Design, modelling and analysis of a novel implantable bone conduction hearing aid with a piezoelectric actuator

Koyuncu, Anıl
This thesis study proposes a novel bone conduction (BC) transducer design, which intends to overcome the drawbacks of conventional bone conduction hearing aids (BCHAs). A piezoelectric actuator design with a rhombus-type mechanical amplifier is chosen as a BC transducer in the first step, and a commercial amplified piezoelectric actuator (APA) is selected for trials. The dynamics of the mechanical amplifier and embedded stacked piezoelectric actuator are formulated separately based on linear analytical approaches. The output displacement of the coupled system is then calculated using linear vibration analysis under low harmonic voltage inputs. Based on the linear analytical model, a new APA is designed as a BC transducer with an attached tip mass, and the new APA prototype is manufactured. Constant-voltage amplitude stepped-sine tests indicate strong softening nonlinearity with the jump phenomenon observed in the frequency response at high voltage levels. Therefore, an accurate dynamical model of an APA is obtained by using a recently developed nonlinear system identification method, namely Response-Controlled stepped-sine Testing (RCT). Then the describing function of the predicted nonlinearity is identified by using describing surface method (DSM), and a nonlinear multi-degree of freedom (MDOF) model is obtained by substructure coupling of the APA and the attached tip mass. Based on the simulation results of the nonlinear MDOF BCHA model, the tip mass of the BCHA prototype is adjusted. The transmitted force-frequency response tests are performed with the optimized BCHA prototype attached to Brüel and Kjær (B&K) type 4930 artificial mastoid in order to validate the nonlinear MDOF BCHA model and compare the performance of the proposed BC transducer design with a conventional electromagnetic bone vibrator (Radioear B71). Finally, hearing threshold tests are performed on normal hearing participants and hearing-impaired patients with the BCHA prototype and the B71 bone vibrator. It is observed that the difference in the threshold level spectrum between the BCHA prototype and the B71 bone vibrator is consistent with the difference in the transmitted force level spectrum obtained from the artificial mastoid tests Consequently, in the thesis study, a novel BCHA transducer is proposed based on a miniature stacked piezoelectric actuator used as a BC transducer for the first time. The sophisticated dynamics of the proposed BCHA transducer are modeled by employing linear modeling and nonlinear identification. By virtue of recently proposed nonlinear dynamic modeling techniques, valuable contributions have been made to the limited body of knowledge on the nonlinear dynamics of APAs. It is demonstrated that the nonlinear dynamics of the BCHA can be captured accurately by the proposed methodology, which can be presented as an exceptional method in the pre-clinical performance evaluation of BC hearing implants.


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Citation Formats
A. Koyuncu, “Design, modelling and analysis of a novel implantable bone conduction hearing aid with a piezoelectric actuator,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.