Many automotive, healthcare, and industrial applications depend on accurate pressure measurement. Petroleum-based polymers are usually employed for fabricating flexible and wearable pressure sensors.
The solid waste produced from these non-biodegradable plastics is toxic to the surroundings. Now, scientists at the Indian Institute of Science (IISc) have fabricated pressure sensors that employ paper as the medium to avoid this problem.
A pressure sensor senses physical pressure and transforms it into an electrical signal which is shown in a numerical form suggestive of its magnitude.
Paper-based electronic devices are receiving increased attention due to their excellent flexibility, natural biodegradability, lightweight, porous fibrous structure, and low price.
Some disadvantages have been seen in traditional paper-based sensors.
In any sensor, there is always a trade-off between sensitivity and dynamic range. We want to have high sensitivity. Sensitivity is essentially a measure of the smallest entity (amount of pressure) that we can detect. And we want to sense that quantity over an extensive range.
Navakanta Bhat, Study Corresponding Author and Professor, Centre for Nano Science and Engineering, Indian Institute of Science
The study was published in the ACS Sustainable Chemistry & Engineering.
Bhat’s team has suggested a design for the paper sensor that, by virtue of its multilayering and structure, attains increased sensitivity and can sense a wide range of pressures (from 0 to120 kPa) with a response time of 1 millisecond.
The sensor is built out of plain and corrugated cellulose papers covered with tin-monosulfide (SnS) arranged alternatively to create a multi-layered architecture. Under certain conditions, SnS — a semiconductor — conducts electricity.
Paper in itself is an insulator. The major challenge was choosing an appropriate 3D device structure and material to give conductive properties to paper.
Neha Sakhuja, Study First Author and Former PhD Student, Centre for Nano Science and Engineering, Indian Institute of Science
On applying pressure on the sensor's surface, the air gaps between the paper layers reduce, which increases the area of contact between these layers. A higher contact area leads to better electrical conductivity.
When pressure is released, the air gaps increase again, reducing electrical conduction. The electrical conductivity modulation drives the paper sensor's sensing mechanism.
“Our key contribution is the simplicity of the device. It is like creating paper origami,” describes Bhat.
The sensor is likely to be developed into a versatile and wearable electronic device, particularly in the healthcare industry. For instance, the study group mounted it onto a human cheek to examine the movement used in chewing, tied it around fingers to record tapping, and strapped it to an arm to observe muscle contraction.
Researchers also designed a foldable numeric keypad built with the in-house paper-based pressure sensor to show the device's usability.
“The future applications of this device are limited only by our imagination. We would [also] like to work on increasing the stability and durability of these sensors and possibly collaborate with industries to manufacture them in large numbers,” concludes Bhat.
Sakhuja, N., (2022). Structure-Driven, Flexible, Multilayered, Paper-Based Pressure Sensor for Human–Machine Interfacing. ACS Sustainable Chemistry & Engineering. doi.org/10.1021/acssuschemeng.1c08491.