Design and Development of a Tri-Coil Bellows Transducer for RW-Drive Implantable Middle-Ear Hearing Aid Using FEA

We describe the design and development of a tri-coil bellows transducer (TCBT) for use in an implantable middle-ear hearing aid for round window (RW) drive. The TCBT provides easy implantation and a better frequency response than previous RW middle-ear transducers. It consisted of three cylindrical coils, a bonded magnet, and a tiny bellows with multiple corrugations. The simulation started with the calculation of the vibrational force required for the RW-drive transducer. Based on the anatomical structure of the RW niche and its volume, the designed TCBT was 1.75 mm in diameter and 2.3 mm long. To maximize the electromagnetic force of a TCBT installed within the limited volume of the RW niche, its structure was designed using an electromagnetic analysis based on finite-element analysis to determine the each length of the three cylindrical coils and the bonded magnet inside the TCBT. Additionally, the resonance frequency characteristics of the TCBT were determined using mechanical vibration analysis. A prototype TCBT was fabricated according to the simulation results, and an experiment to evaluate its vibrational characteristics was performed with the TCBT in an unloaded condition. Finally, the performance of the TCBT for use in RW-drive implantable middle-ear hearing aids was confirmed in experiments with cadaveric temporal bones.