Study On Design And Properties Of Terahertz Metamaterials Absorbers

Metamaterials absorbers are an important branch owing to their special electromagnetic properties and perfect absorption. As the last frequency window to be studied in the electromagnetic spectrum, Terahertz(THz) wave is widely used in non-destructive testing, medical treatment, communications and other fields, owing to its unique properties. Most materials in nature have weak electromagnetic responses in the THz regime. In contrast, THz metamaterials that were invented recently provide an opportunity for the development and application of THz technology. In this thesis, some THz absorbers based on metamaterials, including their modulation, design and manufacture, were investigated. The main contents of our study and the conclusions are shown as follows:(1) Combined with the previous results, we deduce a novel and simple way to adjust the responses of THz metamaterials just by zooming in and out the size of unit. Our simulation results show that THz metamaterials are still impedance-matching even after the ratio change. In addition, the resonance frequency changes inversely with the unit ratio. Moreover, the absorption bandwidth will be widened if the THz metamaterial’s unit is shrunk. According to our approach, any response frequency of THz metamaterials(a value of absorption peak is greater than 98%) can be acquired, within specific frequency bands. Such modulation makes the design of metamaterials more flexible and simple, and particularly, it also provides a new route to theoretical study on metamaterials.(2) Broadband metamaterials are investigated based on donuts. The response frequency of the donuts can be adjusted by adding split in the donuts without changing the outside diameters and widths of the rings. Accordingly, the broadband absorbers are designed by combining different resonators. Moreover, the broadband multiband absorbers based on spiral rings are designed and optimized.(3) It is worth noting that two kinds of novel THz absorbers based on multi-layer metamaterials absorbers(MMAs) are desinged in this thesis. Such MMs are constructed by adding two more layers, including one ultra-thin dielectric spacer and one metal layer, on the surfaces of traditional MMAs. The top and intermediate metal layers have different geometry sizes, and there is an overlap between these two metal layers. Particularly, such novel absorbers exhibit excellent THz characteristics, such as ultra-broadband, wide angle absorption, polarization insensitive, and concentration of loss. To the best of our knowledge, up to now, the related results have never been reported previously. Such designed absorbers hold great potential for applications in devices, and they are believed to be able to promote the development of metamaterials.(4) The preparation technology of THz MMAs is also studied, and the as-fabricated MMAs are characterized and tested. We also investigated the preparation of polyimide film, corrosion of aluminum, and the related technological parameters. Notably, the MMAs have been successfully fabricated by traditional microfabrication technology. The experimental measurements demonstrate that the MMAs designed in this thesis indeed exhibit broadband absorptions, and both the center frequency and absorption bandwidth are in accordance well with the simulation results.