A Low-Cost Flexible Inkjet-Printed Echo State Network for Impact Localization

Impact localization plays a vital role in continuous monitoring of damage and fatigue testing in various healthcare applications. It is particularly important for assessing potential risk factors in spinal cord and orthopedic injuries, and in monitoring the health of athletes. Flexible sensor technology, especially the inkjet printing process on flexible substrates, is gaining significant interest due to its cost efficiency, mass production, simplicity, and environmental sustainability advantages. However, the efficiency of inkjet printed sensors is limited due to the constraints of their low-maintenance fabrication process. The integration of artificial intelligence with inkjet-printed sensors can address the limitations in their operational efficiency. In the field of artificial intelligence, Echo State Network is increasingly being implemented in a wide range of applications due to its computational simplicity. This work presents an Echo state network integrated tactile sensor. Echo state network reservoir is inkjet-printed on a polyethylene terephthalate film substrate and works as a tactile sensor. The readout layer of the Echo State Network is constructed with multilayer perceptrons followed by a majority voting layer. The tactile sensitivity is tested with a pencil impact experiment on different sensor surface areas. Our designed Echo State Network with an integrated tactile sensor accurately predicts the location of the pencil drop with a precision of 92.31%.