The research objective of this project is to develop an extra-sensitive microphone by mimicking hair cells in the cochlea. Human hearing is an extremely sensitive bio-sensing mechanism that has evolved for millions of years. The human ear consists of three parts: the outer ear, middle ear, and cochlea. The outer ear collects incoming sound waves to vibrate the eardrum. The middle ear transduces the vibration to pressure waves in the cochlea. Inside the cochlea, there are thousands of hair cells surrounded by fluid. Hair cells have nano-structured and patterned stereocilia swinging and deforming under tiny pressure fluctuations to sense the incoming sound. The pressure can be as low as 20 micro-Pa with a motion in the sub nm range in cochlea. As humans age, hair cells are gradually lost and hearing deteriorates. Exposure to noise can lead to further loss or damage of stereocilia. For nearly deaf patients (especially children), surgeons insert cochlear implants (CI) in the form of an electrode into cochlea to directly stimulate auditory neurons. The newest endeavor in CI research is to incorporate a microphone inside the cochlea along with the electrode. Such design has the advantage of no bulky external components, more natural hearing via auditory pathways, more versatile speech processing algorithms, and reduced surgical time and complexity. A major bottleneck is the unavailability of a tiny microphone with high enough sensitivity to fit into cochlea. Motivated by the needs for an intracochlear microphone in CI research, the PI plans to develop an extra-sensitive microphone by mimicking hair cells in the cochlea. The device consists of a piezoelectric substrate with electrodes and an array of patterned nanorods. When the pressure of the surrounding fluid fluctuates, each nanorod receives a drag force deforming the piezoelectric substrate to generate electric charge. The large number of nanorods significantly amplifies the generated charge enhancing the sensitivity to the pressure fluctuation. Three specific goals are set to achieve. First, to fabricate the bio-inspired microphone (BIM) using a silicon/PZT and a plastics/PZT substrate with nanorods, second, to conduct calibrated experiments to study the feasibility of the BIM, and third, to conduct an analytical study to understand how the pattern and dimensions of the nanorods affect the sensitivity of the BIM.
It is anticipated that a good portion of the estimated 278 million people who have hearing disability could benefit from this research in hearing sensing. Hearing rehabilitation research will become progressively important, because US population is aging and life expectancy is increasing. The research will also broaden its impact via a well-designed international collaboration, recruitment of underrepresented and undergraduate students, curriculum revision, outreach, and publication of research results.
This research is to study the feasibility of an extra-sensitive microphone by mimicking hair cells in cochlea. The device consists of a piezoelectric substrate with electrodes and an array of patterned nanorods. When the pressure of the surrounding fluid fluctuates, each nanorod receives a drag force deforming the piezoelectric substrate to generate electric charge. The ultimate goal is to integrate the bio-inspired microphone with existing cochlear implants to realize totally implantable cochlear prostheses. We first conduct a theoretical analysis to show that such design would provide measurable voltage in the range of millivolts. The analysis also confirms that the output voltage primarily results from drag force of the ambient fluid, which is quite uniform throughout the microphones. Moreover, the length of the nanorods dominates the sensitivity of the microphones. We then consider critical issues that the microphones must cope with in aqueous environments, such as added mass effect and enclosure design. We estimated the added mass theoretically and confirm that with experimental measurements. We also study an open-end and a closed-end enclosure design to evaluate their stiffness theoretically and experimentally. The research results have led to publication of two conference papers. The funded work also improves research infrastructure. We have developed a unique experimental capability to measure and calibrate electric charge generated from piezoelectric thin-film microphones. We have also developed layout design to fabricate and test the bio-inspired microphones. We conduct a feasibility study to improve our piezoelectric films using nano-particles. Although these results are not immediately publishable, they are extremely valuable to the long-term success of the principle investigator’s research. In this research, the principal investigator educated 1 undergraduate student via research experience for undergraduates (REU) program, 2 PhD students, and 1 postodoctoral researcher. The research fund also sponsored four undergraduate students to travel to Taiwan and to conduct summer research jointly with researchers at National Chung-Hsing University in Taiwan. Moreover, the principal investigator has secured internal funding from the University of Washington to host two exchange students from National Chung-Hsing University of Taiwan for 3 academic quarters each to participate in the research. To further disseminate research results, the principal investigator has been giving guest lectures in courses offered in Material Science and Engineering Departments. The purpose is to train material scientists with interdisciplinary topics such as mechanics, design and instrumentation of PZT thin-film transducers. Research results were publicized annually in University of Washington Discovery Day to educate K-12 students how the technology PZT thin-film transducers could improve our life. Moreover, personnel involved in the research had publicly presented the research results in international conferences, such as ASME International Design Engineering Technical Conferences (2012 in Chicago and 2013 in Portland) and NSF Grantees Conference (2012 in Boston).
