Enhanced microwave absorption performance of geopolymer composites by incorporating hollow Fe3O4 nanospheres

Abstract Hollow Fe 3 O 4 nanospheres (h‐Fe 3 O 4 ) with tunable sizes were synthesized and proposed as fillers to prepare microwave absorbing geopolymer (GP) composites. We studied the effect of different sizes of h‐Fe 3 O 4 on microwave absorption (MA). The MA performance was enhanced as the size of h‐Fe 3 O 4 in GP decreased. Furthermore, the GP composites containing h‐Fe 3 O 4 achieved better MA capability than their counterparts containing solid Fe 3 O 4 nanospheres (s‐Fe 3 O 4 ) of the same size. The GP composites with a small size of h‐Fe 3 O 4 exhibited the best minimum reflection loss (RL min ) of −39.3 dB at 14.0 GHz and an effective absorption bandwidth ( EAB ) of 4.8 GHz at 2.2 mm. The outstanding MA capability, possibly as a result of improved dielectric loss and magnetic loss together with well‐matched impedance, demonstrated that GP composites are competitive construction materials when MA is critical. The radar cross section ( RCS ) simulation was conducted to assess the MA performance of composite materials in practical environments.