. 21 A simple linear mechanical system. , L where di 1 + Ri + ∫ idt = e dt C e is the instantaneous induced voltage (EMF) and i is the instantaneous current. , mechanical and electrical systems. In the mechanical system, energy stored in the mass is given by the kinetic energy storage occurs in a spring from the displacement terms of a spring constant x = ∫ vdt due to a force. This force is expressed in ks , as f x = k s x = ks ∫ vdt . 5mv 2 . 26) J A viscous friction element, such as a dashpot, is an energy dissipating element.

The fringing flux in the air gap has been neglected. 16) Bg in a given air gap volume Vg is directly proportional to the ( BM H M ) and the volume of magnet VM = 2hM wM lM . Following the trend to smaller packaging, smaller mass and higher efficiency, the material research in the field of PMs has focused on finding materials with high values of the maximum energy product ( BH )max . The air gap magnetic flux density Bg can be estimated analytically on the basis of the demagnetization curve and air gap and leakage permeance lines and recoil lines (Appendix A).

Barium and strontium ferrites were invented in the 1950s. A ferrite has a higher coercive force than that of Alnico, but at the same time has a lower remanent magnetic flux density. C. The main advantages of ferrites are their low cost and very high electric resistance, which means no eddy-current losses in the PM volume. c. ) and electric toys. Ferrites are produced by powder metallurgy. Their chemical formulation may be expressed as , MO × 6(Fe 2 O3 ) where M is Ba, Sr, or Pb. Strontium ferrite has a higher coercive force than barium ferrite.