Graphene Research Targets Wireless Sensors for IoT

　　Researchers at The University of Manchester in the United Kingdom have embedded graphene sensors into radio-frequency identification (RFID) devices to enable a battery-free, wireless, smart humidity monitor. The work targets Internet of Things (IoT) applications in manufacturing, food safety, health care, and sensitive operating environments such as nuclear waste handling.

　　The researchers describe their work in a paper just published in Scientific Reports. By layering graphene oxide (GO, a derivative of graphene) over graphene to create a flexible heterostructure, the team developed humidity sensors for remote monitoring with the ability to connect to any wireless network. The experimental device requires no battery source, as it harvests power from the receiver. According to the researchers, the sensors can be printed layer by layer to enable scalable mass production at very low cost.

　　Team leader Zhirun Hu predicted the development would lead “to future possibilities for integration of this technique with other 2-D materials to open up a new horizon of wireless sensing applications.”

　　According to the paper, the work involved measuring the relative dielectric permittivity of GO under various humidity conditions at gigahertz frequencies. The researchers found that the relative dielectric permittivity increases with increasing humidity as a result of water uptake. The behavior at gigahertz frequencies differs from that at frequencies of a couple of megahertz or lower; there, the relative dielectric permittivity increases with decreasing humidity.

　　The researchers used this electrical property of graphene oxide to create a battery-free wireless RFID humidity sensor by coating a printed graphene antenna with the GO layer. The resonance frequency as well as the backscattering phase of the GO/graphene antenna become sensitive to the surrounding humidity and can be detected by the RFID reader. The structure thus enables wireless humidity monitoring with digital identification attached to any location or item and paves the way for low-cost, efficient sensors for IoT applications.

　　Graphene was discovered in 2004 at The University of Manchester and was the first two-dimensional material to be isolated. It is stronger than steel, lightweight, flexible, and more conductive than copper. A host of other 2-D materials have been identified since graphene’s discovery, and the list continues to grow. By layering 2-D materials in a precisely chosen sequence to create van der Waals heterostructures, scientists have found they can fashion high-performance structures tailored to specific purposes.

　　Manchester professor Konstantin Novoselov, who won the Nobel Prize in Physics in 2010 and coordinated the humidity sensor project, called the development “the first example of printable technology where several 2-D materials come together to create a functional device immediately suitable for industrial applications. The Internet of Things is a fast-growing segment of technology, and I’m sure that 2-D materials will play an important role there.”