Stretchable sensor array patch for respiratory monitoring

In recent years, an increasing trend towards sensor systems that are declared as "flexible" or even "stretchable" could be observed. They are often realized as foil-based sensor systems that can be conformably applied to objects with complex shapes without losing functionality or disturbing the system's freedom of movement.
In this thesis a foil-based stretchable 6 x 6 sensor array patch with a sensing area of approx. 30 x 30 mm is presented, which is able to measure its own local bending deformation at 36 points by means of integrated sensors. To suppress sensor response to foil stretching and increase bending sensitivity, a double-sided sensor design with strain gauges located on both sides of a thin polyimide foil is introduced. The mainly targeted application is the respiratory monitoring of premature infants, for which the patch is to be placed on the skin area between chest and abdomen in order to measure the typical oscillating deformations caused by breathing. This information shall be used to trigger the artificial respiration device and also to allow a reconstruction of the body surface, thereby serving as an extended diagnostic tool.
In experiments with a mechanical setup imitating breathing, specially developed algorithms could detect trigger points with a delay of less than 80 ms (± 22 ms) compared to the ventilation pressure stimulus peak and resume detection within 2-3 seconds after external disturbances have been applied. Implemented algorithms for surface reconstruction provided an almost perfect match between well-defined forced foil deformation and the reconstructed foil shape when bending around one axis.