Development of Graphite-Based Flexible and Biodegradable Sensor for Tunable Filtration and Human–Machine Interaction

In this work, a novel method for creating integrated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> filters using pencil-on-paper (PoP) technology has been proposed using office paper and graphite pencil. We showcase a sustainable and cost-effective approach for fabricating tunable high-pass and low-pass filters by using different graphite concentrations on standard office paper. The proposed design integrates an interdigitated capacitor and a rectangular resistor into a single element. The experimental results indicate that the proposed structure exhibits distinct resistance values that range from 4.8 to 112 k<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula>, showing its widening tunable possibility. Furthermore, the fabricated filter exhibits classical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i>-circuit characteristics, which are shown by the charging–discharge and frequency-dependent behavior. This also shows distinct cutoff frequencies of 43 and 120 kHz for low- and high-graphite concentrations, respectively. Further, the device's capability to be used for human–machine interface (HMI) is presented. This study promotes sustainable electronics by offering a straightforward and simple replacement for traditional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> filters and removing the requirement for standard discrete components. This method appears promising for use in disposable electronics, HMIs, and other fields that seek economical, eco-friendly electronic components.