Abstract

With the rapid development of the wireless systems and demands of low-power integrated electronic circuits, various research trends have tended to study the feasibility of powering these circuits by harvesting free energy from ambient electromagnetic space or by using dedicated RF source. Wireless power transmission (WPT) technology was first pursued by Tesla over a century ago. However, it faced several challenges for deployment in real applications. Recently, energy harvesting and WPT technologies have received much attention as a clean and renewable power source. Rectenna (rectifying antenna) system can be used for remotely charging batteries in several sensor networks at internet of things (IoT) applications as commonly used in smart buildings, implanted medical devices and automotive applications. Rectenna, which is used to convert from RF energy to usable DC electrical energy, is mainly a combination between a receiving antenna and a rectifier circuit. This chapter will present several designs for single and multiband rectennas with different characteristics for energy harvesting applications. Single and multiband antennas as well as rectifier circuits with matching networks are introduced for complete successful rectenna circuit models. At the end of the chapter, a dual-band rectenna example is introduced with a detailed description for each section of the rectenna.

Keywords: dedicated RF source, directive radiation pattern, high gain antenna, rectenna (rectifying antenna), RF energy harvesting, wireless power transmission (WPT)

## 1. Introduction

Wireless power transmission (WPT) can be categorized into three different categories as depicted in Figure 1: near-field inductive or resonant coupling, far-field directive powering, and far-field ambient wireless energy harvesting. For the first category, it usually takes place between two coils, one is the primary and the other is the secondary. The main goal is to transfer the power from the primary coil to the secondary coil for several of centimeter as a separation distance between them [1–3]. Many defected ground structure (DGS)-based designs are proposed for this type of the wireless power transfer [4–6] to give a high efficiency coupled system.

2. Literature review on rectennas

DOI: http://dx.doi.org/10.5772/intechopen.89674

Figure 2.

Figure 3.

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2.1 Low input received power rectennas

Rectenna Systems for RF Energy Harvesting and Wireless Power Transfer

In [32], a compact dual-band rectenna is proposed as depicted in Figure 2. The rectenna has a conversion efficiency of 37 and 30% at 915 MHz and at 2.45 GHz,

Rectenna design: (a) design of the top and side view and (b) fabricated rectenna prototype [32].

Layout of the quasi-Yagi subarray. (a) Top view. (b) Side view [33].

Figure 1.

WPT categories (a) near-field inductive or resonant coupling, (b) far-field directive powering and (c) far-field ambient wireless energy harvesting.

The second category of WPT is far-field directive powering that is used with directive power transmission which means the transmission occurs in the far-field zone but with well-defined direction of the source. This sort of WPT is useful for solar power satellites (SPS) applications [7–9] or with intentional powering such as using a dedicating source with well-known direction to power a network of wireless sensors, each sensor has built-in rectenna which is used as a renewable power source to power the connected sensor. The third type is far-field energy harvesting. The receiver does not know the direction of the received power. So, one of the main goals in this type is how to increase the probability of reception by designing antennas with wide beam-width and multiple or wideband resonance frequencies.

Near-field WPT offers a solution to short range powering for electronic devices, it becomes widely commercialized for several wireless applications [10–12]. Near-field transmission can also be useful with wireless implantable devices [13–15]. Nevertheless, near-field WPT suffers from severe issue with regard to the transmitting distance, it covers only very short range distances (few centimeters); therefore this limits its applications. On the other hand, the powering scheme of far-field dedicated source or free ambient powering technique can overcome this problem because of the long-distance charging capability. Several studies are introduced in wireless energy harvesting [16–25]. Although, the great focusing on the wireless energy harvesting, there are many obstacles in the way of free source energy harvesting. One of the main issues is that low input power levels of the ambient energy. Consequently, there are many research papers introduced for rectennas at low input power levels. However, single band rectennas have a simple structures, many research studies [26–31] have investigated the multi-band rectennas as a trial for increasing the scavenging received power with the same rectenna device; various single and multi-band rectennas are presented. Also, there are big challenges with respect to working the rectenna with fixed conversion efficiency values over a wide range of the received signal. Thus, Section 2 introduces a literature survey about single and multiband frequency operation of different rectennas; also, various rectennas' designs working at low input power and over wide input power range are discussed. Finally, in Section 3, dual-band rectenna using voltage doubler rectifier and four-section matching network is discussed as an example for a dualband operation to illustrate the different stages of the whole rectenna system elaborately. The dual-band antenna, firstly, is designed, fabricated and measured separately to check the antenna performance. Then, the rectifier and the matching network between the antenna and the rectifying circuit are also designed and tested independently. After that the integration between the antenna and rectifier is done on the same PCB substrate.

Rectenna Systems for RF Energy Harvesting and Wireless Power Transfer DOI: http://dx.doi.org/10.5772/intechopen.89674
