The National Science Foundation (NSF) says that researchers in the lab of Dr. Karl Grosh at the University of Michigan are developing a novel type of mechanical cochlea. The hydromechanical cochlea, based on a microelectromechanical system, can capture within the normal audio spectrum as well as audio frequencies well beyond those of normal human hearing. Consequently, the device, in addition to its clinical uses, is expected to be used in a wide range of industries:
“The machined cochlea Grosh and White developed fills a critical need for efficient acoustic sensing, as well as a need of the hearing-impaired. It could potentially offer a less-expensive substitute for some hardware in cochlear implants,” says Ken Chong, interim director of NSF’s Civil and Mechanical Systems (CMS) Division.
The hydromechanical cochlea is a microelectromechanical system, or MEMS, device, meaning that it is manufactured–and functions–at a scale of a few millionths of a meter. While it does not yet generate electrical signals, it accurately collects sound data at frequencies between 4,200 hertz and 35,000 hertz, overlapping much of the range for the human ear (20 hertz to 20,000 hertz)
The new device, while not the first of its kind, has three main benefits over existing artificial cochlea: the methods behind its construction are ideal for mass production; its 3-centimeter length is comparable to the unwound human cochlea, which is important for potential hearing aid applications; and because there are no moving parts, the sensor is incredibly efficient–a critical property for potential use on autonomous underwater vehicles such as unmanned military craft that rely on battery power…
In its simplest form, the new device consists of a rigid, micromachined Pyrex glass channel filled with silicone oil and topped by a thin, tapered-width membrane of silicon nitride. The membrane is sensitive to higher frequency vibrations at its skinniest end and gradually lower-frequency vibrations further along the widening structure.
A small, separate membrane of the same material, roughly 1 millimeter by 2 millimeters, provides another “window” to the fluid-filled chamber. This small piece of silicon nitride receives the initial sound waves and transmits them into the main chamber much like the stapes in the ear transmits sounds to a human cochlea.
If one generates a sound, the device resonates in specific locations in response to the vibrations produced. Each part of the membrane resonates with a specific frequency, so when a sound wave strikes the device, the membrane vibrates most excitedly at the location that corresponds to the incoming wave. That is the site where the sound wave “crests,” says White.
While the component can detect sounds, it is not yet configured to do anything with the information. The next step is to affix to the membrane sensors that can convert the vibration energy into electrical impulses a processor can recognize.