“Free energy from the air? Yeah, right!”
Your skepticism is understandable. Though the idea is not so far out there: light can be converted to DC current with solar panels; electricity can be converted to magnetism; in a microphone, sound waves are converted (by vibrating a magnet near a coil) to an electrical signal; solar rays can even be focused and converted to heat.
When we think about it, energy is all around us and can be harvested in an enumerable many of ways. So why not take a novel approach? Anyone who has ever used a compass knows that Earth is magnetic. You also probably know magnetic bodies in motion produce electricity. We can see this in any alternator, like the one in your car. So, therefore Earth is electric as well as magnetic, by their very definitions.
We can detect this energy with a simple radio. That static you hear between stations is your radio picking up naturally occurring energy in the RF spectrum.
But can we use this energy to do work? Absolutely! This has been known for a long time. Crystal radios have been around since before the 1930s and can run with no input energy other than the radio signal. A crystal radio will produce a voltage in the earpiece resulting in a sound (albeit an undesirable one).
Well, this is where it gets interesting…
We can replicate this effect. And with modern components like the high quality crystals found in germanium diodes, we can even increase efficiency. By applying this concept as a contemporary crystal energy receiver, we can also take advantage of a wide range of energetic frequencies, rather than tuning in to just one.
We can also scale it up. Things like micro germanium diodes, high efficiency antennas, and compact contemporary capacitors make the components that are required to build a crystal receiver fit in the palm of your hand. While there may or may not be a more efficient way, this renewable energy solution is simple to employ and can be scaled up, or down, indefinitely.
It sounds like we can build a Crystal Energy Receiver. Let’s give it a shot…
The simplest crystal receiver design needs no power and can be built with only three parts: a coil, a crystal, and a resistor. We’re going to optimize that design in order to produce a cleaner and more reliable output signal by first polarizing the input amplitude, then rectifying and filtering the signal. Then we’ll add an antenna, case, and connections.
10-18 gauge Copper Wire
Ceramic Capacitors (matched)
Electrolytic Capacitors (matched; various types of capacitors can be used)
Germanium Crystal Diodes (1A+)
Project box (optional)
Antenna (a loop antenna or elevated antenna is recommended and can be made with copper wire)
Soldering Iron/ Solder (optional)
You can source individual parts from Digi-Key.
Drew Paul has made a kit of all the components available as well.
Building the Circuit
We’re going to build the simplest version of this circuit variation in order to understand how each component interacts and as a proof of concept.
1.) There are three simple systems at work in the circuit that are composed of capacitors and diodes.
Energy in the band of radio waves, among others, will vibrate a wire antenna on an atomic level, sending a discernible signal to its lead. This signal will then meet the junction between two ceramic capacitors wired in series. This junction will force positive charge from the wave to travel in one direction and negative charge in the other direction which, when collected again, makes the signal uniform and polar.
Connecting the two capacitors in series creates leads on each end. The now positively charged side of one and the now negatively charged side of the other creates a two cell battery. This stage of the circuit takes a signal with a net value of zero and adds the absolute values of the positive and negative amplitudes with respect to the origin and produces a positive integer.
Mathematically, this concept can be thought of as taking:
(+1) + (-1) + (+1) + (-1) = 0
and converting it to:
| [(+1) + (+1)] | = 2
| [(-1) + (-1)] | = 2
2.) Next we will connect two crystal diodes, one facing each direction, to each of these leads from our two capacitors in series to form what is called a bridge rectifier. A bridge rectifier is a configuration that will convert an alternating current to a direct one by cleverly rerouting the signal.
By connecting the bridge rectifier as shown in the circuit diagram, this direct current from the diodes then charges the electrolytic capacitors. This stage normalizes the amplitude, making the current constant and usable.
Components can easily be twisted together for testing and then soldered to a circuit board to secure.
Testing and Optimization
1.) We’ll be using a digital voltmeter and oscilloscope to test and analyze our circuit. Then, by connecting a voltmeter to the output, you'll immediately begin to see a small voltage climbing in the 10-100mV range. If not, check the connections and make sure the circuit is not isolated from the environment by taking it outside to a clear area.
By connecting an oscilloscope to the outside leads of the two ceramic capacitor bank, we will see the the polarized signal being captured from the air around us. We can then connect after the diodes to see our varying direct current and after the electrolytic capacitors to see a normalized, usable direct current at our output.
2.) We can then optimize the input resistance in two ways. Firstly, we can add additional ceramic capacitors in parallel to our original two and make sure our soldered connections are consistent and thick in this area.
3.) We can optimize the circuit’s capacity by adding electrolytic capacitors in parallel to our original two, which will allow this circuit to charge slightly when not in use. For this purpose, a charging circuit can also be added here in order to incorporate an optional battery bank.
4.) We can optimize the antenna by attaching loops and coils of copper wire in various positions, store-bought antennas, or by stringing some wire up to the highest point you can reach.
5.) Optionally, we can now also indefinitely connect multiple circuits in series to increase voltage or in parallel to increase current.
Adding a Case and Antenna
1.) After choosing an antenna in the last step, we’ll now want to permanently wire it. Whether you choose a compact antenna for portability or a tall, fixed antenna for power and range, you will wire it in the same manner according to the circuit diagram in the previous step. Note that the input on the configuration here is grounded to the metallic case, and thus the user's hand, and incorporation of longer antennas will require proportionally more substantial grounding.
2.) We will then attach a terminal to the output to allow us to connect this circuit to an electrical device or charging circuit and battery bank.
3.) Next, we will add a case, making sure to isolate exposed leads with non-conductive material—especially if mounting in a conductive case. A piece of cardboard secured with glue is sufficient for the circuit’s bottom, and shrink wrap or electrical tape can be used in the case of any additional exposed leads. Drill two holes in the enclosure—one for the antenna or antenna lead and another for your output terminals. You can then insert your components, fasten the enclosure, and your device is ready to use!
The Crystal Energy Receiver is ready to use!
I built a portable version for proof of concept and demonstration purposes. However, you can go as big as you want to passively charge batteries or run equipment remotely; or go as small as you want to power sensors, RFID devices, small electronics, and more.
I used this harvested energy to easily power a low-consumption quartz clock, a digital chronograph with integrated circuits and LCD, and was even able to momentarily rotate a small dc motor.
[All images courtesy Drew Paul / Drew Paul Designs]