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The increasing use of microwaves in wireless communications has caused severe electromagnetic pollution. As the frequency range for wireless communication is expanding, it is highly desirable to develop a microwave absorber that can smartly and reversibly tune its absorption and transmission properties on demand to transmit required frequencies and absorb unwanted frequencies. Herein, an absorption-frequency-tunable and absorption/transmission-switchable microwave absorber is developed based on the controlled compression of a chitin-derived elastic carbon aerogel. The maximum absorption frequency is tuned from 10.4 to 11.0, 11.5, and 12.1 GHz by varying the compression strain from 0 to 20, 40, and 60%, respectively, while the maximum absorption intensity is maintained at approximately −40 dB. This frequency-tunable absorption is achieved by reducing the thickness of the carbon aerogel while retaining its moderate dielectric loss tangent. Further compression from 60 to 80% switches the carbon aerogel from being a microwave absorber to transmitter while causing impedance mismatch and changing its dielectric loss tangent from moderate to low levels. The frequency tunability and microwave absorption/transmission switching capability are reversible and repeatable for at least 60,000 cycles of compression and recovery. This study provides insights into the smart and reversible control of microwave absorbing properties and paves the way for multifunctional and robust absorbers.
Li et al. (Sat,) studied this question.