Copper wire based electrical contacts for direct interfacing of stretchable sensors

Stretchable sensors based on piezoresistive polymers enable new conformal and biocompatible wearables. However, physically interfacing such structures to create electrical contacts is still challenging. This is due to the localisation of stresses at the interface between soft polymers and metallic interconnections. Even if stretchable contacts or conditioning circuits are realised, there must be a rigid-soft interface to connect stretchable structures with conventional devices. Here, five ways to electrically connect soft Ecoflex based strain sensors are evaluated. The results show that a filament cable exhibits the most stable behaviour under cyclic loading of the contacts, while using a multi strand cable or a copper mesh results in lower contact resistance. In addition, loading forces from 0.27 N to 6.92 N are supported. Finally, stretchable piezoresistive strain sensors are fabricated using the 5 different contact methods. Employing customised interfaces with an optimal performance trade-off will help to establish reliable contacts with future stretchable electronics.