Advanced methods for characterizing epidermal devices

Epidermal devices often comprise thin metal layers deposited over elastomeric materials which can be used for several purposes (interconnects, sensors, actuators, electrodes,...) and can be theoretically described as resistive networks. The need of individual measurements for the resistors inside these networks performed with the standard 4-wire technique requires extra connections, external wires and junctions that makes the procedure impractical. Moreover, both the fabrication and the characterization of such devices can be complicated by several issues, including the difficulties related to safety releasing the device from the initial carrier substrate and connecting to external circuits without damages. This work introduces a novel approach for applying 4-wire measurements in high-density resistive networks. A theoretical description for the epidermal devices is graphically introduced, together with the methods developed for fabricating and connecting the devices. The development of the new technique (twin-wires) is presented and explained, with experiments and measurements on different resistive networks to demonstrate its robustness and applicability. The new technique can be implemented in different research fields as materials science and wearable devices.