Precision of AC Hum-Noise Based Sensing Enhanced by Novel Calibration Algorithm

At the Tokyo Metropolitan University, scientists have come up with a new calibration algorithm for technology that converts common materials into touch sensors.

Precision of AC Hum-Noise Based Sensing Enhanced by Novel Calibration Algorithm

Electromagnetic waves from everyday power sources induce small currents inside the human body. This can leak out when we touch surfaces. A set of electrodes and an oscilloscope can detect these currents and locate where on the surface was touched. The process requires calibration to correctly convert currents into locations. Image Credit: Tokyo Metropolitan University

HumTouch helps detect the current that runs from the fingertips to any partially conductive surface and finds the place where it was touched. The new algorithm expedites calibration for new users, thereby resolving a significant disadvantage of present versions of the technology. Also, it enhances precision, thereby bringing HumTouch one step closer to practical applications.

During the course of a few decades, touch sensing has gone from cutting-edge tech to an omnipresent part of everyday life. This is particularly apparent in the number of touchscreens that surround us, from smartphones and tablets to everyday interactive tasks like checking out groceries, making a payment, controlling household appliances, or even playing games.

However, the sensing abilities of a touchscreen are restricted to the area of the screen. Capacitive touchscreens, for instance, feature a set of small circuits all over the screen which can detect small, local changes in capacitance when one touches it; there is a static, preinstalled set of circuitry over which the screen could act as a sensor.

A research group from Tokyo Metropolitan University headed by Associate Professor Shogo Okamoto has been working on technology that may turn any moderately conductive surface into a touch sensor.

Through wiring electrodes to the edges of any surface, whether it be made of cloth, wood, or stone, they have come up with sensing technology that can not only detect when the surface has been touched but where it has been touched, similar to a touchscreen. The principle used is dependent on AC hum noise.

Any location with a mains power supply is filled with electromagnetic waves liberated from sources; these induce small currents in the body which could leak into a surface when it is subjected to touching. The technology, named HumTouch, has the potential to convert precise measurements of this current to a location. This could possibly convert almost any surface into a touch sensor.

But a major disadvantage of HumTouch has been how sensitive the change is to the person. A lengthy calibration process is needed for new users that requires them to touch the surface at over 20 locations before a precise touch location can be achieved.

The team has found that data gathered from multiple users could be integrated with data from a single touch from a new user to produce a much more precise location.

The new algorithm was tested by wiring up a paper towel and gathering data from various users. Any new user could touch the paper once, have the measurement mixed with pre-existing calibration data from other users, and enjoy the exact location of consequent touches up to a precision of less than a centimeter.

The research group believes that HumTouch will now be able to bring inanimate, offline objects into the network infrastructure of the Internet of Things, thereby adding unparalleled interactive abilities to the immediate surrounding.

This work was financially supported by MEXT KAKENHI Grant Numbers 21H05819 and 20H04263.

Journal Reference:

Hsia, T-H., et al. (2022) One-touch calibration of hum-noise-based touch sensor for unknown users utilizing models trained by different users. ROBOMECH Journal.

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