Millimeter‐Wave and Sub‐Terahertz‐Band Beamforming Facilitated by Paper‐Based Passive Intelligent Reflecting Surfaces

The low‐cost passive intelligent reflecting surfaces inkjet‐printed on paper substrates are proposed to shape electromagnetic wavefronts and control reflected wave directions in the millimeter‐wave (mmWave) and sub‐terahertz (sub‐THz) bands. Unlike conventional IRSs with circuit elements, an FPGA, and a DC supply, the passive IRSs use inexpensive paper substrates and conductive nanoparticle silver ink, achieving a phase gradient over a 2π period. Simulations and measurements show that these passive IRSs steer incoming mmWave and sub‐THz signals to anomalous reflection angles. For a 0° incidence angle ( θ i ), a 28‐GHz‐band IRS reflects an incident wave to a 30° anomalous reflection angle, ≈12 dB higher than that of copper plate. Another 100‐GHz prototype shows an 8 dB higher anomalous reflection than a copper plate. IRS beamforming efficiency is related to printing resolution and substrate thickness, crucial in realistic wireless communication environments. These passive IRSs can direct communication signals to non‐line‐of‐sight locations, extending coverage for current and next‐generation wireless networks. The low‐cost, simple fabrication process supports potential mass production, facilitating widespread adoption in future wireless communication systems like the internet of things and 6 G.