An Inkjet-Printed Capacitive Sensor for Ultra-Low-Power Proximity and Vibration Detection

The field of inkjet-printed circuits and sensors has yet to reach commercial maturity but is showing significant success in research with ultra-low power, paper-thin, flexible and biodegradable devices that are magnitudes less expensive to fabricate than silicon-based circuits. One such implementation, as discussed in this work, is with capacitive-based sensors, where charge fluctuations in and around the plates' gap region alter the output current signal. The resulting functionalities are vibration/proximity sensing, where the magnitude of the output current reflects the environmental perturbations. The power efficiency, flexibility, and cost effectiveness of the sensor as reported in this work demonstrates that simple fabrication with inkjet-printing can form green-friendly, high-functioning devices as alternatives to standard silicon-based approaches. Silver nanoparticle ink was inkjet-printed onto a PET film substrate with the design of two parallel plates with a narrow gap region between them that is cut and filled with hexagonal boron nitride nanoparticle ink, which is a dielectric and charge trapping material. Fringe-field capacitance emanating from the flat substrate around the gap region of the parallel plates fluctuates according to the vibration and proximity of environmental interference. The sensor operates at an average of 4.9 nano-Watts with a 3.3V supply, senses floor/table vibrations from 5 feet away, costs $0.19 to fabricate, and is compatible with additive manufacturing for high-volume printing. Applications include movement detection near irregularly shaped surfaces, touch-less interfaces for initiating devices, traffic monitoring and prediction with post-processing algorithms, and high-volume deployment for large-area vibration observations.