MEMS piezoelectric energy harvester for cochlear implant applications


Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Mechanical Engineering, Turkey

Approval Date: 2013

Student: LEVENT BEKER

Co-Supervisor: HALUK KÜLAH, HASAN NEVZAT ÖZGÜVEN

Abstract:

This thesis proposes a novel method for eliminating the battery dependency of cochlear implant users. The proposed method utilizes a MEMS harvester mounted onto the eardrum. The harvester converts the vibrations of the eardrum to electricity and supplies the generated electricity to the cochlear implant; thus, reducing the battery replacement/recharge problems. As an extension of the proposed method, by utilizing a multi-frequency harvester, electricity can be generated while sensing the frequency of the vibration. By transferring the generated electrical signals to corresponding regions inside the cochlea, au ditory nerve can be stimulated. Thus, a fully implantable and self-powered cochlear implant can be realized with the harvester, which electromechanically mimics the operation of cochlea. Modeling, design, and optimization studies are conducted by considering operational conditions. Due to comparable mass and stiffness parameters of the eardrum and the harvester, structures are coupled using finite element method (FEM). Initially, the harvester is modeled, and a macro-scale prototype is fabricated for verification. Then, a membrane model is developed utilizing FEM. Eventually, these structures are coupled and optimized. Among possible methods for fabrication of piezoelectric energy harvester, bulk piezoceramics is preferred due to its high strain coefficients and high output power potential. A fabrication method is implemented to integrate piezoceramics into MEMS. The fabrication process involves low-temperature bonding and thinning processes. Finally, the fabricated devices are tested, and it is shown that the harvester is capable of supplying electrical power of 1.33 μW at 0.1g while resonating at its resonance frequency of 474 Hz.