液体中基于动态微悬臂梁的质量检测技术

当利用微悬臂梁动态模式的基频谐振在液体环境检测微弱被测量时,液体中的流体动力阻尼导致检测灵敏度降低。针对此问题,提出了利用微悬臂梁的高次谐振进行质量检测的方法。对于相同的被测量质量变化,微悬臂梁的谐振次数越高,其频率偏移越大,从而达到比基频检测法更高的分辨力。以表面修饰三乙基氢硫基十二基铵层(敏感层)的微悬臂梁为传感元件,以CrO42-为被测物,在原子力显微镜上检测了敏感层吸附CrO42-前后,微悬臂梁的5~8次谐波频率的变化情况。结果显示,该质量检测法能检测出约0.82 ng的质量增量。     

基于微悬臂梁高次谐波的微小质量检测技术研究

针对微悬臂梁动态检测方式无法应用于液体环境,提出了一种利用微悬臂梁的高次谐振进行微小质量检测的方法.对于相同的被测量质量变化量,微悬臂梁的谐振级次越高,其频率偏移就越大,从而达到较高的灵敏度.以表面修饰了三乙基氢硫基十二基铵层(敏感层)的微悬臂梁为传感元件,以CrO 2- 4为被测物,在原子力显微镜(AFM)上检测了敏感层吸附CrO 2- 4 前后微悬臂梁的5次、6次、7次和8次谐振频率的变化.结果证明,谐振级次越高,灵敏度越高,在8次谐振时的检测灵敏度能够达到2.50 Hz/pg.     

带尾纤的全光型硅微谐振器

带尾纤的全光型硅微谐振器引入了集成光学技术,具有独立的拾振光路和简单易行的拾振方式,可以完全脱离光学平台运作．对带尾纤的全光型硅微谐振器进行了实验测量及较详细的理论分析,给出了悬臂梁振子的固有谐振频率、谐振频率的总温度系数、悬臂梁对简谐激励的响应等表达式;归纳出了该谐振器具有光纤与振子间未对准误差容限较大,输出测量信号与光纤有效光学长度无关及振子谐振频率不受硅片内应力影响等特点．     

振梁式负压传感器

对负压力的测量可采用各种真空计或者负压传感器，但其输出量大多为非电量或模拟式电量，本文制作了一种电热激励的微悬臂梁谐振式负压传感器，它利用随微悬臂梁振动的气体分子等效于增加微梁惯性质量的原理测量气压或气体密度，利用Navier-Stokes方程和连续性方程计算作用在微悬臂梁上的惯性阻力，进而计算出谐振器谐振频率与气压的关系，分析表明，增大梁的宽度，减小梁的厚度和长度可提高传感器的灵敏度。     

一种斑马型压电俘能器的有限元分析

提出了一种新型的俘能结构,其是利用压电效应并应用于微机电(MEMS)领域的设计。通常有效的能量捕获装置包括:悬臂梁类型的金属基层及与之粘结的较薄压电层,从而引起谐振响应。越短的悬臂梁其谐振频率越大,因此在微机电领域中,由于较小的结构使得悬臂梁难以形成共振。文中针对此问题提出了一种可以降低自身谐振频率的新型几何结构。对这种斑马型几何结构,利用Ansys仿真软件求解得出其在微机电领域内也可以接近发生共振。     

谐振法确定热激励微梁谐振器厚度及残余应变

精确测量热激励微梁(悬臂梁和桥)谐振器的厚度和残余应变对研究其谐振特性具有重要意义。由于组成谐振器的薄膜厚度远小于占优层厚度，本文首先利用单层梁谐振频率推算得梁的厚度的近似值，从而得到热激励梁的等效杨氏模量和等效密度。在此基础上利用双层梁谐振频率精确推算梁的厚度和残余应变，结果与测量值符合较好。该方法具有非破坏性的优点。     

水平静电驱动式多晶3C-SiC折叠悬臂梁谐振器微结构

介绍了一种微机械叉指静电驱动折叠悬臂梁谐振器的设计和制作方法.将Rayleigh分析法和有限元分析法结合起来分析调整器件尺寸和材料参数对器件性能的影响.制作了三种不同悬臂梁宽度的微机械横向谐振器件,经实验检测它们的谐振频率分别为64.5,147.2,255.5kHz,与模拟结果符合得很好.该结果显示由于具有很高的杨式模量,利用多晶3C-SiC材料体系制作的谐振器件能够具有更高的谐振频率.     

水平静电驱动式多晶3C-SiC折叠悬臂梁谐振器微结构

介绍了一种微机械叉指静电驱动折叠悬臂梁谐振器的设计和制作方法.将Rayleigh分析法和有限元分析法结合起来分析调整器件尺寸和材料参数对器件性能的影响.制作了三种不同悬臂梁宽度的微机械横向谐振器件,经实验检测它们的谐振频率分别为64.5,147.2,255.5kHz,与模拟结果符合得很好.该结果显示由于具有很高的杨式模量,利用多晶3C-SiC材料体系制作的谐振器件能够具有更高的谐振频率.     

压电微泵的特性测试与分析

本文对压电驱动微泵的工作特性进行了系统测试，利用高压方波信号源产生频率和电压可调的信号来驱动微泵，采用高精度电子秤测量固定时间(10s)内微泵输送液体的质量大小，并对工作特性进行相关分析，总结了压电微泵的输送流量随液体黏度、驱动电压和驱动频率之间的关系。结果表明，在相同的驱动条件下，液体黏度越大，压电微泵输送的流量越小，在固定的驱动电压下，当驱动频率为泵膜的谐振频率时压电微泵输送的流量最大，高于或低于驱动频率时输送的流量越来越小，在固定的驱动频率下(谐振频率)，压电微泵输送的流量随驱动电压的升高而增加。研究结果为压电微泵的优化设计和实际应用提供了依据。     

基于微波谐振腔的葡萄糖溶液浓度测量系统

根据微波谐振腔的谐振频率随腔内溶液的介电常数的变化而发生偏移的特性,本文设计了基于微波谐振腔的葡萄糖溶液浓度测量系统,包括谐振腔测量模块、谐振频率跟踪模块和等精度频率测量模块,可实现对溶液浓度的实时测量。谐振频率跟踪模块利用单片机控制压控振荡器(Voltage Controlled Oscillator,VCO)的输出频率,使VCO的输出频率与谐振频率实时保持一致,实现了谐振频率的自动跟踪。等精度频率测量模块在标准频率为50 MHz时,误差达到2×10-8,浓度测量分辨率达到0.01mmol/kg。     

对瞬时信号波长的相频检测

首先,将短基线相差测向严格解和多普勒频移方程联解,获得基于相差测量的频移表达式;然后,利用中心频率、瞬时测频值和多普勒频移间的关系,将频移表示式化为一个仅包含未知信号波长的一元三次函数方程,从中可导出基于瞬时测频和相差测量的信号波长解析公式。在此基础上,还通过模拟比较,采用合并等值项的方法对解析公式进行了简化。对简化解的误差分析表明,对于分米波信号,且在瞬时测频的测量误差大于数兆赫的情况下,由基于短基线相差测量所得到的波长测量误差可小于 1mm。所提出的新方法可能是至今为止最具有工程应用价值的。     

机载平台径向加速度的无模糊相差检测

在由短基线相差测向严格解给出了相移与频移之间的函数关系之后,导出了一个基于相差和辐射频率测量的信号波长解析公式。随后,通过模拟比较,采用合并等值项的方法对解析公式进行了简化。对简化解的误差分析表明,对于分米波信号,且在实测频率的测量误差大于数兆赫的情况下,由基于短基线相差测量的新方法所得到的波长测量误差可小于 1mm。这可能是至今为止最具有工程应用价值的方法。     

A simple prediction method for composite rectangular microcantilevers with equal width and the dimensional optimization

Resonant frequency is a key parameter in designing a resonant transducer with high sensitivity. Eigen-frequency calculation of a composite-layer microcantilever is quite useful for the design of a microcantilever resonant sensor. However, simple methods for predicting the resonant frequency of composite rectangular microcantilevers are poorly developed and invite further research. This paper presents a simple and accurate analytical method called “equivalent model method” to predict the fundamental resonant frequency of composite rectangular microcantilevers with equal width (CRMEW). This novel method, which is much more convenient for practical applications, is then confirmed by both experimental results and simulation results, and presents a strong potential to be used in the design and optimization of micromachined transducers.     

A Model-Based Processor Design for Smart Microsensor Arrays [Applications Corner]

In this article, we discuss the design of a smart-physics-based processor for microcantilever sensor arrays. The processor is coupled to a microelectromechanical sensor and estimates the presence of critical materials or chemicals in solution. We first briefly present microcantilever sensors and then discuss the microcantilever sensor array design, which consists of the cantilever physics propagation model, cantilever array measurement model, model-based parameter estimator design, and model-based processor (MBP) design. Finally, we end with experimental results and conclusions     

用激光光镊测量液体微区的粘滞系数

为了实现对样品溶液粘滞系数的精确、实时和无损测量,利用激光光镊中的光致旋转原理,提出了一种改进的理论和实验方法。首先对样品溶液的粘滞系数随探针粒子半径的变化关系进行了数值模拟,然后通过光镊实验装置测量并计算出具体的探针转动频率和液体粘滞系数值。结果表明,探针半径为2.0m时得到的溶液粘滞系数误差最小,并且测量了不同温度下密封的纯净水和乙醇溶液的粘滞系数,实际偏差均小于7%,验证了本方法的有效性。该方法具有相当高的测量精度和无接触的特点,尤其是在测量粘滞系数较小、易挥发且有害性的溶液方面具有明显优势。     

A novel method of evaluating transient response

In this paper, a novel method of evaluating transient responses of linear time-invariant systems using the state space approach is described. Given the Laplace transform of the response function as a ratio of two polynomials in the complex frequency of proper form, the corresponding linear state space equation is formulated. A recursive formula for the transient response is derived from the exact solution of the state space equation. Numerical solutions can be obtained for any desired interval of the response time. This method is simple, accurate, and effective, especially when used with a digital computer.     

Tunable Capacitor Based on Polymer-Dispersed Liquid Crystal for Power Harvesting Microsystems

A tunable capacitor based on polymer-dispersed liquid-crystal (PDLC) technology is presented in this paper. Its application for robust power harvesting microsystems was investigated. The power harvesting device utilized a piezoelectric microcantilever excited by ambient random vibrations to convert mechanical energy into electric power. For improving the power harvesting efficiency, the PDLC tunable capacitor was used to adjust the resonance frequency of the piezoelectric microcantilever beam to match the frequency of the ambient vibrations in real time. The fabrication process and measurement results of the PDLC tunable capacitor are detailed. The measured tuning ratio of the PDLC tunable capacitor was 63% at 300-Hz excitation frequency when a 25-V driving voltage was applied. The dielectric and optical properties of the fabricated PDLC tunable capacitor have been examined thoroughly. Based on the results of the experiment, an equivalent lumped-element model of the PDLC tunable capacitor has been developed. The simulation results showed that the impedance of the developed model agreed well with that of the fabricated tunable capacitor. This model can be incorporated into the equivalent circuit of the integrated power harvesting system for efficiency optimization.     

Design and fabrication of in-plane resonant microcantilevers

An in-plane resonant bimetal microcantilever based on thermal actuation mechanism was developed utilizing the photolithography technique. The microcantilever structure consists of a platform, a long narrow anchor, and a U-shape actuation loop. Niobium and gold are used as materials for fabrication of the microcantilever. In the cantilever design the shortcoming of low actuation frequency was overcome by separating the thermal actuator part and the microcantilever part. According to the dynamic property tests, the in-plane resonant frequency of our microcantilevers is one order of magnitude higher than the out-of-plane one. With further optimizing the design, our microcantilevers may have applications as actuators and biosensors.