High accuracy microflow controllers using fluidic digital-to-analog converters

Abstract

The thesis presents 4-bit high accuracy microflow controllers using microfluidic digital-to-analog converters. The fabricated microflow controllers are composed of four microchannels with binary-weighted flow resistance. These microchannels are opened and shut by digitally actuating valves for generating a high accurate flow rate. The flow resistance of each microchannel is adjusted by the series connection or parallel connection of unit fluidic resistors in order to reduce the effect of micromachining error. We design three types of microflow controllers including prototype S, prototype P, and prototype V using a CFD program, $Fluent^®$ 5.5 and fabricate the microflow controllers by micromachining. We measure the flow rate and the pressure drop of the fabricated microflow controllers at constant pressure and pulsating pressure. At constant pressure of 2kPa, prototype S, P, and V show the maximum flow rate error of 7.5%, 6.2%, 22.5% and DNL of 0.28 0.27, 0.94, respectively. The negative pressure flow control shows the same tendency as the positive pressure flow control when negative pressure of -2kPa is applied. At pulsating pressure with constant pressure offset of 2kPa, $P_{p-p}$ of 0.87kPa, and frequency of 6.5Hz, the measured flow rate at pulsating pressure coincides with the flow rate at constant pressure that has average magnitude of pulsating pressure within 5% error. We find that fabricated microflow controllers using fluidic digital-to-analog converters show more accurate flow rate control than conventional analog microflow controllers and control flow rate in $2^N$ levels with N valves. We verify experimentally that flow resistance control by the series or parallel connection of unit fluidic resistors reduces the effect of micromachining error.