TABLE OF CONTENTS Materials with a permeability greater than one concentrate magnetic fields and increase flux linkage, therefore increasing inductance for a given inductor size. Silicon-steel and nickel-iron alloys with permeabilities up to 100,000 are available. However, as the frequency is increased, eddy currents induced in the material introduce significant losses. To reduce eddy-current losses, the core is subdivided by winding tape as thin as a thousandth of an inch or less. Even so, above about 1 MHz, eddy-current losses become prohibitive. At higher frequencies, a more successful strategy for preventing eddy-currents is to form cores by pressing together magnetic-material powders in an insulating binder. Representative commercial core materials for high-frequency use, their permeability relative to air, ? r, and useful operating frequency range are given in Table 3-4.
| ? r | Amidon | Fair-Rite | Ferrox-cube | Indiana General | Magnetics | Micro-metals | Stack-pole |
|---|---|---|---|---|---|---|---|
| 1 | #0 | ||||||
| 4 | #12, #17 | ||||||
| 6 | #10 | ||||||
| 7.5 | C/14A | ||||||
| 8.5 | #6 | ||||||
| 9 | #4, #7 | ||||||
| 10 | #2 | ||||||
| 12.5 | C/14 | ||||||
| 16 | Q3 | ||||||
| 20 | #68 | #1 | |||||
| 25 | #15 |
