| The design of novel metamaterials (MMs), the exploration of electromagnetic (EM) response of the unit-cell structure, and completion of its theoretical system and analytical methods has a very significance in promoting its applications of stealthy material, photoelectric devices and so on. On the basis of these research hot points, for realization of perfect loss, transmission and polarization conversion of EM waves, a series scheme of MM unit cell design is proposed. To study the EM response of MMs and explore the internal mechanism of unit cell structure, numerical simulation, experimental test and theory analysis are adopted; the main works and novel results of this thesis are listed as follows.1. Based on the cross structure, the single band, double band and broad band MMs absorbers are constructed. Firstly, the perfect MMs absorber is designed and verified by the simulation and experiment. Based on the theory of resonance circuit, we further studied resonance absorption frequency dependence to the geometric parameters of the cross structure by simulation. Secondly, based on the cross structure, the single layer co-plane dual-band, quad-band and multi-band perfect MMs absorbers are designed, and the corresponding equivalent circuit models are also proposed, and then numerical simulations have been carried out for the theoretical analysis and validation. Finally, based on the principle of superposition of multiple resonances, the multilayer cross structure absorbers are designed and verified by simulation and experiment. For the forty layers cross structure absorber with the absorbance of more than80%, the relative bandwidth is up to63.3%.2. The broadbanding design of the MMs absorber based on the lumped elements. The EM resonance and impedance matching characteristics of MMs can be effectively improved when the traditional MMs unit cell structure loading lumped elements, thusing enhancing the EM loss and broadening absorption band. Based on this idea, two broadband MMs absorbers using different resonators loaded lumped components are proposed, respectively. The corresponding equivalent circuit models are established, and using the S parameters inversion method to extract the equivalent EM parameters, and surface current distributions to explain its absorption mechanism of the unit cell structure, and using energy loss distribution to analyze the absorption characteristics. Finally, the designs are verified by experiments. For the design of the U-shaped structure loaded with lumped elements with the absorbance of more than90%, the relative bandwidth reaches81%. For the design of the four reopen ring composite structure loaded with lumped elements, absorbance is more than90%from2to6GHz. and the corresponding relative bandwidth is up to50%.3. The design of the chiral MMs with giant circular dichroism (CD), huge optical activity, enhanced transmission and negative refraction. Firstly, the planar chiral MMs based on a quad90staggered split ring pairs structure is designed, and the measured CD is up to0.58at resonance frequencies, meanwhile the structure also exhibits the negative refraction. Secondly, based on the Babinet principle, the complementary double layer planar U-shaped structure chiral MMs is designed, and the measured polarization rotation angle is up to83, the optical activity is significantly enhanced, meanwhile the structure also exhibits dual-band negative refraction. When the designed unit cell structure demonsion is further reduced, which also exhibit giant optical activity and dual-band negative refraction at infrared region. Finally, an ultra-thin double layer complementary conjugate structure chiral MMs is designed and verified by simulation and experiment. The designed chiral MMs not only eshibits giant optical activity and negative refraction, but also has strong transmission characteristics, and the transmission coefficient is up to0.87. The dependencies of the transmission coefficient, optical activity and negative refraction to the structural geometric parameters are also studied.4. The polarization transformers design based on the asymmetric structure planar chiral MMs. Firstly, a perfect dual-band circular polarization transformer based on circular asymmetric double split ring resonator (DSRR) structural chiral MMs. The design can transform incoming line polarized wave to a left-handed and right-handed polarized wave, respectively, and the circular polarization extinction ratio is more than30dB, which is verified by experiments. When the unit cell structure demonsion is further reduced, the designed chiral MMs also exhibit a perfect dual-band circular polarization transfromation at terahertz region. Then, a dual-band circular polarization and single band line polarization transformer based on a double rotate90square DSRR structural chiral MMs is designed, at resonance frequencies, the incoming line polarized wave can be transformed to left-handed and right-handed polarized wave, and crossed linear polarized wave, respectively. Finally, a broadband line polarization transformer (rotator) based on three layers staggered circular DSRR chiral MMs is designed and verified by simulation and experiment. The operation bandwidth has been significantly broaden, the measured polarization conversion rate is more than90%in the frequency range of5.5-11.1GHz, and the corresponding relative bandwidth reaches67.5%. The research of MMs absorber for manipulating EM loss laid a theoretical foundation for broadband design of novel absorbing materials, and also opened up a new path for the design and realization of high performance lightweight structural absorbing materials. The research of chiral MMs for manipulating EM transmission and polarization provides a wider space for the design and application of the novel planar chiral MMs and also provides an important theoretical guiding significance for the design of novel broadband polarization transformer. |
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