Ultra-broadband microwave metamaterial absorber with tetramethylurea inclusion.

The absorption region of a water-based absorber was expanded by introducing tetramethylurea (TMU) into the inclusion, whose dielectric properties are tunable through the concentration of TMU. The dielectric spectroscopy of a TMU/water mixture was deconstructed using a Debye model. We designed a four-layer ultra-broadband microwave absorber with a supernatant micro-structure. Simulation and experiment results indicate that the absorber can achieve 90% perfect absorption, covering a broad frequency range of 4-40 GHz. The concentration dependence of the absorber was also studied experimentally and numerically. The concentration control provides a more practical and large frequency-region modulation of perfect absorption.