# Startup claims 1W wireless charging at 10 metres

Another company is claiming to have cracked the mysteries of wireless charging, with an outfit called Ossia saying that using the 2.4 GHz band, it can recharge devices over-the-air at distances of up to 10 metres. Shown off at TechCrunch's Disrupt conference in the video posted here, the charging tech is described as …

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#### Re: Imagine a Starbucks with one of these in the ceiling

No doubt repairing your bald patch at the same time.

#### Re: Imagine a Starbucks with one of these in the ceiling

Yes...and this business of a 'safe' limit of 10mW/cm^2 sounds a bit forgotten as I doubt an iPhone is 100cm^2 of perfect antenna and conversion electronics to get 1W.

"a 2.4 GHz unlicensed transmitter has a maximum power of 4 W"

No - there is no limit (as per EU law) on the transmitter power. However there is an ERP limit...

Exactly. This means that the power emitted in *any* direction must be no higher than the power emitted in *all* directions by an isotropic radiator of the stated power limit.

Plus the fact that regardless of what sort of beamforming array they might have, significant amounts of power will be leaked in other directions.

I suspect this is a Mechanical Turk kind of demonstration.

#### ERP includes antenna gain

So you can have any amount of beam forming or focusing you like, you can still have a maximum of 4 watts radiated.

This also means that no matter how efficient/beam formed/focused you receiving antenna is, you can still only have a maximum of 4 watts (and the recieve antenn

has to be as big as the transmitting antenna). Using iphone 5 as an example, with capacity of 5.45Wh, you could charge it in a bit over an hour........assuming of course 100% efficient transmitter beam forming, no loss of power over the distance, 100% efficient receiver antenna, 100% efficient power conversion from RF to DC and 100% efficient charging circuit.

Add up all the real world inefficiencies and i recon the whole thing is bollocks.

#### Re: ERP includes antenna gain

> So you can have any amount of beam forming or focusing you like, you can still have a maximum of 4 watts radiated.

Nope, that's not what the UK regulation says. If you were allowed to emit 10mW and beam-form it as much as you like, then it would just say that the total power output limit is 10mW.

What it actually says is: you cannot emit more power in any direction than a 10mW isotropic radiator would. Hence Equivalent Isotropically Radiated Power (EIRP).

If you use a high-gain antenna, then you must reduce the power fed into it such that the emissions in the direction of peak antenna gain does not exceed what an isotropic radiator fed with 10mW would emit.

This is widely flouted by people building point-to-point wifi links, but that doesn't change the fact that doing so is illegal.

#### Re: ERP includes antenna gain

That's why this is why it ISN'T a single emitter but a 2D array.

Wack up a beeelion separate devices, each with its own 2.4GHz aerial and *each* emitting at the statutory limit, then with a bit of synchronisation and twiddling with the phases for "beaming" porpoises, you can niftily: charge a suitably equipped phone, feign exemption from regulations, frizz your heirs, bring down every 802.11 b/g/n network within artillery range, reheat the neighbours supper and operate on their cataracts at the same time (they will be pleased), disorientate passing aircraft, jam police communications, and much, much, more!...

Poifect!

#### More than 100W

100W would assume 100% efficiency. Not on your Nelly will you get that! To actually deliver 1W iof useful leccy is going to need perhaps 3 times that or more. We're pretty much talking about a microwave oven with the front glass smashed in.

If it is anywhere near 2.4G then watch out. That's where microwave ovens sit specifically because that's in the water absorption spectrum. 100W of 2.4G is going to cook a lot of kittens. Call me a Luddite if you will, but I'd rather use wires than get that warm sensation all over my body.

#### Re: More than 100W

And that's BEFORE you've considered the "works around corners too" claim! Call me cynical but I cant imagine even a superbly Dr Who tracking parabolic contraption managing that efficiently. Unless you wallpaper with tinfoil perhaps?

#### Re: More than 100W

Domestic microwave ovens use ~2.4GHz for regulatory and cost reasons. Other frequency bands are available and are used depending on the industry, still for food preparation purposes.

#### Re: More than 100W

2.4GHz?

So, charge your phone, and stomp all over every wi-fi network in a half mile radius.

Hmmm...

#### Re: More than 100W

Errm isn't 2.4GHz or thereabouts the resonant frequency of "water" - that's how a microwave works. i.e. any other frequency doesn't.

No.

#### Re: More than 100W

Hmm,

Very suspect as I believe there is power spectral density requirement as well so this cannot be a 4W CW signal but must be spread over several MHz. As it is using multiple antennas these will get added together to calculate the total power radiated.

Still I wouldn't want to go anywhere near such a device as meeting RF Exposure requirements seems a very distant dream, wonder how they would SAR test a wall?

#### Re: More than 100W

"Call me cynical but I cant imagine even a superbly Dr Who tracking parabolic contraption managing that efficiently."

It goes ding when there's stuff. Also, it can boil an egg at 30 paces, whether you want it to or not, actually, so I've learned to stay away from hens.

#### Re: More than 100W

Explicit graphics at

http://www.lsbu.ac.uk/water/microwave.html

#### Re: More than 100W

Microwave ovens work by dielectric heating. Nothing to do with resonance.

The resonance frequency of water vapour (liquid and solid don't have one) is >10GHz.

#### Schmokin'

Reminds me of a story about cattle behaving strangely in a field adjacent to GEC Telecomms transmission systems research unit at Binley. Early Microwave test transmissions were being beamed across a field between a dish mounted on the team's ubiquitous garden shed and a small tower.

Farmer contested that his cattle became sterile.

Maybe these devices are the answer to the world's need for population control.

#### Re: Schmokin'

Farmer contested that his cattle became delicious.

FTFY...

#### Total pass.

No thanks. What hell is wrong with some Qi mats?

#### Look at the article on TechCrunch

2. What is the cost of this for consumers, and size of household device?

A: The Cota will be over \$100, and be about the size of a large tower PC once consumerized.

Hell, why not just say the size of a microwave and be done with it.

#### That burning smell

You would hope there would be some sort of regulations about how many of these could be installed within range of each other. While the article talks about 1 "charger", what happens if your premises puts one in, the shop next door installs one, too - as well as a utility device in the shopping centre and possibly another in the offices above the public area.

A few of these, close together could give the Walkie Talkie building a run for its money in the death ray charts if multiple chargers all locked on to your (pocketed) iPhone at the same time.

#### Tesla would be proud!

Wireless energy transmission, yeah, he thought of that.

#### Witricity

A company formed out of MIT research uses resonant magnetic coupling to achieve this. They have some cool demo videos and some cheap kit you can buy for a great science lesson if you are a teacher.

I do get it. Phase alignment of an array of transmitters. I'm sure it will work as stated with one exception. While I'm sure it's highly improbable that a second point of phase alignment will occur, highly improbable happening with sufficient frequency means it's certain to happen.

Even if you don't believe it yourself. What happens when the wireless charger is on and the phone is in your pocket?

When tissue is already at core body temperature, it doesn't take much extra heating to cook it.

#### erp limits

Last time I checked the erp limit at 2.4gig is +20dBm, or 100mw. You are not going to get much power at 10m or even 1m.

Even if they can raise the power above the regulatory limits they then hit the power safety limits as defined by ICNIRP which are designed to stop you cooking the user.

Whole thing looks like snake oil, even if it works it won't be legal to use in most of the world.

#### Great balls of fire!

So they are going to use beam forming to target your phone; which is in your pocket; right next to your junk....

#### Re: Great balls of fire!

:O Goodness, gracious!

#### Correct me if I'm wrong, but...

If I stick a 1W solar cell on the back of an iphone and then put it on a desk under a big light, then it's basically the same shit as this?

#### Re: Correct me if I'm wrong, but...

> If I stick a 1W solar cell on the back of an iphone and then put it on a desk under a big light, then it's basically the same shit as this?

Except that your system works at about 400THz, not 2.4GHz as these charlatans claim.

#### Re: Correct me if I'm wrong, but...

Nope, if you stuck a solar cell on your phone then you could also charge it outside for free.

(Unfortunately readily available 1W panels are about 2-3 times bigger than your average phone cover, close though)

#### Hmm....

The free space attenuation at 2.4GHz is 60dB, so to get 1W over the area of an antenna is going to require an ERP at 10m of 1MW...shirley?

Sounds like a death ray from Danger 5!

#### Stoopid...

Why didn't they they grab a cheap and cheerful microwave oven and jigger the door interlock so that it'll transmit 600 watts on 2.4 GHz for a total cost of \$50?

This is in addition to the *many* other layers of stoopidity inherent in this concept.

#### Yay for more stupid crap!

We have PLT and this is just extending the realms of useless techno-shite! Bring it on! I'm sure it will play nicely with everything else on 2.4GHz and not de-sense every receiver front end in the surrounding area...

HA HA HA HA HA HA !!!!!!

Why pay more for a device producing power at 2.4Ghz, just bung your new iPhone 5P (plastic) in the microwave and see if it charges.

Awesome.. Was thinking that exactly the same. Cut out the middleman and use kit you've already got.

It's bound to work. 2.4GHz EMR is 2.4GHz EMR agter all.

Try it at home on Christmas morning kids. (...and don't forget to video it so you can post the proof on youtube)

#### On test by PC plod?

Almost sounds like a cut price Taser to me.

#### Re: On test by PC plod?

I expect they're busily fitting them in interview rooms and holding cells as we speak. To keep their phones charged while they're securing confessions - of course - why, what did you think?

2 more things not to forget:

How much would this end up costing just to charge your phone? Thanks to all of the inefficiencies, you can watch your bill skyrocket.

Also, what happens to your phone and its battery when it is trying to charge it all day long? One of the biggest drains on a batteries life is using your phone while it is charging. This is also what causes it to get extra hot.

Yea. I'm going to continue to pass on any form of wireless charging. It's ok, I can manage to plug my phone into a cable while I sleep.

#### yes you can.

The limits are per Transmitter so while you may not be able to have more than 4w from an antenna with whatever gain you put on the antenna if you then make 100 transmitters and had the ability to focus that into the same point from all transmitters you could get 400watts at a receiver 1m away.

Nokia had a much better solution back in 2009. The best part of the Nokia design, you didn't have to buy the wireless charging transmitter. It didn't charge the phone at 1W and a wired charger was still required at times. What they did do, use the ambient radio waves already being transmitted to help charge the phone. This would mean longer standby times but eventually you would need a wired charger to fully charge the battery. But as processors get more power efficient, eventually the power generated by the ambient radio waves could be enough to charge the phone and maybe even enough to fully power it while it is being used.

"The system collects energy from ambient radio waves emitted by antennas, TV masts, Wi-Fi transmitters, and the like." So it is not even picky about the band it uses.

There are some people on here that have as much idea about RF as this "inventor".

Having 100 transmitters connected together does not simply give you 400W. It gives you 100 4W signals.

Do you understand fourier analysis? Go work it out... Also Vsum=V1+V2=Asinωt+(-Asinωt)=0

Using one transmitter and 100 combined 36dBm amplifiers would get you 400W, but that's actually still a single 400W transmitter then and not legal.

The FCC in the US permit 30dBm (1W) into a 6dBi gain aerial for point to point links = 4W EiRP.

For general use, the FCC and the EU rules are the same = 20dBm EiRP.

Not sure if it's still the case, but France used to be 13dBm EiRP.

#### Exceeds safe limit for microwave exposure

Focusing a few watts of microwave power onto something about 5cm on a side results in a power density several times the accepted 0.01 watt per square centimeter safe limit for human exposure.

Geoffery Landis at NASA came up with this idea over a decade ago, and it's patented under US patent #6,967,462. The Ossia patent is just a few tweaks on the Landis patent. The safety issue was described in the Landis patent. That patent proposes detecting backscatter when the beam hit something other than a properly tuned antenna (such as a human) and reducing the power until the human gets out of the way. That might work, but it's iffy from a safety perspective.

At laptop scale, this might work, because the target area is bigger and the energy density of the beam can be reduced by using a wider beam. But charging phones while people are wearing them? Bad idea.

There's no problem doing this. Microwave power transmission has been demonstrated many times. It's just that you don't want people in the beam.

#### savings?

Considering the likely price of one of these, wouldn't you be better off just buying a 1 metre extension cord for your charger?????

#### How many?

Regulation issues aside, I have 10 or more candidate devices at home that would benefit from this technology. A busy Starbucks could easily have 40. He didn't address how to deliver 1W to each of them simultaneously.

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