Indentation measurements on the eardrum with automated projection moiré profilometry

Computer modeling of middle ear mechanics is an important tool to investigate its complex behavior, but correct mechanical and elastic parameters are needed to obtain realistic simulations. A possible way to determine eardrum elasticity in situ is the use of point indentation measurements. The eardrum is, however, a small fragile membrane, so a non-contacting high-resolution technique is needed to measure the shape change caused by point indentation. We have developed a projection moiré interferometer combined with an indentation actuator and a high-resolution force sensor. The apparatus applies deformations up to 1 mm with a resolution of 1μm, while the indentation force is measured with a resolution better than 1 mN. The moiré setup delivers height data on 512×512512×512 points through phase-shifting, with a height resolution of 15μm. Shape recordings are made on a rabbit eardrum at different indentation distances, and indentation force is recorded simultaneously.