An Investigation of the Permeability of Iron at Ultra-High Frequencies

This thesis is the report of an investigation of the permeability of iron and its dependence on temperature at ultra high frequencies. The frequency used was 8,900 megacycles, the temperature range covered was from 50°C to 350°C, and two samples of iron were studied. Both samples were approximately 1½ x 1½ x 1¼ inches and made from standard Armco iron stock. Special heat treatment was used on one sample to remove impurities. The other sample was annealed but not purified. To measure the permeability the effect of an iron sample was compared with that of copper on the resonant length and the shape of the resonance curve when used as end plates of the resonant cavity. This technique eliminated the effect of the other parts of the cavity on the measurements made. Two values of permeability are obtained, µL and µR. The first is obtained from measurements of resonant length while the second is determined from measurements on the shape of the resonance curve. How the two values of permeability are obtained from the measurements made is derived under Theory of Measurement. For the sample of Armco iron purified by special heat treatment µR varied from 80 to 35 in the temperature range 50°C to 300°C. For the annealed iron sample µR varied from 67 to 17 in the temperature range 50°C to 360°C. Values of µL were obscured by the large probable error that resulted from the type of cavity used in the experiment, but all values were less than ten.