Most animals hear sound by detecting airflow. Microphones should do that too.
The detection and transmission of sound is central to human communication and forms much of our perceptual world. After Helmholtz enlightened our understanding of human hearing, ideas began to take shape for creating electronic devices for capturing sound. The resulting microphones (and telephones) sense the fluctuating pressure in a sound field and converted it into an electronic signal, all inspired by the biology of human hearing.
While the development of the microphone as a sensor can be considered as nothing but a great technological achievement, one wonders what might have resulted had the development path proceeded differently. Pressure isn’t the only quantity available to sense in a sound field. Acoustic pressure gradients in the medium lead to an acceleration of the mass contained within that volume. As a result, the air in which the wave propagates experiences motion that fluctuates back and forth as the pressure fluctuates. A sound wave then could be sensed by detecting this air motion rather than sensing the pressure.
While humans, other vertebrates and various other animals detect the pressure fluctuations in a sound field using a tympanal membrane, most animals that can hear sound don’t have these membranes and don’t detect sound pressure at all. Instead, they detect the motion of the air in the sound field. This is the dominant hearing mechanism in insects. While it is far from obvious whether detecting pressure or air motion would lead to the most successful microphone, it seems that our focus on mimicking human hearing to pursue microphone designs was not the only path to pursue. A purpose of the present study is to explore technological approaches to realizing a microphone that senses acoustic air flow rather than pressure.
Bio: R. N. Miles is currently a Distinguished Professor in the Department of Mechanical Engineering at Binghamton University. He has served as the director of graduate studies, director of undergraduate studies, associate chair, and served for two terms as department chair. He has also served as Associate Dean for Research in the Watson College of Engineering and Applied Science. He has served two terms as associate editor for the ASME Journal of Vibration and Acoustics.
Miles has published over one hundred scholarly articles and presented over seventy invited lectures. He holds over two dozen United States and international patents. His research team has included over 80 doctoral, master’s and baccalaureate students with research funding over $17M from federal, state, corporate and charitable organizations.