From: jeroen@nospam.please   
      
   Tom Del Rosso wrote:   
   > AIUI you use iron cores for low frequency and ferrite for high frequency   
   > because ferrite doesn't get magnetized, so why couldn't aluminum do the   
   > same?   
      
   You *want* a transformer core to be easily magnetized! You don't   
   want it to *stay* magnetized when the current goes to zero.   
      
   Iron is good in low-frequency transformers because it has a high   
   saturation field and high permeability, so you can get away with   
   relatively few turns for the windings. Its disadvantage is that it   
   is conductive, so there will be eddy current losses, which get   
   rapidly worse with higher frequency. Those losses can be reduced   
   by making the core out of thin insulated laminations, but this   
   gets impractical quite fast.   
      
   Ferrite has a lower permeability and lower saturation field, but   
   it's an insulator, so it doesn't sustain eddy currents.   
      
   That's the simple view. Magnetic materials are complicated and   
   lots of effort has been spent on finding the best materials for   
   specific applications. There are hundreds of different kinds of   
   magnetic materials, maybe thousands.   
      
   Jeroen Belleman   
      
   --- SoupGate-Win32 v1.05   
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