The concept of a single frequency band, single high-refractive-index metamaterial has been extended and applied in the design of dual frequency band, dual high-refractive-index metamaterials in the THz regime. The structure design consists of twenty five unit cells with a surface area of 250 um by 250 um and a thickness of 5 um. Each cell has metallic structures embedded in a polyimide substrate. The return loss (S-parameter) analysis shows two strong electric responses at two frequency ranges, and the extracted constitutive parameters suggested high values of simultaneous dielectric constant and permeability at these frequencies. Results retrieved from the S-parameters also show high refractive index values. A first peak refractive index of 61.83 was observed at a resonant frequency of 0.384 THz, and another peak refractive index of 19.2 was observed at the resonant frequency 1.416 THz. Analysis show that higher refractive index at the second resonance frequency band is achievable through redesign of the structures, and modifications could lead to a single structure with multiple frequency, multiple high-refractive-index metamaterials that can be put to practical use.

A multiband metamaterial operating in the 0 THz to 2 THz range was designed with two high refractive index values. The dimension of the slab of the metamaterial is 300 um by 300um and the thickness is 17.45 um. Twenty five resonant metallic structures were placed in the substrate material, with a gap of 1.2 um between each unit. Results show enhanced dielectric response as well as suppressed diamagnetic response at these frequencies, which exhibit high permittivity and high permeability. Two bands of high refractive index were observed in the FDTD simulation result.

A comparative study and analysis of the simple and multiple-turn railgun systems from an engineering perspective is presented. The simple railgun system, which has only one pair of rails to let the electric current through, needs very high current source to work effectively, usually from several hundreds of kA to several MA. Construction of a power supply of this magnitude is a technological challenge in itself. A multi-turn railgun on the other hand, which has subdivided rails as the current paths, can greatly reduce the magnitude of the driving current to produce the same electromagnetic force. As a result it lowers the scale and cost of the power supply and broadens the application of the electromagnetic launch technology under certain circumstances. However, multiturn railgun also gives rise to some technical problems, such as degradation of the system efficiency and complication of the mechanical structure. For an efficient device one needs to optimize the two systems and find a balance in the design parameters incorporating both the systems. Current and future work at the University of Missouri is also described.

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