| Nowadays,with the increasing demand for the development of an intelligent society,large-scale sensor networks,Internet of Things and intelligent skin technologies are widely used.How to provide reliable power supply to maintain the autonomous operation of these devices has become the most urgent problem.Traditional equipment relies heavily on primary batteries,but as time goes on,primary batteries will always deplete the stored energy,and large-scale replacement of batteries will inevitably lead to an increase in system costs.In order to avoid this maintenance cost problem and realize the complete autonomous operation of the equipment,environmental energy acquisition technology has begun to receive close attention from the research community.Free space contains a large variety of environmental energy.However,different environmental energy sources have their own unavoidable shortcomings and usually unable to sustainably supply power to equipment in a single case.In order to overcome this limitation,this paper designs a composite energy acquisition system which can simultaneously collect RF energy and solar energy in natural environment.Firstly,the energy harvesters of the energy harvesting system are designed and manufactured.A circularly polarized microstrip antenna with a working frequency of 2.4 GHz is designed.The antenna achieves good transmission performance and circular polarization characteristics at 2.4 GHz by fine-tuning the size parameters and feed point position.Through processing and testing,the physical data are basically in line with the simulation data,and the reasons for the slight deviation between the two are analyzed.Then a dye-sensitized solar cell was made from camphor leaves and its photoelectric performance was tested.Then,the rectifier of the receiving antenna and the power management module of the system are designed.The rectifier consists of a second-order voltage doubling circuit and a single-frequency matching network.By optimizing the discrete elements in the matching network,the rectifier achieves a good impedance matching with the antenna at 2.4 GHz,and the return loss parameter S11 achieves-62.4dB.After making the physical object and antenna for joint testing,80 mV voltage can be output under the condition of input energy of-13.6 dBm.Power management module mainly uses TI’s bq25504 chip.By setting reasonable resistance and capacitance value in its peripheral circuit,the whole module can collect weak energy as low as 80 mV after starting.In order to improve the receiving efficiency and increase the output voltage of the antenna,a three-band microstrip antenna with working frequencies of 1.8 GHz,2.1 GHz and 2.4 GHz is designed by slotting,and a special three-band rectifier is designed for it.The results show that the efficiency of the rectifier can be improved significantly when multiple frequencies are input at the same time.Then,a method to optimize the performance of dye-sensitized solar cells was proposed,that is,graphene powder with a doping ratio of 100:1 in the titanium dioxide powder was doped in the preparation of photoanode.After testing,the conversion efficiency of solar cells has increased by 1.3 times.Finally,the whole energy acquisition system is built and its output performance under four different input conditions is tested.The results show that,compared with single energy source input,the efficiency of energy acquisition is significantly improved under the condition of compound energy source input,and the sensitivity of energy collection is better. |
