Terahertz Devices Based On The Multi-layer And Flexible Metamaterials

Terahertz(THz)functional device is a key issue in the THz technique,and is significant to THz applications.The metamaterials with specific characteristics open the new path for the manipulation of THz wave and novel THz devices.In this dissertation,the fabrication processes of flexible and multi-layer metamaterials is firstly investigated.Then,the flexible wideband bandpass THz filter,the high quality factor of THz resonator,the wideband stealth technique,and high sensitive THz biosensor on multi-frequency transmission windows have been studied.We also present THz extraordinary transmission of superconducting fractal-featured structures.The main contents in this dissertation are classified as follows:1.The fabrication processes of flexible and multi-layer metamaterial in THz has been investigated.We studied the relation between the thickness,the surface smoothness of polyimide(PI)and the spin rate,coating time,and curing temperature.The thickness controllable and smooth surface of flexible substrate can be obtained by adjusting the above parameters.2.A flexible wideband bandpass THz filter has been designed,fabricated and measured.A multi-layer metamaterial structure,composed of PI-metal-PI-metal-PI layers.The center frequency is about from 0.89 THz with a 3dB bandwidth of 0.69 THz.The sharp bandedge transitions are 53 and 70 dB/THz to the rejection bands,respectively.The measured average insertion loss is 1.4 dB with a ripple of 0.8 dB.Furthermore,the transmission feature is insensitive to the polarization of incident wave due to the symmetric structure of the unit cell of the metamaterials.Also,the transmission has a small change as the filter is bent.3.The high quality factor of THz metamaterial resonator has been studied.At the resonance frequency of 0.58 THz,we observed a maximum Q_u(Q_u=62)at h=20 ?m and ?=90° for asymmetric double-layer S-shaped metamaterials.When the electric-field polarization was rotated 90 degrees,a wideband bandpass THz filter was obtained,the center frequency is about from 0.45 THz with a 3dB bandwidth of 0.52 THz.The sharp bandedge transitions are 122 and 28 dB/THz to the rejection bands,respectively.4.The broadband radar stealth of THz based on quasi-random metasurface has been studied.The unit cell is composed of only two kinds of unit cells,which we name as"0" and "1" elements,the quasi-random distributed metal rings.The metasurface can disperse the reflection into a variety of direction,resulting in a random-reflection-like distribution by coading the "0" and "1" elements.Due to symmetric configuration of metallic rings,the refelction is insensitive to the polarization of incident wave.For both TE and TM incident wave,the reflectivity of metasurface is very small in a wider frequency range from 0.8 to 1.4 THz.The experimental results show that the backward RCS of the metallic plate can be reduced at least 10 dBsm in 0.8-1.4 THz for this metasurface.The maximum reduced quantity of the RCS is 23 dBsm.Simulations and experiments are carried out to manifest the metasurface has a nice stealth effect,especailly for the incident angle less than 40 degree.5.Highly-sensitive terahertz biosensor based on the flexible bull's-eye-shaped metamaterial has been studied.Bull's-eye-shaped metamaterial exhibits multiple electromagnetically-induced transparency(EIT)-like windows.The proposed metamaterial unit cell is composed of five concentric metal rings on a PI layer with the th(?)kness of 1 0?m.The characteristics of the THz biosensor have been investigated by the simulation,experiment.Streptavidin-agarose(SA)was fabricated based on THz metamaterial functionalized by octadecanthiols and biotins.At the first,second,third,fourth window of multiple EIT,frequency shifts of 10 GHz,15 GHz,29 GHz and 30 GHz were observed for containing the biological monolayer.6.The extraordinary optical transmission of fractal-featured metallic and superconducting NbN films at THz frequencies has been studied.We reported on fractal-featured square and ring-shaped apertures with two generations of Sierpinski-Carpet pattern(SCP).The characteristic transmission peaks are found to be associated with the interaction of surface plasmons polaritons(SPPs)and localized surface plasmons(LSPs).For the superconducting NbN film,when the temperature is slightly lower than the critical transition temperature Tc,the peak magnitude of SPPs resonances is most prominent due to the non-monotonic temperature dependence of kinetic inductance.