Investigation On Theaccurate Measurement Of Cylindrical Dimension And Refractive Index Of Gases By Microwave

In physics, temperature is a physical property of a system that underlies the commonnotions of hot and cold, which is one of the most important parameters that to determine thestatus of material. Thermodynamic temperature is the actual temperature of the material world,and thermodynamic temperature scale is the scaleplate of the thermodynamic temperature，thevalue of which is also the temperature of the material world. The unit of temperature Kelvin isone of the seven fundamental physical units in the international system of units (SI). Theaccurate measurement of the thermodynamic temperature and the Boltzmann constant is oneof the most important methods to determine the thermodynamic temperature scale andindependence of Kelvin on the physical property of real material. One of the basicallyfundaments to determine the Boltzman constant is to accurate measurement of the dimensionof resonator, and meanwhile the accurate measurement of the refractive index is the keyfactors that to accurataly determine the thermodynamic temperature by microwave resonanceas well as the refractive index thermometer.The microwave resonance technology has the distinguishing feature of high speed andaccurate method. Based on the theory of electromagnetic field and the microwavetechnology， the transformation and the distribution of microwave in the cylindrical resonatoris analyzed in the paper. Meanwhile, combining with the perturbation theory, the imperfectfactors including the skin depth of microwave and the duct which are the perturbations onfrequency is corrected. A cylindrical copper resonator with two needle antennas for theexcitation and coupling of microwave is designed. A adapter with low loss of signal isassembled on the pressure vessel，which reduce the relative uncertainty of the frequency tobelow10ppb and the half bandwidth to lower than0.2MHz. The temperature and pressuresystems with LabVIEW program are designed in order to idealize the automation ofcontrolling and data collection.The radius of the resonator from30℃to145℃are measured through the frequenciesof the modes TM001~TM004with the correction by the perturbation. In the same temperature,the relative deviation between the average radius and the measurement of each mode is within2×10-5. The accuracy of the measurement of the radius is within1μm，with the relativeuncertainty3.987ppm. The refractive index of nitrogen at40℃~145℃and50kPa~800kPa and argon at30℃and50kPa~870kPa are measured. The results show that the inconsistentbetween different modes is below1.8×10-4. At the same pressure, the refractive index isincrease with the temperature, and at the same temperature, it has direct ratio to the pressure.The dielectric constant which has direct relation to the refractive index is very closed to thepublished results determined by the virial coefficient of nitrogen and argon，with the relativedifference below20ppm.