The EarLens Contact Hearing Device is a radically different type of hearing aid that uses light, and an eardrum vibration lens - rather than amplified sound - to move the eardrum.
The EarLens itself is a custom-fitted eardrum vibrator (or "tympanic-membrane transducer"), which is created using a mold of the user's ear. The EarLens is "floated" on top of the user's eardrum using a thin layer of mineral oil. On its own, the EarLens vibrator is not capable of doing much. However, when stimulated by infrared light, the EarLens kicks into action, and begins to vibrate. When the EarLens vibrates, the user's eardrum vibrates in synchrony, producing audible sound.
The microphone for the EarLens is fitted inside the earcanal, along with a light emitting diode. This allows the EarLens microphone to pick up sound from a very natural position (as close to the eardrum as possible), which overcomes the need for a directional microphone. As described in the Features and Benefits section below, sound coming from the front of the listener is naturally amplified by the outer ear (pinna), so picking sound up inside the earcanal is the best place to pick up sound (to be amplified). Background: When people have a conversation, they usually face each other, so sound from the front is considered the most important.
Importantly, the earcanal is left completely open with the EarLens system. This alleviates any sense of "blocked ears" which might accompany traditional (non-open-fitting) hearing aids. One of the consequences of open-fitting hearing aids typically is excessive acoustic feedback. The EarLens system is less susceptible to this issue, since there isn't a speaker emitting very loud sound in close proximity to the speaker. Another consequence of open-fitting hearing aids is reduced low-frequency amplification (less low pitch boost). This is due to the leakage of lower pitch sounds through the open canal, and the difficulty of producing low-pitch sound using tiny hearing aid speakers. The EarLens system is not susceptible to these issues since the eardrum is vibrating directly with lower frequency vibrations (~200Hz).
This animation, produced by EarLens, shows the basic components of the EarLens hearing system in action.