The Sound of Touch: Enhancing UI and VR With Ultrasound

Chirp Microsystems has unveiled a miniature ultrasound sensor for touch-free gesture control that it says will help usher in truly mobile VR and create the next generation of user interfaces.

In the mission to make controlling and interacting with devices as natural as possible we've developed touchscreens, speech recognition, and motion tracking. Chirp Microsystems, a Berkeley,CA-based startup, believes the next evolution of user experience (UI) will happen because of sound.

Chirp has unveiled a microelectromechanical systems (MEMS)-based time-of-flight (ToF) sensor that uses ultrasound transducers to give users touch-free control over their devices, using hand and finger gestures. A recent demo (shown below) of Chirp's technology shows a user controlling a tablet simply by using hand-gestures in the air.

You've probably already seen this done with light and camera-based systems, but Michelle Kiang, CEO and co-founder of Chirp, told Design News that these solutions don't offer the same level of accuracy and consume much more power than ultrasound. “When you think of infrared or camera-based solutions, in terms of power consumption just the device itself can operate in the tens of milliwatts," she said. "With ultrasound we can operate in the tens of microwatts – a thousand times reduction in power consumption.”

Moreover, Kiang added camera-based systems require machine vision, which eats up a lot of processing power, in order to do their job. “Whereas ultrasound only measures range and distance, so even when you use multiple devices the calculations are pretty simple.”

Chirp's sensor utilizes an array of small ultrasound transducers to send out a pulse of soundwaves. Like a bat using echolocation, the soundwaves bounce off of an object (like your hand) and returns to the chip. By calculating the time-of-flight the chip is able to determine the location of the object relative to the device and trigger a programmed behavior. Waving your hand through the air might scroll through a screen, you could control volume or intensity by moving your hand toward or away from a device, or you could click or activate commands with a small finger movement.

Chirp’s technology originated at the Berkeley Sensor and Actuator Center (BSAC) at UC Berkeley and Davis, where researchers discovered a new way to miniaturize MEMS ultrasound sensors that was licensed by Chirp when it was founded in 2013.

The transducers are piezoelectric micromachined ultrasonic transducers (PMUTs) that convert ultrasonic pressure that hits a membrane on the sensor into an electrical signal. Because PMUTs don't use a backplate like convention piezoelectric sensors, there is no hard limit to the membrane's motion, resulting in a better-quality signal.

Chirp's FoT sensor combines a PMUT with a proprietary ultra-low-power, mixed-signal integrated circuit that handles the time-of-flight calculations. As the chip doesn't rely on an external processor, it can accomplish its task with much less power and in a much smaller form factor. And, as it works like echolocation, the sensor allows devices to track movements in 3D space, adding many more control options than the two-dimensional confinements of a touchscreen, for example. David Horsley, co-founder and CTO of Chirp, goes into detail on the technology's inner workings in an article for IEEE Spectrum .

According to the company, its ToF sensor is one-thousand times smaller than a conventional ultrasound transducer and can sense not only broad gestures

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