Techn. Universiẗat, Diss., 2003--Chemnitz.

Zugl.: Karlsruhe, Univ., Diss., 2008 / Hergestellt on demand

No description available.

Fault tolerant control can accommodate the component faults in a control system such as sensors, actuators, plants, etc. This dissertation presents two fault tolerant control schemes to accommodate the failures of power amplifiers and sensors in a magnetic suspension system. The homopolar magnetic bearings are biased by permanent magnets to reduce the energy consumption. One control scheme is to adjust system parameters by swapping current distribution matrices for magnetic bearings and weighting gain matrices for sensor arrays, but maintain the MIMO-based control law invariant before and after the faults. Current distribution matrices are evaluated based on the set of poles (power amplifier plus coil) that have failed and the requirements for uncoupled force/voltage control, linearity, and specified force/voltage gains to be unaffected by the failure. Weighting gain matrices are evaluated based on the set of sensors that have failed and the requirements for uncoupling x1 and x2 sensing, runout reduction, and voltage/displacement gains to be unaffected by the failure. The other control scheme is to adjust the feedback gains on-line or off-line, but the current distribution matrices are invariant before and after the faults. Simulation results have demonstrated the fault tolerant operation by these two control schemes.

Zugl.: Kassel, Univ., Diss., 2009

During storage of grain, there may have significant damage to its quality due to unfavorable physical and biological interactions and thus requires continuous monitoring. Therefore, an easy, cost-effective and environmentally friendly method is necessary for efficient monitoring of stored-grain. Arrays of sensors are being used for classifying liquors, perfumes, quality of food products mimicking mammalian olfactory systems. Monitoring of stored grain is a new application of sensor arrays. The main objective was to fabricate a carbon black polymer sensor array which can easily monitor incipient grain spoilage by detecting spoiling stored grain volatiles (benzene derivatives and aliphatic hydrocarbon derivatives) with minimum interference from relative humidity. Various aspects of a good sensor were analyzed using statistical analysis (RSD, LDA, PCA, t-test). The developed sensor array can identify red flour beetle-infected and uninfected wheat and fungal volatiles at ambient conditions as well as some stored grain conditions (MC 16%, RH 52%).

The covalent modifications to the histone 2A, 2B, 3, and 4 N-terminal tails that affect gene expression have been deemed the “Histone Code.” Mis-regulation of these signalling pathways is of great interest as are important in human disease. A variety of peptides containing post-translationally modified histone 3 and 4 sequences were read using a supramolecular sensor array approach, where two or three sensors gave a unique response for each analyte when compared to others. These sequences were chosen to determine what type of modifications could be read (phosphorylation, acetylation, methylation) and if this type of array would be suitable for reading analytes on which antibodies—the leading technology—typically perform poorly. It was found that three sensors, which operate in neutral aqueous solution, were able to discriminate 16 different histone analytes. Additionally, it was shown that this array could report simultaneously on both concentration and the identities of histone analytes. / Graduate

Numerous applications in the present day ranging from testing humidity in air to detecting miniscule quantities of potentially hazardous chemical and biological agents in the air or water supplies require the development of chemical sensors capable of analyte detection with high sensitivity and selectively. Further, it has become desirable to create lab-on-chip systems that can detect multiple chemical agents and allow for sampling and testing of environments at locations distant from conventional laboratory facilities. Current challenges in this area include design, development and characterization of low detection limit sensors, development of low-noise readout methods, positive identification of analytes and, identification and reduction of the effect of various noise sources - both intrinsic and extrinsic to the sensor. The current work examines the performance limits of a 10-cantilever piezoresistive microcantilever array (PµCA) sensor. The microcantilevers measure analyte concentration in terms of the surface stress associated with analyte binding to the functionalized cantilever surface. The design, fabrication, characterization and testing of this measurement platform is presented. A novel aspect of the sensors developed is the use of n-type doping which increases the sensitivity of the device by one order of magnitude. In addition, design rules for surface stress-based chemical sensors have been developed. Extensive thermal characterization of the piezoresistive microcantilevers has been performed for DC and AC electrical excitation and values of heat transfer coefficient for the associated microscale phenomena are reported. Further, a method of low-noise measurement of cantilever resistance has been developed based on phase-sensitive detection techniques and this has been integrated with a multiplexing circuit to measure piezoresistance change in multiple cantilevers. Finally, the two novel techniques of chemical sensing- double-sided sensing and thermal array-based sensing have been investigated. These methods are presented as a means of extending the applicability and functionality of piezoresistive microcantilever sensors for chemical sensing.

Eidgenössisch Technische Hochschule Lausanne, Diss., 2008.

Zugl.: Berlin, Techn. Univ., Diss.