Structural Design And Performance Of Broadband Metamaterial Absorbers In THZ Frequency

As the hot fields in terahertz metamaterial, broadband absorber, especially with simple construction and excellent performance, has great potential application. However, most terahertz metamaterial absorber has limited bandwidth, complicated fabrication and low duty ratio, which limit the application of broadband absorber in a certain extent.Generally, broadband metamaterial absorber is constructed by alternatively stacking metal-insulation layers, or arraying some metal patterns in a period. In terahertz, these methods are difficult to improve the bandwidth greatly because of accumulated mismatching tolerance and limited size of metamaterial. In this thesis, we investigate the resonance characteristic of closed metal ring and principle of bandwidth superposition, and find that the resonance peak of closed metal ring can be controlled by changing the side length of metal ring. Besides, the neighbor metal rings have little mutual effect, so they are good candidates for nesting to achieve bandwidth superposition. Then, we design a compact metal pattern which is composed of eight concentric nested metal rings, and obtain broad absorption bandwidth in terahertz frequency band. The absorber is polarization independent with absorption bandwidth of 3.70 THz, and the ratio of bandwidth and central frequency as large as 87.5%. The device also keeps high absorption for TE and TM oblique incident electromagnetic wave, and absorption originating from ohmic losses. We adopt impedance matching theory and interference theory to analyze the broadband absorption. In addition, the absorber is not only easy fabrication and high duty ratio, but also can improve absorption by controlling the width of metal and the gap between metals, or improve bandwidth by changing the amount of metal rings.Taking into account of heat conduction and extraction of thermoelectric in practical application, we improve a terahertz broadband absorber with only one metal multiple spiral, which basing on the concentric nested metal ring and taking example by the structure of antenna. The absorber is polarization insensitive with bandwidth of 5.26 THz. The average absorption during the bandwidth reaches up to 80% and the ration of bandwidth and central frequency is nearly 90%. Besides, by making use of amplification of electric field in antenna structure and the scalable of metamaterial, we construct a microwave broadband absorber by combining lumped element and spiral antenna.