Application of piezoelectric multi-layered actuator to floating mass transducer for implantable middle ear hearing devices

Implantable middle ear hearing devices (IMEHDs), which have been developed since the 1970s, directly stimulate the middle ear and can realize a high efficiency of sound transmission with better sound fidelity. For such kinds of IMEHDs, this paper presents the design and application of a piezoelectric floating mass transducer (PFMT) using a PMN-PT multi-layered actuator as a new type of vibrating transducer. The proposed PFMT consists of only three components of a multi-layered piezoelectric actuator, a metal case, and a clamping clip. The actuator's one side is connected with the metal case and the other side is linked to the clamp for the attachment to an incus long process of middle ear ossicles. The vibration displacement of the PFMT attached to the incus is studied theoretically by simplified kinetic model between the PFMT and the incus. Through an in-vitro experiment using a human temporal bone, it has been verified that the proposed PFMT can generate the vibration force equivalent to the sound pressure of about 100 dB SPL. Therefore, the proposed PFMT is expected to be used as an IMEHD transducer with the advantages such as simple surgical implantation, no interference from external electromagnetic fields, and improved productivity.