Well, not entirely out of thin air, but out of the energy that permeates the modern world.
This article presents two works by harshithar76 and vidyashree.2105. In these papers, the authors will talk about their work on “collecting” radio frequency radiation and converting it into electricity for practical purposes. The works are combined into one article, because the authors worked within the same project.
So, let's start with the first diagram of the author harshithar76.
The master's article demonstrates a prototype that collects energy from the environment through an antenna. The circuit works when it is near sources of RF radiation such as Wi-Fi, cell phone, etc., The device collects RF energy from its surroundings, converts it into DC current and charges a supercapacitor with it.
Tools and Materials : -High-frequency diode HSMS 2860;
-Two-layer copper-clad board;
-SMA connector for PCB mounting; -Coaxial cable (resistance 50 Ohm); – Resistors – 47, 1K, 10KΩ; -Capacitors – 1pF , 1nF; -Inductor – 10nH;
-Wires and connecting cables;
-Super capacitor; -Multimeter;
Step one: description
This circuit consists of three main blocks:
Impedance matching circuit
RF to DC converter circuit
The most important part in the implementation of this project is the design and manufacture of the antenna.
The antenna plays an important role in the design of the RF energy harvester. In this project, the master chose the patch antenna over other antennas because of its characteristics such as low profile, compactness, low manufacturing cost, and also because it supports linear and circular polarization.
Step two: design the patch -antennas using HFSS software
Using HFSS (High Frequency Structure Simulator) software, a built-in powered antenna operating at 2.4 GHz was developed.
In order to design an antenna in a simulator, it is very important to know its characteristics as required. There are several parameters to consider when designing and manufacturing an antenna.
Substrate: FR4 epoxy resin with a relative permittivity of 4.4, a loss tangent of 0.009 and a thickness of 1.6 mm.
Impedance: 50 Ohm
Dimensions: Lg = 38.52 mm, Wg = 47.01, Lp = 28.92, Lg = 37.41, a = 3 mm, b = 19 mm.
For more understanding, you can watch the video about the development of the patch antenna below. < br>
Step three: simulating an impedance matching circuit with Multisim software
The next step is to simulate an impedance matching circuit.
Impedance matching is necessary to transfer maximum power between the antenna and the RF-DC converter. This circuit is used in this project to have minimal return loss and improve system performance.
The wizard chose the T-match circuit because of its high Q and low ripple.
T matching circuit designed and simulated using Multisim software.
The output of this circuit is noted and compared to the practical output.
< a href = "https://usamodelkina.ru/uploads/posts/2021-04/1618070236_1-6.jpg" rel = "prettyPhoto"> Step Four: Simulate the RF to DC Conversion Circuit
Low-level RF energy captured by the antenna is fed into the RF-DC/DC converter circuit through an impedance matching circuit. The received electromagnetic waves are converted into direct current using a circuit called “Voltage Doubler”.
The RF to DC converter is constructed using multisim as shown in the diagram below.
Step five: antenna fabrication
Next, the wizard proceeds to fabricate the antenna according to the project.
First, you need to prepare the plate using a chemical etching process.
Then correctly install and solder the SMA connector.
Finally, connect coaxial cable with 50 ohm impedance to the antenna as shown in the picture below.
Step six: manufacturing impedance matching circuits and RF-DC converter
Next, assembles modules according to schemes. Then connect all three blocks. Connects oscilloscope probes to output terminals.
You can also use a DMM to measure the output signal.
Step Seven: Testing
Now you can check the circuit.
As you can see on the oscilloscope, the end result, i.e. the resulting root mean square value, expressed in millivolts, which is approximately equal to the values obtained in the simulation.
This figure is not constant as it is completely dependent on the RF energy. The result can be in millivolts, and sometimes in volts, depending on the intensity of the RF energy waves.
The DC output voltage can be boosted by adding more voltage doubler stages to the RF-DC converter.
This result was obtained when the chain was placed next to a pair of cell phones.
In the next test, the master connects a supercapacitor to the circuit, which keeps charging for some time. After several hours of charging, the capacitor measures its voltage.
Step eight: the second scheme
Now let's turn to another work by the author vidyashree.2105. The work is small, so we will fit it in one step.
This scheme is designed to collect free energy, i.e. RF energy from Wi-Fi routers, Bluetooth, etc.
The RF signal itself is a low energy signal, so the captured output will be low and will vary depending on the environment.
The master uses the following materials for the circuit:
Capacitors: 470uF, 25V1uF, 50V Zener diode: 1N4148
Jumper – FM (for antenna)
Copper wire (SWG26)
The scheme is simple.
High-frequency alternating current is supplied to charge the capacitors, the diodes only allow the current to flow in one direction.
A jumper is used for the antenna. And later, a copper wire 2 meters long is attached to the antenna to increase its capturing ability.
The scheme is assembled by the method surface mounting.
After assembly, he tests the circuit. The multimeter reads 174 millivolts. The output signal is very low as the RF signal itself is a low energy signal and also depends on the environment.
After a while, the circuit was tested with a digital oscilloscope. As you can see in the image, the result is about 6.71 V. This is a pretty good result.
The assembly of a similar scheme and test results can be seen in the video.
Link to the original article of the first work here, the second work here.