Magnetic dust cores

Magnetic dust cores for inductances operating above power frequencies are manufactured from very finely divided magnetisable material, each metal particle being insulated from all its neighbours. The metal powder is of such a fine subdivision that it is commercially known as metal dust. Dust cores for radio work, until recently known as High Frequency Iron Cores, are dealt with in detail, while dust cores for telephone work are omitted unless their treatmentis essential for the tracing of development trends and theories. The historical development is outlined and the need for planned research on metal dust and core problems is stressed. Permeability and loss analysis are discussed, and the need for standard test specifications stated. The relative value of the mathematical loss calculation and the graphical loss analysis methods based on the calculations are reviewed and their accuracy examined. The application of different radio core types is set out and a table of preferred applications is given and discussed. The influence of magnetic dust core developments in connection with i.f. filter design and push-button tuning is described, together with practical implications of permeability tuning. The technological aspect is considered and plant used for the production of dust cores mentioned. The mechanical and electrical tolerances are stated after a survey of suitable metal dusts indicating their useful application.