Auto Electronics

As Accelerometers Spread, They'll Get Better, Smarter

A recently released marketing report optimistically projects sales of automotive-targeted MEMS accelerometers over the next five years, suggesting just how quickly new safety and navigation features will be incorporated into new light vehicles. In “MEMS: A Roadmap to Technologies and Applications,” Business Communications Company (BCC) predicts that unit sales of these sensors will triple or even quadruple in certain applications, as new airbags, vehicle stability systems, and vehicle navigation systems proliferate. The spread of these applications, will in turn, drive development of accelerometers with higher performance and reliability.

It should come as no surprise that the overwhelming majority of MEMS accelerometers are used in airbag applications. And if the market projections are correct, that will still be the case at the end of this decade. According to BCC, approximately 180 million MEMS airbag sensors were shipped in 2004. It's conservatively estimated that this number will rise to 260 million units in 2010. The marketing research firm explains that growth will be driven by the increase in side-impact airbags in North America, Europe and Asia Pacific as well as by developing markets for airbags in South America, Eastern Europe, Southeast Asia, India and China. Other factors cited by BCC include the conversion to global platforms by the major automakers promoting safety products and the maturing supply base in developing countries.

In vehicle stability control (VSC) systems, MEMS accelerometer usage is expected to grow even faster, tripling in five years' time. BCC found that about 6.4 million MEMS accelerometers for VSC systems were shipped in 2004, and that number is expected to reach 18.1 million units in 2010. The sensors used in these VSC applications are described as “low-g” accelerometers, which according to Analog Devices, are those sensors that measure in the range of ±1 g to ±20 g.

But the greatest increase in growth for MEMS accelerometers is expected in vehicle navigation systems. Here, the accelerometers are key elements in inertial navigation systems that are combined with GPS to correct for the GPS unit's inability to get a fix on the satellites in certain driving areas. Though only 4.6 million accelerometers were shipped in vehicle navigation systems in 2004, says BCC, that number should nearly quadruple by the end of the decade when it reaches 17.9 million units.

It's natural to expect that the increasing usage of MEMS accelerometers will spur further development of these components, while also influencing changes in automotive system design. In an article titled, “MEMS Inertial Sensors Move Beyond Airbags,” (Wards Auto Electronics, October 2004) Harvey Weinberg, a senior applications engineer at Analog Devices, describes one of the effects of a growing accelerometer count in the vehicle: “The proliferation of inertial MEMS sensor content in cars is driving system designers to rethink the current stand-alone sensor architecture in favor of an inertial sensing cluster.”

So rather than deploying many accelerometers throughout a vehicle, a few of these sensors could be grouped together near the vehicle's center of gravity. Weinberg notes that with this approach, the performance required from the clustered accelerometers becomes more stringent, as a few sensors must meet the best specifications of all the accelerometers being replaced. While this makes the individual accelerometers more expensive, it saves cost at the system level, says Weinberg, as multiple pc boards, connectors, and other components can be eliminated.

Another development path for MEMS accelerometers involves making them more reliable. “The biggest technological improvement ahead will be in making sensors that are so robust that you can absolutely trust what they're telling you,” says Weinberg, who notes that this level of reliability is already achieved by air bag accelerometers, but must be expanded to the sensors used in stability control and other safety systems. Though there are always conditions under which sensors can produce erroneous data, intelligence in the sensor or in the application, must be able to identify those errors and take corrective action.

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