Toroidal Dipole Metasurface Based on Polyimide Substrate for Flexible Electronic Applications

The flexibility of an antenna structure can influence its
S
-parameters by affecting resonance frequency. Stability in resonance frequency is essential for flexible applications to ensure consistent and reliable antenna performance across varying conditions. In this letter, we present the concept of resonance tolerance for different bending cases utilizing the toroidal dipole metasurface. The flexibility of the polyimide substrate allows for a minor 1.043% shift in the resonance when the planar metasurface of the toroidal dipole is curved at a 4.53-rad angle, and applying a stretching of approximately 0.12% to the structure leads to a decrease of 2.01% in the resonant frequency. Furthermore, when the flexible toroidal metastructure is positioned in proximity (5–10 mm) to a human arm phantom, the consistently favorable reflection coefficients demonstrate that the flexible toroidal metastructure operates effectively within the frequency range of 3.55–3.8399 GHz. This highlights the potential of our proposed flexible toroidal dipole antenna for wearable, flexible electronic devices, with a particular emphasis on its application within the industrial, scientific, and medical band.