You know that feeling. That moment when you find yourself lost. Disconnected. Alone.
You’re searching for that energy to restart.
Until someone saves you with a charger 😉
What if you didn’t need a cable? What if you could have unlimited battery life, or at least, the semblance of it? What if, just by walking into a room with low battery power, your phone could begin to recharge while still in your pocket?
With how fast technology is evolving, how we support their battery life must also evolve.
The next revolution in energy transfer, you ask?
The idea of wireless transferring energy isn’t a new one. 😮
It’s been around since the late 17th and early 18th century.
In the mid-1800s, a scientist named Michael Faraday conceived of electromagnetic induction –one of the underlying keystones of this technology (which I’ll explain later.)
It was at this time that Nikola Tesla, another inventor, took this concept and further developed it. By 1891, he had come up with the idea of wireless energy transfer and had wirelessly illuminated a bulb.
Tesla’s dream was to send wireless power over large distances by using the Earth. So, in 1901 he built a tower in Long Island called the Wardenclyffe tower.
He wanted to use the tower to harness the energy that Tesla believed resided within the Earth, in the hopes of turning our planet into a gigantic dynamo.
The tower would receive energy from a coal-power generator then send it deep into the ground using metal rods. Tesla wanted to use the Earth’s crust to transfer the energy. However, the tower was torn down in 1917 and he was never able to develop this idea.
Why haven’t we built the tower yet?
More importantly, if wireless electricity has been around for so long, why haven’t cables become obsolete yet?
Tesla was incredibly ahead of his time. The need for his invention was severely limited in an era void of cellphones, laptops, internal medical devices etc.
Amidst the current technological revolution, new and urgent demand has emerged to build his idea out. The transfer of energy without any physical link does exist…it’s just very limited.
We have yet to develop this tech enough that it can be used at a large scale. For now, it is only commercially available and can only function over small distances.
Speaking of, why is it that it can only transfer over small distances? The science behind wireless electricity transfer is fascinating — but first — a quick crash course on the physics necessary to understand wireless energy transfer.
Let’s get physics-y’all 😎
Electromagnetism and Traditional Charging
In nature, there are 4 Fundamental Forces. These are
- Strong Interaction
- Weak Interaction
To explain how wireless energy transfer works, we’ll have to gain a better understanding of how wired energy transfer works. To do this, we’ll explore electromagnetism.
Here’s a quick break down of each component that I’ll be explaining. I’ve ordered it so that it’s easier to understand the ones further down by first grasping the ones near the top of the list — building block order if you will🔽
- Electric Fields
- Magnetic Fields
- Electromagnetic Fields
- Today’s Batteries and Wired Charging
First up to bat 🏏… Electric Fields
Charges are a property of matter, just like mass, density etc. We’ve all fiddled with a magnet at some point or another and have come to learn that like charges repel and opposite charges attract.
I’ll pose this question now — how do we know what the strength of the force of attraction/repulsion is between two give charged particles? How does one measure the strength of the electrostatic force between two give charges?
To best explain what an electric field is and how it works, I’ll introduce Coulomb’s Law.
The magnitude of the electrostatic force, represented by F(e) is proportional to the absolute value of the product of the magnitudes of two given charges.
That sounds like a mouthful.
All it means is that the strength of the attraction/repulsion between two charges, q1 and q2 is equal to the absolute value of their product.
K is the electrostatic constant. Its mathematical value hovers around 8.987551 109… It is inversely proportional to the square of the distance between them, represented by r2
So far, we’re at:
The result of this equation will be in the form of Coulombs squared over metres squared. If the values of each charge, q1 and q2 are of the same sign, they will repel. If they are of the different signs, they will attract.
Using this formula when we have an object with a known net charge, we can predict how other electric charges react to it when passing nearby. Michael Faraday found that every charged object creates an electric field that pushes a force onto all charged particles in its vicinity.
An electric field is an effect created by any charged object. Fields carry energy and transfer it to other materials with a net charge by exerting electric force.
This concept allows us to imagine that a charge affects the space around it such that whenever another charge enters the field, we can predict how this field will affect the invading charge.
This is where Coulomb’s Law comes back in to fill knowledge gaps.
Now, let’s say that Q represents an existing charge with an electric field and that q represents a second charge entering that field.
The law will aid in defining an electric field at F(e), the force between two charges, is equal to Coulomb’s Constant, k, multiplied by Qq divided by r2
To make calculations of the field, must figure out how much force is placed per charge at any given point around Q at any given distance d1 basically, for given Q, what is the force going to be?
This formula becomes
This defines the electric field at a given point d1 where the force per charge at a given distance, d1, is represented by F/q and is equal to the product of the electrostatic constant multiplied by the charge of the particle creating the field, kQ divided by the square of the distance between the charges, r2.
To define the electric field in general, the formula becomes
Second up to bat 🏏…Magnetic Fields
Simply put, a magnetic field is an idea that allows us to visualize how magnetic force is distributed among the space around something magnetic. It is the region around a magnet where attraction and repulsion happen.
In mathematical terms, the magnetic field is also called the vector field. It can be plotted as a set of vectors on a grid, where each one points in the direction that a compass would point.
Magnetic force is caused by the motion of charges.
- Two objects with charge moving in the same direction have magnetic attraction
- Two objects with charge moving in opposite directions have a repulsive force
Moving charges surround themselves with a magnetic field. The magnitude of magnetic force depends on how much charge and motion there is — and how far apart the two objects are.
Magnetic fields occur when a charge is in motion — when more charge is put in more motion, strength increases.
Using Lorentz Force Law, we can describe this as a fixed amount of charge, q, moving at a constant velocity, v, in a uniform magnetic field, B, to find the force, F.
Field lines can also be used to demonstrate the magnetic field. These lines
- Never cross
- Bunch at regions where the field is strongest
- Always form closed loops
- Start at the north pole and end at the south pole
- Indicate direction
To measure a magnetic field, two factors must be considered. The first part to measure is the direction — this can be done using a magnetic compass that lines up with the field.
The second part is strength and is measured using magnetometers. These exploit the force the electron feels as it moves through the magnetic field. This video does an awesome job of explaining how magnetometers work.
Nikola Tesla makes a short reappearance here, having contributed to the SI system. Magnetic fields are measured in tesla (symbol T).
Third up to bat 🏏…Electromagnetism
Now that we’ve covered electric fields and magnetic fields it’s time, we bust out the big guns…
Electromagnetism is the interaction between electric fields and magnetic fields.
As one of the four fundamental forces of nature, it’s got a pretty important role. This force generates light and energy and holds atoms and matter together.
All matter has an electric charge — the electric forces bring and hold atoms together. A measurable electric field will form as electrons transfer. If the electrically charged particles start to move — the field becomes a flowing electric current and forms a magnetic field around it.
This electromagnetic field will generate waves of electromagnetic energy, or radiation, and transmit it into space. The intensity of the electromagnetic radiation is determined by its frequency. I’m sure you’ve seen the electromagnetic spectrum before…
Electromagnetism is hugely connected with the Earth — as was Tesla’s suspicion. Thousands of miles below the surface is a liquid layer of flowing metal.
This generates electric currents that then produce magnetic fields which encompass the entire planet. These fields actually shield us from harm and create a geodynamo.
The process causes Earth’s poles to attain positive and negative charges, basically transforming the planet into one giant electromagnet.
I think you’re ready.
J.C. Maxwell showed that you could demonstrate all electricity and magnetism with the idea of a single electromagnetic field that permeates all of space.
He said that at every point in space there is a number that tells us something about the point (i.e. the temperature, direction of the wind, speed of wind etc.)
If you were to create a chart of those numbers for every point in the universe, you would have charted a field.
J.C realized that certain numbers represented the strength and direction of a given electromagnetic field. These numbers would explain how the strength of the field at any particular point would affect the strength of nearby points. This idea is what gave reason to magnetics, static electricity and long-range calls.
Maxwell also found that electromagnetic waves travel at the speed of light — they are light!
Though that’s a topic for another day 🤔
Now that we’ve gathered a sound understanding of the physics necessary to dive deep into wireless energy, let’s preface the emerging technology with some good ole’ juxtaposition, eh?
Today’s Batteries and Wired Charging
Batteries diminish and lose capacity until they die. The origin of the battery dates to the 1780s, when two men, Galvani and Volta, conducted an experiment.
Volta created a tower of zinc and copper layers separated by a cloth soaked in a chemical solution. The tower demonstrated the process of oxidation — which we now use in our batteries.
The zinc lost electrons (oxidation), which went through copper and were regained by the ions in the water, called reduction.
In today’s batteries, we use the oxidation-reduction cycle. It creates a flow of electrons between two substances, and by interrupting the flow with an input such as a lightbulb, objects can be powered.
In general, a metal oxidizes within a battery and sends electrons away before they are regained by a substance being reduced.
Once most of the metal has oxidized, the battery dies. This is where rechargeable batteries came in — they reverse the process. By drawing electricity from the wall, electrons are forced to flow back in in the opposite direction.
This makes more electrons available for oxidation the next time you need them. However, the repetition of this process eventually creates irregularities in the metals’ surface, causing gradual prevention of proper oxidation.
Wireless Electricity Transfer
You are now ready, young one 🔮
I’ll preface this section by saying that there are three main forms of wireless electricity transfer/charging. These are
- Inductive Charging
- Magnetic Resonance Charging
- Radio Frequency Charging
Blast off! 🚀
We’ve done most of the heavy lifting now, in terms of knowledge. So, let’s dive right in. Two conductors are inductively coupled when a change in current through one wire induces a voltage across the other wire.
When electrical current moves through a wire, it creates a circular magnetic field around the wire - bending the wire into a coil amplifies this magnetic field. More loops ▶ bigger the field.
If you put a second coil of wire in the magnetic field, the field can induce a current in the second coil of wire.
Michael Faraday was the one to say that magnetic fields can induce electric currents under circumstances where the magnetic field is changing with time (not a constant magnetic field.)
He described this with Faraday’s Law of Induction: a changing magnetic field will induce an EMF in a loop of wire.
Note: EMF is electromotive force — this is what causes electrons to move and form a current.
Other things such as the area of the loop and angle induce EMF too — even if the strength of the magnetic field stays the same because of a property called magnetic flux.
This is a measure of the magnetic field running through a loop of wire where B is the strength of the magnetic field, A is the area of the loop, and cosѲ is the angle between the magnetic field and a line perpendicular to the face of the loop.
Faraday’s Law of Induction lets us calculate how much EMF, therefore how much current, will be induced in a loop of wire by a change in magnetic flux.
So, how does wireless electricity use induction?
Induction is the creation of a voltage difference across conductive material by exposing it to a changing magnetic field — a process through which magnetism or electricity is passed between two objects without physical contact.
Basic wireless charging pads use induction to inductively charge devices. Using coils and monitoring things like alignment, separation and size, we are now able to decide coupling factors, that is, how much energy is transferred between coils, to our benefit.
Magnetic Resonance Charging
Also called highly coupled magnetic resonance, this is a special form of inductive charging.
Basically, if both coils operate at the same resonant frequency (oscillation at certain frequencies), a strong coupling results and creates an energy tunnel that prevents the leakage of energy transfer over longer distances.
A transmitter coil oscillates at a specific frequency and sends power to the receiver coil which is tuned to the same frequency. This also ensures that only coupled devices connect to one another without affecting other devices.
Radio Frequency Charging
Finally, we have radio frequency charging. This one is unique in that it is uncoupled wireless charging that uses electronic waves or radio frequencies rather than magnetic fields.
This one is quite simple — an RF transmitter transmits RF waves and a receiver embedded within a device will pick them up. The receiver, called a rectenna, converts AC electromagnetic waves into DC electricity. It uses an RF antenna attached to a semiconductor.
The waves are turned into electricity and powers the device. There are two sub-categories:
- Far-Field: emission of RF signals in an open space with a transmitter that locates a receiver in a certain area
- Near-Field: drop the device into a charging station
A cool advance within RF charging has been taken on by a company called Guru. They’ve built a wireless charging system that transmits electricity using high-frequency radio waves, mmWaves. These are a keystone of emerging 5G networks — another disruptive and soon to be revolutionary technology.
Wireless electricity transfer is going to be such a disruptive technology. Some of the implications are huge! Just to name a few — unlimited battery life for starters, but also things like being able to wirelessly charge medical devices inside the human body! There is so much yet to be seen — and it’s only getting more exciting 😊