Charging through wifi/bluetooth


Basically what the title says. Why is it that no one has come up with a solution to try and charge things such as phones through wifi/bt? I know entirely wireless charging exists in some form, but what makes it challenging to make it up to par with normal charging speeds?

In: 1

Wireless charging works through induction (Faraday Effect), where high intensity electric field is passed from one coil through a second coil, and the two coils can be separated by space.

The electric fields in WiFi and bluetooth are very low intensity and carry very little energy. The also spread out in every direction. Low intensity dispersed fields would charge a phone battery very very slow.

Power could be transmitted through a focused laser beam with high intensity, but a laser woth several Watts of power would burn anything that got in the way of the transmitter and receiver.

Wireless energy transfer is hard.

Wi-fi and bluetooth are every low intensity and energy standards of communication. They’re specific names of standards that just establish how things talk to each other and what frequencies they work on.

Wireless charging is limited by power limits since blasting absurd amounts of radio power is frowned upon by governments, power companies, and anyone who needs to stand near it.
Radio frequencies have issues with the inverse square law, so for every 2x the distance, it only delivers 1/4 the power.
Power drop off is fast over distance.

So it is *technically* possible to blast enough power into the air to charge things across the room, but it also requires a metric crap ton of power to do, and the FCC(And likely other regulatory bodies in other countries) places limits on how powerful transmitters can be. 1 watt omnidirectional. Which is not that much power when you add in the inverse square law, and any losses to heat and the antennas.

Some military trials provided 5 watts of power over 20 feet… but with an empty room… since that much power blasting through the air at the wrong frequency is literally a microwave.

Other issues are if it’s omnidirectional, then a lot of power is being blasted out into nowhere. If it’s directional and focused.. then why not just use a close contact wireless charger or plug it in.

Wireless Qu charging on my Samsung phone takes 2.5 times as long as the direct USB charging time.

Wireless protocols like Bluetooth and wifi are not designed to carry power, just information and are extremely low power.

Wireless power is very inefficient.

Shave the insulation off of your charging cable and plug it into the phone. Now grab the wire. That’s the level of energy you’d need to broadcast through the air in order to charge your phone via wifi or bluetooth. Now realize that wifi and bluetooth are omnidirectional, meaning that level of energy is spreading out in all directions from the antenna. You *really* don’t want to be in the same room with that kind of energy. So to keep it safe, you’d need a directed energy emitter, meaning you’d have to put your phone in a very specific place in order to charge it. At that point it’s easier to just plug it in. Safer, too.

Let’s look at Bluetooth.

Bluetooth can transmit at around 100 mW (20dBm) max.

A nearby peripheral will generally see a signal of around -35 dBm (relatively close).

-35dBm is around 3E-7 W.

Your iPhone 13 has a battery with around 12 watt-hours, so even if you had 100% conversion efficiency, that Bluetooth signal would only take 12/3E-7 = 40 million hours (4563 years) to fully charge your depleted phone.