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# Loudspeaker

Problem type:
Axisymmetric problem of magnetostatics

Geometry: Given:
Permanent magnet coercive force: Hc = 500 kA/m
Current of coil I = 1 mA
Coil turns N = 100
Magnetic permeability of core - B-H curve:

Calculate inductance of the loudspeaker coil taking core saturation into account.

Solution:
Inductance of the coil is calculated as L = Ψ/(I*N) * N², where Ψ - coil magnetic flux, I*N - total coil current, N - number of turns.
Magnetic state of the core affects the inductance value. The problem is solved in two parts. First the magnetic field of the permanent magnet is simulated and the core permeability (magnetic state) is calculated. The magnetic state is then imported in the second problem. In the second problem the magnetic field of the coil is simulated and the inductance is calculated. Result:
Coil inductance L = 8.4·10-9/(0.001*100) * 100² = 0.84 mH. • Video: Loudspeaker 