Battery-less NFC Sensors for the Internet of Things

1Wireless Power Transfer Applied to NFC

1.1. Introduction

Our knowledge of physics determines four different fundamental forces: two of them produce forces at subatomic distances and govern nuclear interactions, and the other two, gravity and electromagnetism, produce long-range effects. Each can be mathematically described as an electromagnetic field. Michael Faraday was the first to describe one of these forces in 1831. He studied the magnetic field generated around a conductor through which a current flows. A few years later, in the 1860s, James Clerk Maxwell developed and unified the theory of electromagnetism, summarizing it in four equations that now bear his name. However, it was Heinrich Hertz who, in 1887, proved the existence of the electromagnetic waves predicted by Maxwell’s equations, inventing the dipole oscillator and the resonator (Buchwald 1994). Radio wave evidence was the beginning of wireless power transfer (WPT), and Nikola Tesla was one of the researchers most involved in this regard. He invented radio frequency resonant transformers (Tesla coils) using inductive and capacitive coupling when trying to develop a wireless lighting system. In 1921, he stated: “Power can be, and at no distant date will be, transmitted without wires, for all commercial uses, such as the lighting of homes and the driving of airplanes. I have discovered the essential principles, and it only remains to develop them commercially.” (Wisehart 1921)

Despite the efforts and dedication ...