Detection of movement of ossicular bones using a micro electromechanical system

In a typical cochlear implant design, the sound detection (a microphone) and transmission unit of the implant is placed at back of auricle. This unit transmits audio signals into the electronic system consisting of amplifiers and electrodes that excite the nerve endings in the cochlea. This design has several drawbacks, firstly the subject cannot bath or swim comfortably with the microphone unit on, and secondly having an external attached unit which may be visible is cosmetically disturbing feeling. In this study, we explore the idea of obtaining the acoustic signal that would drive the cochlear nerves (through the implant system) directly from the vibrations of the ossicles. In most of the cases where implant use is recommended, the cochlear nerves are damaged due to genetic reasons, traumas, infections (e.g. otitis media), being exposed to excessive noise, tumors, etc., however the audio sensory part of the hearing system, consisting of eardrum and 3 ossicles, is still functioning. My novel idea is to place or attach a micro-electro-mechanical-system (MEMS) type of tiny and lightweight accelerometer to sense or detect the vibrations of ossicles, namely malleus, incus and stapes. A quick analysis or first-thought reveals that physically longer extension of the incus is the most suitable and/or convenient place to attach such a sensor. One can imagine the difficulty of physically working or experimenting with such a tiny and delicate system, especially if it is a humanly system. Therefore, in an attempt to test the feasibility of our idea we have carried out some simulations studies on a realistic mathematical model of human ear first. The model we have adopted has been optimized to match the amplitude and phase response of the human ear from system analysis point of view, and used frequently in literature to study/mimic different disease conditions of the ear, such as otosclerosis. We have designed some simulation experiments to run on this mathematical model to study and understand possible loading effects of placing a sensor on the incus. Our preliminary results indicate that we can place a sensor of weight about 5 mg without seriously effecting amplitude and phase response of the ear. This study is yet another example of how simulations of physiological system can be advantageous and facilitating in design of biomedical systems. In the forthcoming phases of our "microphoneless" cochlear implant design project/effort, we will actually have a MEMS lab custom design a sensor with our specifications and test it on real subjects after obtaining required ethical committee approvals.