Dielectric gene engineering on biochar for ultrawide-band microwave absorption with a rational double-layer design

Biomass char is very promising in developing microwave absorbing materials with low minimum reflection loss (RL min ) and ultrawide effective absorption bandwidth (EAB) owing to its low cost and natural availability of various pores, but however is facing a dilemma between the conduction loss and interface polarization loss where new heating technology is highly desirable. In this work, a microwave confined plasma/microwave hybrid heating technology is developed based on the unique interaction between porous carbon and microwave for simultaneous enhancement of conduction loss and interface polarization loss of cellulose char. Compared to the conventional heating product at the same temperature, the as-prepared microwave char showed almost doubled conductivity which is beneficial for conduction loss, higher content of C –O bond that has longer bond length and dielectric susceptibility than C O bond, and more condensed carbon nanoparticles embedded in the carbon matrix which is responsible for increasing the heterointerface polarization loss. As such the tangent loss of MW900-40 % ranges from 0.69 to 0.97 while that of CH900-40 % only ranges from 0.34 to 0.64 in the frequency range of 2.0–18.0 GHz. Further, based on multilayer impedance gradient principle, a double-layer absorber is constructed with products of different MW900 loading, yielding a RL min of −59.0 dB at 15.9 GHz with an EAB of 10.0 GHz at 4.0 mm, whose working mechanism is comprehensively studied by simulations in terms of impedance matching and microwave dissipation distribution.