in material science, fabrication techniques, and photonic sensing strategies endow optical microresonators with new functionalities, unique transduction mechanisms, and in some cases, unparalleled sensitivities. In this progress report, the operating principles of these sensors are reviewed, and different methods of signal transduction are evaluated. Examples are shown of how choice of materials must be suited to the analyte, and how innovations in fabrication and sensing are coupled together in a mutually reinforcing cycle. A tremendously broad range of capabilities of microresonator sensors is described, from electric and magnetic field sensing to mechanical sensing, from single‐molecule detection to imaging and spectroscopy, from operation at high vacuum to in live cells. Emerging sensing capabilities are highlighted and put into context in the field. Future directions are imagined, where the diverse capabilities laid out are combined and advances in scalability and integration are implemented, leading to the creation of a sensor unparalleled in sensitivity and information content.     

特殊结构露点传感器的校准特点

露点仪、露点传感器作为环境湿度的检测仪器,广泛使用于工农业生产、工业自动化和生活的各个领域。本文通过对露点传感器校准的现状分析,指出了目前的校准方法中存在的尚不具体明确之处。本文分析了特殊露点传感器结构原理,由此改进了特殊结构露点传感器的校准方法。