Did you know that several industrial, automotive and healthcare applications rely on accurate and precise measurement of pressure? Flexible and wearable pressure sensors are generally fabricated using petroleum-based polymers. But the solid waste generated from using such non-biodegradable plastics is harmful to the environment. But not to worry, as researchers from IISc now have a solution.
A team from the Indian Institute of Science (IISc), Bengaluru, has come up with paper-based pressure sensors that utilise paper as the medium for their manufacture. Though certain types of paper-based electronic devices are currently in use and are gaining greater attention, owing to their natural biodegradability, excellent flexibility, porous fibrous structure, lightweight and low cost, the IISC researchers claim that they have some disadvantages, as per a report by PTI.
"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," said Navakanta Bhat, Professor at the Centre for Nano Science and Engineering (CeNSE) and corresponding author of the paper published in the peer-reviewed journal ACS Sustainable Chemistry & Engineering.
It is his team that proposed a design for the paper sensor. By virtue of its structure and multilayering, it achieves high sensitivity and can detect a broad range of pressures (0-120 kPa) with a response time of one millisecond, IISc said in a statement. The sensor is made of plain and corrugated cellulose papers coated with tin-monosulfide (SnS) stacked alternatively to form a multi-layered architecture. SnS is a semiconductor that conducts electricity under specific conditions, the PTI report has explained.
"Paper in itself is an insulator. The major challenge was choosing an appropriate 3D device structure and material to give conductive properties to paper," says Neha Sakhuja, a former PhD student at CeNSE and the first author of the research paper. She explained that when pressure is applied to the sensor's surface, the air gaps between the paper layers decrease, increasing the contact area between these layers. A higher contact area leads to better electrical conductivity. On releasing the pressure, the air gaps increase again, thus decreasing the electrical conduction. This modulation of the electrical conductivity drives the sensing mechanism of the paper sensor, the scholar added.
"Our key contribution is the simplicity of the device. It is like creating paper origami," Professor Bhat said. Meanwhile, "The sensor shows promise in being developed into a flexible and wearable electronic device, especially in the healthcare sector," the IISc statement said. The statement also says that the research team mounted it onto a human cheek to investigate the motion involved in chewing, strapped it to an arm to monitor muscle contraction and around fingers to track their tapping. "The team even designed a numeric, foldable keypad constructed using the in-house paper-based pressure sensor to demonstrate the device's usability," it added.
"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," Bhat said, as per PTI. For those who do not know, a pressure sensor detects physical pressure and converts it into an electrical signal that is displayed in the form of a number indicative of its magnitude.
