No abstract

No abstract

Hypothesis Whether a prototype direct-drive hearing device (DHD) is effective in driving the tympanic membrane (TM) in a temporal bone specimen to enable it to potentially treat moderate to severe hearing loss. Background Patient satisfaction with air conduction hearing aids has been low due to sound distortion, occlusion effect, and feedback issues. Implantable hearing aids provide a higher quality sound, but require surgery for placement. The DHD was designed to combine the ability of driving the ossicular chain with placement in the external auditory canal. Methods DHD is a 3.5 mm wide device that could fit entirely into the bony ear canal and directly drive the TM rather than use a speaker. A cadaveric temporal bone was prepared. The device developed in our laboratory was coupled to the external surface of the TM and against the malleus. Frequency sweeps between 300 Hz to 12 kHz were performed in two different coupling methods at 104 and 120 dB, and the DHD was driven with various levels of current. Displacements of the posterior crus of the stapes were measured using a Laser Doppler Vibrometer. Results The DHD showed a linear frequency response from 300Hz to 12kHz. Placement against the malleus showed higher amplitudes and lower power requirements than when the device was placed on the TM. Conclusions DHD is a small completely-in-the-canal device that mechanically drives the TM. This novel device has a frequency output wider than most air conduction devices. Findings of the current study demonstrated that the DHD had the potential of being incorporated into a hearing aid in the future.

The direct hearing device (DHD) is a new auditory prosthesis that combines conventional hearing aid and middle ear implant technologies into a single device. The DHD is located deep in the ear canal and recreates sounds with mechanical movements of the tympanic membrane. A critical component of the DHD is the microactuator, which must be capable of moving the tympanic membrane at frequencies and magnitudes appropriate for normal hearing, with little distortion. The DHD actuator reported here utilized a voice coil actuator design and was 3.7 mm in diameter. The device has a smoothly varying frequency response and produces a precisely controllable force. The total harmonic distortion between 425 Hz and 10 kHz is below 0.5% and acoustic noise generation is minimal. The device was tested as a tympanic membrane driver on cadaveric temporal bones where the device was coupled to the umbo of the tympanic membrane. The DHD successfully recreated ossicular chain movements across the frequencies of human hearing while demonstrating controllable magnitude. Moreover, the micro-actuator was validated in a short-term human clinical performance study where sound matching and complex audio waveforms were evaluated by a healthy subject.