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MEMS mics find niche in new applications

Posted: 04 Dec 2014 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS microphones? piezoelectric? ultrasonic sensing?

It seems electret microphones, invented way back in 1962 at Bell Labs, are no longer used in mobile devices. Most microelectromechanical (MEMS) microphones simply replicated the basic principle driving electrets, electrically biased diaphragms whose capacitance changes as sound wave vibrate it. On the frontier, however, are piezoelectric MEMS microphones, which promise unheard of signal-to-noise ratios (SNR) of up to 80dB (versus 65dB in the best current capacitive microphones) in 2015.

Either way, MEMS microphones are growing like gangbusters, because engineers have found a whole bunch of applications that can use them as a substitute for more specialised sensors starting in 2015getting more bang for the buck (or, if you want to be all official about it, a lower bill of materials).

 Vesper's piezoelectric MEMS microphone

Vesper's piezoelectric MEMS microphone (left) gains a 5dB advantage over everybody else's capacitive MEMS microphones (right), giving it a signal-to-noise ratio of 70-80dB, the highest in the industry. (Source: Vesper)

The total MEMS market is predicted to top $14 billion in 2015 and $20 billion by 2018, Jean-Christophe Eloy, CEO and president of Yole Development, told the MEMS Executive Congress, the annual meeting of the nonprofit MEMS Industry Group. Jeremie Bouchaud, principal analyst at IHS, said more than $1.4 billion of that will be for MEMS mics.

The biggest reason for the fast growth curve is that smartphone and tablet makers are putting as many as eight MEMS mics into their devices as they discover new ways to use them to eliminate the need for sensors that are often more expensive, such as proximity sensingbeam forming to zero in on the speaker's location. But one of the most novel new applications is ultrasonic sensing.

 MEMS diaphrams and ASIC electronics

Though Akustica has a small share of the overall market, it offers both side-by-side MEMS diaphrams and ASIC electronics, as well as monolithic MEMS microphones. (Source: Akustica)

Everyone who has a smartphone or tablet is sick to death of having to clean greasy fingerprints over and over and over again. Wouldn't it be cool if you could engage the icons, buttons and whatnot while hovering just a few millimetres above the screen? Believe it or not, prototypes are already demonstrating that it is possible by using the MEMS mics that increasingly surround the screen for noise cancelling anyway. If those mics are tuned to the ultrasonic range, then ultrasonic emitters will be able to sense the finger just above the screen, thus enabling touchless interaction (and no more cleaning over and over and over). There are dozens of other research projects under way to harness MEMS micswhich use very little powerto do tasks that currently require power-hungry dedicated devices, like MEMS gyroscopes.


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