Humidity sensors printed on recycled paper and cardboard

Area of Science:

• Materials Science
• Sensor Technology
• Electronics

Background:

• Paper and cardboard are explored as sustainable dielectric materials for sensor fabrication.
• Screen printing offers a cost-effective and scalable method for sensor manufacturing.
• Existing humidity sensors lack integration with wireless communication for smart packaging.

Purpose of the Study:

• To design and fabricate screen-printed capacitive humidity sensors using recycled paper and cardboard.
• To evaluate the performance of different sensor structures under varying relative humidity conditions.
• To develop a Radio Frequency Identification (RFID) enabled sensor system for smart packaging.

Main Methods:

• Capacitive humidity sensors were fabricated using screen printing with silver nanoparticle ink on recycled paper and cardboard.
• Sensor performance was tested in a humidity chamber (35%-80% RH at 23°C), measuring capacitance and conductance.
• Two sensor designs, lateral (comb) and perforated flat plate, were investigated.
• Wireless modules with UHF-RFID functionality and data logging were integrated.

Main Results:

• Recycled paper-based sensors demonstrated a logarithmic response with a three-order-of-magnitude change in capacitance/conductance.
• Cardboard-based sensors showed a less sensitive response (few tens change) over the RH range.
• Both sensor types exhibited process reversibility.
• A functional passive and battery-supported wireless RFID sensor module was successfully built.

Conclusions:

• Recycled paper is a promising dielectric material for high-performance capacitive humidity sensors.
• The developed RFID-integrated sensors are suitable for smart packaging applications requiring humidity monitoring.
• Screen printing on recycled substrates offers a sustainable approach to sensor fabrication.