We describe a new implantable hearing-aid output device, a piezoelectric bellows round-window driver (PBRD), which is expected to be unaffected by external magnetic fields. The core elements of the PBRD are a piezoelectric element and a gold-coated copper bellows of low stiffness that transmits piezoelectric displacements, without significant attenuation, to the round window (RW). We analyzed structural and mechanical vibrations when confirming bellows transmission efficiency using a finite element model simulation. The PBRD was bench-tested under no-load conditions to determine its frequency response characteristics. We compared the outputs of the PBRD and a commercial floating-mass transducer in situ in human cadaveric temporal bones with responses measured using a laser Doppler vibrometer. PBRD outputs were excellent at both low (0.1–0.7 kHz) and high (2–16 kHz) frequencies; thus, the PBRD has the potential to compensate for conductive and/or sensorineural hearing loss. The frequency-response performance of the PBRD is better than that of conventional RW drivers (actuators or transducers).

Fully implantable hearing devices (FIHDs) have been developed as a new technology to overcome the disadvantages of conventional acoustic hearing aids. The implantable microphones currently used in FIHDs, however, have difficulty achieving high sensitivity to environmental sounds, low sensitivity to body noise, and ease of implantation. In general, implantable microphones may be placed under the skin in the temporal bone region of the skull. In this situation, body noise picked up during mastication and touching can be significant, and the layer of skin and hair can both attenuate and distort sounds. The new approach presently proposed is a microphone implanted at the tympanic membrane. This method increases the microphone’s sensitivity by utilizing the pinna’s directionally dependent sound collection capabilities and the natural resonances of the ear canal. The sensitivity and insertion loss of this microphone were measured in human cadaveric specimens in the 0.1 to 16 kHz frequency range. In addition, the maximum stable gain due to feedback between the trans-tympanic microphone and a round-window-drive transducer, was measured. The results confirmed in situ high-performance capabilities of the proposed trans-tympanic microphone.

We designed and implemented an electromagnetic transducer for implantable bone conduction hearing aids. The proposed transducer is smaller than previous bone conduction transducers for easy implantation and was designed using high permeability metals to produce large electromagnetic forces. In addition, the number of cantilever beams was changed from two to three to minimize distortion of the transducer, potentially due to twisting of the cantilever beam. The proposed transducer consists of a titanium cover with three screw holes, a metal ring, a circular plate, a vibrational membrane with a three-cantilever structure, a metal plate and cylinder, a permanent magnet, top and bottom coils, and a cylindrical titanium case. The transducer was optimally designed based on analysis of electromagnetic and mechanical vibrations, and the target resonance frequency was derived by controlling the variable elements of the vibrational membrane. The transducer was manufactured based on the results of finite element analysis, and the validity of the design was verified by comparing the results of vibration measurement experiments and a simulation. Finally, to evaluate the performance of the proposed transducer, the transducer was attached to the mastoid of participants and functional near-infrared spectroscopy was used to measure brain activation changes of the auditory cortex due to vibration stimulation.

Acoustic hearing aids generate amplified sound in the ear canal, and they are the standard of care for patients with mild to moderate sensorineural hearing loss. However, because of their limited frequency bandwidth, gain, and feedback, there is substantial room for improvement. Active middle ear implants, which directly vibrate the middle ear and cochlea, are an alternative approach to conventional acoustic hearing aids. They provide an opportunity to improve sound quality and speech understanding with amplification rehabilitation. For floating-mass type and direct-rod type (DRT) middle ear transducers, a differential floating-mass transducer (DFMT) and a tri-coil bellows transducer (TCBT), respectively, were fabricated to measure the output characteristics in four human temporal bones. Both were fabricated to have similar output forces per unit input and were placed in four human temporal bones to measure their output performances. The TCBT resulted in higher output than did the DFMT throughout the audible frequency range, and the output was more prominent at lower frequency ranges. In this study, we showed that DRT was a more effective method for round window stimulation. Because of its frequency characteristics and vibration efficiency, this implantation method can be utilized as a driving solution for middle ear implants.