Fabrication and optimal design of differential electromagnetic transducer for implantable middle ear hearing device

A differential electromagnetic transducer (DET), with similar frequency characteristics to those of a normal middle ear, is designed and implemented for use in an implantable middle ear hearing device (IMEHD). To optimize the characteristics of the DET that depend on the electromagnetically forced vibration, a theoretical analysis is conducted to design the vibrating part. The electromagnetic force of the DET is simulated according to the design parameters of the coil size using a finite element analysis (FEA). As a result, the maximal vibration force is achieved when the optimal length and thickness of the cylindrical coil is 70% of the length of the magnets and 56% of their radius. The vibration characteristics of the DET are then simulated when applying the maximal force. The optimally designed DET is implemented using MEMS technology and vibration experiments carried out with the fabricated DET in an unloaded state. The vibrating displacement of the DET is about 200 nm within a range between 0.1 and 1.5 kHz when a current of 1 mA rms is applied to the coil. To investigate the usefulness of the DET, in vitro and in vivo experiments are conducted using the ossicular chain of a cadaver and guinea pig, and the results verify that the implemented DET performs well as a transducer for an IMEHD.