ZnO修饰多针-板结构负电晕放电气体传感器北大核心

基于负电晕放电原理的气体传感器利用局部高压电场将目标气体电离,根据电离特性对气体进行识别。采用MEMS技术制备硅尖阵列电极,利用电喷ZnO纳米颗粒对电极表面进行修饰,结合金平板正电极构建了多针-板结构电晕放电气体传感器。研究了电极间距对传感器负电晕放电特性的影响,综合考虑起晕电压、信号输出范围及稳定放电范围,优化电极间距为100μm。测试了在-0.70 kV放电电压下传感器对乙酸气体的敏感特性。该传感器对乙酸气体的响应灵敏度约为1.05 mV/10-6,理论检测限(三倍噪声)约为8.6×10-6,测试范围内传感器响应同乙酸气体体积分数近似呈线性关系。实验结果表明,ZnO纳米颗粒修饰减小了放电尖端曲率半径,增加了放电尖端个数,消除了硅尖阵列之间高度和顶端曲率半径的差异,从而有效降低了起晕电压,提高了传感器对乙酸气体响应灵敏度及电晕放电的稳定性。     

基于气体传感器阵列的电子鼻对混合气体定量识别的研究

阐述了电子鼻的结构,并根据传感器阵列响应信号特性,推导出气体传感器阵列的响应矩阵及其对混合气体的响应;论述了前馈神经网络在电子鼻中的应用原理。最后,利用自制的实验装置对所建立的电子鼻进行性能测试。实验结果证明气体传感器阵列和神经网络模式识别技术所组成的电子鼻完全可以完成对混合气体浓度的识别。     

电离式三电极碳纳米管乙炔传感器

乙炔(C2H2)气体是变压器油中溶解的主要故障特征气体之一,乙炔气体检测是实现变压器故障在线监测的关键.现有的乙炔传感器存在灵敏度低、结构复杂等问题.采用微电子机械系统(MEMS)加工工艺设计制作了一种电离式三电极碳纳米管(CNT)乙炔传感器,该传感器工作在非自持放电状态,碳纳米管尖端在低电压下产生高场强,使这种传感器...     

碳纳米管光电器件光学特性的电磁模型研究

针对基于碳纳米管阵列构成的光电器件,建立基于场效应器件结构的电磁散射模型,对其光电吸收特性进行了仿真分析。模型仿真结果表明,当碳纳米管阵列间距为入射光波长的整数倍时,碳纳米管的吸收功率达到峰值,当在两个波长之间,吸收功率按线性衰减,对应于入射光的不同倍数波长的吸收功率的峰值随波长的增加而线性衰减。在吸收功率峰值附近,吸收功率随阵列周期间距的变化而敏感。     

电离式碳纳米管气体湿度传感器

研究了一种新颖的碳纳米管气态离化结构的碳纳米管气体湿度传感器。该传感器具有一对或多对叉指状侧壁电极结构,电极上覆盖一层多壁碳纳米管薄膜,其利用碳纳米管高长径比的尖端电场收敛作用增大局部电场,有效地增强了传感器对气体湿度的敏感性。通过搭建的气体湿度测试平台,对传感器的静态和动态气体湿度特性进行了研究,结果显示传感器对60%以上相对气体湿度表现出了较强的灵敏度。与吸附式等传统气体湿度传感器对比,该气体湿度传感器具有较快的响应速度(约为0.15 s)和回复速度(约为0.6 s),较传统湿度传感器高了一个数量级,能够用于实时并且快速的气体湿度参量标定。     

极间距可调的ECT系统差分传感器设计

针对电容层析成像传感器相邻电极间耦合电容引起的测量噪声及传统传感器需根据被检测管道的外径变化而需重新制作安装的问题，设计了一种便携式、电极对于管道轴心距离（极间距）可调节的差分电极传感器。通过控制模块调节极间距，使单一传感器能够适用于外径在60～100 mm动态范围内变化的管道测量。采用差分电极结构，解决了传感器无法固定合适长度的径向电极的问题，消除了传感器内部分寄生器件引起的测量噪声。实验结果表明，新型传感器可实现多种不同外径的管道的检测，差分电极的使用提高了多相流成像质量。     

片上集成三电极体系微电极阵列的表征

设计制作了片上集成三电极体系微电极阵列。工作电极分为圆形和方形两种,电极特征尺寸为100~900μm,工作电极与对电极间距为50~200μm。利用循环伏安法,在氧化还原电位探针二茂铁甲醇的作用下,对各三电极微系统进行了电极性能表征,具体分析了工作电极的形状、大小、与对电极的间距对输出特性的影响,为片上集成三电极体系的微电极阵列的设计优化提供了实际依据。     

基于优化的GA-BP网络算法的混合气体识别

基于还原氧化石墨烯(RGO)复合材料设计并制备气体传感器构成气体传感器阵列,对NO_2和NH_3组成的混合气体进行性能测试,构建算法对混合气体进行识别。通过主成分分析法发现混合气体的响应与气体浓度具有非线性关系,选择BP网络作为识别工具;根据多次模拟结果的预测均方误差(MSE)箱线图,对BP网络的参数进行优化,使其性能大幅提升;采用均匀分布U(-3,3)生成随机数并经过遗传算法(GA)优化后,作为GA-BP网络算法的初始权重和阈值,采用BP网络算法对混合气体进行识别。结果表明,优化的GA-BP网络算法在300次模拟中对混合气体的定性识别准确率均为100%,定量预测在最坏情况下的相对误差不超过30%,可靠性胜过BP网络算法,具有较好的参考价值。     

用于气体传感的电容式微机械超声阵列设计

电容式微机械超声阵列(CMUT)是微机电系统(MEMS)气体传感器的常用结构之一。为了在尽可能降低功耗的前提下,提高气体传感器的灵敏度,对电容式微机械超声阵列尺寸进行优化。首先基于一阶集总电机械振动模型进行理论分析,发现其灵敏度与塌陷电压成正相关,并主要受振膜厚度、电极间距和电极半径影响,以此为依据设计符合要求的参数。然后使用COMSOL多物理场仿真软件,综合结构特点、空气阻尼、外接电路、弹性软化等因素的影响,提出一种更接近实际的有限元模型。将理论分析结果代入,对尺寸参数进行进一步优化,得到塌陷电压11.3 V,灵敏度-3.253×1017 Hz/kg,共振频率4.858 MHz,品质因数121.45的电容式微机械超声阵列。     

基于凸优化的稀疏阵列方向调制信号综合算法研究

方向调制技术利用多天线发射阵列的空间调制能力在天线端综合出具有方向特性的数字调制信号是近年来物理层安全通信领域研究的热点之一。该文提出一种基于凸优化的稀疏阵列方向调制信号综合算法。首先算法建立以阵列稀疏为目标函数以及方向调制信号不同性能要求为约束的非凸优化问题;然后针对这个非凸问题,给出了两种不同的求解方案：一种基于迭代加权l1算法,但稀疏算法得到的结果可能存在阵元间距小于半个波长的情况;另一种基于混合整数规划,确保稀疏算法得到的阵元间距至少为半个波长;最后在混合整数规划算法的基础上建立以方向调制信号功率利用率为目标的优化问题,优化稀疏阵列方向调制信号发射机的功率利用率。仿真结果表明,相比于与现有的基于均匀等间距直线阵列的方向调制信号综合算法,所提算法在方向调制信号的安全性能、方向调制信号发射机的功率利用率以及阵列的稀疏程度之间具有良好的设计灵活度。     

碳纳米管-氢氧化镍复合电极电化学电容器

采用催化裂解法制备了碳纳米管并进一步制备了碳纳米管薄膜电极。基于该种材料的超电容器电极比容量为36 F/g。研究了在碳纳米管薄膜基体上使用电化学方法沉积氢氧化镍的新工艺,制备出碳纳米管/氢氧化镍复合电极。伏安特性曲线以及直流充放电实验证明复合电极的单电极比容量达到63 F/g,交流阻抗谱证明复合电极具有优良的阻抗特性。     

High‐Sensitivity,Skin‐Attachable,and Stretchable Array of Thermo‐Responsive Suspended Gate Field‐Effect Transistors with Thermochromic Display

The fabrication of a skin‐attachable, stretchable array of high‐sensitivity temperature sensors is demonstrated. The temperature sensor consists of a single‐walled carbon nanotube field‐effect transistor with a suspended gate electrode of poly(N‐isopropylacrylamide) (PNIPAM)‐coated gold grid/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate and thermochromic leuco dye. The sensor exhibits a very high sensitivity of 6.5% °C^?1 at temperatures between 25 and 45 °C. With increasing temperature, the suspended gate electrode bends due to the deswelling of the PNIPAM, resulting in the reduction of the air gap to increase the drain current under a constant gate voltage. At the same time, the leuco dye coated on top of the transparent gate electrode changes color to visualize changes in temperature. The 4 × 6 integrated temperature sensor array integrated using liquid metal interconnections exhibits mechanical and electrical stability under 50% biaxial stretching and allows for the spatial mapping of temperature with visual color display regardless of wrist movement while attached to the skin of the wrist. This work is expected to be widely useful in the development of skin‐attachable electronics for medical and health‐care monitoring.     

Sensor Allocation for Source Localization With Decoupled Range and Bearing Estimation

The source localization accuracy is known to be affected by the placement of sensors. This paper addresses the problem of optimum sensor allocation for decoupled range and bearing estimation, as well as position estimation of an emitting source, under the constraint that all sensors must be confined within a certain area. The source is assumed to be distant and has a curved wavefront when arriving at the sensors. The optimization criterion is the minimum estimation variance defined by the Cramer–Rao lower bound that is derived under Gaussian noise model. A geometric approach is employed to arrive at the optimum geometries and no complicated optimization technique is required. The optimum sensor allocations for time difference of arrival (TDOA), angle of arrival (AOA), and time of arrival (TOA) positionings are derived and their estimation accuracies are contrasted. The optimum geometries belong to the generic structure of a ring array plus some sensors at the center. TDOA and TOA are found to have identical optimum geometries for bearing estimation and yield the same accuracy, although the position localization accuracy of TDOA is known to be worse than that of TOA. Simulations are included to confirm the theoretical development and illustrate the improvement of using an optimum array compared to a random sensor placement array.      

Sensory Arrays of Covalently Functionalized Single‐Walled Carbon Nanotubes for Explosive Detection

Chemiresistive sensor arrays for cyclohexanone and nitromethane are fabricated using single‐walled carbon nanotubes (SWCNTs) that are covalently functionalized with urea, thiourea, and squaramide containing selector units. Based on initial sensing results and ¹H NMR binding studies, the most promising selectors are chosen and further optimized. These optimized selectors are attached to SWCNTs and simultaneously tested in a sensor array. The sensors show a very high level of reproducibility between measurements with the same sensor and across different sensors of the same type. Furthermore, the sensors show promising long‐term stability, which renders them suitable for practical applications.     

分段圆型碳纳米管阴极结构的三极FED制作

利用钠钙平板玻璃形成阴极板;结合丝网印刷技术在阴极板上制作了分段圆型碳纳米管阴极结构。烧结固化的银浆层用于分别构成矩形底电极和圆型底电极,其良好的导电性能确保阴极电势能够被顺利传导给碳纳米管。对矩形底电极采取了分段条形电极形式,多个分段条形电极整体排列在阴极板表面,形成分段条形电极矩阵,改进的矩形底电极能够有效降低整体显示器的无效电压降;而制作的圆型碳纳米管层和圆型底电极用于提高碳纳米管的场发射性能。结合分段圆型碳纳米管阴极,研制了三极结构的场致发射显示器。该显示器具有良好的场致发射特性和高的图像发光亮度,能够正确显示简单的字符图像,其开启场强为2.16 V/μm。     

Design of an integrated low-noise read-out system for DNA capacitive sensors

This paper presents an electronic system for a fast DNA label-less detection. The sensitivity of the capacitive sensor in use is improved by depositing an insulating self-assembled monolayer (SAM) over the golden electrodes. The capacitance shift due to the hybridization effect is monitored by means of a charge-sensitive amplifier and digitalized by means of a comparator and a counter. The read-out solution demonstrates the ability to identify a 0.01% variation on the capacitive value of the sensor. Results from measurements with the optimized sensor show the reliability of the electronics. The investigated solution is suitable for monolithic systems or for a micro-fabricated array of sensors. An example of the integrated front-end is described and performances and noise evaluation are reported here.     

碳纳米管非对称接触结构制作及电学性能研究

实验研究了多根或单根单壁碳纳米管与非对称金属电极接触结构的制作方法。先用介电泳方法(DEP)将碳纳米管定向排列在Au电极对之间,再用电子束光刻(EBL)在碳纳米管的一端加工Al电极,获得多根碳纳米管与金铝电极的非对称接触结构。先用EBL在Au电极对一端覆盖Al电极,再用DEP排列碳纳米管,实现单根碳管与金铝电极的非对称接触结构。非对称结构器件的电学测试研究表明,器件的I-V曲线不再对称,呈现出整流特性。     

Hydrogel Cryo-Microtomy Continuously Making Soft Electronic Devices

Standard fabrication of soft electronic devices with both high controllability and yield is highly desirable but remains a challenge due to the modulus mismatch of component materials through a one-step process. Here, by mimicking the freeze-section process of multicomponent biological tissues containing low-modulus muscles and high-modulus bones, for the first time, a hydrogel cryo-microtomy method to continuously making soft electronic devices based on a sol-solid-gel transition mechanism is presented. Polyvinyl alcohol (PVA) electrolyte and aligned nitrogen-doped multi-walled carbon nanotube (N-MWCNT) array electrode are demonstrated as low- and high-modulus components to fabricate soft supercapacitors with high performances. Stable interfaces form between frozen PVA electrolyte and N-MWCNT electrodes with matched moduli at subzero temperature and are well maintained during cryo-microtomy process. The resulting soft supercapacitors realize controllable patterns, tunable thicknesses from 0.5 to 600 μm, high yields such as 20 devices per minute even at lab scale, and high reproducibility with over 75% devices in 15% performance fluctuation. This cryo-microtomy method is further generalized to fabricate other soft devices such as sensors with high sensing properties.     

变压器油中溶解一氧化碳气体的光纤传感技术

为了满足变压器中绝缘纸板因过热或者放电故障产生的一氧化碳气体的在线监测需求, 提出了一种基于光纤光声传感的油中溶解一氧化碳气体检测技术。采用光声光谱气体检测技术、并结合光纤传感和膜分离技术, 设计了集成油气分离和气体检测功能于一体的光纤光声传感探头, 油中溶解的一氧化碳气体通过油气分离膜进入到光纤探头中的微型气腔; 采用两根光纤将探头连接到解调仪器, 分别传输近红外激发光和探测光; 气体吸收光能产生的光声信号被光纤法布里-珀罗传感器探测, 并被设计的光纤光声解调模块进行信号处理, 获得系统对一氧化碳气体体积分数的检测灵敏度为0.345pm/10-6。结果表明, 所设计的光纤传感系统对油中溶解一氧化碳气体体积分数检出限达到5×10-6。该研究具有精度高、抗电磁干扰、脱气简单的优势, 为变压器油中溶解一氧化碳气体的检测提供了新方法。