Characterization of Ossicular Chain Vibration at the Umbo: Implications for a Middle Ear Microelectromechanical System Design

• Published in: Ear, nose, & throat journal Vol. 89; no. 1; pp. 21 - 26
• Main Authors: Young, Darrin J., Zurcher, Mark A., Trang, Tung, Megerian, Cliff A., Ko, Wen H.
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA SAGE Publications 01-01-2010; Sage Publications, Inc; SAGE PUBLICATIONS, INC
• Subjects: Acceleration; Acoustic Stimulation; Biomechanical Phenomena; Care and treatment; Cochlear Implants; Diagnosis; Ear diseases; Ear Ossicles - physiology; Ear, Middle - physiology; Ears & hearing; Health aspects; Hearing aids; Humans; Microelectromechanical systems; Otitis media; Prosthesis Design; Technology application; Vibration; United States
• ISSN: 0145-5613; 1942-7522
• DOI: 10.1177/014556131008900107

We propose the use of a microelectromechanical system (MEMS)
accelerometer as a middle ear microphone for future totally implantable
cochlear prostheses. The MEMS accelerometer would be attached to the umbo to
detect and convert the natural bone vibration that occurs in response to
external sounds into an electrical signal that represents the acoustic
information. The signal could be further processed to stimulate cochlear
implant electrodes. To determine the feasibility of our proposal, we
conducted a study to investigate whether the characteristics of umbo
vibration along two orthogonal axes—one axis being perpendicular to
the tympanic membrane and the other axis being parallel to the tympanic
membrane plane but orthogonal to the long process of the
malleus—differ significantly enough to compromise the sensing
performance of the proposed accelerometer should a position misalignment
occur during the implant procedure. We used laser Doppler vibrometry to
measure the displacement of the umbo along the two orthogonal axes in 4
cadaveric temporal bones at multiple frequencies within the audible
spectrum. We found that the peak-to-peak displacement frequency response
along both axes was nearly flat from 250 Hz to 1 kHz, and it gradually
rolled off with a slope of approximately −20 dB and −40 dB per
decade above 1 kHz and 4 kHz, respectively. At each frequency, the
displacement exhibited a linear function of the input sound level with a
slope of 20 dB per decade. A comparison of measurements along the two axes
indicated a similar frequency response, with an average amplitude difference
of 20%. The characterization data suggest that the performance of a
miniature ossicular vibration-sensing device attached on the umbo would not
be degraded in the event of a position misalignment. The data also indicate
that a MEMS accelerometer needs to achieve a resolution of i g /√ Hz
to detect normal conversation.