Microengineered systems for the hearing impaired

To overcome some of the technical and cosmetic objections, several research teams, most recently Maniglia et al. (1995), have investigated the direct electromechanical stimulation of either the ossicular chain or of the oval window of the cochlea, by means of a device implanted in the middle ear. For a smaller group of hearing impaired, alternative temporal bone-conduction devices which bypass the outer and middle ear function, or cochlea implants to provide direct electrical stimulation of the auditory nerve, can be considered. An implantable device has only been developed to the feasibility study stage. Much of the work already carried out on the diaphragm of the microspeaker looks promising and a prototype device is ready for testing. Results from this will also go some way towards proving the study on the implantable device. New topologies of magnet and coil are possible and will be investigated for their potential to improve both devices. Clearly, if the SPL figures of the microspeaker are to be maintained, any reduction in the area of the diaphragm must be accompanied by an increase in its deflection. For some applications such a size reduction could prove to be essential and possible improvements to the diaphragm such as corrugating the edges may then be necessary