Negative Refractive Index Of Microwave Media Design Research

Negative Refractive Index Materials (NRIM) is a kind of substance with negative permittivity and permeability simultaneously. NRIM have some interesting and unusual EM transmission and refraction properties which mean that they will have broad potentialities in both military and civil applications. The research work of this dissertation was supported by the National Natural Science Foundation of China which has presented a novel approach to design NRIM by incorporating metal wire array with negative effective dielectric constant into ferrimagnet such as YIG whose permeability is negative when an external magnetic field applied. The main research activities and innovative achievements gained are as the following:1. A composite medium having a negative refraction index in C band was designed, and its effective electromagnetic properties was computed analytically base on the effective medium theory. The result shows that the effective permittivity and permeability of the composite medium are negative simultaneously in a C-band frequency region where the effective permittivity is negative in the frequency range from 5.587 GHz to 6.149 GHz and the effective permeability is negative in the frequency range from 5.269 GHz to 7.332 GHz. It demonstrates the effective refractive index of the designed composite medium is indeed negative and ascertains the proposed method synthesizing microwave substance of negative refraction index is viable.2. The electromagnetic (EM) properties of the designed composite medium have been simulated by use of EM EDA package based on time-domain finite integration method. The simulation results show①the effective permittivity of the designed metallic wire array is negative in the frequency range from 7.02 GHz to 9.80 GHz,②the permeability of YIG substrate immersed into an external magnetic field is negative in the frequency range from 5.22 GHz to 8.14 GHz,③EM wave can pass through the composite medium synthesized by the above designed metallic wire array and YIG substrate, and④the negative refraction behavior occurs on the interface between the composite medium and the normal material with positive refractive index in 7.51-8.13 GHz frequency range, in which the effective permittivity of the metallic wire array and the permeability of YIG substrate are negative simultaneously. The full wave simulation results have demonstrated the effective refractive index of the designed composite medium is indeed negative and ascertained the proposed approach to design microwave medium with negative refractive index is valid.3. Two types of magnetic-field-provider have been designed and fabricated for providing the external magnetic field applied to ferrimagnet-YIG. One is DC magnetic-field-provider based on A3 steel, and the other one is AC magnetic-field-provider based on ferrite. The performances of the implemented magnetic-field-providers have been measured systematically. On the plane of 92 mm×92mm within gas-gap, the field magnitude of DC magnetic-field-provider operating at a DC current of 3.56 ampere is from 2570 Gs to 2600 Gs, the field magnitude of AC magnetic-field-provider operating at a DC current of 5.99 ampere is from 2480 Gs to 2510 Gs, the field magnitude ripples of DC and AC magnetic-field-providers are all less than 30 Gs. It shows the measured performances of two kinds of magnetic-field-providers satisfy the design specifications.4. A test apparatus used to measure EM wave propagation properties in NRIM and EM wave reflection properties on the interface between NRIM and the normal material with positive refractive index has been designed and manufactured successfully. The EM wave propagation properties in a NRIM formed by the array structure of metallic wires and split ring resonators have been measured and investigated experimentally by use of the implemented apparatus. The experiment results ascertain the developed test system and measure method are viable and reliable, it can be used to experimentally study EM wave properties in NRIM based on ferrimagnet-YIG and metallic wire array in the next step.