These New Sensors Can Sense Things Without Even Touching

Researchers at the East China University of Science and Technology (ECUST) have developed an innovative flexible film that can detect the movements of nearby objects without physical contact. This technology was demonstrated through glasses that can track eye blinks. The human skin’s ability to sense nearby objects without contact inspired this development.

Such noncontact sensors have potential applications in enhancing devices like smartphones, enabling them to recognize more finger gestures through static electricity detection. However, previous attempts to create effective noncontact sensors have faced significant challenges.

The main issues with existing noncontact sensors include their limited charge retention, difficulty in fabrication, and the types of objects they can detect. Yiming Wang, a researcher at ECUST, highlighted the complexity of selecting appropriate electret materials and designing sensor structures as major obstacles.

“The difficulties in fabricating the noncontact sensors are the selection of electret materials and the design of the sensor structure,” said Yiming Wang.

Electrets, materials that hold an electric charge and produce an electrostatic field, are crucial for these sensors. Typically, noncontact sensors rely on friction-induced charges, which tend to dissipate within hours.

“Most of the currently developed noncontact sensors are charged by friction, and the charges disappear within a few hours,” Wang added.

To address these challenges, Wang, along with Xunlin Qiu, Fuzhen Xuan, and other researchers, developed a new electret material comprising a three-part system: a top sensing layer of fluorinated ethylene propylene (FEP), a middle electrically conductive film, and a flexible plastic base.

This material was charged using a commercial polarization instrument and demonstrated effective proximity detection. The sensor could detect various materials, including glass, rubber, paper, and aluminum, within a range of 2-20 mm from the FEP surface. The sensor maintained its charge after 3,000 approach-withdraw cycles in two hours, attributed to the high charge retention ability of FEP.

In practical applications, the researchers placed the sensor inside the lens of eyeglasses to detect eyelash movements. This setup successfully detected blinks coded as E-C-U-S-T in Morse code, showing potential for communication aids for people unable to speak and for monitoring driver alertness.

However, the researchers identified a need to improve the sensor’s transparency, as the current ITO conductive layer slightly reduces it. Future developments aim to use more transparent conductive materials to enhance the sensor’s usability.

“The ITO conductive layer we currently used slightly reduced the transparency of the sensor. Next, conductive materials with higher transparency would be highly desired,” Wang concluded.