Optically transparent and mechanically stretchable fractal-structured wave-absorbing metamaterial in low frequency range

Development of microwave absorption technology triggers higher requirements for the multi-function of microwave absorbing materials. An optically transparent and mechanically stretchable wave-absorbing metamaterial based on fractal structure has been proposed numerically and experimentally in the microwave low frequency range. It is designed to possess two spectrally overlapped resonances located at 4.42 GHz and 7.02 GHz, which originate from the first-order cross resonance and the second-order cross resonance, respectively. Microwave absorbing mechanisms are elaborated by normalized impedance, surface current and power loss density. Moreover, the optical transmittance of the designed wave-absorbing metamaterial is higher than 70 % in the visible region. By stretching the absorber, the frequencies of two resonant peaks occur remarkable red shift with a adjustable frequency band range of 0.64 GHz. The corresponding relationship between the variation of substrate thickness and square resistance and the shift of peak absorption frequencies is discussed. Ultimately, the wave-absorbing performance of the proposed wave-absorbing metamaterial are illustrated at different incident angles for both TE and TM waves. Research results could provide and enrich instructive guidances for realizing optically transparent and mechanically stretchable metamaterial absorber.