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.

Traditional microwave absorbers usually use the epoxy resin dielectric board, which is neither flexible nor optically transparent, so cannot be used in certain applications. In this work, a flexible and optical-transparent broadband absorber is reported, which is based on the indium tin oxide (ITO) and polyethylene terephthalate (PET) material system with an ITO-PET-ITO structure. It showed more than 75% transmittance in the visible light range. The microwave absorption was above 0.8 from 19.9 GHz to 51.8 GHz. The absorption decreased when the absorber was bent, though the variation was not big. Further analysis pointed out that the absorption decrease could be attributed to the change of the incident angle. Theoretical simulation results agreed well with the measured absorption spectra.

5G mobile communication is developing at a faster-than-expected pace, especially in the mid-frequency band (so-called sub-6G band). This paper presents a transparent and flexible broadband absorber for the sub-6G band of 5G mobile communication. A sandwich-structured metamaterial absorber (MMA) was designed and tested. The transparent and conductive material Indium Tin Oxide (ITO) was used for the surface resonant structures and the backplane ground layer; and polyethylene terephthalate (PET) and polydimethylsiloxane (PDMS) were used as the dielectric layer, separately, both are transparent and flexible. The absorber featured >80% broadband absorption, covering a wide frequency range of (3.0~10.0) GHz for PET dielectric layer, and (3.2~11.0) GHz for PET-PDMS-PET dielectric layer. The thickness of the absorber made of the latter was 6.25 mm only (0.067 times of the wavelength corresponding to the lowest absorption frequency). With additional advantages of excellent flexibility and transparency, the MMA perfectly covers the frequency bands of the sub-6G band and can play an active role in the 5G communication in the near future.

The WiFi technology has become a world-wide everyday service, and the accompanying electromagnetic pollution has attracted more and more attentions. This paper presents a transparent and flexible broadband metamaterial absorber (MMA) covering the whole WiFi waveband. The transparent and conducting material Indium Tin Oxide (ITO) was used for both the frequency select surface and the backplane ground layer, and polydimethylsiloxane (PDMS) was used as the dielectric layer for the microwave MMA. The absorber featured >80% absorption covering a wide frequency range of (2.2-5.85) GHz, which includes all the frequency bands of WiFi signal. The absorber was insensitive to the polarization angles and dropped little for incident angles less than 30°. Signal shielding experiments in 2.4 GHz and 5 GHz were carried out to demonstrate the application potential of the absorber. With additional advantages of optical transparency and mechanical flexibility, the broadband MMA can be useful in WiFi related applications in the future.

pressure sensors (FPSs) are widely demanded for accurate pressure sensing on complex surfaces. FPSs using metal nanoparticles (NPs) as the sensing material have high conductivity and good mechanical properties, but poor gauge factor as a trade-off. In this work, a novel design of the AgNP-based FPS is proposed and testified with the help of the electrohydrodynamics-printing technology, so that the gauge factor can be improved from 8 to 286.8, resulting from the localized micro-zone piezoresistance effect. The working principle of the piezoresistive characteristic is discussed, and two methods to further improve and adjust the gauge factor are proposed and experimentally demonstrated.

A mechanically-flexible and optically-transparent millimeter-wave broadband absorber was proposed and fabricated. The absorber showed >90% absorption in (73.5-110) GHz, covering the whole W-band. The key frequency selective surface (FSS) used a concise metal mesh structure fabricated by the electrohydrodynamics (EHD) printing technology, which formed a classic sandwich structure together with a transparent dielectric layer and a transparent and conductive backplane. The transmittance of the sample in the visible light region was 58.1%. To testify the flexibility, the absorber was conformed to cylinders with radius of 34 mm and 16 mm, respectively. The measured normalized S11 increased with bending. Simulation results also showed that the absorption over W-band was >80% within (0-45) ° incident angle, and was insensitive to the polarization angle.