A Fully Additive Approach for the Fabrication of Split-Ring Resonator Metasurfaces

Metasurfaces, as a two-dimensional (2D) form of metamaterial, offer the possibility of designing miniaturized antennas for radio frequency (RF) energy harvesting systems with high efficiency, but fabrication of these antennas is still a major challenge. Printed circuit board (PCB) lithography, utilizing subtractive etch-and-print techniques to create metal interconnects on PCBs, was the first technique used to create metasurfaces antennas and remains the dominant technique to this day. The development of large-area fabrication techniques that are flexible, precise, uniform, cost-effective, and environmentally friendly is urgently needed for creating next-generation metasurfaces antenna. The present study reports a new fully additive manufacturing method for the fabrication of copper split-ring resonator (SRR) arrays on a PCB as a planar compact metasurfaces antenna. This new method was developed by combining sequential build up (SBU), laser direct writing (LDW), and covalent bonded metallization (CBM) methods and called (SBU-CBM). In this method, standard FR-4 covered with a layer of polyurethane was used as a basic PCB. The polymer surface was coated with a grafting molecule, followed by LDW to pattern the SRR array on the PCB. Finally, in electroless plating, only the laser-scanned area was selectively plated, and copper covalent bond metallization was selectively plated on the SRR pattern. Copper SRR arrays with different sizes were successfully fabricated on PCB using the SBU-CBM method. Copper strip lines within the SRR repeating building block were miniaturized up to 5 μm. To the best of our knowledge, this is the smallest size of a PCB antenna that has been reported to date.