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Using the Floating Mass Transducer (FMT) as a microphone – a possibility to develop a fully implantable CI?
18 April 2018 (online)
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.
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.
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.