How reputable is it to use RF for wireless charging?

[post355]

I came across Energous, a company that claims to be using RF at 5.8GHz to transmit enough power to charge 12 phones from 15ft away.

They have no product on the market yet they still managed to IPO, which sounds like a scam.

It looks like they are using patch antennas to directionally transmit RF after they have located the receiving device.

How reputable is their technology?

Links:
[URL unfurl="true"]http://www.theverge.com/2015/1/8/7518559/wattup-energous-wireless-charging-from-15-feet-away-ces-2015[/url]
[URL unfurl="true"]http://www.engadget.com/2015/01/05/energous-wattup-wireless-charging-demo/[/url]
[URL unfurl="true"]http://techcrunch.com/2015/07/01/a-look-at-the-tech-that-could-mean-we-never-have-to-charge-our-phones-again/[/url]

 

[IRstuff]

Why even ask about the technology? Just do the math. A typical smart phone can easily take about 1.5W during charging, multiply by 15, multiply by about 90 because the transmit is probably omnidirectional. That gets you to what?

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[Comcokid]

Wow! charge your phone, heat your toes (and the rest of your body), and keep you coffee warm all at the same time! Downside is after a few years you will have kids with two heads - that is if you can still have kids.

Greatest invention since thorium toothpaste and radium suppositories.

http://www.dvorak.org/blog/2010/06/...s-radioactive-toothpaste-and-other-fun-stuff/

 

[post355]

@IRstuff Their antennas aren't omnidirectional. They're directional patch antennas. So the loss for the reception at a single point using directional power transfer is much lower than the loss associated with omnidirectional transmission.

I'm curious, is this directionality enough to provide meaningful wireless power to charge a phone, even slowly over a longer period of time. I mean if we'll be in these charging hotspots for an extended period of time, either at work or in the home, it wouldn't matter so much that our phones are charging slower since we're already in those places anyways.

 

[IRstuff]

Even assuming perfect RF transfer, that's 23 W of RF, which is likely to swamp out 5G WiFi receivers. The 1.5W was already a relatively slow charging, requiring about 7 hr to charge a fully depleted battery.

However, the pictures in the article imply that the transmitter is at least somewhat directional, since it's supposedly able to recharge devices anywhere within the room. There may be some sort of beamforming that could potentially minimize the amount of transmitted power required.

Note, however, there's a minimum level of power required to charge and run the devices, so you can't have too low a charger power if you want to use it while it's charging.

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[VEBill]

23 watts (?) of microwave bouncing around the room, in clear violation of common sense, let alone RF safety rules. While causing RF interference and wasting most of the energy.

Meanwhile, other people worry about getting brain cancer from the power lines on the distant horizon, or the 'smart' power meter making the occasional data connection.

 

[IRstuff]

WiFi routers are typically under 1 W of transmitted power, which is less than what's available from a USB port.

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[post355]

Where is the 23W coming from? Why did you multiply 1.5W by 15?

 

[VEBill]

I don't where the "23 W of RF" came from. I see no mention of how much power the system emits. Derived from '12 phones'?

I'm not the slightest bit concerned by moderate levels of RF floating around, but if the power emitted starts to rise to tens of watts and the duty cycle is continuous, then common sense and Health Canada's Safety Code 6 start to raise real concerns.

The gap where such a system could work and be safe is very narrow.

 

[post355]

In the US, the FCC regulates the power emissions of antennas. From my understanding, the power limits were set at a time where interference was a huge issue since the communications protocols being used were still nascent. Therefore the FCC restricted the power limits to be low in order to limit the range of Wi-Fi and other protocols and thereby reduce interferences. Most countries also followed the FCC with regards to this limit.

Now that we have much more sophisticated interference-avoidance algorithms such as OFDM, HARQ, Turbo error codes, MIMO, TCP/IP, etc, power limits are less of an interference issue.

Obviously, we still have to worry about safety, but there haven't been any conclusive evidence for the harmful health effects of low power RF in the 200 years we've been using it. At the extreme end, 1kW+ will heat up your food. But microwave ovens operate in a reflective cavity that traps and amplifies the transmission.

In the tens of watts, I don't see heating be an issue as the power levels are just too low, especially when it's not confined in a reflective cavity. Have you heard of any actual, confirmed (repeated by multiple scientists) studies of the effects of RF at these power levels?

 

[IRstuff]

"Now that we have much more sophisticated interference-avoidance algorithms such as OFDM, HARQ, Turbo error codes, MIMO, TCP/IP, etc, power limits are less of an interference issue."

They help, but I doubt they eliminate. From within my house, I can detect at least eight standard and two 5G WiFi signals, with the standard WiFi limited to the few channels that are available. My WiFi data capacity varies with the time of day, so there's some interference.

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[VEBill]

The science behind RF safety is sufficiently mature that one can calculate the radius of exclusion from various sources without needing to go digging into the journals to prove it all again.

If a system claims to recharge a dozen gadgets at once, and each gadget is at least a couple of watts, Conservation of Energy does hint that it must be emitting at least a couple of dozen watts. Probably more as much the emitted energy will inevitably miss the intended gadgets.

(Or perhaps they're not being entirely honest.)

The exclusion zone for roughly 20-something watts at 5.8 GHz is about 1.5 feet, or much more if the system is using antenna gain (which it apparently is). Therefore it's not safe for use in a room where people might sit in the line of fire.

Unless there's some new magic technology not detailed.

This isn't paranoia of RF (I'm not paranoid about it). This is roughly what the present safety standards are, and they're supposed to be based on the best available science.

The whole wireless power concept is deeply flawed. Because the gap between the practical and the safe is so small.

 

[VEBill]

On the subject of interference.

If the amplitude of the interference is sufficiently high, then it's likely to 'swamp' (exceed the headroom) the first LNA stage. Once that happens, the LNA is clipping and is itself generating a broad spectrum of noise.

The interference notching algorithms, perhaps expecting narrow ISM "tones", wouldn't be able to cope with that.

Distant receivers would perhaps be fine.