Precision agriculture allows farmers to maximize yields using minimal resources such as water, fertilizer, pesticides and seeds. By deploying sensors and monitoring fields, farmers can manage their crops at micro scale. Today sensors that are used in agriculture are hampered by extremely high costs and excessive battery power consumption - but graphene ­based wireless, reflective, sensor nodes could help address these issues.

A typical wireless sensor node used by farmers today consists of a sensor that is inserted inside the soil close to the roots and records information about the environmental conditions.

It uses a simple soil moisture sensor to transmit the details to the cloud. In order to monitor a network of 1,000 plants, the operating cost will typically rack up hundreds of pounds per field, and will gobble 20 milliwatts per plant.

In our research project we have tried to address these shortfalls by opting for each plant to have a radio with an antenna, one transistor that acts as a switch, and one microcontroller. 

The sensor (a part of it pictured, above) uses 5G wireless communication based on a reflections technology known as backscatter. The antenna acts as a mirror and when it is illuminated with a signal, it reflects back the wave. The signal comes from an FM radio station and is freely available in the air. 

The plant can modulate information by a very smart switching of this antenna. We are trying, under laboratory conditions, to combine this low power, low cost technology with graphene­ based leaf sensors. Graphene is a two dimensional form of carbon, with a hexagonal structure just one atom thick.

The humidity sensors will be made to adhere to leaf surfaces to monitor water movement within plants upon irrigation. They will detect the electrical resistance changes of graphene in different moisture environments. 

Our goal is to develop tape ­based, flexible graphene humidity sensors that can interact with plant leaves for real time monitoring. The sensor will be embedded on a simple sticker, which a farmer can apply to a leaf on each plant. It will then send the water data wirelessly to a nearby reader. 

Nanotechnology enables flexible inkjet printed electronics to revolutionise Internet of Things applications. We hope that our nanomaterial­ based printed  circuit sensors will help push state ­of the art additive manufacturing in agricultural technology applications.