Fluidic technology: adding control, computation, and sensing capability to microfluidics

Abstract

This paper presents an overview of fluidic technology - a technology that provides an additional dimension to conventional microfluidic technology by adding sensing, computation (both analog and digital) and control. The US Army Diamond Ordnance Fuze Labs officially recognized fluidics as a comprehensive technology comparable to electronics with its announcement in 1959. Because fluidic elements have very few or no moving parts the technology provides significant operational advantages in harsh environments (EMI, radiation, high temperature and vibration). It also offers advantages when dealing with fluid variables (flow, pressure, density, viscosity, etc.) by eliminating the need for interfaces. With the elimination of the inertia and friction associated with moving parts there are even greater advantages as a result of higher speed of operation. Where mechanical and micromechanical devices may be limited to only hundreds of hertz true microfluidic systems can operate at tens of thousands of hertz. We discuss the fundamental principles of jet deflection amplification and vortex modulation and present circuit building blocks such as the laminar proportional amplifier, vortex valve, oscillators, and positive-feedback digital components. However, most importantly, we present and discuss three specific applications illustrating the power of fluidics in microfluidics and MEMS. These are: a gas analyzer-on-a-chip, capable of simultaneous analysis of multiple gas mixtures with clinical accuracies; an intermittent oxygen delivery system that provides supplemental oxygen to ambulatory patients through a nasal cannula; and, an array of vortex microvalves capable of controlling propellants for micropropulsion systems or for the temporal and spatial modulation of fuel for the optimal control of gas turbine combustors. A sampling of other fluidic in microfluidic application are mentioned to include pressure and acoustic amplification (a kosher public address system is referenced), active noise cancellation for aircraft engines and passenger compartments, optical-pneumatic transduction in optical fiber missile controls and natural gas processing, angular rate sensing, and microcytometry for cellular processing. Fluidics may be the enabling technology for many as yet undeveloped applications, particularly when recent advances micro-fabrication are taken advantage of.