Natasha Drake, April 21, 2021
How do wireless technologies work?
From wireless charging to 5G, why the electromagnetic waves emitted
by our devices aren’t dangerous to our health
In our article on fake news, we promised you an interview with Igor Spinella, CEO of Einova and mechatronic engineer, all about wireless charging and electromagnetic waves. The 5G revolution has raised some concerns about the nature of this technology and possible consequences for our health. That's why we asked Igor to explain how wireless charging and telecommunications work, what electromagnetic waves are, and why the electronic devices that we use every day aren’t a danger to human health. Let's get started!
Igor, could you explain the physical principles behind wireless charging?
We must first distinguish between short range wireless charging and long range wireless charging. Both make use of electromagnetic waves, but in different ways. Short range wireless charging uses the principle of electromagnetic induction. This is the principle behind commercial wireless chargers today. Let's take, for example, our Wireless Charging Stones: when we insert the charger’s plug into a wall socket, the flow of alternating current goes through the transmitting coil embedded inside the stone pad and generates a time-varying magnetic field. This field reaches the receiving coil integrated in the compatible smartphone. And this, in turn, generates electric current and converts it into charging voltage.
No electromagnetic radiation is released into the air because the two coils are very close to each other — in fact, they are adjacent. This limits energy loss (thus achieving high energy efficiency) and makes any interaction between electromagnetic waves and the human body impossible. Our inductive chargers can transmit up to hundreds of watts, depending on the application, but they are all efficient and safe, as evidenced by the mandatory certifications required to market them (e.g. CE, FCC), and quality certifications (e.g. Qi and UL).
On the other hand, long range wireless charging technology is still being explored. As an example, Motorola and Xiaomi have recently developed prototype transmission systems for smartwatches, Bluetooth headsets, and other small devices. Let's emphasize right away that, compared to induction charging, the efficiency is reduced: much of the transmitted energy gets dispersed and lost because the process is physically much more complex.
When you throw a stone into a body of water, the ripples created by the impact grow smaller and weaker as they move away from the point where the stone fell. The same phenomenon happens with energy. The farther electromagnetic waves travel from the source (that is, the transmitting antenna), the weaker they become. The receiving antenna can only pick up a very small part of the power output originally sent from the transmitter.
To get around this problem, Motorola and Xiaomi have come up with a way to direct power to the receiving device. How? By replacing the singular transmitting antenna with an array. The array — a collection of many small antennas — creates a collimated beam, a column of electromagnetic waves that concentrates together all of the waves formerly dispersed in circular, omnidirectional “ripples”. The array then can direct the collimated beam towards the device to be charged.
Although this solution does improve efficiency, the high frequencies involved and the difficulty in controlling the beam mean that, of the 5W of power emitted by the transmitter, less than 1W reaches the receiver. Very little indeed!But that’s not the only limitation inherent here. If the collimated beam transmitted the same amount of power as traditional inductive wireless charging — up to hundreds of watts, enough to power TVs and appliances, as I mentioned before — it would be dangerous to the human body to come into contact with it. Thus, FCC regulations limit current long range wireless charging to just 5W, in order to avoid risks to human health, though this precaution comes at the expense of charging speed and efficiency.
What about wireless telecommunication? How does that work?
The principle is identical to that of long range charging: there’s a transmitting antenna and a receiving antenna that traffic in electromagnetic waves. In the case of telecommunications, however, the waves don’t carry power, but signals — that is, information. Obviously, there’s still transmission of energy, but it’s significantly reduced compared to wireless charging systems.
What do the electromagnetic waves of wireless charging look like?
When discussing electromagnetic waves, three factors must be taken into account: amplitude, wavelength, and frequency of oscillation. The wavelength describes the distance between the crests of the wave, while the frequency indicates the number of crests in a given unit of time. These two quantities, in fact, are inversely proportional, because the smaller the distance between the crests, the greater their recurrence in a period of time. Amplitude, on the other hand, is proportional to the strength of the signal.
To better understand what these parameters correspond to, we can think of the mechanical waves of sound. Amplitude describes the intensity of the sound — a whisper has a smaller amplitude than a scream. And frequency indicates the register; the high-pitched sound of a violin has a higher frequency than the low-pitched sound of a double bass.
Electromagnetic waves have much higher frequencies than mechanical sound waves. Let's imagine a path in the electromagnetic spectrum, which proceeds in an increasing direction. First, we find radio waves, with frequencies ranging from tens of kHz (1 kHz = 1000 Hz) to hundreds of MHz (1 Mhz = 1 million Hertz): these wavelengths are as long as buildings.
Next up are microwaves, with frequencies from 300 MHz to hundreds of GHz (1 GHz = 1 billion Hertz). WiFi, 5G and your kitchen’s microwave all work in the GHz frequencies. Should we be concerned? Absolutely not, because the amplitude of these waves — the other key parameter — is quite different. An oven needs high power to cook food, unlike WiFi or 5G, which use very low and harmless power to transmit signals.
Continuing to go up in frequency, we now meet some electromagnetic waves that we know well: light waves, that is, visible light. No one is worried about the negative health effects of visible light and colors, so why are some of us so needlessly afraid of 5G, which also has relatively low frequencies? I suspect it’s simply a matter of familiarity: because we can see light and colors, we don't perceive them as a threat. And this is despite the fact that we really do need to protect ourselves from some light waves — that is, the higher frequency ultraviolet light. Otherwise we risk sunburn, wrinkles, or even, in extreme cases, skin cancer.
In short, fears about 5G and wireless chargers are misplaced! To recap, frequency plays an important role (think back to the sound of the violin and double bass), but amplitude is also crucial (how loud the sound is). That's why those who produce wireless charging and telecommunications systems must comply with standards that establish within which frequency bands the electromagnetic waves emitted must fall, depending on their purpose, and how much power they can transmit.
“No one is worried about the negative health effects of visible light and colors, so why are some of us so needlessly afraid of 5G, which also has relatively low frequencies?”
So electromagnetic waves can in no way be harmful to our health?
It’s useful to remember that exposure is key. As we have seen, in wireless charging and wireless telecommunications, wave propagation only occurs either in the air or directly between two adjacent electronic devices. In both cases there are no repercussions for the human body: we are not exposed to the electromagnetic waves here. Studies on the effects of radio-frequency electromagnetic fields mainly concern the emissions generated by our smartphones.
When we make a phone call, we expose our ears to the waves produced by the magnetic field of the cell phone: they are low frequency and low energy waves that, once absorbed by the body, produce heat, inducing a slight increase in temperature. You can experience this very easily if you touch your ear after ending a call. Absorption is expressed in SAR (electromagnetic power absorbed per unit mass) and measured in W/kg. By law, cell phones cannot exceed a SAR of 2W/kg. This is a very safe, largely forward-looking threshold that takes into account the maximum power levels a smartphone can reach — for example, when the signal is poor, or during phone dialing.
There is also no scientific evidence on the correlation between electromagnetic wave absorption at these frequency levels and the onset of disease. Even so, using earphones instead of holding the phone to your ear is an excellent way to limit the absorption of electromagnetic waves.
In conclusion, are wireless technologies safe and reliable?
Absolutely, 100% yes. In the last century, wireless technologies have revolutionized our lives. We can now communicate over distance; we’ve emancipated ourselves from the physical barriers imposed by electrical wires. And excitingly, this technology is continuing to evolve. In the very near future, it will allow us to transmit and receive data and energy much faster, to synchronize our devices better, and to connect our lives more.