“Ultrasonics offers a broader space of control and command than touch alone, it covers a lot wider space above the device than just the size of the screen — so your hand is not always obscuring your view of the screen. Also you can define new gestures such as moving your hand from bottom to top to move to the next line, or moving from side to side to bring up and adjacent screen,” Thibault Kassir, senior director, Product Management, Mobile Consumer Electronics, told EE Times. “The other advantage of ultrasonics is the 3-D depth-effect — you can define algorithms to use the third dimension for control — for instance to zoom in or out by bringing your hand closer or further away from the screen.”

Ultrasonic MEMS microphone arrays sense fingers above and alongside smartphone and tablets giving a new third dimension to their control.
(Source: Knowles)

Knowles’ SPH0641LU4H-1 measures just 3.50-by-2.65-by-0.98 millimeter making it small enough to use multiple units around the screen — you need at least three to triangulate the position of a finger — and as many as five to take full advantage of the touchless control possibilities.

“Depending on the precision needed for an application, we’ve seen applications using as many as five ultrasonic MEMS microphones,” Kassir told EE Times. “The ultrasonic microphones can also be used for audio, but it really depends on the use cases — if you are trying to do audio and finger tracking at the same time, it may require you to have additional microphones for audio purposes only. For example, we’ve seen applications using up to seven microphones — five are ultrasonics and two are just used for audio purposes.”

Ultrasonics also can instantly transmit data like photos from handheld to handheld and track special ultrasonic sensitive styluses with unprecedented accuracy. The ultrasonic microphones already consume three-times less power than other digital microphones, according to Knowles, but also go into an “always on” voice-activated super low-power mode when not in use, then quickly power back up when needed.

The signal-to-noise ratio (SNR) is 64.3 dB(A) with a flat frequency response up to 20 kHz. Power consumption: 235microAmp in low-power mode and sensitivity is matched between units by plus or minus 1 dB. Mass production of the new ultrasonic microphones will begin in the third quarter of 2014.

— R. Colin Johnson, Advanced Technology Editor, EE Times

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