基于MEMS技术的微流体混合器及相关技术

介绍了基于MEMS技术的微流体混合器及相关技术,给出了各种微流体混合器的结构、原理和特点,同时对微管道中流体混合的仿真、实验技术以及微管道中微量流体混合程度的评价方法等作了概述。     

微混合器研究进展

微混合器作为微全分析系统重要的组成部分,是目前微机电系统(MEMS)领域内的研究热点。文章介绍了微混合器的设计要求与目标、加工方法与材料的选择、微混合的特点与混合机理。微混合器一般可分为主动混合器与被动混合器,基于此分类方法,文章综述了微混合器的国内外研究现状,并讨论了目前研究中存在的一些问题,展望了微混合器的研究前景。     

被动微混合器的研究进展(英文)

综述了被动微混合器的混合原理、结构、微制作技术以及在数值仿真计算等方面的研究进展。着重讨论了几种主要被动微混合原理,如多层流、混沌对流、分裂-重合、流体弯曲和压缩以及循环流动。重点分析了近年来低雷诺数下高混合效率的复合式微混合器。复合式微混合器利用其他简单的外界作用来提高其混合效率,诸如施加离心力、采用几何压缩和三个入口结构,或利用多入口结构,使其中的流体产生周期性的流动。指出随着对低雷诺数和高黏度要求的不断提高,SAR型复合式微混合器成为更为广泛的一个研究方向,其内部的分裂-重合结构单元能够使流体产生旋转,同时通过采用几何压缩结构,缩短扩散长度.从而大大提高了流体的混合效率,但同时也提高了对微制作技术的要求。     

一种低成本高效率气动式微流控混合器

液体混合是微流控芯片的重要功能之一,微流控液体混合方式可分为主动式和被动式两种。针对目前微流控混合器存在的被动式混合效率不高和主动式混合器制作工艺复杂等问题,研究设计了一种基于雕刻机加工的低成本、高效率气动式微流控混合器。该微流控芯片采用数控雕刻机快速加工微模具,经PDMS固化、翻模、打孔和键合等工艺,实现了微流控混合器的制作。同时研究设计了多气室脉冲气体驱动模式,有效实现了微量试剂和样品的快速混合。实验结果表明,所研究的主动式微流控混合器可以产生对流混沌作用,显著提高微尺度下的混合效率,为实现低成本的微流控芯片制作和高效试剂混合的MEMS生化检测系统提供了一种有效的技术途径。     

一种挡板结构被动式微混合器的设计与仿真北大核心

基于在微通道内设置障碍物可以提高混合效率的方法,以T型方波通道微混合器为基础,设计了一种新型的、具有挡板结构的被动式微混合器,并采用有限元方法建立了仿真模型,分析比较了T型直通道微混合器、T型方波通道微混合器和具有挡板结构的T型方波通道微混合器在不同雷诺数（Re）下器件内流体的流动特性和混合效率。研究结果表明,具有挡板结构的T型方波通道微混合器在挡板阻塞比为1/4时具备最优的综合性能,也即在较宽Re值范围（5～60）内可实现流体的快速、高效混合,混合效率高于95%。     

基于PDMS的静态微流体混合器的制作与仿真

通过采用模塑法制成一种基于聚二甲基硅氧烷(PDMS)的静态微流体混合器.根据流体动力学理论对其进行了理论分析,并给出了两种流体混合的仿真分析结果.对以数值模拟为依据制作的微流体混合器进行了水与红墨水的混合实验,获得了相吻合的结果.     

数字化微混合反应器的研究

设计了一种数字化微混合反应器,对不同流体通过数字化微喷射生成微液滴,利用液滴间的碰撞和聚合实现试样与试剂间的微混合与反应。该微混合反应器由玻璃微流体器件拉制仪拉制的微管道进行粘接组合而成,内部无可动件,无需复杂的微加工技术,结构简单,制造成本低。进行了氢氧化钠溶液和酚酞溶液的混合反应实验,实验证明该混合反应器可以用于微混合反应。     

一种非对称结构微流体混合器的设计与分析

微流体混合器可以用于不同流体之间的混合与反应,其与化学传感器结合构成的化学分析测试系统,具有灵敏度高、响应时间短和稳定性好的特点。在微电子机械加工技术的基础上,设计了一种新型的、具有非对称分离重组结构的微流体混合器,并应用有限元方法建立了仿真模型,讨论了在不同雷诺数(Re=10~80)下,通道几何结构参数对微混合器内的流体流动特性和混合效率的影响。研究结果表明,微流体在该混合器内形成了扩展涡、分离涡和迪恩(Dean)涡,实现了涡系的叠加和强化,加大了流体间的扰动,增加了流体的接触面积,从而大大增强了混合效率。     

二维变形方波微混合器混合效果

设计并制作了多种二维变形方波微混合器,通过荧光观测及标准偏差数值分析,在低Re数(Re≤13.33)时,考察拐角和单元长度对混合器混合效果的影响。结果表明,集成拐角的混合器存在一个临界Re值1.3,当Re<1.3时,混合基于分子扩散,拐角大小对混合效率无影响,混合效率保持在28%左右;当Re>1.3时,可以产生回流,混合效率随着拐角的减小逐渐提高。对于集成6个单元、拐角为45°、单元长度(s)为3132μm的微混合器,在雷诺系数Re=13.33时,混合效率为56%,约提高了1倍;但当拐角与混合单元长度增大时,混合效率明显降低。     

微气泡执行器强化微混合的实验研究

微尺度流动的雷诺数(Re)比较低,其混合主要通过扩散来完成,因此需要较长的距离与时间才能混合均匀。为实现微尺度低Re数流体的快速均匀混合,以甲醇及染色甲醇为工质,采用脉冲电压激励微铂膜产生可控气泡,并以气泡周期性胀缩产生的脉冲压力为动力源,研究脉冲压力横向扰动产生的混沌流对微通道内流动混合的影响。结果表明:脉冲压力横向作用使流体的交界面产生了强烈的卷曲拉伸,有效地强化了混合,该微混合器能够在毫米级混合长度及毫秒级混合时间内快速均匀混合,脉冲频率越高,混合效果越好。本研究结果为解决微尺度下低Re数流动混合难题提供了一种有效的崭新手段。     

W-Band CMOS down-conversion mixer using micromixer-based gain-enhanced technique

We demonstrate a W-band down-conversion micromixer for imaging and gesture recognition transceiver. Micromixer-based gain-boosted technique, i.e. inductive-peaking gain-boosted single-to- differential transconductance (g_m) stage, is adopted to increase the output impedance and restrain the feedback capacitance C_gd of the g_m stage. This leads to the conversion gain (CG), noise figure (NF) and LO-to-RF leakage of the micromixer being significantly improved. The micromixer dissipates 7.2 mW and attains marvellous RF-port return loss of ?12.7~ ?14.7 dB for 85 ~ 110 GHz. That is, the ?10 dB matching bandwidth is wider than 25 GHz. Moreover, for 90 ~ 96 GHz, the micromixer attains CG of 10.5 ~ 12 dB and LO-to-RF isolation of 40.2 ~ 46.2 dB, one of the highest values ever demonstrated for a W-band mixer/micromixer. The 3 dB CG bandwidth is 22 GHz (83 ~ 105 GHz), and the input third-order intercept point (IIP3) is 1 dBm. These results indicate the micromixer is appropriate for W-band imaging and gesture recognition transceivers.     

Realization of planar mixing by chaotic velocity in microfluidics

We present the design, fabrication and characterization of an effective planar passive micromixer with relatively simple construction for microfluidic applications. This micromixer consists of a zigzag microchannel in which realization of fluid mixing is expected because the variation of the flow velocity direction and magnitude in the channels may cause the laminar flow to become chaotic. Simulations were made to study the influence of geometry of the microchannel on the mixing effect and it has been found that the turning angle plays a very important role in the mixing process. Prototype devices were fabricated using polydimethylsioxane soft lithography technology. Mixing efficiency of the micromixer was examined by tracing the color uniformity of de-ionized water and red ink travelling through the microchannel. It was found that, for these two flows with a wide range of flow rates, the resulted fluid at the outlet of the micromixer would always show good color uniformity, indicating a high mixing efficiency. A prototype micromixer system for future fast chemical and biological analysis was proposed and fabricated based on this design. Easy to fabricate and use, we believe that our micromixer can be used as a general-purpose component for microfluidic systems.     

一种微通道换热器的设计与分析(英文)

设计了一种用来测试微通道换热性能的实验装置。该系统由微通道换热器、模拟热源、微型水泵、连通管、测试三通及其它测试元件构成。通过检测温度、压力和流量等参数能够得到微通道的传热和摩阻参数。针对该实验装置,对微通道中流体的压降和传热分别进行分析和研究。实验表明,当微通道水力直径为381μm时,宏观理论公式已不适用于微通道摩阻及其换热的计算。此时,微通道的摩阻比宏观理论计算值小31.6%～41.9%;微通道结构具有良好的换热性能,其Nu可达9.2。     

波瓣混合器对双S形二元排气系统红外特性的影响

为了研究波瓣混合器对排气系统红外特性的影响,设计了波瓣数分别为12、15、18的波瓣混合器双S形二元排气系统,通过数值计算研究了波瓣数对排气系统红外抑制效果的影响,并与相应的环形混合器双S形二元排气系统对比。研究结果表明,随着波瓣数的增加,排气系统的推力略微升高,最大差值在0.1%以内;波瓣数越少,排气系统内、外涵气流的热混合度越高,尾喷流的最高温度和红外辐射强度越低,波瓣数由18减少到12时,喷流辐射强度最大降低了18.1%;相比环形混合器双S形二元排气系统,在侧向和下方探测面上纯喷流辐射的90方位角,三种波瓣数的波瓣混合器双S形二元排气系统辐射强度分别降低了20.9%和26.9%以上。因此,为了得到更好的红外抑制效果,建议使用较少波瓣数的波瓣混合器。     

Nonuniform temperature distribution in electronic devices cooled byflow in parallel microchannels

We fabricated a novel thermal microsystem (simulating a computer chip) consisting of a heater, microchannels, inlet and outlet plena and we studied the effect of the geometry on the flow and heat transfer. The vapor-water two-phase flow patterns were observed in the parallel microchannels through a microscope and high-speed video camera. It was observed that hydraulic instabilities occur. Existence of a periodic annular flow was also observed, which consists of a symmetrically distributed liquid ring surrounding the vapor core. Along the microchannel axis, the periodic dry zone appears and develops. The thermal visualization and temperature measurements of the heated device were carried out using infrared thermography. As long as the flow was single phase liquid, the forced convection heat transfer resulted in a moderate irregularity on the heated chip. These temperature differences do not cause damage to a real electronic device. The steady-state heat transfer for different types of microchannels has been studied also at the range of heat flux where phase change of the working fluid from liquid to vapor took place. Under conditions of flow boiling in microchannels, a significant enhancement of heat transfer was established. In the case of uniform heat flux the hydraulic instabilities lead to irregularity of temperature distribution on the heated chip. In the case of nonuniform heat flux the irregularity increased drastically     

Scale effects on fluid flow and heat transfer in microchannels

Many investigators have recently experimentally established that fluid flow and heat transfer characteristics in microchannels, used to cool electronic chips, deviate from those of normally sized channels. Deviations increase as the channel size decreases. Many hypotheses were advanced to explain some of the observed deviations. However, they were usually in contradiction with other observed deviations. Hence, no conclusive explanation has been given so far for these phenomena. In this work, observed deviations will be listed, different hypotheses advanced to interpret these deviations will he critically revised. Finally, a new hypothesis will be advanced based on the increased role of surface roughness on flow and heat transfer in microchannels. Simple models will be built capable of reproducing observed trends for both friction and heat transfer coefficient in the laminar region, as well as giving an improved prediction for the laminar turbulent transition     

波瓣混合器排气系统红外特性的模型实验和数值分析

通过模型实验和数值计算相结合的方法研究了带波瓣混合器的涡扇发动机排气系统的红外辐射特性，并与相应的环形混合器排气系统对比。研究结果表明:波瓣混合器可以有效的增强内、外涵气流的掺混作用，降低尾喷流的温度,从而降低喷流红外辐射；相比环形混合器排气系统，波瓣混合器排气系统红外辐射强度在喷管正后方0方位降低9%以上，在侧向90方位降低39%以上；轴对称喷管壁面的低发射率高反射率对排气系统内部高温部件辐射的反射作用强烈，对排气系统在40~70方位角的红外抑制效果不利，因此，对于涡扇发动机自身温度较低的喷管壁面，建议使用高发射低反射特性的材料或涂层，以增加排气系统的红外抑制效果。     

A Rigorous Study of Package and PCB Effects on W-CDMA Upconverter RFICs

A Volterra-series analysis is presented to study the package and printed circuit board (PCB) effects on the linearity of two wideband code-division multiple-access upconverter RF integrated circuit (RFIC) designs. The first design adopts a recently popular micromixer with a class AB input stage. The second design is based on a commonly used Gilbert mixer with emitter degeneration. Both upconverter RFICs are designed to have the same adjacent channel power ratio (ACPR) in the chip-level simulation. After fabrication, packaging, and testing on the PCB, the micromixer-based design consumes less direct current, but causes more degradation in the ACPR performance due to the influence of package and PCB when compared to the Gilbert mixer-based design. The theoretical analysis indicates that the micromixer-based upconverter RFIC is rather susceptible to the parasitic effects from the ground interconnect and, therefore, it needs a better package solution with a lower ground inductance for practical use. Comparison between theory and measurement shows good agreement in predicting the variations of conversion gain and ACPR due to the presence of the package and PCB.     

电子束重复曝光加工PCR微通道的工艺研究

对PCR微流控芯片通道中流体的流动特性进行了分析,发现流体在横截面为圆形的通道中流动时由摩擦引起的等效水头损失及表面张力均小于微矩形通道。以此为依据,将PCR芯片微通道优化设计成圆形通道。在JSM-5CF电子束曝光机上采用束斑尺寸80nm、能量20keV的电子束对1μm厚的聚甲基丙烯酸甲酯进行了单次曝光剂量40μC/cm2的8次重复增量扫描曝光实验,显影后得到的PCR芯片微圆通道轮廓清晰,边缘连续光滑。证明了电子束重复增量扫描曝光方式制作PCR微流控芯片微圆通道的可行性。