The Study Of Wireless Gas Sensors Based On Graphene

With the advent of the Internet of Things era,the demand for wireless sensor networks continues to grow.As the core component of the wireless sensor network,the sensors directly affect the function of the entire system by their performances,and thus are widely used in communications,biomedicine,environmental detection,artificial intelligence and other fields.In the field of gas sensors,on the one hand,it is necessary to develop sensitive materials with high sensitivity,and on the other hand,it is necessary to realize wireless sensing for toxic gases.Graphene is a two-dimensional material composed of hexagonal honeycomb lattices of sp~2 hybridized carbon atoms with the characteristics of high electron mobility,large specific surface area,and high sensitivity to gases,etc.The surface resistivity of graphene changes when gas adsorption occurs on the surface,enabling graphene as a sensitive material for gas sensors.In this thesis,high-sensitivity gas sensing and long-distance wireless gas sensing are realized combining interdigital electrodes and patch antennas with hybrid sensing materials prepared from reduced graphene oxide and silver nano-particles.The main research contents of the thesis include:(1)Three commonly used wireless sensor antennas,namely the coil antenna,the dipole antenna and the microstrip patch antenna,were introduced systematically.The principle of each antenna is briefly analyzed.The coil antenna is mainly based on electromagnetic induction,while the dipole antenna and the microstrip patch antenna are based on backscattering.According to their working principles,the sensing distance of the coil antenna is relatively close while those of the other two are comparatively further.The main parameters involved in wireless sensor antennas are introduced in details,basically including impedance,radiation efficiency,gain,directivity and recognition distance.(2)A reduced graphene oxide dispersion was prepared.Interdigital electrodes were printed on a flexible substrate using an inkjet printer.The reduced graphene oxide dispersion and the nano-silver conductive ink were mixed as a gas-sensitive material,and was covered on the surface of the interdigital electrodes through drop coating.Finally,the sensing performance of the material was tested in a self-made airtight chamber.The response of the interdigital electrodes based sensor to ammonia at concentrations of 15ppm,50ppm,100ppm,and 200ppm were 4.25%,6.1%,10.08%,and 14.7%,respectively,with high sensitivity and good flexibility.(3)Firstly,a wireless flexible gas sensor based on dipole antenna was designed and simulated,which was prepared by inkjet printer and verified through simulation.However,its performance was not desirable.Secondly,a high-performance microstrip patch antenna was designed,at the end of which a graphene hybrid sensing material rGO/Ag-ink was loaded.Through wired measurements,it was found that the antenna had a frequency shift of~10MHz in ammonia with a concentration of 200ppm.Afterwards,the change of ammonia concentration is detected through wireless sensing tests on the two antennas detecting the change of the return loss of the transmitting antenna,and its working mechanism is explored.Finally,the radiation performance of the graphene antenna sensor was tested,and the results are in good agreement with the simulations.The microstrip patch antenna sensor not only realized wireless sensing but also had 5.15dBi high gain.