Bio-Inspired Inner-Ear Microphones via a Piezoelectric Substrate and Nanorods

University Of Washington, Seattle WA

Investigators

Abstract

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.