More information: Ting-Kuo Kang. “Tunable piezoresistive sensors based on pencil-on-paper.” Applied Physics Letters 104, 073117 (2014). DOI: 10.1063/1.4866440 Using graphite pencils to draw on regular paper, researchers can make some very inexpensive piezoresistive (PZR) sensors. Due to the piezoresistive effect, a sensor’s resistance changes under an applied strain, allowing it to sense mechanical stress and pressure. The first of these pencil-on-paper PZR sensors was fabricated a few years ago as an alternative to silicon PZR sensors, which are costly and require sophisticated fabrication processes. Explore further © 2014 Phys.org. All rights reserved. A pencil-on-paper PZR sensor with an integrated circuit for measuring the sensor’s voltage change under an applied stress. Credit: Kang ©2014 AIP Publishing Journal information: Applied Physics Letters “PZR sensors can be drawn by anyone with a graphite pencil and paper,” Ting-Kuo Kang, a researcher at Cheng Shiu University in Kaohsiung City, Taiwan, told Phys.org. Although graphite PZR sensors are much easier to fabricate than silicon ones, they generally are not as sensitive because graphite’s electrical properties are not as good as those of silicon. In a new study published in Applied Physics Letters, Kang has further investigated the underlying mechanisms of graphite’s PZR properties and improved the sensitivity of graphite-based PZR sensors.PZR sensitivity is characterized by the gauge factor (GF), which is defined as the ratio of the change in electrical resistance to the applied strain. While silicon PZR sensors have GFs above 100, the GFs of graphite PZR sensors are in the single digits.In experiments, Kang used 12 different grades of graphite pencils to draw U-shaped PZR sensors on paper. The pencils are graded by their ratio of graphite to clay. Grades ranged from 9B to 2H, where H denotes the hardness caused by the pencil’s clay content, and B denotes the blackness due to the graphite content.