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Flexible Static Electricity-Based Sensor for Noncontact Positioning

In a recent study published in American Chemical Society (ACS) Applied Materials & Interfaces, researchers from ACS have created a flexible, soft film that senses the presence of objects nearby without coming into contact with them. The new sensor technology used in the study allows blink-tracking glasses to detect the proximity of eyelashes.

Flexible Static Electricity-Based Sensor for Noncontact Positioning
When attached to eyeglasses, a clear, flexible sensor can detect how close eyelashes are to the lens, enabling blink tracking. Image Credit: Adapted from ACS Applied Materials & Interfaces 2024, DOI: 10.1021/acsami.4c02741

If a person hovers their finger over your skin, it may feel as if they are touching you. However, this sensation is not always the result of physical contact. 

Similarly, noncontact sensors can detect and measure objects without physically contacting them. These devices include infrared thermometers and vehicle proximity notification systems.

One form of noncontact sensor uses static electricity to detect proximity and minor movements, and it has the potential to improve smart devices by allowing phone displays to identify more finger gestures.

However, they have been limited in terms of the types of objects detected, the length of time they remain charged, and the difficulty of fabrication. Xunlin Qiu, Yiming Wang, Fuzhen Xuan, and colleagues intended to develop a flexible static electricity-based sensor that could overcome these challenges.

The researchers created a three-part system: fluorinated ethylene propylene (FEP) for the top sensing layer, an electrically conductive film, and a flexible plastic foundation for the middle and bottom layers, respectively. FEP is an electret, a substance that is electrically charged and generates an external electrostatic field, similar to how a magnet generates a magnetic field. They then electrically charged the FEP-based sensor, preparing it for usage.

As objects approached the FEP surface, their inherent static charge induced an electrical current to flow through the sensor, allowing it to “feel” the object without making a physical touch.

The resulting transparent and flexible sensor recognized objects (made of rubber, glass, aluminum, and paper) almost touching it but not quite, ranging from 2 to 20 millimeters (less than an inch) apart. Over nearly two hours, the sensor maintained its charge through over 3,000 separate approach-withdraw cycles.

The researchers demonstrated the novel sensing film by attaching it to the inner side of an eyeglass lens. When worn by a person, the glasses detected the approach of eyelashes and recognized when the wearer blinked the Morse code for “E C U S T,” the researchers’ institution. In the future, the researchers believe their noncontact sensors could be used to aid people unable to talk or utilize sign language to communicate, as well as detect fatigue while driving.

The authors acknowledge funding from the Natural Science Foundation of China Grants, the Shanghai Pilot Program for Basic Research, the "Chenguang Program" supported by the Shanghai Education Development Foundation and 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.

Journal Reference:

Liu, J., et al. (2024) Facile Electret-Based Self-Powered Soft Sensor for Noncontact Positioning and Information Translation. American Chemical Society (ACS) Applied Materials & Interfaces. doi:10.1021/acsami.4c02741.

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