A new, flexible pressure sensor designed by researchers from the Korea Advanced Institute of Science and Technology (KAIST) is believed to have a wider range of applicability.
The researchers have developed a piezoresistive pressure sensor that has high uniformity with low hysteresis. To achieve this breakthrough, the team chemically grafted a conductive polymer onto a porous elastomer template.
The researchers observed that the uniformity of the pore shape and size and the uniformity of the sensor are directly associated with one another. They also observed that the variability of the sensor properties is directly proportional to the variability of the pore size and shape.
The researchers demonstrated that the recently developed sensor showed relatively higher uniformity with 2.43% coefficient of variation when compared to other sensors made up of pores of random shapes and sizes and had a coefficient of variation in relative resistance change of 69.65%. The team was headed by Professor Steve Park from the Department of Materials Science and Engineering.
The study was published as a cover article in Small journal on August 16th, 2019.
Flexible pressure sensors have been intensively studied and extensively used in electronic equipment, like wearable healthcare devices, robots, touch screens, human-machine interfaces, and electronic skin.
Specifically, piezoresistive pressure sensors, which are based on elastomer‐conductive material composites, are significantly promising because of the several benefits they offer, such as easy and cost-effective fabrication process.
There have been numerous research results on ways to enhance the performance of piezoresistive pressure sensors, and a majority of these methods have been targeted on boosting the sensitivity.
In spite of its importance, increasing the sensitivity of composite-based piezoresistive pressure sensors is not required for several applications. However, hysteresis and sensor-to-sensor uniformity are two characteristics that are highly critical to achieve any kind of application.
The significance of sensor-to-sensor uniformity is evident. For example, measurement reliability is affected if the sensors developed under the same kinds of conditions have varied properties, and this would make the sensor unsuitable for practical applications.
Moreover, low hysteresis is equally important for better measurement reliability. Hysteresis can be defined as a phenomenon where the electrical readings vary based on how slow or fast the sensor is being pressed, whether the pressure is being applied or released, and to what extent and how long the sensor has been pressed.
A high hysteresis in a sensor means the electrical readings will vary even under the same kind of pressure, and this would make the measurements inconsistent.
According to the scientists, they noticed a slight hysteresis degree, which was just 2%. This was due to the powerful chemical bonding existing between the conductive polymer and the elastomer template, which inhibits their relative sliding and displacement, and also due to the elastomer’s porosity that improves elastic behavior.
This technology brings forth insight into how to address the two critical issues in pressure sensors: uniformity and hysteresis. We expect our technology to play an important role in increasing practical applications and the commercialization of pressure sensors in the near future.
Steve Park, Professor, Department of Materials Science and Engineering, KAIST
The study was supported by the KUSTAR‐KAIST Institute and was performed as part of the KAIST‐funded Global Singularity Research Program for 2019.