An optically transparent ultrabroadband microwave absorber was proposed and experimentally verified, which achieved 23.4-GHz deep absorption bandwidth (absorption >0.8 from 15.6 to 39.0 GHz). What is more, the whole absorber is transparent in the visible light range (transmittance >0.8 from 400 to 1100 nm). The absorber thickness was 1.1 mm only, about 1/10 of the center wavelength (9.23 mm, or 32.5 GHz), and can be further reduced. Further analysis showed that the absorber was insensitive to the polarization angle and dropped only little for incident angles smaller than 30°. In general, this absorber can achieve ultrabroadband low reflection in both visible-light and microwave frequencies, providing a new solution for the design of stealth systems.

A high-performance microwave absorber with simultaneously ultra-broadband microwave absorption, mechanical flexibility and high optical transparency is proposed. A patterned indium–tin–oxide (ITO) conductive metasurface is used as the upper surface resonance layer. ANSYS HFSS 15.0 was used for the infinite period structures of the absorber simulation, and the Floquet port, master-slave boundary condition and adaptive meshing were set in the software. As a result, the absorber features >90% broadband absorption, which covers a wide frequency range of 17.6 GHz (21.6-39.2 GHz) and includes part of the K and Ka frequency bands. What is more, the absorption is above 99% in the range from 30 GHz to 33.6 GHz. The optical transmittance of the absorber in the visible light band is 85%. The thickness of the absorber is only 0.1 times of the wavelength corresponding to the lowest absorption frequency (13.89 mm). Furthermore, the absorber maintains stable absorption at different incident and polarization angles due to the quadruple centrosymmetric pattern.

In recent years, the metamaterial has become a popular and powerful tool in the electromagnetic polarization conversion design. In this paper, a flexible and transparent broadband cross-polarization-converter (CPC) was designed, fabricated and tested. ANSYS HFSS was used for the cross-polarization-converter simulation, and the Floquet port and master-slave boundary condition were set in the software. The multi-layer split-ring-resonator (SRR) structure was used to form the metamaterial for the CPC. As a result, >77% polarization conversion ratio (PCR) was achieved in the range of (7.8-18.2) GHz, with little change within 45° incident angle. The experimental results were consistent with the simulation data.

To address the limitations of current microwave absorbers in terms of conformity and Optical opaqueness, this letter proposed a flexible and transparent broadband absorber based on gridded indium tin oxide (ITO) ground. The absorber adopts a classical sandwich structure and is made of optically transparent materials. By etching the ground into a grid pattern, a transparency of 74.04% was achieved. The equivalent circuit model and the distribution of surface-induced electric and magnetic fields are used to analyze the working mechanism. The absorber achieves over 90% absorption in the 19.9-44.6 GHz frequency range, and its resonant pattern is symmetric, making it polarization-insensitive. The thickness of the absorber is only 1.35 mm, making it particularly suitable for military applications such as warships and electronic devices that require electromagnetic absorption, optical transparency, and flexibility.

As 5G technology rapidly advances, the extension of spectrum into millimeter-wave bands enables higher data speeds and reduced latency. However, this frequency expansion introduces significant electromagnetic interference (EMI) issues, particularly in environments with dense equipment and base stations. To tackle these challenges, this paper presents a multilayer transparent ultra-wideband microwave absorber (MA) using indium tin oxide (ITO) that operates between 4 and 26 GHz. This optimized MA design successfully achieves absorption from 4.07 to 25.07 GHz, encompassing both the 5G Sub-6 GHz and n258 bands, with a relative bandwidth of 144% and a minimal thickness of 0.129λ_L (where λ_L is the free-space wavelength at the lowest cutoff frequency). For TE and TM polarization with incidence angles ranging from 0° to 45°, the MA demonstrates exceptional performance, maintaining a relative bandwidth exceeding 120%. Notably, for TM polarization with incidence angles between 60° and 70°, the MA can sustain an absorption capacity with a relative bandwidth greater than 100%. By integrating the principles of impedance matching, surface current theory, and equivalent circuit simulation fitting, the absorption mechanism is further analyzed, thereby confirming the reliability of the design. This design offers exceptional wideband absorption, optical transparency, and wide-angle incidence characteristics, demonstrating great potential for applications in electromagnetic stealth, EMI suppression, and electromagnetic compatibility (EMC) in 5G communications.

A multilayer transparent microwave absorber that possesses a broadband, is bendable, and covers the frequency band near 5 GHz is proposed in this work. The absorber uses three layers of 110 Ω/sq etched patterned indium–tin–oxide-polyethylene terephthalate (ITO-PET) films as the resonant layers. The infinite cycle structure of the absorber is simulated by using the CST STUDIO SUITE. The absorber shows >90% absorption effect in the frequency band 4.16-7.48 GHz and a 99% absorption effect in the band near 5 GHz (4.98-5.83 GHz). Furthermore, by replacing the intermediate medium with polydimethylsiloxane (PDMS), the absorber obtains excellent bendability characteristics.