J. Reibel

New miniaturized SAW-sensor array for organic gas detection driven by multiplexed oscillators

Abstract The use of sensor arrays with polymer-coated surface acoustic wave (SAW) devices as the key element for analytical sensor systems is a very promising technique for organic gas detection in process or quality control. In this work we present a new improved array of eight SAW sensors showing up reduced size, sampling volume and assembling costs. Moreover, its most important novelty is an in-built multiplexing technique which allow an automated and fast adjustment of the phase position of the SAW devices within the oscillators, respectively. This enables an easy optimization of the signal to noise ratio, expands the choice of coatings for the SAW sensors and improves the sensor to sensor reproducibility for a certain coating material.

SAGAS: gas analyzing sensor systems based on surface acoustic wave devices-an issue of commercialization of SAW sensor technology

In this work the potential of commercialization of sensor systems based on SAW devices in contrast to other sensor principles is discussed. After given motivation for this sensor technology a first series of three different prototypes of analytical sensor systems for organic gas detection based on commercially available SAW devices is presented. Central component is an array of eight polymer coated SAW devices working at a frequency of 433.92 MHz. By an adequate selection of polymers and the use of neuronal networks for automatic pattern recognition of sensor signals a broad variety of gaseous organic analytes can be determined. Of particular interest are realistic tasks of organic gas detection for the industrial process control. Examples of a quantitative determination of the composition of ternary gas mixtures are shown as well as a qualitative discrimination of typical complex gas mixtures arising from raw food products in different states of spoilage.

Gas analysis with SAW sensor systems

Abstract At the institute of instrumental analysis, a family of three gas analysis instruments based on mass-sensitive gas sensor devices are developed. The SAW Aroma and Gas Analyzing Systems (SAGAS) are used to detect and analyze a large variety of gases and aromas. The common heart of these systems is a sensor head with eight differently polymer-coated surface acoustic wave (SAW) devices. These “semi-selective” sensors are used to generate typical signal pattern (“finger prints”) of analyte gases and gas mixtures. Using chemometrical data analysis, such as PCA, classification and PLS, as well as artificial neural networks, these signal patterns are used for qualitative analyte recognition and for quantitative gas mixture determination. In the following, some sensor properties are discussed and some applications of the systems are presented.

Validation of an industrial analytical sensor procedure realized with a SAW-based sensor system

Abstract Mass-sensitive sensors based on surface acoustic waves (Suface Acoustic Wave Devices, SAWs) can be used for qualitative as well as for quantitative determination of volatile organic compounds (VOCs). An analytical procedure for a SAW-based sensor system used for on-line process control of VOCs in pharmaceutical industry was developed. Analytical procedures applied in pharmaceutical development and production have to meet the requirements of good manufacturing practice (GMP) and therefore a validation in compliance with the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH)-guidelines had to be performed. It is shown that these procedures can be successfully validated as non-chromatographic procedures according to ICH-guidelines. As a typical example, the on-line control of a HPLC gradient former was investigated. In this particular case, the sensor system has to determine the actual composition of the mobile phase and furthermore it has to discriminate possible avoidance. The following analytical performance parameters are investigated to prove the validation of the analytical procedure: ∘ Specificity, ∘ Linearity, ∘ Limit of Detection and Quantitation, ∘ Accuracy, ∘ Precision, and ∘ Robustness.

Influence of phase position on the chemical response of oscillator driven polymer coated SAW resonators

The use of oscillator operated SAW resonators as chemical sensors is widely accepted to have the best sensing properties. However, some important parameters of influence are not sufficient resolved, yet. In general, these are effects arising from the electronic circuitry such as the phase situation on the chemical response of these sensors. We have found that they can be almost dramatic for several types of sensitive coatings and, thus, are not negligible, especially their influence on the sensitivity. In this work some exemplary results with SAW resonators working at 433,92 MHz coated with different polymeric films such as polyisobutylene (PIB), polyepichlorohydrine (PECH) or polydimethylsiloxane (PDMS) and sampled with toluene as analyte. Depending on thickness and homogeneity of the polymer film serious influences of the set phase positions on the quality of the chemical response were observed such as curve shape, and signal to noise ratio. Also, a simulation using an equivalent circuit model of the transducers including the polymer coating is used for a deeper understanding of these phenomena.