B4.3 - Curvature Effects on Elongated Capactive Proximity Sensors

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B4 - Mechanical Sensors II
T. Schlegl, T. Bretterklieber, H. Zangl - Graz University of Technology (Austria)
283 - 287


Capacitive sensing technology has proven to be an interesting alternative for proximity sensing compared to state of the art systems based on optical methods or contact based methods. An important measurement task is to identify the presence of a human in dangerous environments. In this application, sensor systems have to reliably detect the human proximity within a well defined region under various environmental conditions. Typical application scenarios comprise seat occupancy detection for safe airbag deployment, clamping protection for automatic doors or automatic power tools etc.

Capacitive sensors work with a variety of materials and offer the advantages of a volumetric measurement principle. The sensor elements (i.e. the electrodes) are simple while providing high versatility with respect to geometrical constraints. Hence, this technology also allows monitoring of complex structures or machines, where traditional systems e.g. based on a line of sight principle may fail.

Common techniques for capacitive proximity measurements evaluate the capacitance between one electrode and ground or between two electrodes in different ways. The developed test setup uses simple electric wires as electrodes. This permits a very flexible electrode structure. The capacitive sensor covers an area with no line of sight and different changes in direction between the start point and the end point. A wireless transmitter connects to the host controller for evaluating the measurement results.

The individual shapes of the sensor electrodes dictate the coupling mechanisms between the electrodes to objects in the environment. These coupling mechanisms have been recently studied for planar sensor geometries. However, investigations towards complex electrode structures comprising non-planar electrode arrangements (i.e. the electrode planes are arbitrarily oriented) have not been reported are presented in this paper. Additionally, the measurement system is described and impacts on the sensitivity due to bending electrode structures are analyzed.