Flexible and stretchable electronic systems for soft robotics and medical care

The electronic devices we use in our daily life shape the modern lifestyle. In recent years, the production of electronic devices increases in efficiency, variation and produced equipment due to the global competition. The development of portable and wearable equipment increases the demand on flexible/stretchable electronics to enhance comfortable usage. A problem that emerges from this growing industry is the increasing amount of electronic waste (e-waste), which is barely dismantled under controlled conditions. Moreover, the used materials lag on biodegradability and are partially toxic. Thus, dumping the e-waste in landfills damages the environment and causes a health risk for residents in the surrounding regions. To target this problem, I investigated on the design of two stretchable electronic sensor skins (e-skins) consisting only of biodegradable and biocompatible materials. The substrate of the e-skin is a gelatin-based hydrogel and the electronic conductors are laser cut out of a zinc foil (laser processed zinc structures). Furthermore, I developed an autonomous reusable measurement system on a flexible PCB (Printed Circuit Board), which is applicable for both e-skins. The PCB, run by a lithium-ion (Li+) battery, features a micro controller, a 64-channel impedance converter, two 4-channel ADC, a LED Driver, and a 1-Cell fuel gauge. Additionally, the micro controller is wirelessly connectable to any external device supporting BLE (Bluetooth-Low-Energy). In order to handle the outgoing data and control the PCB externally, a software has been specifically written for a PC (tested on Windows). The first e-skin is designed to measure the temperature, humidity and the applied strain on the skin. The sensors have been calibrated in a climate chamber for various temperature and humidity settings. Adjusting the climate between 20-30C and 40-60%r.H. results in an impedance change of up to 50% with temperature and 80% with humidity. Additionally, the e-skin has been successfully attached on a human arm for several experiments demonstrating the functionality of the measurement system. The second e-skin constitutes a stretchable touch panel with 16 pressure sensors aligned in a 4x4 grid. It has been demonstrated that the sensors are sensitive to the applied pressure and the e-skin resolved the shape of a simple frame. The sensitivity of a single sensor is determined by applying several loads (10/20/50g) resulting to an impedance change of up to 40%.eingereicht von Roland Pruckner, Bsc.Universität Linz, Masterarbeit, 2019(VLID)378026