Design and Fabrication of a Micromachining Preconcentrator Focuser for Ethylene Gas Detection System

Abstract

Highly portable MEMS gas detection system produced by micromachiningtechnologies to determine contamination of air has been an ongoing area ofresearch in many fields such as environmental monitoring, food inspection,biomedical diagnostics and industrial processing. Traditionally, the analyzes ofcontaminated air samples are performed by the conventional bench-top gasmeasurement system in the laboratory. Recent efforts have been made todevelop field-portable detection systems to provide portability and near real timeanalysis capability. However, these systems are large and require large powersupplies and they need long analysis time and require large sampling volumes.Therefore, there is considerable interest in a fast, lower power, highly portablesystems that can provide real time monitoring for identification analysis of gases.A preconcentrator-focuser (PCF) in a high-performance monitoringsystem is required when the sensitivity of the ethylene sensor is limited by thelow parts per milion (ppm) concentrations of analytes. The principle of PCFoperation is that as the low-concentration complex compound mixture passesthrough the device, these compounds will be adsorbed over time for subsequentrapid thermal desorption. The thermally released compounds provide narrowdesorption peaks at the output with relatively high concentration resulting asignificant enhancement of the system efficiency. Conventional preconcentratorsthat have been used are large in size and consume high power during thermaldesorption. They also suffer limited heating efficiency due to their large thermalmass. A microfabricated preconcentrator-focuser using micromachiningtechnology can overcome these limitations by significantly reducing the deviceiiiDesign and Fabrication of a Micromachining Preconcentrator Fo cuser for Ethylene Gas Detection Systemsize, thermal mass, and power consumption and thus increase the performanceof the device. A microfabricated preconcentrator has to be designed to enhancethe detectection of ethylene gas. However, the devices will be designed topreconcentrate ethylene so it will be easily detected by the sensor system. Thedevice design, including the adsorbent material, capacity of the microheater, thefabrication technology, the thermal measurements, and the desorptionperformances will be studied. To design and fabricate a Micropreconcentratorfocuser for ethylene gas sensing applications, many designing factors have to beconsidered. However, these factors include checking and characterization ofavailable adsorption materials that could be used, microheater design shouldprovide both large volume between heating elements for large adsorbentcapacity and large heating surface for uniform heating of the adsorbents andoptimization and combination of fabrication process steps.