**7. Microwave power transfer (MPT)**

Microwave power transmission refers to far-field directive powering, where the power transmission occurs in the far-field using a well-defined directional transmitter. Microwave power transmission depends on the propagation of electromagnetic radiative fields where it is preferred in long-range WPT applications. This sort of WPT is useful for space-based solar power satellites (SPS) applications or with intentional powering such as using a dedicating source with a well-known direction to power a network of wireless sensors, each sensor has its built-in rectenna. One of the first applicable trails of MPT was conducted by William Brown et al. in 1965 by powering an aircraft using a MPT at an altitude of fifty feet for ten continuous hours [51].

There are many challenges regarding RF-to-DC power conversion efficiency, matching circuit design, the dependence of the DC output voltage as well as the conversion efficiency on the input power, load impedance, and operating frequency. In order to solve these issues, many rectennas have been introduced [52, 53]. Several single frequency band rectennas were used for energy harvesting [54, 55], and dual and multiband rectennas were discussed in [56–58]. In [59, 60] we proposed a dualband rectenna using voltage doubler rectifier and four-section matching network. An enhanced-gain antenna with Defected Reflector Structure (DRS) is integrated with the rectifying circuit for increasing the rectenna capability for scavenging. A voltage doubler circuit is used for the rectification. Moreover, a four-section

**Figure 28.**

*Dual-band rectenna using four-section matching network, (a) high-gain received antenna, and (b) integration between the receiving antenna and the rectifying circuit [59, 60].*

matching network is employed for the matching between the antenna and the rectifier circuit. This matching scheme is used to match between a complex and frequency dependent rectifier input impedance and a real impedance of the antenna (ZAnt) by using different sections (Sec.#1, Sec.#2, Sec.#3, and Sec.#4) as shown in **Figure 28**.

Also in 2020 [61], we proposed a dual-band rectenna for low power applications. The rectenna is comprised of a co-planar (cpw) rectifier integrated with a rectangular split ring antenna loaded by a meandered strip line. A single diode series connection topology is used to miniaturize the losses at low input power operation. For maximum power transfer between the antenna and the rectifying circuit, the matching circuit that consists of a spiral coil in addition to two short circuit stubs is used as shown in **Figure 29**. The proposed rectenna operates at low input power with relatively high measured RF-DC conversion efficiency up to 74% at an input power of −6.5 dBm at the first resonant frequency f1 = 700 MHz and 70% at −4.5 dBm at the second operating frequency f2 = 1.4GHz with a resistive load of 1.9 K.

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**8. Conclusion**

**Figure 29.**

This chapter presents a study of wireless power transfer technologies. A survey

of employing several techniques such as inductive coupling, **resonant inductive coupling,** strongly coupled magnetic resonance, and capacitive coupling for increasing the power transfer efficiency for WPT systems. Metasurface-based WPT systems are also discussed. Many recently published WPT designs are listed with a highlight for the used techniques. Microwave Power Transfer (MPT) also intro-

duced, and two rectenna designs are described.

*Low power rectenna, (a) rectifier geometry, and (b) measurement setup [61].*

*WPT, Recent Techniques for Improving System Efficiency DOI: http://dx.doi.org/10.5772/intechopen.96003*

*WPT, Recent Techniques for Improving System Efficiency DOI: http://dx.doi.org/10.5772/intechopen.96003*

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

matching network is employed for the matching between the antenna and the rectifier circuit. This matching scheme is used to match between a complex and frequency dependent rectifier input impedance and a real impedance of the antenna (ZAnt) by using different sections (Sec.#1, Sec.#2, Sec.#3, and Sec.#4) as shown in

*between the receiving antenna and the rectifying circuit [59, 60].*

*Dual-band rectenna using four-section matching network, (a) high-gain received antenna, and (b) integration* 

Also in 2020 [61], we proposed a dual-band rectenna for low power applications. The rectenna is comprised of a co-planar (cpw) rectifier integrated with a rectangular split ring antenna loaded by a meandered strip line. A single diode series connection topology is used to miniaturize the losses at low input power operation. For maximum power transfer between the antenna and the rectifying circuit, the matching circuit that consists of a spiral coil in addition to two short circuit stubs is used as shown in **Figure 29**. The proposed rectenna operates at low input power with relatively high measured RF-DC conversion efficiency up to 74% at an input power of −6.5 dBm at the first resonant frequency f1 = 700 MHz and 70% at −4.5 dBm at the second operating frequency f2 = 1.4GHz with a resistive

**140**

load of 1.9 K.

**Figure 28**.

**Figure 28.**

**Figure 29.** *Low power rectenna, (a) rectifier geometry, and (b) measurement setup [61].*
