用于气体检测的热激励MEMS悬臂梁谐振器

笔者设计了一种电热激励压阻检测的微悬臂梁谐振器．悬臂梁上的敏感层吸附特定的气体后,可以通过测量质量变化所导致的悬臂梁谐振频率的变化而得出待测气体的浓度．该谐振器的加工基于SOI硅片和ICP刻蚀技术．通过有限元仿真得出了悬臂梁的应力温度分布曲线,从而证实了该方案可以提供比普通结构更适宜于气体敏感材料工作的温度分布．从理论和实验上分析了谐振器在不同激励电压下的频率响应．实验结果表明,该谐振器具有较高的谐振频率和品质因数,其激励电压与振动幅值成线性关系．     

用于挥发性有机化合物探测的微悬臂梁传感器

在研制成功的用于化学气体探测的热驱动微悬臂梁谐振器的基础上,提出了基于这种微悬臂梁谐振器,并以聚合物涂层作为挥发性有机化合物吸附敏感层的谐振式气体传感器.利用3种聚合物材料：聚氧化乙烯（PEO）、聚乙烯醇（PVA）和聚乙二醇乙醚醋酸酯（PEVA）,在微悬臂梁谐振器上制备气体敏感层,探测6种挥发性有机化合物：甲苯、苯、乙醇、丙酮、己烷和辛烷.通过有限元分析估计了聚合物涂层的工作温度.用喷射法制备了PVA和PE-VA涂层,用点滴法制备了PEO涂层.测试了传感器的开环幅频特性,实验检测了气体传感器的谐振频率变化与分析物蒸气浓度的关系以及传感器对相对湿度的响应,分析了传感器的灵敏度和线性度.实验结果表明,这种涂覆聚合物敏感层的热驱动微悬臂梁谐振器为探测挥发性有机化合物提供了良好的平台.根据实验结果,可开发几种基于不同聚合物敏感层的高灵敏度微型气体传感器.     

硅微谐振式压力传感器中的单端口静电激励-电容检测方法研究

采用静电激励-电容检测方式的硅微谐振式压力传感器具有温度稳定性好、灵敏度高、功耗低等优点,但同频耦合干扰是限制电容检测精度的主要因素。采用频域分离法可有效地克服同频耦合干扰带来的影响。在研究基于频域分离法的单端口静电激励/电容检测的基础上,提出了单端口静电激励/电容检测方案。     

微机械谐振子单端口电容检测方法研究

针对微机械谐振子电容信号难以检测的问题,本文采用基于频域分离的单端口静电激励／电容检测方案,并配合以隔离变压器应用技术。这种检测方式时域连续,除此,单端口检测既简化了谐振器结构,又避免了双端口检测中激励信号与检测信号存在耦合干扰的问题。实验结果表明：所设计的方案可以有效观测到梁的谐振现象并解算出谐振子的振动信息,为下一步实现单端口谐振子的闭环奠定了基础。     

基于异质双周期结构光子晶体加速度计的设计

对于异质双周期结构的光子晶体而言,不需要掺杂即可形成多条透射谱。理论结果显示,在实际应用范围内,透射率与光子晶体所受的轴向应力呈简单的线性关系。据此,设计了一种单悬臂梁结构的多量程、超灵敏的宽频带加速度计。在单悬臂梁根部所受应力最大处,用异质双周期光子晶体替代以往的压敏电阻,只需检测出透射光强与入射光强的比值,即可测出加速度。ANSYS软件仿真结果表明,当透射光强改变万分之一时,该加速度计可以感知0.01gn的加速度变化,测量量程可达100gn。从模态分析图中可以看到该加速度计可以稳定地工作,可用在自控、车辆、测试等领域。     

硅基反铁电薄膜微悬臂梁力学仿真分析

采用双层微悬臂梁理论模型,对基于反铁电薄膜微悬臂梁驱动构件的力学行为进行分析研究.以反铁电薄膜材料体积应变ε=0.8%为设定量,实现硅基反铁电薄膜微悬臂梁结构的应变-应力载荷转化,运用ANSYS11.0对基于反铁电薄膜应变效应的硅基微悬臂梁结构进行了静态分析、模态分析和谐响应分析,通过对此微驱动结构的优化设计、仿真,得出了不同几何参数硅基微悬臂梁构件的挠度和谐振频率.从而无需进行大量的工艺流片,为大量程的微悬臂梁驱动构件的设计加工提供指导意义.     

超声Lamb波在缺陷处的二维散射特性研究

利用散射系数周向分布图研究了超声Lamb波在缺陷处的二维散射特性。建立了超声Lamb波与缺陷交互作用的有限元仿真模型,采用双元激励法产生单一S0模态入射信号,利用吸收边界消除边界回波的影响,采集缺陷所有方向上的散射信号并产生散射系数周向分布图。此模型的计算结果与实验结果一致,证明了模型的正确性。研究了S0模态与通孔和通透裂纹两种缺陷的交互作用,并测量了S0模态以零度角入射缺陷时的周向散射系数分布图,利用其图形特征可以进行缺陷种类识别。分析了散射场中多模态信号的能量分布,指出检测中若激励单一模态,而接收多模态信号,可以防止漏检,更有效地检测缺陷。     

阵列EMAT相控延时激励实现兰姆波模态控制与增强的研究

兰姆波具有频散、多模态特性,导致在检测过程中难以区分回波信号.针对这一问题,进行阵列EMAT相控延时实现单一模态兰姆波控制激励与增强的研究.在不改变EMAT配置方式、结构及参数的情况下,通过计算阵列EMAT频率响应取得最大值时的延迟时间,将其施加到各个阵元,实现单一模态兰姆波的激励与增强.同时,研究了激励频率对增强阵列...     

光纤光栅流速传感器的设计和实验

本文通过实验验证了一种新型的测量液体流动的流速传感器。液体流动的力作用在小圆盘上,导致悬臂梁的扭曲变形。将布拉格光纤光栅植于悬臂梁上。通过检测布拉格光纤光栅波长漂移,就可以得到液体流速。实验结果显示了这种传感器的可行性。实验实现的测量范围为0--120cm／s,测量精度最高可达到5cm／s。同时,本文提出了通过改变传感器的材料可以扩大测量范围。     

一种谐振式传感器频率特性测试平台

谐振式传感器的谐振频率和Q值可以通过其频率特性计算得到,因此需要有一种通用的测试平台来测量各种不同谐振式传感器的频率特性.本文描述了一种谐振式传感器频率特性测试平台,并提出了一种采用间歇激励方法测试谐振式传感器谐振频率的新方法,采用线性调频信号激励谐振式传感器,传感器自由振动状态下的振动频率即是传感器的谐振频率;测得传感器自由振动状态下的振动频率,即可得到谐振式传感器的谐振频率.     

Resonating Frequency of a SAD Circuit Loop and Inner Microcantilever in a Gas Sensor

A self-actuating and detecting (SAD) circuit loop that drives a micro-cantilever in a gas sensor, in which the resonance frequency shifting of the beam is monitored to detect its mass change caused by adsorption of certain gas molecules, is presented. The loop cannot only drive the cantilever but also trace the fundamental resonance frequency shift of the beam. The motivation of the SAD circuit is simplifying structure and process of the microbeam. This paper presents simulation and experiments of the mechanical resonance of the microbeam and resonance of the electric signal in the SAD loop. The relations between the two resonance frequencies are discussed and analyzed. While the beam is driven in resonating mode, the resonance frequency shift of the signal in the SAD circuit is approximately equal to the mechanical resonant frequency shift of the cantilever. The frequency resolution of the SAD with the microbeam is 0.6–0.7 Hz in our work, and theoretical measurement range of the system is 18750 Hz.      

Nanocantilever signal transduction by electron transfer

Microfabricated cantilever beams promise to bring about a revolution in the field of chemical, physical, and biological sensor development. The resonance frequency of a microfabricated cantilever shifts sensitively because of mass loading from molecular adsorption. The minimum detectable adsorbed mass on a cantilever sensor can be increased by orders of magnitude by changing the dimensions of the device; smaller and thicker cantilevers offer higher resonance frequency and therefore better mass detection sensitivity. Here we describe micromachined silicon cantilevers that are 0.5 to 4 microns in length, fabricated with the use of a focused ion beam (FIB). In addition, we demonstrate a technique for detection of the cantilever resonance frequency that is based on electron transfer.     

Magnetically actuated complementary metal oxide semiconductor resonant cantilever gas sensor systems

In the present paper, an electromagnetically actuated resonant cantilever gas sensor system is presented that features piezoresistive readout by means of stress-sensitive MOS transistors. The monolithic gas sensor system includes a polymer-coated resonant cantilever and the necessary oscillation feedback circuitry, both monolithically integrated on the same chip. The fully differential feedback circuit allows for operating the device in self-oscillation with the cantilever constituting the frequency-determining element of the feedback loop. The combination of magnetic actuation and transistor-based readout entails little power dissipation on the cantilever and reduces the temperature increase in the sensitive polymer layer to less than 1 degrees C, whereas previous designs with thermally actuated cantilevers showed a temperature increase of up to 19 degrees C. The lower temperature of the sensitive polymer layer on the cantilever directly improves the sensitivity of the sensor system as the extent of analyte physisorption decreases with increasing temperature. The electromagnetic sensor design shows an almost 2 times larger gas sensitivity than the earlier design, which is thermally actuated and read out using p-diffused resistors. The gas sensor is fabricated using an industrial complementary metal oxide semiconductor (CMOS) process and post-CMOS micromachining.     

Smart MEMS Flow Sensor: Theoretical Analysis and Experimental Characterization

This paper presents analytical and experimental studies of a new microelectromechanical system (MEMS) smart flow sensor for the measurement of gas flow. The flow sensor has an array of curved-up cantilever beams that are surface-micromachined with two layers of deposition under two sets of different process parameters. The differential residual stress between the two layers of the polysilicon deposition causes the beams to curve upward from the substrate surface when the sacrificial layer is released. Each beam of the array of beams of different lengths vibrates successively as the flow rate increases, enabling more accurate sensing and identification of range of flow rates based on the vibration characteristics, thus making this a smart sensor design. Design and fabrication of these sensors are discussed. Experiments were conducted on this MEMS flow sensors to characterize the deflection of the curved cantilever beams with respect to flow rates. In addition, backflow tests were also conducted separately. Results of the analytical study are presented to investigate the cause of vibration of beams when subjected to flow. Finite-element analyses of vibration of the sensors comply with the experimental observation. Based on the analysis of fundamental natural frequencies, possible arrangement for the distribution of lengths of the beams is proposed to enhance its functionality as a sensor. Future work and plan of the on-board capacitive metrology and other practical issues are discussed     

气敏类智能包装标签技术的研究进展

目的研究气体监测类智能包装标签技术的原理、特点及研究进展。方法综述气敏类智能包装中泄漏指示标签、新鲜度指示标签、射频识别标签的研究现状及应用。重点阐述面向CO_2气体监测和识别的智能包装的分类及其制作方法,并对CO_2传感器在气敏类智能包装中的应用进行阐述。结论近年来智能包装标签技术方面取得了大量研究成果,推动了食品保鲜包装行业的快速发展。气敏类智能包装能够有效检测和监测被包装食品的质量及安全性,对推进包装技术的信息化与智能化起到了重要作用。CO_2传感器在食品新鲜度智能监测方面具有广泛应用,也是未来食品保鲜包装技术领域的发展方向。     

Liquid-phase chemical and biochemical detection using fully integrated magnetically actuated complementary metal oxide semiconductor resonant cantilever sensor systems

A novel resonant cantilever sensor system for liquid-phase applications is presented. The monolithic system consists of an array of four electromagnetically actuated cantilevers with transistor-based readout, an analog feedback circuit, and a digital interface. The biochemical sensor chip with a size of 3 mm x 4.5 mm is fabricated in an industrial complementary metal oxide semiconductor (CMOS) process with subsequent CMOS-compatible micromachining. A package, which protects the electrical components and the associated circuitry against liquid exposure, allows for a stable operation of the resonant cantilevers in liquid environments. The device is operated at the fundamental cantilever resonance frequency of approximately 200 kHz in water with a frequency stability better than 3 Hz. The use of the integrated CMOS resonant cantilever system as a chemical sensor for the detection of volatile organic compounds in liquid environments is demonstrated. Low concentrations of toluene, xylenes, and ethylbenzene in deionized water have been detected by coating the cantilevers with chemically sensitive polymers. The liquid-phase detection of analyte concentrations in the single-ppm range has been achieved. Furthermore, the application of this sensor system to the label-free detection of biomarkers, such as tumor markers, is shown. By functionalizing the cantilevers with anti-prostate-specific antigen antibody (anti-PSA), the corresponding antigen (PSA) has been detected at concentration levels as low as 10 ng/mL in a sample fluid.     

Multimode Air-Coupled Excitation of Micromechanical Structures

The development of an acoustic measurement system for multimode air-coupled excitation and detection of micrometer-scale cantilever structures, which are, for example, used in micro-electromechanical systems (MEMSs), is detailed and reported for the first time. The source of noncontact vibrational excitation is a pulsed acoustic field generated by an air-coupled transducer. In the experimental system, the transient response of the cantilever beam is obtained at various points along the beam axis to extract its resonance frequencies and corresponding mode shapes. We demonstrate that measurable amplitudes of vibrations can be obtained at various excitation levels in the megahertz range, and higher harmonics of vibration of a microbeam can be excited by the air-coupled mechanism from a distance on the order of 10 mm. In the specific utilizations of the reported system, resonance frequencies and mode shapes can be related to the mechanical properties and geometric attributes (dimensions and defects), as well as the residual stress state in a microstructural element using various established computational and experimental inverse techniques. Another potential application area of the reported system is in the sensors for detecting the bending stiffness of deposited films on cantilever oscillators (in addition to its film mass loading) to increase the detection sensitivity and selectivity in a single sensing element.     

Low-Cost Surface-Mount LED Gas Sensor

A low-cost chemical sensor comprising surface-mount light-emitting diodes (LEDs) has been developed for colorimetric gas detection. The device consists of a pair of LEDs connected to a simple PIC microcontroller circuit and in the most basic form, requires the use of only two input–output (I/O) pins on the chip. The key features of this sensor are the use of a LED rather than a photodiode for light detection and an all-digital light detection protocol that leads to a reduction in cost and power consumption by avoiding the need for an analog-to-digital converter. The surface-mount diodes employed are more compact than standard LEDs and are more amenable to coating by solid-state sensor films. Results from sensors employing a chemochromic ammonia sensitive film are presented, and the detection of this target is demonstrated in the parts-per-million range. The configuration is applicable to a wide range of colorimetric gas sensing materials.     

Carbon dioxide gas sensor based on ionic liquid-induced electrochemiluminescence

Electrochemiluminescence of the luminol-O(2) system in an electrolyte-free N,N-dimethylformamide (DMF)-dipropylamine (DPA) cosolution is induced by the formation of a carbamate ionic liquid (IL) from the reaction between CO(2) and DPA, on the basis of which a facile ECL sensor for measuring atmospheric CO(2) has been developed. This ECL sensing method shows several advantages in the detection of CO(2), such as high safety, high selectivity, wide linear response range, and good sensitivity. The gas sensor was found to have a linear response range from 100 ppm to 100 v/v% and a detection limit of 80 ppm (at signal-to-noise ratio of 3). This is the first reported IL-induced ECL sensor for a gas, thus the principle of this type of sensor and the IL-induced ECL mechanism have been demonstrated in detail.     

Dynamic Passivation in Perovskite Quantum Dots for Specific Ammonia Detection at Room Temperature

Perovskite structured CsPbX₃ (X = Cl, Br, or I) quantum dots (QDs) have attracted considerable interest in the past few years due to their excellent optoelectronic properties. Surface passivation is one of the main pathways to optimize the optoelectrical performance of perovskite QDs, in which the amino group plays an important role for the corresponding interaction between lead and halide. In this work, it is found that ammonia gas could dramatically increase photoluminescence of purified QDs and effectively passivate surface defects of perovskite QDs introduced during purification, which is a reversible process. This phenomenon makes perovskite QDs a kind of ideal candidate for detection of ammonia gas at room temperature. This QD film sensor displays specific recognition behavior toward ammonia gas due to its significant fluorescence enhancement, while depressed luminescence in case of other gases. The sensor, in turn‐on mode, shows a wide detection range from 25 to 350 ppm with a limit of detection as low as 8.85 ppm. Meanwhile, a fast response time of ≈10 s is achieved, and the recovery time is ≈30 s. The fully reversible, high sensitivity and selectivity characteristics make CsPbBr₃ QDs ideal active materials for room‐temperature ammonia sensing.