Investigation of PCB generated Magnetic Field as an Acoustic Noise Source on Wearable Devices

Wireless earbud is the most sold wearable type in the consumer electronics market. As wireless earbuds offer more functionalities, the increased complexity and integration may introduce undesirable coupling between different components. One of the undesirable coupling is the magnetic coupling between the earbud main logic board (MLB) and the speaker coil. The low frequency current ripples on the MLB power rail may induce current with acoustic frequency components on the speak coil and lead to unpleasant audible noise. In this paper, the magnetic field generated by an earbud MLB is investigated through simulation with 3D FEM solvers and measurement with a low frequency H-field probe.