SRRs designs formed on paper based substrates. (a) SRRs being drawn on paper using rollerball pen with conductive silver ink, (b) Schematic diagram of the electromagnetic simulation model and the dimensions of SRRs, (c and d) SEM images of silver trace on the substrate, (e) SEM image of silver pen trace on a single paper fiber, (f) energy dispersive spectroscopy (EDS) mapping of area marked by square in (d) [71]. Reproduced with permission from Z. Wang et al., J. Clean. Prod. 234, 588 (2019). Copyright 2011 Elsevier. (This figure is subject to copyright protection and is not covered by a Creative Commons Commons license.)