Magnetic circuit design by topology optimization for Lorentz force maximization in a microspeaker

Bipolar magnets are common in most magnetic circuits, but circuit efficiency can be enhanced if multipolar magnets are used instead. However, the use of multipolar magnets is rare. In this investigation, the possibility of using multipolar magnets for maximizing the Lorentz force in a microspeaker is considered. The design problem of a multipolar magnetic circuit is formulated as a topology optimization problem. The circuit design region is discretized by finite elements, and a material state among a multipolar magnet, a yoke and air for every element is so determined as to maximize a desired Lorentz force component. Numerical results show that multipolar magnetic circuits obtained by the topology optimization outperform a conventional bipolar circuit.