Contents



Preface

Wireless Power Transfer (WPT) is an old concept with over 100 years of history, and it has been advocated and intensively investigated by notorious scientists, such as Nikola Tesla or William C. Brown. It can be defined as a set of technologies and systems with the purpose of transmitting electrical energy from a source to a certain destination, without using any physical connection. This technology can be useful, not only for applications where the usage of interconnecting wires is inconvenient or not possible, but also to reduce the toxic waste resulting from disposing of 6 billion batteries each year, used for battery operated sensors or electronic circuits.

Recently, several companies and products have been focusing and investing on wireless power transmission components and applications. In this context, the Internet of Things (IoT) and Internet of Nano Things (IoNT) concepts'

massification could be achieved by significantly reducing or even eliminating the

Generally, there are two main techniques considered for WPT systems: the nearfield and the far-field radio-frequency (RF) methods. Near-field operation methods, such as inductive and/or capacitive coupling, are only capable of transferring power over short distances. On the other hand, WPT based on the far-field RF techniques (referred as far-field WPT), where the power is transmitted by electromagnetic radiation, allows for the transmission of electrical energy over longer distances, but at the cost of lower efficiencies. This feature makes the farfield method an attractive WPT option solution for powering the billions of connected devices that are expected to be ubiquitously deployed worldwide.

The main characteristics of the WPT methods are presented in Table 1.

Some interests have been referenced in the recent years towards the low profile, low power, energy efficient, and self-sustainable sensor networks. Many applications and devices have fulfilled these requirements, such as Radio Frequency Identification (RFID), wireless sensor networks (WSNs), wearable and implantable medical devices, structural health monitoring, and IoT/IoNT. Such applications can involve a wide range of power levels (μW to few W), depending on the target applications

Since the concept of WPT is still an active demand, and every day there are new developments in this area, this book aims to promote and present some of the recent

Near-field Low Hz to MHz Weak Short Strong High

strong

Directivity Achievable Range

Penetration Capacity

Long Medium to weak Medium to

Efficiency

low

sensors' battery requirements.

and the distance from the controlled source.

Operation Frequency

Far-field Medium MHz to THz Medium to

Range

Comparison of WPT methods.

WPT method

Table 1.
