Soft, flexible non-contact sensor can enhance smart devices

I won’t touch you! When another person’s finger glides across your skin, you may feel like they are touching you, not necessarily feeling contact, but feeling close to you. Similarly, researchers reporting in Materials and interfaces used ACS designed a soft, flexible foil that senses the presence of nearby objects without physically touching them. The study used new sensor technology to detect the proximity of eyelashes in blink-tracking glasses.

Non-contact sensors can identify or measure an object without directly touching it. Examples of such devices are infrared thermometers and vehicle proximity notification systems. One type of non-contact sensor uses static electricity to detect proximity and small movements and could improve smart devices, such as enabling phone screens to recognize more finger gestures. So far, however, their scope has been limited in terms of what types of objects are detected, how long they remain charged and how difficult they are to produce. Therefore, Xunlin Qiu, Yiming Wang, Fuzhen Xuan and colleagues wanted to create a flexible static electricity-based sensor that would overcome these problems.

The researchers started by simply fabricating a three-part system: fluorinated ethylene propylene (FEP) in the top sensing layer, with an electrically conductive film and a flexible plastic base in the middle and bottom layers, respectively. FEP is an electret, a type of material that is electrically charged and produces an external electrostatic field, similar to the way a magnet produces a magnetic field. They then electrically charged the FEP-based sensor, making it ready for use.

As objects approached the FEP surface, their inherent static charge caused an electric current to flow in the sensor, thereby “sensing” the object without physical contact. The resulting transparent and flexible sensor detected objects – made of glass, rubber, aluminum and paper – that almost touched it, but not quite, at a distance of 2 to 20 millimeters (less than an inch). The sensor maintained its charge for more than 3,000 different approach and departure cycles over a period of almost two hours.

In a demonstration of the new sensing film, the researchers attached it to the inside of an eyeglass lens. When worn by the person, the glasses detected the approach of the eyelashes and recognized when the wearer blinked in Morse code, which stands for “ECUST,” an abbreviation for the researchers’ institution. Scientists say that in the future, their non-contact sensors could help people who don’t speak or use sign language communicate and even detect drowsiness while driving.

The authors acknowledge funding from grants from the Natural Science Foundation of China, the Shanghai Basic Research Pilot Program, the “Chenguang Program” supported by the Shanghai Educational Development Foundation and the Shanghai Municipal Education Commission, the National Key Research and Development Program of China, the Natural Science Foundation of Shanghai and the Open Project of the State Key Laboratory of Chemical Engineering.

-Note: This press release was originally published on the website of the American Chemical Society. Because it has been republished, it may differ from our style guide.