Polarization-Insensitive, Broadband, and Tunable Terahertz Absorber Using Slotted-Square Graphene Meta-Rings oleh Subhan Zakir, Rana Muhammad Hasan Bilal, Muhammad Ashar Naveed, Muhammad Abuzar Baqir, Muhammad Usman Ali Khan, Muhammad Mahmood Ali, Muhammad Ahsan Saeed, Muhammad Qasim Mehmood, Yehia Massoud