Development of Printed Conformable Sensors

Electronics is already controlling a large number of everyday items. Due to that, electronics are found from all kinds of devices and surfaces. The traditional rigid circuit boards are the most common options in adding electronics to the surroundings. However, a new class of electronics is needed to enable the transition to a higher level of seamless integration. This transition can be done with so-called conformable electronics. Using printed electronics could bring down material consumption and allow the use of new materials in conformable electronics. In the present thesis, three different printing methods – spray coating, screen printing, and inkjet printing – were investigated to fabricate different conformable electronics: transparent touch panel, ECG electrodes, and on-skin temperature sensors. It was also studied how the printed electrode patch compares to the commercial single electrodes and how well they function in real-life situations.

A transparent touch panel with 64.7% transparency was fabricated using spray- coated graphene/PEDOT:PSS ink on a piezoelectric film. The touch panel exhibited 35 pC N-1 sensitivity, and it was able to be used both in dry and moist environments. Screen printing and stretchable silver inks were used to manufacture ECG monitoring patches on a stretchable polyurethane substrate. The ECG signal quality of the printed patch was compared with commercial electrodes in volunteer trials to verify the functionality before testing with cardiac patients. The overall signal quality was similar, and thus the electrode patches were tested with cardiac patients. E-jet printing was used to fabricate silver temperature sensors on bacterial nanocellulose substrate with a 20 µm line width. Also, inkjet-printed graphene/PEDOT:PSS temperature sensors were fabricated on thermoplastic polyurethane. The temperature sensors exhibited TRC of 0.06% that does not compete with the most efficient sensors but indicates that alternative substrate materials such as nanocellulose can be used instead of plastics. Additionally, inherently conformable materials like thermoplastic polyurethane and graphene/PEDOT:PSS ink can be used to make temperature sensors.

Printed structures do not yet compete with the efficiency with some of the already existing systems, but the benefits arise from the novel materials and reduced material consumption in conformable electronics manufacturing. However, for example, the ECG monitoring system, with stretchable conductors and soft substrate, provided similar signal quality as its commercial counterpart. Also, novel materials and fabrications processes enable new applications that are not limited by the traditional electronics fabrication processes and materials.