Research On Broadband Electromagnetic Wave Absorbers Based On Metamaterials

Electromagnetic metamaterial(EMM),is regarded as an artificial electromagnetic(EM)material whose EM parameters can be manually arbitrarily manipulated.As the dispersion and material losses of natural medium is generally determined by the electron microscopic level,they cannot be manually arbitrarily manipulated.As the EMM could gain a lot of extraordinary properties which cannot be obtained from natural materials and can be used to regulate the propagation of the electromagnetic waves.This thesis focuses on the broadband electromagnetic wave absorbers based on metamaterials through theoretical analysis,simulating calculation and experimental measurements.Two means,including introducing lumped resistors and adding a new resonance,are explored and broadband absorbers are designed in the target bandwidth successfully according to these two methods.The contents are arranged as:1.We report a EMM absorber with nearly octave bandwidth in the microwave frequency by employing resistance loaded resonance unit cells to reduce the quality factor of the resonance in the EMM and expand the absorption bandwidth.The proposed planar EMM absorber composes two slabs of print circuit board(PCB)bonded together.The upper one is a dielectric with copper film coated on both sides while the lower one is a single side grounded PCB substrate.The unit cell is composed of vertical metallic loop with serially loaded resistance element through conducting via holes.The optimal design demonstrated a broad microwave absorption with a nearly octave bandwidth from 8.45 GHz to 15.57 GHz for normal incidence in which the power absorption is over 90%.The principle of the resonances on the working bandwidth and the influences of the structural parameters are analyzed.We have also fabricated prototype by PCB technique and characterized its performance through free space transmission measurement in an anechoic chamber.The measurements and simulations agree with each other quite well across the whole frequency range.2.Based on the absorber mentioned before,the structure is improved to add a new resonance so that the absorbing bandwidth can be expanding to lower frequency.The new absorber can gain a rather broad bandwidth about 80%with the center frequency near 10GHz.We have also fabricated prototype by PCB technique and characterized its performance through free space transmission measurement in an anechoic chamber.The measurement results are basically consistent with the simulations.