2.1 Low input received power rectennas

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,

Figure 3. Layout of the quasi-Yagi subarray. (a) Top view. (b) Side view [33].

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

WPT categories (a) near-field inductive or resonant coupling, (b) far-field directive powering and (c) far-field

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

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.

frequencies.

154

Figure 1.

ambient wireless energy harvesting.

Recent Wireless Power Transfer Technologies

respectively, at input power of 9 dBm with resistive load of 2.2 kΩ. A dual-band rectenna using Yagi antenna for low input power applications shown in Figure 3 is introduced in [33]. The rectenna offers an acceptable values for the conversion efficiencies, it reaches up to 34% at 1.84 GHz and 30% at 2.14 GHz for input power level of 20 dBm. A combination between the solar energy and RF energy harvesting is discussed in [34]. This solar rectenna, displayed in Figure 4, achieves RF-DC conversion efficiency of 15% with input power of 20 dBm at 850 MHz and 2.45 GHz. In [35], a 130 nm CMOS rectifier is proposed for ultra-low input power. Figure 5 shows the rectenna structure. It consists of 10 stages to give the maximum efficiency of 42.8% at 16 dBm input power and output DC voltage of 2.32 V at

Figure 5.

Figure 6.

157

(a) Proposed RF rectenna equivalent circuit, (b) self-compensated rectifier [35].

Rectenna Systems for RF Energy Harvesting and Wireless Power Transfer

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

(a) Complete prototype of the rectenna, (b) measurement set-up for rectenna system [16].

Figure 4. Hybrid solar/EM rectenna [34].

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

Figure 5. (a) Proposed RF rectenna equivalent circuit, (b) self-compensated rectifier [35].

respectively, at input power of 9 dBm with resistive load of 2.2 kΩ. A dual-band rectenna using Yagi antenna for low input power applications shown in Figure 3 is introduced in [33]. The rectenna offers an acceptable values for the conversion efficiencies, it reaches up to 34% at 1.84 GHz and 30% at 2.14 GHz for input power

harvesting is discussed in [34]. This solar rectenna, displayed in Figure 4, achieves RF-DC conversion efficiency of 15% with input power of 20 dBm at 850 MHz and 2.45 GHz. In [35], a 130 nm CMOS rectifier is proposed for ultra-low input power. Figure 5 shows the rectenna structure. It consists of 10 stages to give the maximum efficiency of 42.8% at 16 dBm input power and output DC voltage of 2.32 V at

level of 20 dBm. A combination between the solar energy and RF energy

Recent Wireless Power Transfer Technologies

Figure 4.

156

Hybrid solar/EM rectenna [34].

resistive load of 0.5 MΩ. A compact co-planar waveguide-fed rectenna using single stage Cockcroft Walton rectifier and L-shaped impedance matching network, shown in Figure 6, is presented in [16]. The RF-DC conversion efficiency is 68% with a received input signal power of 5 dBm at 2.45 GHz. This rectenna also gives conversion efficiencies around 48 and 19% at 10 and 20 dBm, respectively.

#### 2.2 Single and multi-band rectennas

The simplest way in energy harvesting is to harvest from single frequency band; this in turn makes the design of matching circuit, which is used for maximum power transmission between the receiving antenna part and the rectifying circuit, is a little bit easier. In [36], a pentagonal antenna is used with series connection single diode to produce a single band rectenna at 5 GHz. The rectenna has maximum conversion efficiency of 46% at resistive load of 2 kΩ. In [37], a 3 2 rectangular patch array with a gain of 10.3 dBi is used with three-stage Dickson charge pump circuit for energy harvesting. The rectenna works at 915 MHz. Figure 7 shows the antenna array as well as the rectifying circuit. The maximum rectifier efficiency is 41% at input power of 10 dBm. A semicircular slot antenna was presented for Xband planar rectenna (at 9.3 GHz) as depicted in Figure 8 [38]. The rectenna gives RF-to-DC conversion efficiency of about 21% at an input power density of 245 μW/cm<sup>2</sup> . 35 GHz rectenna using 4 4 patch antenna array, displayed in Figure 9, is proposed in [39]. The maximum RF-to-dc conversion efficiency is 67% with input RF received power of 7 mW.

Due to the variety in transmission bands for different wireless systems, there is a large ambient wasted energy at different frequencies. Consequently, the demand for harvesting from different bands increases. In [40], triple-band implanted rectenna is discussed. It works at 402 MHz, 433 MHz and 2.45 GHz with antenna has a stacked and spiral structure. Figure 10 shows the antenna structure in addition to the rectifier design. It gives a conversion efficiency of 86% at input power of 11 dBm with 5 kΩ load resistor. A compact reconfigurable rectifying antenna has been presented in [41] for dual-band rectification at 5.2 and 5.8 GHz. The measured maximum conversion efficiencies of the proposed rectenna are 65.2 and 64.8% at 4.9 and 5.9 GHz, respectively, with 15 dBm input power. The rectenna fabricated prototype is shown in Figure 11. A dual frequency band rectenna has been developed in [42]. A planar inverted F-antenna is used with a voltage doubler circuit to configure a dual band rectenna.

With increasing the number of frequencies at which rectenna can harvest, the complexity of the matching circuit and the size of the rectenna increase. Therefore,

dual-band is the best choice in the designing of rectenna systems because it combines between the simplicity and the scavenging from more than one

There are several studies that are proposed to guarantee stable fixed RF-DC conversion efficiency over a wide band of the input power. In [43], dual-band rectifier with extended input power range is proposed. The rectifier schematic circuit and the fabricated design is displayed in Figure 12. The rectifier offers above 30% conversion efficiency with input power range from 15 to 20 dBm and the

frequency band.

Fabricated rectenna [39].

Figure 9.

159

Figure 8.

Geometry of the X-band rectenna [38].

Rectenna Systems for RF Energy Harvesting and Wireless Power Transfer

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

2.3 Wide input received power rectennas

Figure 7. Six elements antenna array (a) fabricated patch antenna array, (b) fabricated rectifier [37].

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

Figure 8. Geometry of the X-band rectenna [38].

resistive load of 0.5 MΩ. A compact co-planar waveguide-fed rectenna using single stage Cockcroft Walton rectifier and L-shaped impedance matching network, shown in Figure 6, is presented in [16]. The RF-DC conversion efficiency is 68% with a received input signal power of 5 dBm at 2.45 GHz. This rectenna also gives conversion efficiencies around 48 and 19% at 10 and 20 dBm, respectively.

The simplest way in energy harvesting is to harvest from single frequency band;

this in turn makes the design of matching circuit, which is used for maximum power transmission between the receiving antenna part and the rectifying circuit, is a little bit easier. In [36], a pentagonal antenna is used with series connection single diode to produce a single band rectenna at 5 GHz. The rectenna has maximum conversion efficiency of 46% at resistive load of 2 kΩ. In [37], a 3 2 rectangular patch array with a gain of 10.3 dBi is used with three-stage Dickson charge pump circuit for energy harvesting. The rectenna works at 915 MHz. Figure 7 shows the antenna array as well as the rectifying circuit. The maximum rectifier efficiency is 41% at input power of 10 dBm. A semicircular slot antenna was presented for Xband planar rectenna (at 9.3 GHz) as depicted in Figure 8 [38]. The rectenna gives

RF-to-DC conversion efficiency of about 21% at an input power density of

a large ambient wasted energy at different frequencies. Consequently, the demand for harvesting from different bands increases. In [40], triple-band implanted rectenna is discussed. It works at 402 MHz, 433 MHz and 2.45 GHz with antenna has a stacked and spiral structure. Figure 10 shows the antenna structure in addition to the rectifier design. It gives a conversion efficiency of 86% at input power of 11 dBm with 5 kΩ load resistor. A compact reconfigurable rectifying antenna has been presented in [41] for dual-band rectification at 5.2 and

5.8 GHz. The measured maximum conversion efficiencies of the proposed rectenna are 65.2 and 64.8% at 4.9 and 5.9 GHz, respectively, with 15 dBm input power. The rectenna fabricated prototype is shown in Figure 11. A dual frequency band rectenna has been developed in [42]. A planar inverted F-antenna is used with a voltage doubler circuit to configure a dual band

Six elements antenna array (a) fabricated patch antenna array, (b) fabricated rectifier [37].

. 35 GHz rectenna using 4 4 patch antenna array, displayed in Figure 9, is proposed in [39]. The maximum RF-to-dc conversion efficiency is 67%

Due to the variety in transmission bands for different wireless systems, there is

With increasing the number of frequencies at which rectenna can harvest, the complexity of the matching circuit and the size of the rectenna increase. Therefore,

2.2 Single and multi-band rectennas

Recent Wireless Power Transfer Technologies

with input RF received power of 7 mW.

245 μW/cm<sup>2</sup>

rectenna.

Figure 7.

158

Figure 9. Fabricated rectenna [39].

dual-band is the best choice in the designing of rectenna systems because it combines between the simplicity and the scavenging from more than one frequency band.
