The Role of Interdigitated Electrodes in Printed and Flexible Electronics

Flexible electronics, also referred to as printable electronics, represent an interesting technology for implementing electronic circuits via depositing electronic devices onto flexible substrates, boosting their possible applications. Among all flexible electronics, interdigitated electrodes (IDEs) are currently being used for different sensor applications since they offer significant benefits beyond their functionality as capacitors, like the generation of high output voltage, fewer fabrication steps, convenience of application of sensitive coatings, material imaging capability and a potential of spectroscopy measurements via electrical excitation frequency variation. This review examines the role of IDEs in printed and flexible electronics since they are progressively being incorporated into a myriad of applications, envisaging that the growth pattern will continue in the next generations of flexible circuits to come.

Multi-Layered Carbon-Black/Elastomer-Composite-Based Shielded Stretchable Capacitive Sensors for the Underactuated Robotic Hand

Soft and flexible strain sensors are becoming popular for many robotic applications. This article presents a stretchable capacitive sensor by combining a conductive filler of carbon black with elastomers and implementing shielding to reduce parasitic interference, applied to an underactuated robotic hand. Sensors with different configurations were explored. The results show that a shield introduced to the sensor does have some mitigation effect on external interference. Two sensor configurations were explored: longitudinal interdigitated capacitive (LIDC) sensor, where the interdigitated fingers lie along the same axis as the strain, and transverse interdigitated capacitive (TIDC) sensor, where the interdigitated fingers are orthogonal to the strain direction. The LIDC configuration had better performance than TIDC. The fabricated two-layered LIDC sensor had a gage factor of 0.15 pF/mm and the rates of capacitive creep of 0.000667 pF/s and 0.001 pF/s at loads of 120 g and 180 g, respectively. The LIDC sensors attached to an underactuated robotic hand demonstrate the sensors’ ability to determine the bending angles of the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints.

Multimodal Deformation of Liquid Metal Multimaterial Composites as Stretchable, Dielectric Materials for Capacitive Pressure Sensing

Traditional electronic devices are composed of rigid materials and components that tend to be unsuitable for soft robotic and stretchable electronic applications, such as wearable or continuous pressure sensing. However, deformable materials have the potential to improve upon traditional devices through enhanced sensitivity and responsiveness, better conformability and biocompatibility at the human-machine interface, and greater durability. This work presents deformable composite materials composed of the gallium-indium-tin alloy galinstan (GaInSn) that combines the conductivity of a metal and the intrinsic deformability of a liquid. Dispersing galinstan in an elastomer allows for the formation of deformable dielectric materials that have tunable mechanical and electrical behavior, for example, modulus and relative permittivity. Galinstan composites have been shown previously to have a minimal modulus impact on the elastomer but concurrently achieve impressive dielectric performance. However, galinstan dispersions can be costly and face challenges of mechanical and electrical reliability. Thereby, this work investigates multimaterial composites composed of galinstan and a rigid filler, either iron or barium titanate, with respect to morphology, mechanical behavior, dielectric behavior, and pressure sensing performance for the purpose of achieving a balance between a low modulus and superior electrical performance. By combining galinstan and rigid fillers, it was found that the mechanical and electrical properties, such as modulus, permittivity, loss behavior, sensitivity, and linearity of the multimaterial composites can be improved by tuning filler formulation. This suggests that these dielectric materials can be used for sensing applications that can be precisely calibrated to specific material properties and the needs of the user. These deformable multimaterial composites, found to be stretchable and highly responsive in sensing applications, will expand the current mechanical abilities of deformable dielectric materials to improve soft robotic and stretchable electronic devices.