A magnetic probe to study the vibration of the tympanic membrane: Experimental aspects

The study of the dynamics of the human tympanic membrane is important for better understanding of the hearing mechanism of the normal and reconstructed middle ear. A middle ear implant, for instance, needs to have the same transmission properties as a normal human middle ear. The transmission properties are determined by evaluating the transfer function of the middle ear, which is determined by measuring the displacement amplitude at both the input (tympanic membrane) and the output (stapes footplate) of the system. On the other hand, in general any pathology that affects the middle ear results in changes in the vibration amplitude of the tympanic membrane. An otosclerosis, that is a fixation of the ossicular chain of the middle ear results in a stiffening of the tympanic membrane, and therefore in a decreasing of the displacement amplitude. On the contrary, a disarticulation of the ossicular joints results in an increasing of the compliance at the tympanic membrane. In this paper a new magnetic probe based on a magnetoresisitve sensor is proposed to study the vibrations of the human tympanic membrane. The probe was evaluated with respect to its applicability to detect displacement amplitudes in the tympanum by measurements performed in an excised temporal bone. A sensitivity sufficient to detect vibrations of the order of 50 nm was observed.