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Sensors 2013, 13(9), 12012-12029; doi:10.3390/s130912012

Practical Strategies for Stable Operation of HFF-QCM in Continuous Air Flow

1
Chemische Institute, Abteilung Elektronik, Rheinische Friedrich-Wilhelm-Universität Bonn, Gerhard-Domagk-Str. 1, Bonn D-55121, Germany
2
Institut für Organische Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, Mainz D-55128, Germany
*
Author to whom correspondence should be addressed.
Received: 23 July 2013 / Revised: 1 September 2013 / Accepted: 1 September 2013 / Published: 9 September 2013
(This article belongs to the Section Chemical Sensors)

Abstract

Currently there are a few fields of application using quartz crystal microbalances (QCM). Because of environmental conditions and insufficient resolution of the microbalance, chemical sensing of volatile organic compounds in an open system was as yet not possible. In this study we present strategies on how to use 195 MHz fundamental quartz resonators for a mobile sensor platform to detect airborne analytes. Commonly the use of devices with a resonant frequency of about 10 MHz is standard. By increasing the frequency to 195 MHz the frequency shift increases by a factor of almost 400. Unfortunately, such kinds of quartz crystals tend to exhibit some challenges to obtain a reasonable signal-to-noise ratio. It was possible to reduce the noise in frequency in a continuous air flow of 7.5 m/s to 0.4 Hz [i.e., σ(τ) = 2 × 10−9] by elucidating the major source of noise. The air flow in the vicinity of the quartz was analyzed to reduce turbulences. Furthermore, we found a dependency between the acceleration sensitivity and mechanical stress induced by an internal thermal gradient. By reducing this gradient, we achieved reduction of the sensitivity to acceleration by more than one decade. Hence, the resulting sensor is more robust to environmental conditions such as temperature, acceleration and air flow.
Keywords: quartz crystal microbalance; high fundamental frequency; allan deviation; turbulences; laminar flow element; acceleration sensitivity; temperature gradient quartz crystal microbalance; high fundamental frequency; allan deviation; turbulences; laminar flow element; acceleration sensitivity; temperature gradient
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Wessels, A.; Klöckner, B.; Siering, C.; Waldvogel, S.R. Practical Strategies for Stable Operation of HFF-QCM in Continuous Air Flow. Sensors 2013, 13, 12012-12029.

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