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Recognition of lying postures using capacitive proximity sensing

: Rus, Silvia
: Große-Puppendahl, Tobias; Kuijper, Arjan

Darmstadt, 2013, 87 S.
Darmstadt, TU, Master Thesis, 2013
Master Thesis
Fraunhofer IGD ()
capacitive sensors; realtime sensor visualization; detection

In recent years, capacitive proximity sensing made significant advances in the field of gathering implicit contextual data. These systems find broad usage in pervasive activity-recognition systems, installed stationary or made portable. In the domain of context recognition new ways of interaction with the environment opened up since conductive objects can be detected under certain conditions at distances up to 50 cm.
This master's thesis investigates an approach to recognize lying positions using capacitive proximity sensing. The overall goal is to develop a technological concept that can be applied to recognize lying postures of patients in elderly homes. Using this contextual data may lead to many desired benefits in elderly care. For example, the occurrence of Decubitus, a condition caused by prolonged pressure on the skin resulting in injuries to skin and underlying tissues, can be avoided better by knowing how the patient is bedded. In order to achieve a desired high resolution, the multiple access schemes CDMA and FDMA are investigated as a basis for capacitive proximity measurements. For this purpose CDMA has been implemented using Gold Codes while the correlation serves the purpose of a measure. In a test setup measurements for CDMA and FDMA have been conducted. They lead to the conclusion that at close distances FDMA has a slightly better spatial resolution than CDMA but as the distance increases the spatial resolution of FDMA will be twice as high as the one of CDMA. The real-world setup achieves a resolution of 48 measurement points, by applying a low-cost grid of crossed wires under the slatted frame of a bed. The experimental results show that the presented approach and the decisions derived from the evaluation of multiple access schemes lead to a well-suitable system for recognizing lying postures.