A better way to produce microphones

Associate Professor Shahrzad (Sherry) Towfighian from the Thomas J. Watson School of Engineering and Applied Sciences’ Department of Mechanical Engineering
Associate Professor Shahrzad (Sherry) Towfighian from the Thomas J. Watson School of Engineering and Applied Sciences’ Department of Mechanical Engineering studies microelectromechanical systems. (Jonathan Cohen)

Binghamton University researchers have found a way to improve the performance of tiny sensors that could improve the design for microphones and other tiny electrical devices.

With the help of a National Science Foundation grant, the researchers have found a more reliable way to use actuators that control MEMS (microelectromechanical systems) devices, microscopic devices with moving parts that are often produced in the same way as electronics. The team found that combining two methods for electrostatic actuation—parallel-plate and levitation actuators—led to a predictable linearity that neither of those systems offered on its own.

This investigation was conducted by PhD student Mark Pallay under the supervision of principal investigator Shahrzad (Sherry) Towfighian and co-principal investigator Ronald N. Miles from the Thomas J. Watson School of Engineering and Applied Sciences’ Department of Mechanical Engineering.

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The Watson School team’s findings could have significant implications for microphone manufacturing, because with this design the signal can be boosted high enough that the background noise from the electronics is no longer an issue. More than 2 billion microphones are made around the world each year, and that number is growing as more devices feature vocal interaction.

“The electronic noise is really hard to get rid of,” Miles said in a statement. “You hear this hiss in the background. When you make really small microphones—which is what we want to do—the noise is a bigger and bigger issue. It’s more and more of a challenge. This is one path toward avoiding that and getting the noise down.”

Towfighian explained that actuators in the micro-devices are normally just two plates with a gap between. Those plates close and the device activates when it receives a certain voltage.

“Combining the two systems, we can get rid of nonlinearity,” she said. “If you give it some voltage, it stands at some distance and maintains that over a large range of motion.”

Miles said that predictability is crucial when building actuators for microphones, which have been the focus of his recent research.

“In a sensor, life is much easier if it moves one unit and the output voltage increases in one unit, or something in proportion as you go,” he said. “In an actuator, you’re trying to push things, so if you’re giving it twice as much voltage, you want it to go twice as far and not four times as far.

The Binghamton researchers didn’t know that combining the two ideas would provide as desirable an outcome as it has.

“By having both of these electrode configurations, it gives you more knobs to turn and more adjustments you can make with applying voltages to different electrodes,” said Miles. “With a simple parallel plate, you have one voltage across them, and you don’t have much design freedom. With this, there are more electrodes and you get much more control over the design.”

Towfighian believes the new actuator design can be used in gyroscopes, accelerometers, pressure sensors and other kinds of switches.

“We showed this concept at a basic level, but it has wide applications,” she said. “It can improve the function of many devices, so the impact could be huge.”

RELATED: Time-of-flight sensor leverages MEMS technology

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