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Forschungsbericht 2011 / Hochschule für Angewandte Wissenschaften - Fachhochschule Regensburg
(2011)
We present a sensitive UV LED photoacoustic setup for the detection of gaseous acetone and discuss its applicability towards breath analysis. We investigated the performance of the sensor for low acetone concentrations down to 0.1 parts per million (ppmV). The influences of temperature, flow, pressure, optical power and LED duty cycle on the measured signal have been examined. To gain a better understanding of the different effects on the photoacoustic signal, correlation analysis was applied and feature importance was determined using a large measured dataset. Furthermore, the cross-sensitivities towards O2, CO2 and H2O have been studied extensively. Finally, the sensor’s performance to detect acetone between 0.1–1 ppmV within gas mixtures simulating breath exhale conditions has been investigated, too. With a limit of detection (LoD) of 12.5 parts per billion (ppbV) (3σ) measured under typical breath exhale gas mixture conditions, the sensor demonstrated a high potential for the application of acetone detection in human breath analysis.
A digital dual-phase lock-in amplifier that is capable to run on a low-cost, low-power platform comprising a 16-bit fixed-point digital signal processor was developed. This is achieved by a set of optimised digital filters including an exponential averager to adjust the time constant of the overall filter. The reference frequency is generated using a direct digital synthesis source utilising angle decomposition with a resolution of 1 Hz. The digital lock-in algorithm is described and the performance of the algorithm is analysed. The experimental results show that the developed lock-in amplifier achieves similar performance to a commercially available lock-in amplifier.
Development of a miniaturized photoacoustic multigas sensing system for trace gas measurement
(2014)
Development of a miniaturized photoacoustic multigas sensing system for trace gas measurement
(2013)
Diese Abhandlung beschreibt das Konzept eines mikroeletromechanischen Systems (MEMS), das im Messverfahren der cantilever enhanced photoacoustic spectroscopy (CEPAS) Verwendung finden soll.
Es wird die Herstellung eines einseitig eingespannten Biegebalkens aus Silizium mittels deep reactiv ion etching (DRIE) beschrieben. Des Weiteren wird die Resonanzfrequenz dieses Cantilevers mit Hilfe Laservibrometertechnik untersucht. Die resultierenden resonanten Schwingungen 0.Ordnung werden mit den Ergebnissen einer vereinfachten theoretischen Näherung verglichen. Die Messergebnisse stehen in gutem Zusammenhang mit den theoretischen Werten. Solche Cantilever, die aus silicon on insula tor (SOI) Wafer angefertigt wurden, weisen bei einer Zielfrequenz ein mittlere Abweichung von Δf = 118±26Hz (bzw.Δf =0,76±0,17%) auf.
