Aaron A. Astle

A fully integrated high-efficiency peristaltic 18-stage gas micropump with active microvalves

We report the design, fabrication, and test results of a fully integrated peristaltic 18-stage gas micropump consisting of 18 serially-connected pumping chambers and 19 microvalves. The peristaltic micropump achieves (1) high-pressure differentials by accumulating small pressure differentials that are evenly distributed across the individual stages using a low-compression multi-stage design, (2) high flow rate by operating pumping membranes at fluidic resonance and high frequency (>10 kHz), and (3) gas flow regulation by actively controlling the open/close timing of microvalves for either high flow or high pressure. The 18-stage micropump includes several new innovations, such as checkerboard microvalves, dual drive electrodes, and dual pumping chambers to achieve efficient electrostatic pumping. The fabricated 18-statge pump has produced an air flow rate of ~4.0 seem and maximum pressure differential of-17.5 kPa with a total power of only ~57 mW. It has a total package volume of 25.1 x 19.1 x 1 mm3 and each individual membrane is only 2x2 mm2.

A Micropump-Driven High-Speed MEMS Gas Chromatography System

We report (1) the integration of the first functioning MEMS gas chromatography system ( muGC) featuring a micropump, a micro-column, and a micro-chemiresistor sensor array; and (2) experimental demonstration of the state-of-the-art multi-vapor gas separation and detection. In particular, we report the best GC analysis data from the first micropump-driven muGC system to date: the separation and detection of 11 volatile organic compounds (VOC)s within only 78 seconds while consuming only 15.1 mW of power within a small volume of 0.5 cc. We also report the use of temperature programming (TP) of the separation column for fast analysis, which shortened the analysis time from 78 seconds to 24 seconds while maintaining gas analysis resolution.

Bi-directional electrostatic microspeaker with two large-deflection flexible membranes actuated by single/dual electrodes

This paper reports a bi-directional electrostatic microspeaker that has three main features: (1) a thin and flexible Parylene membrane for large deflection (>7.5 mum), thus, large acoustic pressure generation, (2) dual electrodes on both sides of the membrane to pull it in two opposite directions and overcome the weak restoration force of the polymer membrane, thus allowing the use of flexible membranes as a high-speed vibration element, and (3) bi-directional (forward/backward) packaged structures for symmetric and loud acoustic sounds of 113.4 dB (SPL: sound pressure level) at 7.68 kHz when actuated using a single electrode, and 98.8 dB (SPL) at 13.81 kHz when actuated using two electrodes at a distance of 1 cm from the microspeaker. By actuating two membranes, the microspeaker also produced symmetric sound pressures at both the front and back sides of the device. The generated sound frequency range is from 1 kHz (measurement cut-off frequency) to 25 kHz, and the sound level was reasonably uniform over a wide frequency range. The fabricated microspeaker has an active area footprint of 3 times 5 mm2, while the total packaged device (including electrical pads area of 3.5 times3.5 mm2) has a volume of 13 times 16 times 1 mm3. The micropump is built on two bonded silicon wafers and incorporates a flexible polymer, Parylene, membrane as the actuation membrane

An Integrated Electrostatic Peristaltic 18-Stage Gas Micropump With Active Microvalves

We report the development of fully integrated peristaltic multistage (18-, 4-, and 2-stage) electrostatic gas micropumps with integrated active microvalves. These micropumps uniquely combine a number of approaches to achieve highpressure, high flow rate, multimode, and low-power pumping of compressible gases: (1) multistage (up to 18-stage) configuration to generate high pressure accumulation across the pump, while allowing each stage to operate at low pressure burden; (2) gas resonance-based high-frequency (>10 kHz) operation of both the micropumps and the microvalves to achieve high mass flow rates despite the small volume displacement of microscale membranes; (3) active timing control of microvalves to regulate compressible gas pumping into multiple modes for either high flow rate or high pressure; and (4) electrostatic actuation to minimize power consumption despite multiple (up to 28) membrane operation. The multistage micropumps contain 18, 4, and 2 pumps connected in series sandwiched by 19, 5, and 3 microvalves, respectively. The fabricated 18-, 4-, and 2-stage pumps, respectively, produced high air flow rates of ~4.0, 3.0, and 2.7 sccm and maximum pressure differentials of ~17.5, 7.0, and 2.5 kPa with total power consumptions of only ~57, 15.1 and 9.1 mW, respectively. They have active areas of 15.5 × 12.7 and 18.3 × 7.1, 15.0 × 7.0 mm2, and total package volumes of 25.1 × 19.1 × 1, 27.8 × 11.6 × 1, and 23.0 × 12.4 × 1 mm3, respectively. They demonstrated two pumping modes using different microvalve timing (high flow rate timing and high pressure timing), resulting in notable changes in flow rates and pressure generation. One 4-stage micropump has been actuated for a total running time of more than 700 min over 32 months.

Analysis and Design of Multistage Electrostatically-Actuated Micro Vacuum Pumps

A new concept for a MEMS-fabricated micro vacuum pump is proposed. The pump is designed to operate in air and can be easily integrated into MEMS-fabricated micro fluidic systems. The pump consists of a series of pumping cavities with electrostatically actuated membranes interconnected by electrostatically actuated microvalves. A thermodynamic model of the micropump has been developed and used to determine the pump performance. It is shown that volume ratio plays an important role in the operation of the pump. For a fixed number of stages, at high volume ratio, pumping action is uniformly distributed among the stages. In contrast, at low volume ratio most of the pumping takes place in the latter stages of the pump. Detailed calculations of the flow through key components of the micropump are also reported. In particular the flow through a checkerboard microvalve and electrode perforations is discussed, and new correlations for the pressure loss in these components are proposed.Copyright

Dynamic Modeling and Design of a High Frequency Micro Vacuum Pump

A dynamic model of MEMS-fabricated multistage micro vacuum pumps for use in a highly-integrated chemical monitoring system is described. A thermodynamic analysis shows that in order to meet the performance requirements of the system, the micro pump must be operated at very high frequency of approximately 50 kHz. At these frequencies, dynamic effects and resonances due to the interaction of the valves and the pump cavities can play an important limiting role in pump performance. Dynamical effects can also increase the pressure difference between pump cavities increasing the required actuation voltage. The present dynamic model uses integral forms of the momentum and mass conservation equations. Key components of the model are the viscous and inertial terms of the pump’s “checkerboard” microvalves, which are evaluated using a CFD model of the valves. At low frequencies, the model results show increased mass flow rate with increased frequency in good agreement with a thermodynamic model. Maximum performance is reached at frequencies of the order of the resonant frequency of the micro pump. The model is also used to study the effect of valve timing and operating point on mass flow rate and power consumption at high frequency.Copyright

Directional pumping performance of an electrostatic checkerboard microvalve

This paper reports experimental characterization of directional gas pumping generated by MEMS-fabricated checkerboard-type electrostatic microvalves. It is found that the oscillatory motion of the checkerboard microvalve membrane provides both the pumping and valve functions of a pump, namely: 1) to cause the volume displacement and, thus, compression and transfer of gas, and 2) to direct gas flow in one direction by closing and opening air paths in the proper sequence. Here, we describe the microvalve-only design, and report the pumping performance producing a maximum flow rate of 1.8 sccm and a maximum pressure differential of 3.0 kPa for five microvalves driven simultaneously with a sinusoidal signal of ± 100V amplitude at 5.5 kHz.Copyright