It is an impedance-based sensor, using screen-printed interdigitated carbon-based electrodes on a substrate made from the bio-degradeable polymer PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate)).
Also deposited using screen-printing, the sensitive layer over the electrodes is molybdenum disulfide which, said the university, breaks down into a micro-nutrient and a macro-nutrient.
“Lab tests showed the sensors can reliably monitor soil pH levels, with consistent performance demonstrated in solutions ranging from pH 3 to pH 8 over the course of two weeks,” according to Glasgow. “The team also demonstrated that that the sensors can detect traces of ethephon, a widely used plant growth regulator that can be toxic to humans and wildlife if it contaminates groundwater. At the end of their useful lifecycle, the sensors degrade into key primary and secondary nutrients to support future plant growth.”
The sensing electronics are not compostable, but are reusable, said the research team. They perform a frequency spectrum analysis to determine pH, transmitting this to a central location using Zigbee.
Sensing periodically and transmitting every four hours, daily energy consumption is 14.3mWh – solar cell plus supercapacitor power is planned.
“The sensors themselves can be ploughed back into the fields to help nurture crops, and the electronic modules with less environmentally friendly printed circuit materials can be reused for several years,” said researcher Andrew Rollo, of the university’s James Watt School of Engineering. “Our analysis suggested that replacing the sensors once every three months could reduce the environmental impact of the system by 66%, and 79% over five years compared to disposing of the entire device each time.”
“We’re keen to continue expanding our biodegradable sensor’s ability to detect other key indicators of plant growth and soil health,” said project lead Professor Jeff Kettle. “That could include adding sensitivity to ‘forever chemicals’ like PFAs, which have significant environmental impact.”
The project was shared with Poland’s Łukasiewicz Institute of Microelectronics and Photonic, and Central South University of Forestry and Technology, and is part of a wider international project led by Glasgow called Tesla (Transient electronics for sustainable ICT in digital agriculture).
The Łukasiewicz Institute is part of Tesla, ad are: Canada’s McGill University, Finland’s Tampere University, VTT Technical Research Centre of Finland, and Switzerland’s CSEM Centre Suisse d’Electronique et de Microtechnique.
For more information, read ‘Hybrid Agricultural Monitoring System with Detachable, Biodegradable, and Printed pH Sensors with a Recyclable Wireless Sensor Network for Sustainable Sensor System‘, a freely available paper published in Applied Electronic Materials.
