【作者】 雷声；

【导师】 陈裕泉；

【作者基本信息】 浙江大学 ， 生物医学工程， 2011， 博士

【摘要】 湿度在工业控制、医疗卫生、环境监控等多个领域都必须得到严格地监控。湿度检测在仓储、粮食及食品防霉、温室种植、环境监测、仪表电器、交通运输、气象、军事等方面都起着越来越重要的作用,甚至处于不可或缺的地位。但在常规的环境参数中,湿度却是最难准确测量的一个参数。因而对具有高灵敏度、快速响应速度等高性能的新型湿敏传感器的研究具有重要意义。声表面波器件由于其对表面扰动的特殊敏感性,被广泛应用于传感器领域。其灵敏度高、稳定性好、体积小、成本低、易于集成的优点使之得到越来越多的关注和研究。声表面波传感器对表面扰动的响应是多种因素、多种机理共同作用的结果,这也是声表面波传感器能够具有极高灵敏度的根本原因。对声表面波传感器扰动理论模型及其质量负载效应、声电耦合效应等响应机理进行了深入剖析,从根本上为声表面波传感器的结构设计、湿敏材料选择提供理论依据和参考。使用精密光刻工艺制备高频声表面波单端谐振器作为湿敏传感器的基本换能元件。湿敏材料的选择及制备是决定声表面波湿敏传感器性能的重要因素。只有湿敏材料的特性与声表面波换能元件的多重响应机理相匹配,才能使传感器达到最佳性能。包括水分子吸附效率、吸湿后电导率变化、粘弹性在内的多项材料特性都必须进行综合考虑与设计。新型纳米材料、复合材料是目前湿敏材料的主要发展方向和研究热点。深入讨论了声表面波湿敏传感器中湿敏材料的选择与设计思路,给出Nafion/MWCNTs复合材料、氧化石墨烯等几种新型纳米功能材料的合成及制备方法。湿敏材料的成膜方法是关系到湿敏传感器最终性能的又一关键技术。高频声表面波元件可成膜面积小,并且对表面敏感膜的厚度、均匀性都有很高要求。纳米纤维薄膜由于具有更大的比表面积,可以极大地改善传感器的灵敏度及动态性能。静电纺丝技术是一种新兴的纳米纤维薄膜制备方法,其制备的纳米纤维薄膜具有比表面积大、孔隙率高、纤维径细、质轻、形貌均匀等突出优点,并且较之其他微纳成膜方法,该方法更为简便易行。将静电纺丝成膜技术引入到声表面波湿敏传感器制备过程中,制备具有微纳结构特性的Nafion/MWCNTs复合纳米纤维感湿薄膜。声表面波传感器工作在射频频段,很容易受到环境或自身所产生的电磁辐射的干扰,因而对检测电路的设计有更严格的要求,这也是声表面波传感器的设计难点之一。设计了高性能的声表面波高频振荡电路及整套的检测系统,具有良好的稳定性和抗干扰性能。通过射频无线唤醒技术实现无线半无源声表面湿敏传感器标签设计。提出新型的叉指电极串联式声表面波传感器结构,为高频声表面波传感器的设计提供了一个新的思路。实验主要对灵敏度、稳定性、重复性、响应时间、温度系数等几个湿敏传感器的重要指标进行测试。实验结果表明设计的几种湿敏材料在声表面波湿敏传感器的应用中均取得了理想的效果,其性能较之前的研究及目前的商品化元件都有较大地提升。同时,也验证了静电纺丝成膜技术对传感器性能的影响,证实了其在提升传感器灵敏度及动态性能上的有效性。串联结构的新型声表面波传感器在湿度检测中的有效性也得到检验,确认了这一新方法的可行性。低湿度(<10%RH)及露点检测一直是湿度检测的难点,常规的电阻或电容型传感器都难以对10%RH或更小的湿度进行精确检测。开发低成本、小体积、使用灵活的低湿或露点传感器具有重要的研究价值和现实意义。将本文设计的传感器用于低湿和露点的检测中,实验结果表明其在低湿及露点检测中也具有良好的应用前景。更多还原

【Abstract】 Humidity must be strictly monitored and controlled in many fields, such as industry, medical treatment and environment monitor. Humidity detection is playing quite an important role in storage management, cereal stocking, greenhouse conditioning, electronic devices, transportation, meteorology and military affairs. However, among all the environmental parameters, humidity is still hard to be accurately measured until now. So there’s great meaning to research and develop new humidity sensors with more excellent performance, such as high sensitivity and quick response time.Surface acoustic wave (SAW) device was extremely sensitive to the perturbation on its surface, so it has been widely used as sensor components. Its great advantages such as high sensitivity, excellent stability, small size, low cost and ease-to manufacturer made it getting more and more attention. For SAW sensors, their response to the perturbation was caused by multiple factors and mechanisms, which is the basic reason that SAW sensors have so large a sensitivity. The Perturbation Model for the SAW sensors and its mechanisms such as mass loading effect and acoustoelectric effect were deeply analyzed, based on which SAW sensing component and humidity sensitivity material were designed. MEMS photoetching technique was used to fabricate a single port SAW resonator (SAWR) as the final transducer.Humidity sensitive material is a key factor that could determine the humidity sensors’performance. Only when the characteristic of the material was coordinated with the sensing mechanism of the SAW sensors, the humidity sensor could achieve the best performance. The characteristic including adsorption efficiency, conductivity variance and viscoelasticity must be taken into consideration. Polyelectrolyte material, nano material and composite material is the main developing direction and research focus. Designing method of the humidity sensitive material used in SAW humidity sensor was carefully discussed. Nafion/MWCNTs composite material and novel graphene oxide were designed as the alternative material.Coating method of the humidity sensitive film is another critical technique for humidity sensor design. For the SAW device with high frequency, there’s only a little area could be coated with the sensing film. Furthermore, there are many restrict requirements for the film, such as reasonable thickness and well-proportioned topography. In another aspect, the sensing film with nano-structure could greatly improve the sensor’s performance. Electrospinning is an emerging technique for nano material design. The sensing film made by this method has the advantages of high specific surface, large poriness and uniform morphology. The coating methods based on electrospinning technique were introduced into the design process of the SAW humidity sensor. Nafion/MWCNTs composite nano-fiber films were prepared by the new techniques.SAW sensors are usually working in the RF band. Thus its signal was prone to be interfered with the electromagnetic radiation and other environmental factors. So there are great difficulties for designing SAW sensor detection system. A high frequency resonator circuit and assorted detection system with stable performance were designed. At the same time, a novel RF-triggered semi-passive SAW humidity sensor tag was researched. Furthermore, a new serial topology was studied to propose a new idea for SAW sensor design, but not limited to humidity sensors.Experiment was set up to examine the key indicators for humidity sensors, including sensitivity, stability, repeatability, response-time and temperature coefficient. The results showed that the two types of humidity sensitivity material designed in this paper are all effective in humidity detection. Performance of the SAW humidity sensor has made a great breakthrough compared the commercial devices. The positive effect of electrospinning coating method was also tested. It was really helpful to improve the sensor’s sensitivity and dynamic characteristic. The SAW humidity sensor with novel serial topology was also tested in the experiment. The result proved that it was a promising method for high frequency SAW sensor design.Low humidity (<10%RH) or dewpoint detection is always a difficult point in humidity detection. Common resistor type or capacity type humidity sensors are both difficult to meet the accuracy requirements. So there’s great meaning to develop a low humidity sensor or dewpoint sensor with low cost, small size and ease-to-use. The present SAW humidity sensor was tried to be used for low humidity and dewpoint detection. The excellent result provided a good prospect for its future.更多还原