New ultra-thin capacitive sensor design is ideal for sensing sounds

Technology News | June 28, 2018

By Rich Pell

The thin and flexible sensor represents a new design for ultra-thin capacitive sensors – such as those commonly used for microphones in smartphones – which work by measuring changes in capacitance. The new sensor, says the researcher, is ideal for sensing sounds because it can move with the airflow made by even the softest noises and addresses issues with accelerometers, microphones, and many other similar sensors.

“The goal was to create a sensor that only resists gravity,” says Distinguished Professor Ron Miles. “The sensor needed to stay connected to the device but other than that, I wanted it to move with even the slightest sounds or movement of the air.”

Miles had previously worked on developing acoustic sensors by using spider silk dipped in gold as a thin, flexible sensor to make a microphone with remarkably flat frequency response. That sensor used a magnet to convert the silk motion into an electronic signal.

To avoid using a magnet, Miles set out to create a capacitive sensor, which requires a voltage added to it via electrodes. While capacitive microphones are nothing new, making them both small and effective is challenging using existing methods.

Miles’ new platform provides a way to detect the motion of extremely thin fibers or films by sensing changes in an electric field without the use of a magnet. Previously, this hasn’t been feasible – the electrostatic forces used in capacitive sensing can either damage or impede the movement of such extremely flexible, thin materials.

“Researchers want the sensor to move with small forces from sound, without being affected by the electrostatic forces,” says Miles. “The way the sensor is designed now, means that it has a nearly constant potential energy but can also return to its equilibrium after large motions.”

Miles’ design allows a thin, flexible sensor – which could be spider silk or any other material just as thin – to swing above two fixed electrodes. Because the sensor is at a 90-degree angle from the electrodes, says Miles, the electrostatic forces don’t affect its movement.

This is critical, he says, as the sensors need to have a high bias voltage – the voltage required for a device to operate – to be effective since the sensitivity of the sensor increases with bias voltage. The design promises smaller and more efficient capacitive sensors, says Miles, as well as provides other benefits important in various applications.