Three-dimensional digital scanner based on micromachined micromirror for the metrological measurement of the human ear canal

Manufacturers of hearing aids have made initial testing of rapid prototyping of hearing aid shells using laser scans of ear impressions, but they have not performed any actual scans of the human ear canal. We report the direct scanning of the human external auditory canal by using an electromagnetically actuated torsion micromirror fabricated by using a micromachining technique as the scanner. This demonstrates the actual scanning of the human external auditory canal by a single integral microelectro-optical- mechanical system (MEOMS). A prototype three-dimensional (3D) scanning system was developed: It is based on the acquisition of optical range data by a conoscopic holographic laser interferometer using an electromagnetically actuated scanning MEOMS micromirror. A fabrication process, based on a poly(methylmethacrylate) sacrificial layer for the fabrication of a free-standing micromirror was used. Micromirror actuation was achieved by using a magnetic field generated with an electromagnetic coil stick. The micromirror and electromagnet coil assembly compose the opto-mechanical scanning probe used for entering the auditory canal. Based on an actual scan map, a 3D reconstructed digital model of the ear canal was built using a surface point distribution approach. The prototype system allows a no-invasive 3D imaging of the ear canal with spatial resolution in the 10 μm range. Fabrication of two complete hearing aids from in vivo ear canal scanning is also accomplished.