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

In this work, a novel method for creating integrated RC 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$\Omega$, showing its widening tunable possibility. Furthermore, the fabricated filter exhibits classical RC-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 RC 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.