Using the Floating Mass Transducer (FMT) as a microphone – a possibility to develop a fully implantable CI?

Introduction: Loudspeakers and microphones share common characteristics. Consequently, in early intercommunication systems loudspeakers were used as microphones. Utilising the FMT of the Vibrant®Soundbrige® (VSB) as a microphone has interesting potential applications such as within fully implantable CI. Material and Methods: Using an earcanal-eardrum-model, measurements were recorded using the FMT as a microphone via the Direct-Drive-Stimulator. Standard pure tone- and CCITT-signals from 250 Hz up to 8 kHz and Click- and Chirp-Signals were generated via an intra-aural earphone (EAR3A) and recorded and analysed using a professional Digital Audio Workstation (Studio One, Presonus). Additionally, soundtracks and speech-signals were also recorded. Results: The signal to noise ratio was good over the entire frequency range. Optimal sensitivity was obtained at 1,5 – 2 kHz and decreased at lower and higher frequencies. Recordings of music and speech-signals were also clear and comprehensible. Discussion: It is possible to use the FMT as a microphone. The frequency response is nonlinear which could be balanced in this setup using an EQ. The FMT as a middle ear microphone is an interesting new potential application. Temporal bone measurements are currently being performed. Publication History Publication Date: 18 April 2018 (online) © 2018. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/). Georg Thieme Verlag KG Stuttgart · New York