We are part of growing community of researchers who are developing a new class of fully integrated soft machines that include power, communications, and control sub-systems. From our point of view, including Integrated circuit (IC) microelectronics into soft machines provides a means for delivering practical functionality to soft-subsystems, including procedural control, amplification and feedback, and digital communications.
We found challenges in integrating sensors, which are based upon eutectic gallium alloys in microfluidic channels, into complex electronic systems. These difficulties are due to the complexity of finding a proper interconnect material. Conventional single-core copper wires are not suitable for interconnecting eutectic liquid-metal microfluidic devices since they have a high bending moment, meaning that any mechanical reaction force acting upon the surrounding soft material can cause delamination, leak of liquid metal, and device failure. Thus, it is essential to look for an interconnect material which is electrically conductive, mechanically flexible, and stable over prolonged periods of time.
In this paper, we proposed that conductive thread can be used as interconnect in soft electronic systems to alleviates problems arising due to the mechanical mismatch between conventional metal wires and soft or liquid materials. Conductive thread is a low-cost commodity material made of steel fibre, it is readily wetted by the liquid metal, it produces little bending moment into the microfluidic channel, and it can be connected directly onto the copper bond-pads of the flexible printed circuit board.
We present a high-resolution pressure-sensor soft system that can transduce normal force into a digital output. In this soft system, which is built on a monolithic silicone substrate, a galinstan-based microfluidic pressure sensor is integrated with a flexible printed circuit board (PCB). The printed circuit board provides a bridge, an amplifier, a microcontroller and LED outputs. The conductive thread lies in a serpentine shape and forms a mechanically, and electrically, robust connection between the soft microfluidic pressure sensor and the flexible PCB.
To show, visually, the high sensitivity of our integrated pressure sensing system, we used coins (UK £1) to weigh down the sensor. Two coins create 0.18N force and ~200Pa on the sensor.
Using these methods, we hope that more researchers will be able to integrate soft devices with electronic systems. By enabling strong-and-stable electrical connections we hope to enable the community to be one-step-closer to developing fully integrated soft robotic, or wearable systems.
For more information on this work, you can read the original paper here: https://www.research.ed.ac.uk/portal/files/53403275/Manuscript_v2.pdf
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