Magnetic field effect analysis of electromagnetic transducer for implantable hearing device

Purpose: Electromagnetic transducers are widely used for implantable hearing devices because they can be miniaturized, and their vibration intensity is suitable for middle ear stimulation. There are two types of electromagnetic transducers: a floating mass transducer (FMT) and differential floating mass transducer (DFMT). Both transducers have a permanent magnet and a coil to generate electromagnetic force. However, FMTs have disadvantage in that unwanted vibration can be generated in a static magnetic field, such as in MRI. Methods: In this paper, a magnetic field effect analysis of two types of electromagnetic transducers was performed. The torque that is generated by the static magnetic field has been calculated through finite element analysis (FEA). Then, the effects of the static magnetic field in both transducers were compared through an experiment based on the simulated results. Results: The results of FEA and the experiment show that the torque of the DFMT are smaller than that of the FMT in a static magnetic field. Conclusions: Therefore, it is expected that the DFMT is a suitable transducer for implantable hearing devices.