A Multiparameter Gas-Monitoring System Combining Functionalized and Non-Functionalized Microcantilevers

Abstract

The aim of the study is to develop a compact, robust and maintenance free gas concentration and humidity monitoring system for industrial use in the field of inert process gases. Our multiparameter gas-monitoring system prototype allows the simultaneous measurement of the fluid physical properties (density, viscosity) and water vapor content (at ppm level) under varying process conditions. This approach is enabled by the combination of functionalized and non-functionalized resonating microcantilevers in a single sensing platform. Density and viscosity measuring performance is evaluated over a wide range of gases, temperatures and pressures with non-functionalized microcantilevers. For the humidity measurement, microporous Y-type zeolite and mesoporous silica MCM48 are evaluated as sensing materials. An easily scalable functionalization method to high-throughput production is herein adopted. Experimental results with functionalized microcantilevers exposed to water vapor (at ppm level) indicate that frequency changes cannot be attributed to a mass effect alone, but also stiffness effects dependent on adsorption of water and working temperature must be considered. To support this hypothesis, the mechanical response of such microcantilevers has been modelled considering both effects and the simulated results validated by comparison against experimental data.

A Review of Gas Measurement Set-Ups

“…Generally, in order to reduce inertia in the measuring stand of gas sensors, measuring chambers with as small a volume as possible are used. Such a solution has been presented by Huber et al [ 83 ]. Photographic documentation of the prepared measuring chamber with a volume of 20 cm 3 is presented in Figure 4 c. All elements, including the tested sensor, are mounted on both sides of the printed circuit board (including temperature and pressure sensors).…”

“…All signals are routed externally through appropriate connectors. The described gas-measuring chamber enables measurements up to pressures of at least 10 bar [ 83 ]. An additional advantage of using small-volume chambers and the shortest possible connections is also gas and energy savings, and thus the measuring station is more environmentally friendly.…”

“…Bottom right: sensor PCB and dew point sensor mounted in a pressure-tight measuring chamber (numbers in the scale correspond to cm). Reprinted with permission from [ 83 ].…”

“…In such a solution, the electric current was fed to the heaters placed in the substrate, which, flowing through the resistance heaters, heats the sample [ 20 , 84 ]. Examples of the geometries of micro-heaters used in sensor substrates are shown in the literature [ 84 ] and in Figure 6 [ 83 ]. Simons et al [ 70 , 79 ] used the source meter sensor for heating, which powered the previously described heaters in the substrate.…”

Review: Cantilever-Based Sensors for High Speed Atomic Force Microscopy

“…Another variable that can be used to quantify the amount of the adsorbed gases in the microcantilever is the change in the resonant frequency caused by the surface stresses. However, when compared to the mass loading, the effects of such stresses on the resonant frequency are found to be insignificant [ 76 , 77 ].…”