DIY Electronics

A new approach

We propose to use non-functionalized and widely abundant off-the-shelf materials such as paper and aluminum foil, to build a truly low-cost and eco-friendly high performance multisensory flexible sensors network, integrating the maximum sensory functions of a human skin. We call it Paper Skin. The proposed platform can be used for simultaneous and real-time detection of various environmental stimuli (using a 3D stacking configuration of sensor arrays), or for monitoring the body vitals of the carrier (using an in-plane integration of sensors), valuable for extracting essential medical information such as heart rate and blood pressure in real-time. For the detection of external stimuli, the 6 x 6 array of Paper Skin is composed of an array of pressure sensors, superimposed with an array of temperature sensors, and finally topped with the array of humidity sensors. As for the carrier’s intimate detection, the Paper Skin is composed of a patch with in-plane integration of temperature, pressure, and humidity sensors.

For both architectures, temperature sensors are made out of a simple resistive structure using conductive aluminum foil taped on a Post-it paper substrate. Silver ink pen (Circuit ScribeTM) can be also used instead of aluminum foil for scaling purposes. The temperature coefficient of resistance (TCR) is around 0.004/oC, in accordance with the theoretical values found in the literature. Humidity sensors rely on an interdigitated capacitive structure where the post-it note acts as the humidity sensing material. This sensing capability is enabled through the porous cellulose structure of paper which absorbs water molecules on its surface. The measured sensitivity is 0.18%/%RH, with an outstanding recovery time of 1.3 seconds, which is orders of magnitude faster than the ones reported in the literature.

“Multi-sensory electronic skin sees applications in robotics, prosthetics, mapping of the surrounding environment, human-machine interfaces, and healthcare monitoring systems.”

Finally, the pressure sensor is a parallel-plate capacitor structure where aluminum foil is used as the metal electrodes and a sponge or a napkin acts as the compressive pressure-sensing dielectric film. Fine sensitivity to low pressure regimes, as low as 9 Pa, is enable through the high compressibility of the porous network structure of the dielectric used, with an overall sensitivity of 0.11 kPa-1. The pressure sensor also exhibits exceptional multi-functionality, with distinct sensitivity to pressure, touch, flow, directionality, and proximity with an outstanding detection range of 13 cm. Temperature and humidity sensors were used to monitor the body temperature and sweating effect of the carrier, whereas the pressure sensor allowed us to accurately resolve the pulsating peaks for a robust detection of heart rate, blood pressure, and arterial stiffness.

So where to from here then?

Using only off-the-shelf materials, we demonstrated a recyclable paper-based skin capable of sensing temperature, humidity, PH, pressure, touch, air flow and direction, motion and proximity. The platform is affordable and accessible to anyone, without affecting performance. We show higher performance per cost, with similar or improved performances compared to sophisticated sensor networks made from carbon nanotubes (CNTs) and nanowires (NWs). Paper Skin will revolutionize sensing in IoT where sensing diversity, surface adaptability, and large-area mapping are all required. Examples include touchless motion systems, environmental mapping, and health monitoring systems. Future work will tackle the full system integration, where RFID tags, data processing unit and storage, power management and readout circuitry will be integrated on a flexible paper platform. This will be a key enabler towards the development of widely accessible low-cost wireless monitoring systems.

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