Preparation And Analysis Of Microwave Absorbing Structure Of Ferromagnetic Thin Films

Artificial electromagnetic multi-layers structure composited by artificial materials and conventional dielectric material can combine both advantages to improve the overall electromagnetic performance. Usually people add a new type of artificial elec-tromagnetic materials or use new materials to replace traditional materials to form a new composite structure. Recently electromagnetic wave absorbing structure of fer-romagnetic thin film is formed by replacing the traditional resistive layer by the fre-quency selected layer of periodic structure of nanometer ferromagnetic thin films, on the basis of the traditional Salisbury screen. This new multi-layers absorbing structure, which has both the electric and magnetic loss from the nanometer-magnetic thin film, can significantly improve the overall performance of the entire absorbing structure.In this thesis, firstly frequency selective surface (FSS) and the research back-ground of composite electromagnetic wave absorbing structure including FSS is de-scribed. In the second chapter, the structure, type and principles of FSS are summa-rized. Chapter Ⅲ presented a multilayer absorbing structure, composited by artificial metal periodic structure and traditional magnetic absorbing materials. Both the simu-lation analysis and sample preparation as well as test of the multi-layer structure is carried out. In chapters Ⅳ and Ⅴ, an artificial periodic absorbing structure based on ferromagnetic multilayers nanometer-film is introduced. The specific description of the production of ferromagnetic thin films, the transmission and reflection measure-ments, TRL calibration and time domain gate technology is discussed in chapter IV. In chapter Ⅴ, we explored the composite structure of the ferromagnetic thin film from three aspects:electromagnetic full-wave simulation and equivalent circuit model and the actual sample measurement. Choosing different size of the periodic structure of ferromagnetic thin film, different thickness of dielectric layers and different specifica-tions of the sample, we obtain the optimized performance of broadband microwave absorbing.Two composite absorbing structure are proposed in this paper, by theoretical analysis and actual sample measurements, and the following conclusions is achieved:1. Adding artificial periodic metal structure to the conventional absorbing material can improve the absorbing performance. Multilayer absorbing structure formed by the artificial metal periodic structure and traditional magnetic materials can im-prove the performance in lower microwave band without increase of the overall thickness. The working frequency can be lowered from4.3GHz to2.5GHz with-10dB bandwidth up to1GHz. By changing the geometric parameters of the pe-riodic metal structure, the working frequency of the artificial structure allows con-tinuous tuning within2-4GHz.2. The new composite absorbing structure based on multi-layers ferromagnetic nano-film can achieve-10dB absorbing bandwidth up to12GHz in the2-18GHz band, by optimization of the thin film parameters. In a variety of parameter range-10dB bandwidth can be kept better than10GHz. By adjusting the size parame-ters of the FSS layer we can fine-tune the work frequency of the composite struc-ture. The ferromagnetic thin film absorber structure with advantages of controlla-ble parameters, extremely light weight, large area, flexible texture promises ap-plications in electromagnetic protection, electromagnetic compatibility, as well as radar stealth technology.