%T Design of a radiofrequency (RF) energy harvesting system for low-power sensor applications at microwave bands
%D 2018
%A Antonio Alex Amor
%X Energy harvesting is defined as the process of obtaining energy from external
sources, such as wind, sunlight, heat or radiofrequency (RF) transmitters; which
is later conveniently processed and stored in order to feed, in general, low-power electronic systems. Generally, a RF energy harvesting system is formed by four stages:
-	RF harvester: an antenna capable of acquiring RF ambient power from the bands of interest of the radio spectrum.
-	Conditioning circuit: a circuit that converts the signal acquired by the antenna, which is a sum of radio spectrum carriers, into a DC supply.
-	Matching circuit: it is situated between RF harvester and conditioning circuit stages. It maximizes the power delivered from the antenna to the conditioning circuit.
-	Storage circuit: it stores the available energy in order to feed an electronic system (typically a sensor).

The aim of this project is the design of a radiofrequency energy harvesting system as a “free" power source for low-power electronic systems. The work is presented with the following phases and main development tasks:
Firstly, a set of different antennas are being studied. We will focus this
chapter on the study of multiband, wideband, ultrawideband, and frequency
independent antennas. Simulations will be carried out with CST Microwave Studio Suite, in order to optimize the design that will later be manufactured and measured.
Secondly, we will focus on the conditioning circuit. One of the topologies of
our interest is the Cockcroft-Walton voltage multiplier, a circuit that rectifies and
elevates the signal acquired by the antenna. We will simulate and test different
element configurations on it.
Thirdly, we will maximize the power transfer (from the antenna to the circuit)
by placing an impedance transformer circuit. We must study which is the source impedance (the receiver antenna can be seen as a generator with a source
impedance) that maximizes the output power, and then transform the antenna
impedance into this one. For this task, we will lay on the use of simulators
that implement \harmonic balance", a technique commonly used to calculate the
steady-state response of nonlinear differential equations, and it is mostly applied to nonlinear circuits (as the Cockcroft-Walton multiplier).
Finally, we will design an energy storage circuit in order to conveniently store and manage the previously conditioned power. It actually serves as a battery for the low-power electronic system to be fed. Supercapacitors (capacitors of units or tens of Farads) seem as the best candidate for this purpose.
%I Telecomunicacion
%L upm53023
%K Energy harvesting, antenna design, Archimedean spiral antenna,ultrawideband, matching circuit, Cockcroft-Walton multiplier, storage circuit