Tham khảo tài liệu 'micromachining techniques for fabrication of micro and nano structures part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Microwave Meta-Material Absorbers Utilizing Laser Micro-Machining Technology 69 and thickness t mm using standard photolithography technique and an experiment was carried out. The photographs of the fabricated two-layer metallization MTM absorber sample are shown in Fig. 7 a . In order to verify the effectiveness of the double-negative MTM absorber cells without a metallic backing plate a planar array of absorber unit cells 13 X 3 was mounted on a polystyrene foam substrate with a relative permittivity of . The inter-element spacing between two unit cells was set to 6 mm. As shown in Fig. 7 b this planar absorber structure was placed inside a rectangular waveguide WR430 and measurements were taken with the waveguide over the frequency range from GHz to GHz. At these frequencies the EM wave propagation was confined to the TE10 mode. The measured magnitudes of S11 and S21 parameters for the planar arrayed 13 X 3 unit cells are plotted in Fig 8. This results show that the backplane-less planar absorber structure is able to achieve the well matched broadband absorber. However the experimental transmission minimum frequency of GHz is shifted approximately 90 MHz lower compared to the simulated transmission minimum frequency. By using the measured S11 and S22 parameters the calculated corresponding absorbance A 1- IS11I2- S2112 was plotted in Fig. 9. It exhibits a maximum absorbance of 90 at GHz with a full width at half maximum FWHM of 120 MHz over the frequency range from to GHz. This broader bandwidth performance is likely due to a mutual coupling effect between the cells. Although the field distribution of the TE10 mode wave is different compared to the plane wave the proposed planar absorber structure shows the possibility of the planar-type absorber without metallic backing plates or a resistive sheet. A new idea for a backplane-less planar-type microwave absorber based on the arrayed double-negative MTM unit cells has been .
