The pump, developed with support from NSF's Small Business Innovation Research program, converts the alternating, compression-expansion waves of sound into a direct-flowing stream of molecules, filling the membrane using only minimal energy from the headphone speaker. The pump has enough force to both inflate the ear lens and keep the device comfortably in the ear canal for as long as the device is worn.
"The lens maintains desirable audio fidelity, especially at bass frequencies, and prevents feedback," says Gido. "The flexible membrane vibrates with the oscillating sound pressure in the sealed ear canal and radiates excess sound energy out of the closed space in front of the ear drum. In a sense, the flexible polymer membrane behaves like a second ear drum, which is more compliant than the real ear drum, allowing it to direct excess sound energy away from the sensitive structures of the ear."
The pump takes advantage of a physical property called a synthetic jet, a column of fluid that erupts when an acoustic wave passes through a small hole.
Sound waves are compression and rarefaction waves - specifically, symmetric pulses of alternating compressed and expanded air molecules. Our ears interpret the alternating pulses as sound.
"As sound waves pass through any given small hole, the alternating pulses emerge and retract through the orifice like a small air-piston, hitting and knocking the surrounding air molecules forward like billiard balls," says Ambrose. "Other molecules join in the stream from the sides due to the low pressure created by the flow. This results in a sustained jet of air."
By integrating an inward flowing jet into the side of the sound port, Asius transformed a standard synthetic jet into a real pump capable of harvesting and storing inflation and deflation pressures.
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National Science Foundation