When someone’s finger hovers over your skin, you may feel like they’re touching you, even if there’s no contact. You sense their closeness. In a similar way, researchers reporting in ACS Applied Materials & Interfaces have made a soft, flexible film that can detect nearby objects without touching them. The study shows the new sensor technology being used to track eyelash closeness in blink-tracking glasses.
Noncontact sensors can measure an object without directly touching it. Infrared thermometers and vehicle proximity notification systems are examples of these devices. One kind of noncontact sensor uses static electricity to detect closeness and small motions. It could improve smart devices, such as letting phone screens recognize more finger gestures. However, until now, these sensors have been limited in what objects they can detect, how long they hold a charge, and how difficult they are to make. Xunlin Qiu, Yiming Wang, Fuzhen Xuan and coworkers wanted to create a flexible static electricity-based sensor that solved these issues.
The researchers started by making a simple three-part system: fluorinated ethylene propylene (FEP) for the top sensing layer, an electrically conductive film in the middle, and a flexible plastic base on the bottom. FEP is an electret, a material that’s electrically charged and produces an external electrostatic field, like how a magnet produces a magnetic field. Then they electrically charged the FEP-based sensor, making it ready to use.
When objects came close to the FEP surface, their natural static charge made an electrical current flow in the sensor, allowing it to “feel” the object without physical contact. The resulting clear and flexible sensor detected objects made of glass, rubber, aluminum and paper that were nearly touching it but not quite, from 2 to 20 millimeters (less than an inch) away. The sensor held its charge for over 3,000 different approach-withdraw cycles over almost two hours.
To demonstrate the new sensing film, the researchers attached it to the inside of an eyeglass lens. When a person wore the glasses, they noticed the approach of eyelashes and identified when the wearer blinked Morse code for “E C U S T,” the abbreviation for the researchers’ institution. In the future, the researchers say their noncontact sensors could be used to help people who are unable to speak or use sign language communicate or even detect drowsiness when driving.
