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Winged MEMS keep dust away

Posted: 08 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS? sensors? air flow?

MEMS downsize the sensing element in a detector to reduce costs, improve accuracy and offer integration rivaling semiconductors. Unfortunately, the world does not downsize just because the element being used to sense it does. Consequently, the smaller MEMS devices become, the more easily they are clogged by dust and other particulate. Now Omron Electronic Components LLC claims to have solved this problem for MEMS airflow sensors with an innovative mechanical architecture it dubs the "penguin."

"Our newest D6F airflow sensor, whose code name was penguin, never needs a filter, which can interfere with air flow readings when it gets clogged," said Yoshio Sekiguchi, general manager at Omron's electronics components division. "We do it with the centrifugal force we generate with cyclonic air flow."

Omron's Sekiguchi claims the market for conventional flow sensors today is $1 billion worldwide, where they are used for everything from medical respirators that monitor patients to consumer AV projectors that detect clogs in fan filters. Industrial uses include variable air volume (VAV) ventilators today and tomorrow to sense gas exchange processes in fuel cells.

How does the penguin work?

Penguin wings
Like all MEMS sensors, the solution depends on how the mechanical structures in the device are crafted. For Omron's D6F airflow sensor, the mechanical structures have sprouted outside the chip, forming a waveguide-like path, resembling a penguin with outstretched wings, that accelerates the airflow down one "wing" around a sharp corner and out the other "wing." In a nutshell, Omron generates a cyclonic air flow with a cleverly sculpted air path whose centrifugal force propels heavy particulate, like dust, away from the centrally located path to the MEMS sensor, thereby enabling a direct measurement of air flow without the inhibiting factor and maintenance of filters to keep dust from contaminating the sensor readings.

The air flow measurement itself is performed by a MEMS sensor with dual thermopiles on each side of a centrally located heating element. With no airflow, both thermopiles measure the same air temperature. But when air is flowing over the thermopiles, the one at the entrance of the flow path runs cooler than the thermopile at the exit of the flow path which heats up. The differential in the temperature is directly proportional to the air flow volume.

Today Omron has MEMS sensors for pressure, inertia (accelerometers), airflow, temperature and infrared. The company is also currently sampling a MEMS high-frequency 15GHz switch for 4G cellphone applications to compete with TeraVicta Technologies Inc., currently the only supplier of high-frequency MEMS switches.

"We estimate that 4G mobile phones will need five high-frequency switches," said Sekiguchi. "Our high-frequency MEMS switch will offer twice the longevity of current [non-MEMS] devices, or about 100 million switches."

MEMS mics
Omron is also currently sampling a novel new MEMS microphone design, its first surface-micromachined MEMS, which they plan to sell in competition with Akustica Inc., Knowles Acoustics and Sonion MEMS A/S, all of whom are currently competing for both cellphone and PC microphone applications.

Omron is also developing a MEMS-based "optical eye" that integrates a smart vision sensor with both control and communications capabilities in the same module, which they plan to sell in competition with Canesta Inc., International Electronics & Engineering S.A. and the Swiss Center for Electronics and Microtechnology.

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