High Efficiency Low Power Rectifiers and ZVS DC to DC Converters for RF Energy Harvesting

Abstract

In recent years, advancements in modern technologies have grown the demand for low-power wireless devices. Considering that enhancing the lifetime of the required battery to maintain the operation of these devices is still impractical, harvesting energy from ambient sources has become a promising solution to power portable low power electronic devices. Harvesting ambient energy from the electromagnetic wave (EM), which is referred to as radio frequency energy harvesting (RFEH), is one of the most popular power extracting methods. Scavenging energy can be used to fully supply the power required for wearable electronics devices, RFID, medical implantable devices, wireless sensors, internet of things (IoT) etc. RF energy is readily available in urban environments due to the abundant existence of HF and UHF technologies. Therefore, there is a great interest in studying systems working in UHF bands, including 300MHz to 3GHz frequencies. Radio frequency energy harvesting is a method which converts the received signals into electricity. This technique offers various environmentally friendly alternative energy sources. Specifically, RFEH has interesting attributes that make it very practical for low-power electronics and wireless sensor networks (WSNs). Ambient RF energy can be provided by commercial RF broadcasting stations such as Wi-Fi, GSM, radar or TV. In this study, particular attention is given to design efficient low power circuits suitable to be applied for RFEH as a green technology, which is very suitable for overcoming problems such as powering wireless sensors located in inaccessible places or harsh environments, the possibility to power directly electronic devices, recharge batteries and etc. In RFEH, it is very important to enhance the efficiency of the circuits and systems to maximize the amount of harvested energy. This thesis is mainly concerned with the design, simulation, and implementation of AC to DC circuits including phase shifter, rectifier, and DC to DC converter which is specifically designed for RFEH. It can be applied in various applications such as telecommunications, wireless sensors, medical devices, wireless charging, Internet of Things (IoT) and etc. In the designed system in this thesis, the signal must be passed through a phase shifter, rectifier, and voltage multiplier to reach the required level of output voltage. In another word, this system rectifies the sinusoidal AC waveform to DC and multiplies it to get higher voltages. In this thesis, we propose 1 and 7-stage rectifiers, phase shifters and isolated/non-isolated DC to DC converters will be investigated individually in a general manner and integrated together to have the desired range of outputs for considered applications. This research methodology has three major phases: Phase 1: Theoretical analyses, Phase 2: Simulation investigations and Phase 3: Practical verification. This thesis presents a review on the history of different circuits used to design a low power system for EH. Certain achievements in recent decades make power harvesting a reality, capable of providing alternative sources of energy for a wider range of applications. This review provides a summary of RFEH technologies to use as a guide for the design of RFEH units. Additionally, comprehensive analysis and discussions of various designs of rectifiers, isolated and non-isolated DC to DC converters and phase shifters in addition to their trade-offs for RF energy harvesting purposes are included. In this thesis, novel designs of Dickson rectifiers with high voltage gain and efficiency operating with an input frequency of 915MHz is presented. The proposed circuits introduce a new method of deriving output characteristics of rectification circuit in terms of voltage. The design consists of different stages of the Dickson voltage multiplier. The rectifiers benefit from two input AC sources with 180° phase shift. This Dickson circuit is further discussed in two levels; the first one is a 1-stage rectifier operating with Schottky diodes or diode-connected MOSFETs, and the second is a 7-stage rectifier discussed with both Schottky diodes and diode-connected MOSFETs producing higher output voltages. Furthermore, the prototype of 1-stage rectifier is presented where the input voltage is between -10dBm and 2dBm and the output voltage gained is from 318mV to 1700mV, respectively. Also, the prototype of 7-stage rectifier is presented where the input voltage is -10dBm, -8dBm and -6dBm and the output voltage is gained 1220mV, 1330mV and 1550mV, respectively. Additionally, a new non-isolated high voltage gain, high efficiency zero voltage switching (ZVS) resonant DC to DC converter working under ZVS condition is introduced, which can work in high frequencies with high power conversion rate as well as low losses. The proposed converter can provide 5V output from 350mV input voltage with efficiency of 72.8%. Furthermore, we proposed an isolated DC to DC converter which provides the output voltage of 6V with efficiency of 68%. Due to have an isolation transformer, this converter prevents electric shocks which makes it suitable for applications requiring more safety. All the theoretical analyses are verified by MATLAB and circuits are simulated in PSIM. In addition, two combinations of high voltage gain circuits are introduced for low power applications such as RFEH. The first combination consists of a phase shifter, 1-stage rectifier and resonant ZVS DC to DC converter which has an output voltage of 6V with an efficiency of 71%. The second consists of a phase shifter, 1-stage rectifier and isolated resonant ZVS DC to DC converter with output voltage and efficiency of 5V and 65%, respectively. In conclusion, this thesis is presented in 6 chapters discussing the designed high voltage gain high efficiency low power circuits to convert AC input with frequency of 915MHz to DC output. The circuits can be applied in different low power applications such as energy harvesting systems specifically RFEH.