Radio Frequency and Microwave Circuits for Wireless Power Applications

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The impact of wireless communications has been revolutionary. It is difficult to imagine a world without the mobility, convenience, and services that wireless access provides. Building on the enormous success of wireless communications, the emerging area of wireless power is likely to create another evolutionary step in terms of technology development. With wireless power, a device can autonomously recharge, and the days of needing to plug in to recharge will pass into another chapter of technological history. However, there are many challenges to realize ubiquitous wireless power technology, and the long term goals of this research program are to contribute to the advancement of wireless power technology. Similar to wireless communication links, a wireless power link consists of one or more power sources (transmitters), a gap or medium through which power is transferred, and a load circuit (receiver). Wireless power systems can be categorized into near field systems that are designed to efficiently transfer power for large loads over short distances on the order of centimetres, and far field wireless power systems are designed to transfer power over large distances of many metres to kilometres. One of the main challenges in near field wireless power systems is to develop methods to compensate for impedance mismatches that are created by spatial changes between the transmitter and receiver. Developing circuits and methods to compensate for spatial changes is a long term goal of this research program. Three short term research objectives are defined to investigate solutions to this problem. Objective 1 will investigate active matching methods that use multiple transmitters to control the amplitude and phase of the receive signal at the input of the rectifier. Active matching will be used to effect fine impedance control and compensate for small spatial variations. Objective 2 will investigate multi-band frequency tracking as a method of providing coarse impedance control in the wireless link. Together, active impedance matching and multi-band frequency control are expected to provide a robust method of compensating for a large range of spatial variation. Objective 3 will focus on the design of broadband amplifiers and rectifiers to support the implementation of methods developed in Objectives 1 and 2. The research program will also have a second theme focused on far field wireless power systems for low power embedded sensors. The research goals are to implement a wireless power subsystem in CMOS technology that can be used to either recharge a battery in a sensor or autonomously power the sensor. Research into the design of efficient synchronous rectifiers and DC load tracking circuits that are compatible with modulation schemes to harvest RF power will be investigated.