FERRITE CORE INDUCTORS 291 



metallic core coil. Ferrite coils, on the other hand, have been made 

 having Q's as high as 1000, and inductors with Q's between 500 and 

 600 are available commercially. 



2. Formulas have been derived which show how ferrite can be used 

 to realize the best inductor characteristics in the smallest volume. The 

 1509 type inductor, for instance, is only about 1/3 as large as the nearest 

 equivalent permalloy core coil, yet its Q is over twice as high. 



3. It is physically practicable in ferrite coil designs to include in- 

 ductance adjustment facilities to meet a wide range of requirements. 



It should not be concluded that the day of metallic cored inductors is 

 over. For power applications, especially those involving direct current, 

 present-day ferrites are inferior to silicon iron and permalloy. At voice 

 frequencies there are many applications for which ferrite is, at best, no 

 better than some of the older materials, although in others it has dis- 

 tinct advantages. In higher frequency ranges, however, and especially 

 for low power level applications, the advantages of ferrites are out- 

 standing enough to justify the expectation that they will largely replace 

 the older iron and nickel-iron powders. 



ACKNOWLEDGEMENTS 



The development of ferrites and their application to inductors has 

 been carried out by several teams in Bell Telephone Laboratories, in- 

 cluding J. H. Scaff, F. J. Schnettler and their associates in the metal- 

 lurgical department, V. E. Legg and CD. Owens in the magnetic ap- 

 plications group, and S. G. Hale, R. S. Duncan and others in the 

 inductor development area. I don't know who was first to conceive of 

 using ''dissipation factor" instead of "Q" to simplify his mathematics, 

 but it was not the author. Equation (24) is derived by inserting l/Dr, 

 for Q in an expression originally worked out by P. S. Darnell. 



REFERENCES 



1. Legg, V. E., Survey of Magnetic Materials and Applications in the Telephone 



System. Bell Sys. Tech. Jl., 18, pp. 438-464, July, 1939. 



2. Legg, V. E., and F. J. Given, Compressed Powdered Molybdenum Permalloy, 



Bell Sys. Tech. JL, 19, pp. 385-406, July, 1940. 



3. Snoek, J. L., Non -Metallic Magnetic Materials for High Frequencies, Philips 



Tech. Review, 8, pp. 353-360, December, 1946. 



4. Wien, M., tlber den Durchgang schneller Wechselstrome durch Drahtrollen, 



Ann. D. Phys. [4], 14, P. I, 1904. 



5. Edwards, P. G., and L. R. Montfort, Type-0 Carrier System, Bell Sys. Tech. 



JL, 21, pp. 638-723, July, 1952. 



6. Legg, V. E., and C. D. Owens, Patent Application Serial No. 184602, Filing 



Date — 9/13/50. 



7. Hale, S. G., and C. W. Nuttman, Patent Application Serial No. 263564, Filing 



Date — 12/27/51 . 



8. Duncan, R. S., and H. A. Stone, Patent Application Serial No. 262248, Filing 



Date — 12/18/51. 



