Design and Experimental Assessment of Low-Noise Piezoelectric Microelectromechanical Systems Vibration Sensors

Optimal Position and Orientation of an Ossicular Accelerometer for Human Auditory Prostheses

In this study, a method for determining the optimal location and orientation of an implantable piezoelectric accelerometer on the short process of the incus is presented. The accelerometer is intended to be used as a replacement for an external microphone to enable totally implantable auditory prostheses. The optimal orientation of the sensor and the best attachment point are determined based on two criteria-maximum pressure sensitivity sum and minimum loudness level sum. The best location is determined to be near the incudomalleolar joint. We find that the angular orientation of the sensor is critical and provide guidelines on that orientation. The method described in this paper can be used to further optimize the design and performance of the accelerometer.

The UmboMic: A PVDF Cantilever Microphone

Objective

We present the "UmboMic," a prototype piezoelectric cantilever microphone designed for future use with totally-implantable cochlear implants.

Methods

The UmboMic sensor is made from polyvinylidene difluoride (PVDF) because of its low Young's modulus and biocompatibility. The sensor is designed to fit in the middle ear and measure the motion of the underside of the eardrum at the umbo. To maximize its performance, we developed a low noise charge amplifier in tandem with the UmboMic sensor. This paper presents the performance of the UmboMic sensor and amplifier in fresh cadaveric human temporal bones.

Results

When tested in human temporal bones, the UmboMic apparatus achieves an equivalent input noise of 32.3 dB SPL over the frequency range 100 Hz to 7 kHz, good linearity, and a flat frequency response to within 10 dB from about 100 Hz to 6 kHz.

Conclusion

These results demonstrate the feasibility of a PVDF-based microphone when paired with a low-noise amplifier. The reported UmboMic apparatus is comparable in performance to a conventional hearing aid microphone.

Significance

The proof-of-concept UmboMic apparatus is a promising step towards creating a totally-implantable cochlear implant. A completely internal system would enhance the quality of life of cochlear implant users.

Design and Analysis Method of Piezoelectric Liquid Driving Device with Elastic External Displacement

In piezoelectric drive, resonant drive is an important driving mode in which the external elastic force and electric drive signal are the key factors. In this paper, the effects of the coupling of external elastic force and liquid parameters with the structure on the vibrator resonance frequency and liquid drive are analyzed by numerical simulation. The fluid-structure coupling model for numerical analysis of the elastic force was established, the principle of microdroplet generation and the coupling method of the elastic force were studied, and the changes in the resonant frequency and mode induced by the changes in the liquid parameters in different cavities were analyzed. Through the coupled simulation and calculation of the pressure and deformation of the cavity, the laser vibration measurement test was carried out to test the effect of the vibration mode analysis. The driving model of the fluid jet driven by the elastic force on the piezoelectric drive was further established. The changing shape of the fluid jet under different elastic forces was analyzed, and the influence law of the external elastic force on the change in the droplet separation was determined. It provides reference support for further external microcontrol of droplet motion.

Piezoelectric Multi-Channel Bilayer Transducer for Sensing and Filtering Ossicular Vibration

This paper presents an acoustic transducer for fully implantable cochlear implants (FICIs), which can be implanted on the hearing chain to detect and filter the ambient sound in eight frequency bands between 250 and 6000 Hz. The transducer dimensions are conventional surgery compatible. The structure is formed with 3  × 3 × 0.36 mm active space for each layer and 5.2 mg total active mass excluding packaging. Characterization of the transducer is carried on an artificial membrane whose vibration characteristic is similar to the umbo vibration. On the artificial membrane, piezoelectric transducer generates up to 320.3 mVpp under 100 dB sound pressure level (SPL) excitation and covers the audible acoustic frequency. The measured signal-to-noise-ratio (SNR) of the channels is up to 84.2 dB. Sound quality of the transducer for fully implantable cochlear implant application is graded with an objective qualification method (PESQ) for the first time in the literature to the best of the knowledge, and scored 3.42/4.5.

An Implantable Piezofilm Middle Ear Microphone: Performance in Human Cadaveric Temporal Bones

PURPOSE

One of the major reasons that totally implantable cochlear microphones are not readily available is the lack of good implantable microphones. An implantable microphone has the potential to provide a range of benefits over external microphones for cochlear implant users including the filtering ability of the outer ear, cosmetics, and usability in all situations. This paper presents results from experiments in human cadaveric ears of a piezofilm microphone concept under development as a possible component of a future implantable microphone system for use with cochlear implants. This microphone is referred to here as a drum microphone (DrumMic) that senses the robust and predictable motion of the umbo, the tip of the malleus.

METHODS

The performance was measured by five DrumMics inserted in four different human cadaveric temporal bones. Sensitivity, linearity, bandwidth, and equivalent input noise were measured during these experiments using a sound stimulus and measurement setup.

RESULTS

The sensitivity of the DrumMics was found to be tightly clustered across different microphones and ears despite differences in umbo and middle ear anatomy. The DrumMics were shown to behave linearly across a large dynamic range (46 dB SPL to 100 dB SPL) across a wide bandwidth (100 Hz to 8 kHz). The equivalent input noise (over a bandwidth of 0.1-10 kHz) of the DrumMic and amplifier referenced to the ear canal was measured to be about 54 dB SPL in the temporal bone experiment and estimated to be 46 dB SPL after accounting for the pressure gain of the outer ear.

CONCLUSION

The results demonstrate that the DrumMic behaves robustly across ears and fabrication. The equivalent input noise performance (related to the lowest level of sound measurable) was shown to approach that of commercial hearing aid microphones. To advance this demonstration of the DrumMic concept to a future prototype implantable in humans, work on encapsulation, biocompatibility, and connectorization will be required.

A polymeric piezoelectric MEMS accelerometer with high sensitivity, low noise density, and an innovative manufacturing approach

The piezoelectric coupling principle is widely used (along with capacitive coupling and piezoresistive coupling) for MEMS accelerometers. Piezoelectric MEMS accelerometers are used primarily for vibration monitoring. Polymer piezoelectric MEMS accelerometers offer the merits of heavy-metal-free structure material and simple microfabrication flow. More importantly, polymeric piezoelectric MEMS accelerometers may be the basis of novel applications, such as fully organic inertial sensing microsystems using polymer sensors and organic integrated circuits. This paper presents a novel polymer piezoelectric MEMS accelerometer design using PVDF films. A simple and rapid microfabrication flow based on laser micromachining of thin films and 3D stereolithography was developed to fabricate three samples of this design. During proof-of-concept experiments, the design achieved a sensitivity of 21.82 pC/g (equivalent open-circuit voltage sensitivity: 126.32 mV/g), a 5% flat band of 58.5 Hz, and a noise density of 6.02 µg/√Hz. Thus, this design rivals state-of-the-art PZT-based counterparts in charge sensitivity and noise density, and it surpasses the performance capabilities of several commercial MEMS accelerometers. Moreover, this design has a 10-times smaller device area and a 4-times larger flat band than previous state-of-the-art organic piezoelectric MEMS accelerometers. These experimentally validated performance metrics demonstrate the promising application potential of the polymeric piezoelectric MEMS accelerometer design presented in this article.

Design of Piezoelectric Dual-Bandwidth Accelerometers for Completely Implantable Auditory Prostheses

For the last 20 years, researchers have developed accelerometers to function as ossicular vibration sensors in order to eliminate the external components of hearing aid and cochlear implant systems. To date, no accelerometer has met all of the stringent performance requirements necessary to function in this capacity. In this work, we present an accelerometer design with an equivalent noise floor less than 20 phon equal-loudness-level over a 0.1-8 kHz bandwidth in a package small enough to be implanted in the middle ear. Our approach uses a dual-bandwidth (two sensing elements) microelectromechanical systems piezoelectric accelerometer, sized using an area-minimization process based on an experimentally-validated analytical model of the sensor. The resulting bandwidth of the low-frequency sensing element is 0.1-1.25 kHz and that of the high-frequency sensing element is 1.25-8 kHz. These sensing elements fit within a silicon frame that is 795 μm × 778 μm, which can reasonably be housed along with a required integrated circuit in a 2.2 mm × 2.7 mm × 1 mm package. The estimated total mass of the packaged system is approximately 14 mg. This dual-bandwidth MEMS sensor fills a technological gap in current completely implantable auditory prosthesis research and development by enabling a device capable of meeting physical and performance specifications needed for use in the middle ear.