| The research on electromagnetic theory,structural design,characteristic analysis of metamaterials and mechanism.It is of great significance to promote its application in the fields of electromagnetic interference,electronic countermeasure,and electromagnetic stealth.The main content of this paper is to optimize the design of metamaterials and study their electrromagnetic functions.The method of electromagnetic field numerical simulation,electromagnetic theory analysis and microwave experiment verification is adopted.Research and design of metamaterial absorber,metamaterial polarization converter and adjustable metamaterial.The main work and achievements are as follows:(1)Two kinds of metamaterial absorbers are proposed and designed to meet the demand of multi-frequency and broadband in electromagnetic stealth technology.Firstly,a wide-angle multi-frequency metamaterial absorber is proposed.When the incident microwave increases from 0°to 45°,the absorber can almost achieve perfect absorption at three frequency points of 5.92GHz,6.12GHz and 8.54GHz.The surface current at three frequency points exhibits that the electromagnetic absorption at 5.92GHz and 6.12GHz is mainly caused by the electromagnetic resonance,and the electric absorption at 8.54GHz is caused by the magnetic resonance.The simulation results show that the proposed absorber is insensitivity to polarization.This method can provide reference for the study of multifrequency or even wide-band metamaterial absorber.Based on the above study,a wideband metamaterial absorber composed of sloped metal wire loading lumped resistors is proposed with wide band,wide angle and polarization insensitivity.The simulation results show that the absorptance of the designed absorber is more than 80%between 1.3GHz and 3.51 GHz.The correctness of the simulation results is verified by the microwave experiment,and the error between the simulation results and the experimental results is analyzed in detail.The mechanism of wideband absorption is discussed using equivalent circuit,equivalent impedance,surface current distribution,electric field energy distribution and magnetic field energy distribution.(2)Reflection and transmission polarization converters are designed for different application scenarios of electronic countermeasure and electromagnetic interference.The polarization conversion performance of the polarization converter can be changed by changing the structural parameters of the polarization converter based on the classical sandwich structure of metal film-dielectric-metal film by combining the resonance ring with the metal strip.A wideband microwave linear polarization converter based on split ring is designed,and it is working on reflected mode.The vibration direction of the polarization wave can be rotated by 90° in the wide band range of 19.2-3 7.1 GHz.According to the distribution characteristics of current on the surface of the metal film,magnetic resonance exists in the medium,which generates an electric field perpendicular to the incident polarization wave,which indicates the polarization conversion principle of the structure.Microwave experiment verifies the correctness of the simulation results.In the second part,a linear polarization conversion device based on metal grating and metal split ring is designed.The polarization conversion device is realized by asymmetric combination of chiral metamaterials working on transmission mode.Simulated results that it can achieve efficient polarization conversion in the frequency range of 6-36GHz,and the polarization conversion rate is above 98%.The results show that the transmission polarization conversion device has the characteristics of wideband asymmetric transmission,high efficiency and insensitive to incident angle.Similarly,experiment verifies the correctness of the simulation results.(3)Two kinds of tunable metamaterials loaded with lumped elements were designed for multifunctional applications.One is a wideband tunable absorbing/transmission metamaterial loaded with lumped resistance.The metamaterial is composed of a transmission layer with switchable frequency and an impedance layer isolated by an air layer.The metamaterial has the characteristics of insensitivity to polarization,wide band absorption and wide-angle incidence.The proposed metamaterials can switch between two wave transmittance frequencies:high frequency wave transmittance state(PIN diode on),absorption band range is 3.1 GHz-7.2GHz and 9GHz-10GHz,transmission frequency is 8.8GHz,transmittance is 50%.Low frequency wave transmittance state(PIN diode off),absorption band range of 3.1GHz to 5.5GHz and 6.66GHz to 9.67GHz,transmission frequency is 6GHz and transmittance of 45%.The other is a low frequency and wide band polarized tunable metamaterial designed by loading metal grating structure diode,which can independently control the transmission characteristics of horizontal and vertical polarized electromagnetic waves.The polarization regulation characteristics of transmitted wave in the range of 0.3GHz-3GHz are verified by simulation and experiment.The tunable metamaterial can be used in electromagnetic wave radiation and polarization sensing research combined with antenna based on its four working states.In this thesis,by means of simulation design,theoretical analysis and experiment,we have studied the multi-frequency absorption,wide-band low-frequency absorption,wide-band reflection and transmission polarization conversion and tunable metamaterial loaded with lumped elements.The designed metamaterials can be used in many fields such as electromagnetic stealth,antenna,etc. |
PDF Full Text Request