一种空间压电润滑装置的建模与仿真

提出一种主动按需供油的压电润滑装置,以解决航天器运动部件润滑失效问题。首先运用有限元分析软件ANSYS对压电振子进行了瞬态分析,再利用多相流流体软件CFD-ACE+建立喷嘴气-液两相流体模型。最后对液滴喷射过程进行数值模拟,以考察脉冲电压幅值变化对各喷射参数的影响。数值模拟结果表明,增加脉冲电压幅值,可增加液滴长度和速度,但对液滴产生时间影响不大。     

压电式喷射点胶控制系统的电路设计

基于新型压电式点胶头采用的双压电陶瓷的推挽驱动作为胶体喷射的作用机制,设计并搭建了压电式喷射点胶控制系统,完成了硬件与软件模块的组装调试,实现对下压电陶瓷信号的频率、占空比、幅值、上压电陶瓷信号幅值的连续可调,具备人机交互、清洗、喷射点数可调等功能。经测试,系统各参数达到预定指标,频率显示误差:±1.2 Hz;占空比显示误差:±1%;幅值显示误差:±8 mV。在驱动方波电压200 V、频率65 Hz、占空比20%、喷嘴直径250μm、供料压力4 bar、喷射高度3.5 mm的条件下,得到平均直径为1.07 mm左右的喷射胶滴,一致性误差为±2%。     

新型电磁铁驱动的撞针式微滴喷射装置

液滴喷射技术具有广泛的应用前景和技术优势,结合现有技术设计了一种能够实现有效的微滴喷射的装置,该装置基于电磁铁驱动,采用撞针式结构。本装置包括电磁铁、滑轨、撞针、喷嘴、弹簧、垫圈等几个主要部分,通过电磁铁驱动撞针撞击喷嘴从而使液滴从喷嘴中喷射出。整体而言其结构简单、成本较低、易于加工,可实现液滴稳定喷射。以甘油溶液(丙三醇)作为喷射实验材料,进行了多粘度溶液及多种喷嘴直径的喷射实验,并对实验结果进行分析,总结了该装置液滴喷射的相关性能,实现了粘度为0～1 410 mpas的多种粘度液滴的稳定喷射,丰富了微滴喷射装置的结构设计。     

基于液滴打印的纸质微流控芯片制备

介绍了一种基于液滴打印技术制作纸质微流控芯片的简单方法。蜡以液滴的形式喷射到滤纸上,加热蜡图案形成疏水屏障,用于生物试剂测定。制作的玻璃微喷嘴无需复杂的制造技术,成本低廉,简单且容易制作。喷射蜡滴稳定均匀。通过改变驱动电压、频率和加热温度及时间来实验研究蜡线的宽度,最终在纸质芯片上制备出宽度为2 600μm、长度为10 mm的蜡质疏水流道。用所制的纸质微流控芯片装置实现蛋白质、葡萄糖和pH值的多重测试。采用以液滴打印技术为基础的蜡滴生成系统制作纸质微流控芯片,成本低,简单,易于使用且制作快速。     

压电驱动器电压及其频率对驱动速度的影响

为探究压电陶瓷驱动器电压及其频率与驱动速度的关系,利用压电陶瓷的应力应变关系导出了位移的二阶微分方程。通过解该微分方程,得到了基于输入电压的压电陶瓷驱动器位移和速度的解析表示。利用压电陶瓷驱动器速度的解析表示,证明了对任何给定的时间,压电驱动器的速度与输入电压的幅值成线性关系;频率与驱动器速度的关系是一条幅值不断变化的连续余弦曲线,随着给定时间的增大,曲线的峰点逐步远离纵坐标轴,余弦曲线的频率也逐步增大。     

应用于微滴喷射的墨水特性参数仿真研究及验证

本文针对微滴喷射过程中存在的墨雾、卫星滴以及喷头堵塞问题,使用COMSOL仿真软件通过水平集方法对微滴喷射过程进行仿真分析,得到墨水黏度、表面张力等工艺参数对液滴喷射过程中形态的影响规律。采用CCD液滴观测仪对微滴喷射过程进行实时观测和图像采集,将观测图像与仿真结果进行对比,得到微液滴在打印过程中最佳的工艺参数,确定墨水最优的打印温度,仿真和实验结果验证了理论分析的正确性和所提方法的可行性。     

压电微泵驱动信号及流量影响因素分析

压电微泵的泵出流量由微泵结构、压电振子特性及驱动系统驱动信号的形式决定。在机械结构及材料特性确定的条件下,压电振子的驱动信号决定着微泵输出微流量的可靠性和稳定性。在分析压电微泵驱动基理的基础上,通过Ansys对驱动压电振子有效振动的一、二阶频率进行有限元模拟分析,确定了驱动信号电压幅值、频率对微泵流量的影响。以此为基础搭建压电微泵流量测试实验平台,在相同电压和频率条件下,研究了3种不同脉冲信号（正弦波、三角波、矩形波）对输出流量的影响。通过实验对理论模型进行修正,得到了压电微泵输出流量简化模型。实验验证了所得模型在正弦波、三角波、矩形波3种不同波形驱动下最大误差不超过4%,控制范围内可靠性在99.0%以上。综合比较可知,方波脉冲信号为压电微泵最佳驱动信号。     

新型压电微喷的研制

介绍了一种能够实现微量样品精确供给的压电微喷。该微喷利用压电陶瓷围成液体腔,通过厚度切变振动产生压力波,使液滴喷射。从理论推导、有限元模拟、实际测量三个方面研究了微喷的性能,三者得出的谐振基频基本吻合,从而验证了理论设计和有限元优化的正确性。该微喷工作稳定,施加一个驱动脉冲,只会产生一次喷射。当驱动电压为40 V时,最大喷射距离为3 cm,喷出液滴的体积小于1 nL。     

基于聚酰亚胺介质的单平面微液滴驱动芯片

根据介电润湿(EWOD)原理,建立了电润湿力与驱动电压的关系,提出一种基于聚酰亚胺介质的单平面微液滴驱动芯片设计方案。该芯片利用MEMS技术在铬版玻璃上分别制作出金属微电极阵列和聚酰亚胺介质膜,再使用聚四氟乙烯分散液进行疏水处理,通过在电极阵列和微液滴之间直接施加电压以实现微液滴的驱动。对单平面微液滴驱动芯片的液滴介电润湿效应进行了仿真分析,结果表明仅使用疏水层便可观察到明显的介电润湿现象,接触角测量值与理论值吻合较好。使用该驱动芯片成功实现了微液滴的稳定传输,传输速度达到3.31 mm/s左右,并在实验基础上分析了传输速度与驱动电压幅值和频率的关系。     

基于同轴式组合微喷嘴的虾卵细胞微胶囊封存北大核心

为探究同轴式组合微喷嘴的喷射方向性以及制备虾卵细胞微胶囊时的封存效率,搭建了以电磁铁为驱动器的微流体数字化脉冲驱动控制喷射平台,并通过COMSOL Multiphysics 5.3建立二维仿真模型,对同轴式组合微喷嘴及单微喷嘴内的微粒运动状态进行了对比仿真。仿真结果表明同轴式组合微喷嘴中的内喷嘴对喷射的粒子流有明显的限制作用,并在以铬粉为主体材料的粉体喷射实验中得到验证。在此基础上,探究了驱动电压及微喷嘴尺寸对水相微液滴直径和虾卵细胞封存效率的影响规律,以及亲疏水性对同轴式组合微喷嘴喷射效果的影响。结果显示所获得的水相微液滴的直径正比于微喷嘴出口尺寸和系统驱动电压,通过改变微喷嘴出口尺寸和系统驱动电压的大小,获得了直径为500-1 500μm的水相微液滴;使用经过疏水化处理后的同轴式组合微喷嘴制备的虾卵细胞微胶囊,其粒径均匀,单细胞封存率可达84%。     

Drop-on-Demand Solder Droplet Jetting System for Fabricating Microstructure

The novel drop-on-demand (DOD) solder droplet jetting system, which can be characterized as the non-heat affection of the piezoelectric actuator, the control mechanism of the piston head-to-nozzle distance, and disposable nozzle parts, is devised. This system consists of the piezoelectric actuator, insulator, piston head-to-nozzle distance control apparatus, pressure control unit, and furnace. For the modulation of the droplet size, the distance from piston head-to-nozzle exit can be controlled by using the piston head-to-nozzle distance control apparatus. The working temperature is improved by locating the piezoelectric actuator outside of the furnace and by inserting the insulation block between the print head and the actuator. From a practical point of view, the DOD solder droplet jetting system has a simple structure for easily interchangeable nozzle parts. We derived the equation of the ejected droplet volume as a function of design parameters and operating conditions. The prototype of the DOD solder droplet jetting system was fabricated and the performance was verified. The diameter, volume and velocity of the ejected solder droplet are around ${hbox {65}}{hbox {–}}{hbox {150}} mu{hbox {m}}$, 140 pl–1.8 nl, and 2.8–4 m/s, respectively. We also experimented with the effect of varying the chamber pressure, piston head-to-nozzle distance, and operating frequency on the ejected droplet diameter and velocity. The high aspect ratio vertical columns and inclined columns were fabricated by using the DOD solder droplet jetting system.      

压电驱动微型喷雾器的研究

研究开发了一种压电驱动微型喷雾器。利用微机械加工技术,制作微米级的喷孔阵列,基于喷墨打印机原理,微喷换能器采用压电驱动方式在其较高阶谐振状态下工作。实验分析了这种微喷换能器的阻抗特性、谐振状态下振动特性以及微型喷雾器的工作性能。实验结果表明,这种喷雾器喷出的雾滴直径大小集中,工作稳定且容易控制喷雾量。     

交流电场作用下电场流动聚焦装置内微液滴的生成实验

采用非接触式电极放入方式,避免了电化学效应的产生,通过改变外加交流电场强度和电场频率,研究了液滴交流电场流动聚集断裂过程的流型转变、液滴当量直径和生成频率.结果 表明,流量不变时,仅通过改变外加电场,依次可观测到液滴从弹状流、滴状流到喷射流的流型转变.当毛细数＜0.1时,生成的液滴当量直径随毛细数增加呈指数减小,且低频...     

Electrohydrodynamic Jet Printing Driven by a Triboelectric Nanogenerator

Electrohydrodynamic jet (e‐jet) printing is a high‐resolution printed electronics technique that uses an electric field to generate droplets. It has great application potential with the rapid development of flexible and wearable electronics. Triboelectric nanogenerators (TENG), which can convert mechanical motions into electricity, have found many high‐voltage applications with unique merits of portability, controllability, safety, and cost‐effectiveness. In this work, the application of a TENG is extended to printed electronics by employing it to drive e‐jet printing. A rotary freestanding TENG is applied as the high‐voltage power source for generating stable ink droplet ejection. The TENG‐driven droplet generation and ejection process and printed features with varied operation parameters are investigated. Results reveal that the jetting frequency could be controlled by the TENG's operation frequency, and high‐resolution printing with feature size smaller than nozzle size is achieved using the setup. Notably, TENG as the power source for e‐jet printing supplies a limited amount of current, which leads to better safety for both equipment and personnel compared to conventional high‐voltage power supplies. With the superiority of TENG in the sense of safety and cost, the work presents a promising solution for the next‐generation of high‐resolution printed electronics and broadens the scope of TENG application.     

压电式射流激励器工作特性的实验研究

实验设计了压电式合成射流激励器及压电振子振幅测量系统和合成射流速度测量系统.此射流激励器为换能装置,产生的合成射流速度与电参数如驱动频率、信号波形、驱动电压等因素有关.只有驱动频率在一定范围内时才会产生射流速度,且存在着最佳的驱动频率;方波与正弦波、三角波相比可产生更大的射流速度;合适的射流口尺寸也可提高射流速度.     

Control of droplet formation for low viscosity fluid by double waveforms applied to a piezoelectric inkjet nozzle

When dispensing liquid through a piezoelectric inkjet nozzle, a single droplet without a satellite is formed in the limited range of the Ohnesorge number. Especially, it is difficult to eject low viscosity fluids such as a silver nanoparticle suspension in the form of a single free drop using conventional single waveforms to drive the piezoelectric actuators. To overcome the lower limit of fluid viscosity, in the present study, double waveforms with two square pulses have been applied to control the droplet formation in the piezoelectric inkjet nozzle and its response has been observed. With regard to the double waveforms, the effect of the driving voltage and time separation between the pulses was investigated. The present nozzle shows that several satellites are produced by the successive ejection in a single pulse because the oscillating pressure wave is rarely damped out in the low viscosity fluid. On the other hand, a single droplet is easily formed in the double waveform and the droplet formation could be precisely controlled by changing the time separation between the pulses. The upper and lower limits of the time separation are discussed in view of the kinetic phenomena of a primary drop and a transient satellite for the low viscosity fluid. In addition, it is addressed how the time separation and driving voltage in the double waveform affect the droplet size and velocity.     

Low temperature fabricated conductive lines on flexible substrate by inkjet printing

The optimal conditions of inkjet-printed nano-silver suspension and silver nitrate solution for fabricating continuous narrow conductive lines on a polyimide substrate are investigated by varying the driving pulse and droplet overlap. The dimensionless Weber number and Reynolds number are used to evaluate the droplet size after impact. It was found that the presence of a suspension of nanoparticles increases droplet diameter. With appropriate droplet overlap and driving pulse conditions, continuous lines of AgNO₃ with 24.3 μm in width and nano-silver suspension with 33 μm in width were fabricated. In addition, the effects of driving pulse voltage and droplet coverage on the bulging of as-printed conductive lines are also examined.     

T型微流控芯片中的液滴形成

以水为分散相、硅油为连续相,对高度为30μm、宽度800μm的T型垂直交错结构微通道中油包水型液滴的形成进行了实验研究。通过改变分散相和连续相流量配比,生成了大小可控的nL级液滴。对流量和液滴直径的关系以及流速、压力在液滴形成过程中的变化趋势进行了分析,得到黏性剪切力和界面张力是液滴形成的主要因素。发现流量较大时,两相在主通道内形成层流,并在微通道的台阶突扩处生成两种类型液滴。同时,在台阶突扩处液滴出现三种排列方式:交错双排Z字型、珍珠项链型和单排型液滴排列,并在低流速下出现液滴破碎现象,其发生主要取决于界面张力和流动阻力的影响。