HP MEMS could shake up motion sensing

Its new chips are small, precise, and inexpensive enough for use in massive arrays

That accelerometer in your new iPhone 3GS must seem pretty cool, switching the phone to landscape view and steering you through racing games and all. But it's nothing compared with what Hewlett-Packard has come up with.

Accelerometers, or inertial sensors, are devices that sense shocks, vibrations and changes in velocity. The ones used in cell phones and other consumer devices are MEMS (micro-electromechanical systems), essentially integrated circuits with moving parts. Though small and relatively inexpensive, they haven't been able to match the more sensitive sensors used in airliners and other commercial applications until now, according to HP.

Now the company has developed an MEMS accelerometer that can do the work of the high-end sensors, which until now have been mechanical devices the size of a brick that cost about US$1,000 per axis, with each axis sensing motion in one direction. It did so partly with technology developed in its printer division, which uses another type of MEMS in print heads. For now, these HP sensors aren't cheap enough to put in consumer electronics, but because they're MEMS, they may get there in a few years. In the meantime, they could revolutionize the use of accelerometers in buildings and geology.

The very touchy chips are 1,000 times as sensitive as the ones in consumer devices today, according to HP. As an indication of how sensitive they are, a business card dropped at one end of a table would generate a very strong signal on one of these sensors at the other end, according to David Erickson, engineering manager in the Technology Development Organization.

Because of their size, cost and low power consumption, the new sensors could be used in large arrays distributed throughout an area or structure. HP is talking to potential users about what kinds of miniature inertial sensors they could use, and the company hopes to sell them the sensors along with wireless networks, storage systems and data centers to collect, keep and process the information that comes out of the arrays.

For example, a large collection of these sensors on the San Francisco-Oakland Bay Bridge might have given engineers critical information to help them prevent the cable break last week that forced the bridge to close for six days, Erickson said. A few hundred or so tiny MEMS attached to the bridge could have sensed how various parts of the structure moved under various conditions, such as wind or heavy traffic. By comparing all the data they collected against a model of how the bridge ought to move, engineers might have been able to predict that a part was going to give way, he said. That kind of structural health monitoring could also be applied to buildings, with many small devices attached to all the structural components.

Another possible application is geophysical mapping, which is to mining, drilling and seismic analysis what an MRI (magnetic resonance imaging) is to medicine. After planting motion sensors underground at regular intervals to form a grid, scientists use a sledgehammer or explosion to send a vibration through the ground. Those vibrations bounce off the various materials beneath the surface and are detected by the sensors, so when all the data is combined, it forms a virtual map.

HP designed its inertial sensors with three layers of silicon. Inside the middle layer is a tiny movable mass suspended on springs, with electrodes on either side of it. As the mass moves, it changes the signals between the electrodes, and that change is registered as vibration or motion, said Erickson.

The chips, about 5 millimeters square by 2mm thick, consume only about 50 milliwatts of electricity, according to HP. At that level, they could run on power "harvested" from the surrounding environment, said Rich Duncombe, distinguished technologist and strategist at HP. The possibilities include harvesting energy from radio waves or temperature changes in the environment, or even from the very movement the sensors are detecting, he said.

Research company Gartner expects the market for non-optical sensor chips such as MEMS to grow by 10 percent per year, from US$2.7 billion in 2007 to about $4.4 billion in 2012. That's nearly twice the growth rate of the overall semiconductor market, according to Gartner. HP's breakthrough with MEMS accelerometers, which overcomes trade-offs among size, weight, cost and performance, is likely to lead to higher volumes and lower prices, as has occurred other chip industries, said Gartner analyst Jim Walker.

If the highly sensitive MEMS make it into consumer products, they could give phones some interesting new capabilities. They're sensitive enough to discern location, so users could constantly know where they were even on city streets with poor GPS coverage, Erickson said. Gartner's Walker thinks health care is another area where they could come in handy. A sensor on a cell phone might be able to feel the user's heartbeat, detect a heart attack and automatically call emergency services, he said.

HP is concerned about more than bridges, mining or cell phones. It wants to use the tiny inertial sensors as part of the Central Nervous System for the Earth, an information ecosystem made up of various sensors tied to networks, storage, servers and software around the world. For example, all those sensors installed in buildings and bridges might form a giant collective seismograph to help scientists detect and predict earthquakes.

"We're just on the front edge of really understanding how pervasive networks of this kind will be developed and how they're going to contribute to (solving) the larger problems that society is working through," HP's Duncombe said.

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