Research On RF Electromagnetic Wave Energy Harvesting System And Its Application

RF energy harvesting technology can be used to supply power for low-power sensors,implantable bio-medical chips and other electronic devices by harvesting RF Electromagnetic wave signals.As a kind of universal energy form in the current environment,the RF energy has a varied number of features: such as environmentally friendly,stable power supply and can be applied in a wide range,etc.So,the RF energy harvesting technology has a broad development and application prospects.To solve the problems that the traditional battery powered mode requires huge human resource to replace the batteries and some batteries can not be replaced under the special environment,the RF energy harvesting system needs to be studied and designed.The traditional RF energy harvesting system can only harvest single RF band signals.In this paper,the dual-band and broadband RF energy harvesting systems were designed.The main works are listed as follows:(1)Research on the design of the broadband receiving antenna.Two kinds of self-similar broadband antennas were designed and fabricated based on fractal concept.The simulated bandwidth of the first antenna is from 1.05 GHz to 3GHz and the measured bandwidth is from 1.4GHz to 2.9GHz.The simulated bandwidth of the other one is from 0.93 GHz to 2.72 GHz and the measured bandwidth is from 1.0GHz to 2.6GHz.Moreover,a 4-way Wilkinson power divider was designed and fabricated.The simulated and measured results show that he return loss of the input port is more than 20 dB,and the return loss of the output ports is more than 15 dB.The isolation between the four output ports is more than 15 dB,the insertion loss is between 6dB and 7dB,which shows that the power divider achieves good performance.The measured bandwidth of the antenna array that consists of the introduced fractal antenna as the antenna element and the power divider is from 1.5GHz to 2.6GHz,which can cover GSM-1800,UMTS-2100 and Wi-Fi bands.In addition,the effects of patch slotting,thickness of the substrate and dielectric constant on antenna bandwidth were studied.Two kinds of 2×2 circular broadband microstrip antenna arrays have been proposed to achieve the dual-band and broadband responses by using two modes,increasing the thickness of the dielectric layer and reducing the relative permittivity.The simulated bandwidth of the first microstrip antenna array with slots is from 1.82 GHz to 1.9GHz and from 2.06 GHz to 2.16 GHz.The measured bandwidth is from 1.8GHz to 1.88 GHz and from 1.95 GHz to 2.11 GHz.The simulated bandwidth of the other one is from 2.35 GHz to 2.59 GHz,and the measured bandwidth is from 2.3GHz to 2.53 GHz.(2)Research on the design of the matching and rectifying circuit.The rectifying circuit and matching network were designed and optimized in order to improve the conversion efficiency.A series-shunt Schottky HSMS-2852 diode was inserted in the voltage doubler as the rectifying diode.The change of the diode impedance at different input power and different input frequencies was analyzed.The voltage doubler rectifying network was designed and the value of the load resistance and the capacitances were optimized.Two kinds of matching circuits were designed and fabricated.An L-shape matching network was designed to cover the Wi-Fi band and a T-shape matching network was in the GSM-1800 and UMTS-2100 bands.The measured conversion efficiency of the rectifying circuit can reach 23% for the-10 dBm input.(3)Research on the test and application of RF energy harvesting system.The proposed antenna,antenna array and the rectifying circuit are used to form several different RF energy harvesting systems for measurement and applications.The measured system RF-DC conversion efficiency can reach 18%.The measured results of the single-way system show that the output power is 5?W when the fractal antenna is used and it is 10 cm away from the wireless Wi-Fi router.In addition,the output power is 10?W when the microstrip antenna array with slots is used,which is 10 cm away from the wireless Wi-Fi router.The measured results of the multi-way system which is composed of the fractal antennas and power divider show that the output power is 5?W when it is 30 cm away from the wireless Wi-Fi router.Finally,two novel RF energy harvesting cube devices formed of four microstrip antenna arrays and four rectifiers were designed to harvest RF energy.They can harvest the RF energy from the mobile phone with the output power of 1.68 mW,the maximum output DC voltage is 2.3V and DC current is 0.73 mA,which can drive four LEDs,an electronic watch and a clock as well.