Carbon Nanocoils/Carbon Foam as the Dynamically Frequency‐Tunable Microwave Absorbers with an Ultrawide Tuning Range and Absorption Bandwidth

The absorption frequency of conventional microwave absorbing materials (MAMs) is hardly tuned in operando, while such dynamic frequency regulation of MAMs is of great significance to meet the high demands of modern radars and intelligent electron devices. Here, an ingenious frequency-tuning strategy by means of the pressure variations is developed by fabricating highly compressible carbon nanocoils/carbon foam (CNCs/CF) as a dynamically frequency-tunable microwave absorber. Through adjusting the compression strain, the absorption bandwidth of CNCs/CF can be precisely tuned from S-band (2-4 GHz) to Ku-band (12-18 GHz). The adjustable effective absorption bandwidth is as wide as 15.4 GHz, which covers 96% of the entire microwave frequency. Under 10% compression strain, CNCs/CF shows an attractive bandwidth of 9.0 GHz and a strong reflection loss of -64.6 dB. Furthermore, the CNCs/CF also exhibit a good thermal insulation, strong hydrophobicity, and strain-sensitive conductivity, endowing them with fascinating functions of heat insulation and self-cleaning. The method of utilizing an external pressure to dynamically adjust the absorption frequencies of CNCs/CF is demonstrated for the first time, which opens an avenue for the applications of dynamically frequency-tunable MAMs with an ultrawide adjusting range and absorption bandwidth.