Several industrial, automotive, and healthcare applications rely on accurate measurement of pressure. Flexible and wearable pressure sensors are typically fabricated using petroleum-based polymers which are non-biodegradable. To avoid this issue, researchers at the Indian Institute of Science (IISc) have now fabricated pressure sensors that use paper as the medium, says a press note.
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. Paper-based electronic devices are gaining greater attention owing to their natural biodegradability, flexibility, porous, fibrous structure, lightweight and low cost. However, paper-based sensors developed so far have certain disadvantages.
“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,” says Navakanta Bhat, Professor at the Centre for Nano Science and Engineering and corresponding author of the paper published in the ACS Sustainable Chemistry and Engineering. His team has proposed a design for the paper sensor that achieves high sensitivity and can detect a broad range of pressures with a response time of 1 millisecond.
The sensor is made of plain and corrugated cellulose papers coated with tin-monosulfide stacked alternatively to form a multi-layered architecture. “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 doctorate student and the first author of the paper.
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 drives the sensing mechanism of the paper sensor.
The sensor shows promise in being developed into a flexible and wearable electronic device, especially in the healthcare sector. For example, 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, says the press note.
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