Sensors are all around us: they enable the interaction between ourselves and the environment or they deliver us detailed information about our surroundings. Many applications require sensors for recording shear stress, ranging from robot hands equipped with tactile sense in order to improve handling of objects, over prosthetic sockets to the foot-sole interaction detectors in sports and rehabilitation sciences. Especially when used in the medical sector, it is important that these shear stress sensors are thin, unobtrusive and easily embedded. In this masterthesis, we are going to develop a matrix of shear sensors which can be used for monitoring foot-sole interaction. Already available are sensors to measure the foot pressure distribution. However, the pathogenesis of an often occurring problem such as foot blisters is related to excessive frictional forces experienced on or under the foot. Therefore the goal is to realise a foot-sole interaction sensing sheet.
At our research group, Cmst (Elis Department), a 1-point shear stress sensor has already been developed. The sensor’s principle of operation is based on changing coupling of light between a light source and an adjacent photodiode. When both components, which are located on opposite sides of a transparent, deformable rubber layer, move laterally with respect to one another, a difference in photodetector current can be observed.
In order to map the shear interaction between a foot and a shoe sole, a matrix of several independent sensing points is necessary.
The goal of this project is to realise a 20cm x 30cm shear stress sensor sheet (corresponding with the size of a shoe) in a stretchable technology (available at Cmst), as schematically shown below. Two circuit layers will be designed and fabricated (one layer incorporating the photodiodes and another incorporating the LEDs) which will be laminated with a transparent deformable intermediate layer to obtain the shear sensor array. Since at least 1 circuit layer will consist of islands, interconnected using stretchable conductors, the different shear sensing points can move independently and a true sensor matrix is obtained.
Apart from the physical realisation of the shear sensor itself, it is also needed to develop a low-power electronic circuit enabling the operation and the visualisation of the sensor.
More specifically, the several subtasks in this master thesis are: