摘要:

Previous experiments have indicated that the magnetic permeability of sintered iron compacts is to a large extent determined by the final density of the compact. The permeability of five different iron powders has proved to be independent of the origin of the powder, if the compacts were sintered at the same temperature. The results were compared with the theory of Polder and Van Santen and agreed very well with their predicted curve, if the residual pores were assumed to be flat disks. It could be expected that at higher sintering temperatures, the disk‐shaped pores would change into a more equiaxed or spherical shape.Experiments to check this theory have been made, and the results are in good agreement. Compared for identical densities, the permeability of different iron powders is appreciably higher if sintering is done at 1250–1350°C and for 24 hours, instead of at 1150°C for one hour. Different powders, however, now show quite different permeabilities, which could be explained by a different inclination of the powder to form spheroidal pores.It is shown that coining after high temperature sintering brings the permeability values back to the curve of the disk‐shaped flat pores. The effect of the increase in permeability at higher temperature cannot, therefore, be due to a purification process, but must be attributed to a change in the pore shape.

ISSN:0021-8979    

DOI:10.1063/1.1698513

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Calculations are carried out which show that, because of the smallness of the cathode spot, the cathode is not able to dissipate the heat generated with heavy currents by conduction. Therefore, a much higher vaporization of cathode material per coulomb occurs for heavy currents than for low currents.

ISSN:0021-8979    

DOI:10.1063/1.1698514

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The present work contains an investigation of the e.m.f. method to determine the input impedance of a thin biconical antenna as first suggested by Schelkunoff. By considering the various components of the currents flowing on the antenna, it has been shown that the sinusoidal part is, indeed, the dominating component among all these currents. An investigation of the total current at the end of the antenna, where the lateral surface of the cone and the spherical cap meet, shows that the current is not identically zero at that point, but vanishes as the reciprocal of the square of the characteristic impedance of the cone. The two approximate expressions of the complex conjugate power used in the e.m.f. method are derived, as well as the exact expression. Computation of some integrals occurring in the formulation is also treated in detail to show the various approximations involved.

ISSN:0021-8979    

DOI:10.1063/1.1698515

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698518

出版商:AIP    

年代:1949

数据来源: AIP