Wireless transmission of power for sensors in context aware spaces

Abstract

In the present thesis I create and use wireless power as an alternative to replace wiring and batteries in certain new scenarios and environments. Two specific scenarios will be highlighted and discussed that motivated this research: The Interactive Electromechanical Necklace and the Wireless-Batteryless Electronic Sensors. The objective is to wirelessly gather energy from one RF source and convert it into usable DC power that is further applied to a set of low-power-demanding electronic circuits. This idea improves the accomplishments of Radio Frequency Identification (RFID) tags systems. The RF-to-DC conversion objective is accomplished by designing and characterizing an element commonly known as a Rectenna, which consists of an antenna and an associated rectification circuitry. The rectenna is fully characterized in this dissertation and it is used for powering electronic lights, sounds, transmitters, and different types of sensors as well. The wireless power transmission system is presented in the first place with the development of a special set of wearable beads for an interactive necklace. These beads allow physical interaction between the necklace and electronic elements placed in the environment. This scenario demonstrates that passive electronics without batteries are possible. Next I also design and implement low-power sensors that will use the energy delivered from the rectennas to perform active tasks. The switching sensor provides visual/audio feedback to the user when there's a change in the state of the sensed object (i.e. LEDs lit when a stapler runs out of staples); the humidity sensor permits monitoring the humidity in the soil of a flower pot. The sensor actively transmits the information of any of two possible stages (dry soil/humid soil) to its environment. This scenario extends the capabilities of common RFID tags, where not only they transmit information but also can react to their environment in an active fashion.