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Demands for self-sustainable energy sources are rising as we become more and more reliable on electronic devices in our daily lives. Scientists and engineers have been exploring various novel methods to harvest energy from existing resources in order to eliminate or reduce the usage of battery and/or conventional power equipment. Solar, water, tide, wind, and terrestrial heat are renewable and green resources that have been widely adopted and commercialized[1]. With the rapid development of technology, more resources can be used for providing energy and compressing the size of devices. For example, piezoelectricity, vibration, and electromagnetic energy can also be used in the large-scale area[2]. Electromagnetic energy, especially in WIFI frequencies, is recently gaining more and more interest because of the wide signal coverage on campus and residential areas. An unique advantage of harvesting electromagnetic energy is its little dependence from weather related factors, unlike solar, water, tide, wind and terrestrial heat[3]. Given the circumstances, the interest in this work is to design a novel rectenna device to harvest energy from WIFI frequencies and to provide a parametric study in efficiency improvement. Our comfort and fast life in modern society roots in massive volumes of data exchange through wireless transmission. In modern communication systems, different radio spectrum’s only use is for single media to prevent interference between users and different devices. International telecommunication Union (ITU) established rules to allocate spectrums for various purposes; the chart [4] shows specific distributions for mobile, broadcast, satellite, and other devices. Since antenna is the only component worked as receiver and transmitter in a device, the main problem in communication systems are the versatility of antenna. So, antenna with reconfigurability is desired in today’s multi-band multi-mode communication system front end. The key solution is to widen the operating frequency band for antenna and, eventually, it can cover more radio spectrums. The target in this work is investigating a tunable wide band antenna which can cover more frequency range. In this thesis, there are two applications proposed and the CPW folded-slot antenna structure is served in both designs. The first one is a rectifying antenna system, or rectenna, which receives WIFI energy at both 2.45 GHz and 5.8GHz channels at a compact size of 2.475x10-3m2. An efficient Schottky diode with low build-in voltage and high reverse breakdown voltage is implemented in a half-wave rectifier which converts RF power to DC power. A swept parametric study is performed to achieve an optimized conversion efficiency. The overall conversion efficiency is expected to reach around 30% at each resonance. Compared to similar designs from literature, this rectenna system is featured by its compact size from dual-band design and adjustable matching between receiving antenna and rectifying circuit, and ease of fabrication due to its single metal layer. Another design is a BST IDC based tunable wide band antenna which has predominant advantage in multiple wireless communication applications. The tunable antenna is designed to operate in K band with a bandwidth from 2.67GHz to 4.42GHz. |
