The application of acoustic wave microsensors for mass sensing will be reviewed with focus on the quartz crystal microbalance
(QCM) and surface acoustic wave (SAW) devices. The use of QCM and SAW devices in chemical sensing as well as in the determination
of solid and liquid properties will be described. In chemical sensing, it is unlikely that a single sensor with a single coating
will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as the use of
sensor arrays and the use of sampling devices can be used to improve performance. QCM sensors (QCMs) will oscillate under
liquids; their use in under-liquid sensing will be discussed.
DTA and TG has been used to study the thermal stability of cross-linked epoxidized polydienes. Cross-linking has been achieved using some derivatives of hydroxycarbostyrils, triazines and phthalimide. The new properties of the polymers after curing are interpreted on the basis of the results of DTA and TG.
Steady state conditions are assumed in impulse response analysis and well explained in literature for the tracer test to realise the results, but this is not always the case when dealing with the wastewater treatment plants, where flow processes are always in unsteady state conditions. Beside stimulus response, the flow rate has to be measured at the same during experiment. Several figures were prepared to demonstrate the influence of variable flow rate, these figures are important in order to understand the changes of impulse response by variable flow rate. The unexpected change in the flow rate should be strictly observed to avoid misinterpretation the impulse response results. The base information in data treatment for variable flow analysis of impulse are presented, to assist in data treatment and to obtain more practical performance of the WSP.
Headspace analysis by means of sensor arrays has been successfully applied to a wide range of qualitative applications. In this study, a six element array of coated Quartz Crystal Microbalance (QCM) sensors was used for the headspace analysis of milk volatiles. The sensors were exposed to uncontaminated samples of milk and samples contaminated with Pseudomonas fragi (Ps. fragi) or Escherichia coli (E. coli). Principal component analysis (PCA) was used to analyse the sensor array responses. No discrimination between uncontaminated milk samples and those contaminated with Ps. fragi was observed. This can be explained by Ps. fragi being a poor fermenter of milk. However, encouraging results were found for the discrimination between the milk samples and those contaminated with E. coli.
We will review the application of acoustic wave mass sensors in chemical and biological sensing with focus on quartz crystal microbalance and surface acoustic wave devices. In chemical sensing, it is unlikely that a single sensor will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as use of sensor arrays and sampling devices will be discussed to improve performance. We will also discuss applications of quartz crystal microbalance as biosensor in the liquid phase.
Authors:Z. Ali, W. O'Hare, T. Sarkodie-Gyan, and B. Theaker
Quartz crystal microbalances have high mass sensitivities. Their application in gas sensing has been limited because they
are required to have both high selectivity and reversibility. Yet by the inherent nature of their operation these properties
are mutually exclusive. One approach to this problem is to use an array of quartz crystal microbalances. We have used an array
of six coated quartz crystal microbalances for the classification of methanol, propan-1-ol, butan-1-ol, hexane, heptane and
toluene. A novel classification scheme using fuzzy membership functions was found to be highly efficient.
Authors:Th. Gast, T. Brokate, E. Robens, Z. Ali, and K. Pavey
The influence of mass and force on the frequency of vibrating bodies today is widely applied. In Part I of the survey the historical roots are reviewed and the physical principles of the several arrangements modes of operation explained.
Authors:Z. Ali, D. James, W. O'Hare, F. Rowell, and S. Scott
An electronic nose utilising an array of six-bulk acoustic wave polymer coated Piezoelectric Quartz (PZQ) sensors has been developed. The nose was presented with 346 samples of fresh edible oil headspace volatiles, generated at 45°C. Extra virgin olive (EVO), Non-virgin olive oil (OI) and Sunflower oil (SFO), were used over a period of 30 days. The sensor responses were then analysed producing an architecture for the Radial Basis Function Artificial Neural Network (RBF). It was found that the RBF results were excellent, giving classifications of above 99% for the vegetable oil test samples.