Flexible Electronics for Large Area Sensing and Stimulation

Abstract

Advancements in soft materials and hybrid flexible electronics have enabled developments in flexible circuits and wearables. Where rigid electronics are extremely precise over small physical areas, flexible electronics have the capability to sense over large curved areas. From the onset of epidermal electronics and flexible transistors, there have been great advancements in sensing over soft curved objects, such as human skin or brain tissue. This thesis focuses on hybrid flexible electronics to sense and stimulate over large areas. The aim of the systems presented is to provide insight into complex navigation and sensor processing systems. In addition to the design, fabrication, and characterization of each device, several important characteristics of each device are investigated: material choice, curvature limits, and device sensitivity. The first device presented in this thesis uses strain gauges to track the bending of neurosurgery navigation stylets for catheter placement. The strain gauge fabrication and characterization is presented. Adhesive testing, stylet bending modeling, and noise techniques are also discussed as they were found to be critical components of the system. The device's limit of detection is 1 mm tip displacement. The purpose of the second set of devices presented is to gain object information from curved or edged robotic structures. Three sensing modes were explored: piezoelectric, strain, and capacitive. The piezoelectric sensor was founded to have a 6.7 times increase in sensitivity when an open-cell foam compliant layer is used. The strain sensor was found to have a gauge factor of 2.83 on a silicone layer and 1.5 on a polymer layer. The combination of the piezoelectric and strain sensing modes is presented. The capacitive sensor is able to detect object shape using inverse problem mathematical techniques. The third device and system presented is a flexible electrode array for stimulating the electroreceptors of electric fish. The spatial and temporal control of a conformal stimulation array enables the decoding of motor signals in the brain. The array fabrication and system development is presented. Surface modification of the electrode array successfully altered the surface energy of the array to match that of the fish for the optimal array-fish interface. In summary, the development and integration of these flexible electronic devices has been achieved. It was found that the interface between the flexible electronic devices and binding objects is critical to device sensitivity and reliability