(Phys.org)—A team of researchers at China's University of Science and Technology has found that lines drawn on paper by an ordinary pencil can be used as a simple sensor. In their paper published in Advanced Functional Materials, the team describes how they tested the paper and pencil sensor idea and suggest applications for which it might be useful. Newscientist offers some background on the work done by the team.
When a person draws a line on a piece of paper with a pencil, they are laying down a layer of graphite, a material that is not very conductive. But, the researchers note, by measuring how much resistance occurs when electricity is sent though the graphite, it is possible to note changes that occur, such as when the page is bent. If a large rectangle is drawn on a piece of paper, for example, it is possible to tell by measuring resistance alone, which way the paper is bent and how much—that constitutes a sensor.
To see if their sensor might be useful, the researchers applied it to a single finger and found they were able to detect degrees of finger bending, the same thing occurred when gluing it to a ruler, they were able to tell how much it was being bent. They also found that when placed in an open book, they could deduce the angle created. The simple sensor, they note can be operated using nothing more than two small batteries constituting just 3 volts—it also demonstrated fast response/relaxation times—just 110ms.
The point of the research, the team explains, is to explore new possibilities for wearable sensors. They acknowledge that the paper/pencil sensor would not work right for that application, but believe it could work with alarm systems, or with other simple applications or even as a teaching aid for young people. They note that their crude sensor proved to work as well as commercially available sensors, which suggests it might provide a way to mass produce very inexpensive sensors for a wide variety of applications, particularly for short term uses or where sensors need to be replaced often.