Metapocket: A Tri-Band Flexible Metasurface for Smartphone Antenna Performance Enhancement

In this letter, a flexible tri-band reflective metasurface, the metapocket, is presented to work with smartphone antennas to enhance its realized gain and radiation efficiency and reduce its specific absorption rate (SAR). Considering the limitation of the on-body scenario, the metasurface unit cell number is considered as a variable, and an artificial intelligence-driven method [the self-adaptive Bayesian neural network surrogate-model-assisted differential evolution for antenna optimization (SB-SADEA)] is applied to achieve the optimal performance. The designed reflection phase operates at 2.33 GHz to 2.44 GHz (Wi-Fi band), 3.39 GHz to 3.56 GHz (5G N77 band), and 5.05 GHz to 5.39 GHz (WLAN band). Polydimethylsiloxane substrate is utilized for good flexibility and biocompatibility. A state-of-the-art 5G smartphone (VIVO IQOO) is employed in both simulation and measurement. In free space, realized gain enhancement by 4.23 dB, 4.67 dB, and 5.8 dB is achieved, and radiation efficiency enhancement by 16.6%, 11.5%, and 12.1% is achieved, respectively. Furthermore, calculated SAR reduction by 90.2%, 88.9%, and 89.9% is achieved. All results verify that the proposed tri-band metapocket is of significant value to smartphone antenna performance in an on-body scenario.