Abstract - Energy harvesting techniques are emerging as environmental friendly en ergy sources, which form a promising alternative to existing energy resources. These include rectennas, solar cells, harvesting human energy and wind power. GHz/THz rectennas already exist and have some characteristics such as small size and wideband. Thes e rectennas have a lot of disadvantages such as power fading, complicated design procedure and high fabrication technology. Thus, the present paper suggests using FM rectennas to solve these problems and by using fractals we will keep the advantages. The present paper discusses the design and implementation of a rectenna prototype operating in the FM range. Using Fractal antennas (which offer broadband/multiband operation) and simple tricks from circuit design, God’s willing, proves to be a successful strategy for obtaining useful power from a cheap easy to fabricate rectenna that can be even made in home by interested users. The paper includes theoretical discussion, simulation results and practical prototype results. Keywords: rectennas, fractals,rectifying circuits, antennas, energy harvesting. I. INTRODUCTION Energy harvesting techniques are emerging as environmental friendly energy sources, which form a promising alternative to existing energy resources. These include energy harvesting from rectennas , passive human power, wind energy and solar power. Energy harvesting from human power is used to generate useful power by portable equipments are wearable devices in which digital systems are integrated in everyday personal belongings, like clothes, watch, glasses, etc. Human body can be considered as a storehouse of energy. There exist two possibilities: power can be scavenged from the user's everyday actions or can be intentionally generated by the user. This method has a lot of advantages. It allows the decrease in both size and power consumption of complex digital systems. The power harvesting can be stored in capacitors, rechargeable batteries, etc. The disadvantages of this method arise because the portable products are powered by rechargeable batteries and they will remain as the main source for this kind of consumer products. However the disadvantage of batteries is the need to rather place or recharge them periodically. Typical candidate applications are extracting power from pedaling which can generate power up to 1.6 mJ, from typing which can generate pewer up to 2 mJ with every push of the button of 15 N and power from body heat which can recoverable 2.8 - 4.8 W of power. [1] Another method to harvest energy is offshore wind energy where rese archers are developing new technologies to provide electricity offshore. The new Spar - WARP wind machine developed by ENECO can produce and store clean, safe electricity offshore in many areas where there is sufficient wind speed. Most offshore areas provid e good sites for wind technology. A good land site usually has mean wind speeds of 13 to 17 mph, while typical offshore mean wind speeds range from 15 to 20 mph [2]. The WARP, which stands for Wind Amplified Rotor Platform, is designed to further amplify w ind by as much as 50 to 80 percent, and has many advantages for providing electricity in offshore areas. It can be installed in any depth of water –– on a foundation in shallow water or on a floating platform tethered to the bottom by cable in deep water. A third method to harvest energy the solar power may be used. Solar energy is an environment energy available to power portable devices. A photovoltaic system generates electricity by the conversion of the sun's energy into electricity. Photovoltaic systems are found from the Megawatt to the milliwatt range producing electricity for a wide range of applications: from wristwatch to grid - connected PV systems. The examples of consumer products that contain PV solar cells are: calculators, radios, headphones, l ap tops, battery chargers, etc. [1] Moreover, we can use solar rectennas to harvest solar power but those rectennas are operating at GHz/THz and have a lot of disadvantages such as power fading, complicated design procedure and high fabrication technology . Thus, it has been suggested to use FM rectennas operating at FM range of frequencies using fractal antennas not to harvest solar power but to harvest electromagnetic waves instead of all those energy harvesting techniques because those FM rectennas are simp ler and cheaper to construct. To maintain rectennas advantages, fractal antennas are used. DC - up converter circuits can be used to raise the voltage harvested by the rectenna. The organization of the remaining of the paper is as follows. In secti on II, we will explain the rectenna concept and offer a brief literature survey which shows the efforts of some researchers. Section III explains fractal antennas and especially Sierpinski triangle fractals. This section will show the complete rectenna design applied of a fractal antenna called FRACTENT [5]. Finally in section IV the simulation and the pra ctical results of complete recte nna are given including steps of constructing the cheap simple prototype. Simulations are performed using NEC2 software and P -SPICE software. II. RECTENNA CONCEPT AND A BRIEF LITERATURE SURVEY A rectenna is a device that can harvest microwave energy. It can be constructed using an antenna, rectifier circuit, smoothing circuit. A basic rectenna is shown in Fig.1. [1]
