Green ultra-wideband antenna utilizing Mie resonances in cactus

Abstract

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.