Abstract
To better understand the phenomena of various thrust outputs with constant energy input in the RF Resonant Cavity Thruster, a theoretical space travel propulsion system, the impact of microstructural variations in the cavity material was investigated. Specifically, copper samples with various grain sizes were tested for RF (microwave) reflectivity. The device studied, also known as the EmDrive, is constructed of a copper material. It is hypothesized that variations in the grain size of the copper will produce variations in reflected output to microwave inputs, resulting in a possible explanation for differences in output thrust. Copper samples with varying grain size were examined. The two specimen sizes were 1/2-inch x 1/2-inch x 1/8-inch and 3-inch x 3-inch x 1/8-inch. Samples were heat-treated in a NEY 6-525 programmable oven. The samples were polished and etched to expose the grain vi structure prior to microscopy. The small samples were also mounted for microscopy. The grain size of the samples was determined using the ASTM E112 intercept method and verified using calibrated Motic Images Plus software. Once the sample grain size was determined, samples were re-polished in preparation for microwave reflection experiments. Microwave reflection data were collected in an anechoic chamber using Windfreak Technologies SynthUSB II 3.5 MHz-4.4GHz Radio Frequency Synthesizer was used with an Altelix panel antenna to generate the appropriate frequency incident input, the output signal from the specimen was then measured by a second Altelix panel antenna and an RF Instruments Spectrum Analyzer. Raw data were collected via RF Instruments software provided with the hardware. The size of samples 1 through 6 made it difficult to ensure that the variations in reflectivity recorded were due to the samples themselves, which is why the second set of larger samples were made. A few trends indicating a possible relationship between annealing and reflectivity, and grain size and reflectivity were noted. Further research should be completed to validate these trends.