Green ultra-wideband antenna utilizing Mie resonances in cactus

While plants are typically supposed to restrict the performance of radio frequency transceiver systems, they can act as efficient biogenic elements of control. A high fraction of water inside vegetation gives rise to multiple electromagnetic Mie resonances, originating from interplaying a naturally high permittivity and a form factor. Opuntia ficus-indica, known as nopal cactus, is a representative example whose succulent stems or cladodes contain nearly 75–85% water. Here, we present an Opuntia-based broadband omnidirectional antenna element, operating at several Wi-Fi communication bands, spanning from 900 MHz to 7.7 GHz. A high relative permittivity in the GHz range exceeds 20. As a result, a variety of Mie resonances within the cladode are measured and revealed by the multipole expansion technique. Modal hierarchy, resonantly excited with a coaxial cable, is demonstrated to provide a broadband impedance matching below −10 dB over the ∼150% bandwidth. Further investigations of plants as functional electromagnetic elements can contribute to the general trend of environment friendly multifunctional devices, promoting development of green technologies.