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Researchers at the University of Michigan are developing a mechanical cochlea designed to function like its human counterpart.
The new device differs from other artificial cochleas in three ways: 1) the methods behind its construction are suitable for mass production; 2) its 3-centimeter length is comparable to the unwound human cochlea, a key factor for potential hearing aid applications; and 3) it is efficient because it has no moving parts.
Composed of micro-machined parts and integrated circuits, the apparatus should be inexpensive to manufacture. Researchers say it could potentially capture a range of frequencies well beyond those of human hearing. National Science Foundation student-fellow Robert White and NSF Career awardee Karl Grosh are developing the device. The project has been underway for five years.
The mechanical cochlea is being designed as a highly efficient sensor to detect sound waves underwater, but it could one day substitute for the microphone and much of the electronics in cochlear implants at a much lower cost.
The cochlea is a micro-electromechanical system (MEMS) device, meaning that it is manufactured-and functions-at a scale of a few millionths of a meter. It accurately collects sound data at frequencies between 4,200 and 35,000 hertz, overlapping much of the range for the human ear (20 to 20,000 hertz). It is an example of what is called micro-nano technology-a combination of mostly micron scale features with some nanoscale ones.
In its simplest form, the device consists of a rigid, micro-machined 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 most narrow 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.
Although 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.
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