Metamaterials waveguide for electric space propulsion

Among the different types of propulsion systems used today, one stands out for its high specific impulse, extended burning duration, and great operational flexibility: electric propulsion. Unlike chemical propulsion systems, where the energy required to produce thrust is stored within the propellants themselves, whether solid or liquid, an electric propulsion system relies primarily on electrical energy. This energy, typically ranging between 500 watts and 1 kilo watt depending on the satellite, serves to convert a gas propellant, such as xenon or iodine, into plasma. The plasma is then directed and accelerated using an electromagnetic field. A widely adopted method for generating plasma is through the use of electromagnetic radiation in the microwave frequency range, specifically around 2.45 GHz. This radiation is delivered into the ionization chamber using waveguides and coaxial cables. This technology has also been successfully implemented in CubeSats, nanosatellites with a cubic shape,typically measuring 10 by 10 by 10 cm and weighing no more than 2 kilograms, based on the 1U CubeSat standard. However, the compact size and weight constraints of CubeSats pose significant engineering challenges when designing and building the entire propulsion system. Miniaturizing components offers a promising solution. When it comes to the systems that transmit microwave radiation, reducing the dimensions of the waveguides results in altered performance characteristics. Parameters such as cutoff frequency, operational bandwidth, and the proportion of transmitted and reflected power all change compared to standard-sized waveguides. To address this issue and gain greater design flexibility, this thesis presents a transition model between coaxial cable and circular waveguide where the cutoff frequency is reduced by up to 74% from 2.10 GHz down to 0.54 GHz, the S12- S21 parameters were maximized with an average percentage increase of +10.3% and the S11- S22 parameters were minimized by-46% through the use of metamaterials. These artificial materials can be engineered to exhibit the desired optical and electromagnetic properties. The thesis begins with a general introduction to electric propulsion, waveguides, coaxial cables, and metamaterials. Then, the mathematical model of the transition will be presented, followed by the same transition model that incorporates metamaterials. Finally, the results of the 3D simulations conducted using CST Studio Suite® software will be shown for both the transition model with metamaterials and the model without metamaterials. During these simulations, some geometric features of the transition are varied to gain deeper insights into its behavior. Specifically, the height of the coaxial probe inside the waveguide is varied between 36.28 and 26.76 mm; the position of the transition is changed from 55.74 to 72.55 mm; and the surface impedance of the metamaterial layer is modified between 376.73 Ω and 753.46 Ω.