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Magnetostatic speaker

QuickField simulation example

Magnetostatic speaker consists of a set of permanent magnets and a planar diaphragm. Aluminum strips carrying current are attached to the diaphragm.

Engineering question
How to find magnetostatic speaker magnetic field?

Engineering answer
Set up a plane-parallel QuickField DC Magnetics problem for a magnetostatic speaker and evaluate magnetic field distribution from computed field results.

Typical applications
planar magnetostatic speakers, flat-panel loudspeakers, permanent magnet audio drivers

Problem Type
Plane-parallel problem of DC magnetics.

Geometry
Magnetostatic speaker Magnetostatic speaker consists of a S N S N Mylar foil Aluminum strips I+ I-

Given
Permanent magnet coercive force HC = 500 kA/m;
Current I = 0.1 A
Lz = 1 m

Task
Calculate force acting on a diaphragm.

Solution
In real device the AC current flows in the strip. Peak force value depends only on the current magnitude, and does not depend on frequency. This allows us to simulate DC problem instead of AC to calculate peak force value.
Due to model symmetry we can reduce simulation domain.

Results
Magnetic force acting on a strip of the diaphragm is 0.033N per 1m of strip z-length.
Magnetic flux density distribution in magnetostatic_speaker

Reference: Wikipedia: Magnetostatic loudspeaker