Electromagnetic wave absorption materials have attracted significant research attention due to their potential applications in numerous fields, including wireless communication, commerce and military. Unfortunately, the development of broadband and high-efficiency electromagnetic wave absorbing materials in the gigahertz region is very difficult and challenging. Generally, the absorption properties of these materials are derived from magnetic and dielectric losses. However, the impedance matching of a single dielectric or magnetic loss material still remains a significant challenge. Existing literature has reported that magnetic-dielectric composites exhibit great potential for designing synthetic high-efficiency absorption materials with broader and effective absorption bandwidth as well as reduced density. Consequently, the combination of magnetic and carbon materials has been identified as good candidates for tuning the microwave absorption performance of composites and improving the impedance matching of the material.
In an effort to address the difficulty of developing broadband and high-efficiency electromagnetic wave absorbing materials, a team of researchers from Anhui University of Science and Technology: Dr. Shengtao Gao, Dr. Yuanchun Zhang, Professor Honglong Xing and Professor Hanxu Li prepared typical magnetic-carbon composites under controlled reduction process from semiconductors to magnetic materials. This approach was then used in a controlled reduction synthesis of yolk-shell [email protected]@C for electromagnetic wave absorption, using core-shell a-Fe2O3@PDA precursor. The authors also comprehensively investigated the chemical composition, morphology and magnetic properties of the resulting [email protected]@C powders. In this approach, the storage and loss ability toward electromagnetic wave energy was analyzed by testing the related electromagnetic parameters of all the samples. Their work is currently published in the Chemical Engineering Journal.
The research team found that through controlling the reduction process, magnetic-dielectric Fe3O4@C and [email protected]@C composites were obtained after annealing. Interestingly, both Fe3O4@C and [email protected]@C composites exhibited high-performance energy absorption in the microwave band, even though [email protected]@C performed better compared to Fe3O4@C. The absorber thickness was observed to highly influence the minimal reflection loss value. For instance, Fe3O4@C recorded a minimal reflection loss of -45.4 dB at an absorber thickness of 1.5mm, while that of Fe3O4@[email protected] was -66.5dB at an absorber thickness of 1.6mm. Moreover, the efficient absorption frequency for the two composites covered almost all the Ku-band and ranged between 5.1 to 18 GHz, which is desirable for the high-efficiency electromagnetic wave absorbing properties. It was worth noting that the excellent behaviors of magnetic-carbon composites toward electromagnetic energy conversion could be attributed to the properly controlled magnetic loss, dielectric loss and synergetic effects.
In summary, the authors successfully synthesized magnetic yolk-shell Fe3O4@C and Fe3O4@[email protected] composites via a controlled reduction strategy that saw the conversion of pure semiconductor of Fe2O3@PDA precursor to magnetic carbon composites. Results showed that both the magnetic [email protected]@C and Fe3O4@[email protected] composites exhibited remarkable high-performance energy absorption in the microwave band due to the increased magnetic properties and polarization behaviors. In a statement to the Advances in Engineering, Dr. Shengtao Gao said that the controlled reduction process results in magnetic-carbon composites with desirable magnetic loss, dielectric loss and synergistic effect, which are potential candidates for the development of high-performance electromagnetic wave absorbing materials.