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Thursday, December 28, 2017

Further thoughts on Energous

Yesterday's blog post on the Energous FCC Part 18 approval was written quite quickly, so I'll follow on with some additional thoughts here:

1) After the initial kick to stock price, it sat quietly for most of the day and then shot up in the afternoon, ending up 160% or so. This morning it's up a further 25% or so, and is approaching $30. At around $50 they become a billion dollar company. Looking at who is buying and what happens to the shorts once that data is available will be interesting. It reminds me again that this is a stock to stay away from, its volatility is what makes it attractive, and as the average guy that's where you get fleeced. Put your money in if you will, be aware it's a gamble. This is also the time where I preemptively point out that I do not hold any position on WATT stock, and make no money whether it goes up or down.

2) I used the Friis equation to calculate power to various distances - that's only truly valid in the far field, and with distances of 50 cm and wavelengths of 33 cm, that's not really the case. Unfortunately I don't have the details with which to do the near-field modeling, so this is the best approximation I have unless Energous want to give more information. I expect it's there to within a factor of two, but that the geometry of the transmitter strongly increases the gain at around the 50 cm mark at the expense of further out.

3) Powercast, who have had long distance wireless charging by RF available as a product for years, also got FCC approval for their product this week. (FCC approval details here) Unlike Energous, Powercast seem to be very open about their numbers and actually have products you can buy. Why aren't they taking off like Energous did if they already have such a product? Yeah, exactly... 

4) Lots of Energous fans are saying "it's only the beginning, it all takes off from here and they just improve". No, no they don't. There are fundamental laws of physics here that mean you don't just suddenly get to get 10x better. Semiconductor processes, shrinking feature sizes every few years, have conditioned people to think that is possible with everything - it simply isn't. Now if you could shrink the wavelength without changing any other characteristics of the wave or system then sure, you could do it. Or maybe if you reduce how much RF radiation gets absorbed by water. How about being able to get the benefit of focusing the power while broadcasting in all directions? Those would be awesome and make this RF method safe, efficient, and effective, so let's just do that. Except those are impossible - you may as well tell them to invent time-travel. 

Just. Not. Happening.

Where it could transmit more power is if the FCC literally raise the output limits, which has significant implications for safety as well as operation of other equipment. I do have strong concerns about the potential for inappropriate pressure from the FCC chair on the regular FCC employees to revisit output limits to favor Energous at the expense of our safety. Why? Well...

5) The FCC chairman tweeted his congratulations to Energous. We've got used to changing norms over the last year, but a government office promoting a private company is out-of-order. If they do for one, they do for all, so where's his mention of Powercast? Of all the things I see happening with Energous, this is the most disturbing, and yet I see no-one blinking anymore about such an abuse of office. 

6) I continue to be in awe of Energous' genius in playing this game. They have a pair of twos and just keep raking in the cash.

I wrote three more posts on Energous in the subsequent 4 days, you can find them herehere, and here.


  1. Thanks for your blog and these updates! Always an interesting read.
    What's your take on Powercast, then? Do you know how their technology is different from Energous's, and what their limitations are?

    1. Thanks. Very quickly, Powercast are using essentially the same methodology but are just being honest about what they can do. I'll answer in more detail later.

  2. what is the frequency at which they are operating? Also if the radiation from their charger has strong directivity, that means that the battery cannot exactly be sitting anywhere. I can do some modeling since that is my job.

    1. 913MHz. They have 12 antenna, in a shallow arc, each emitting around 0.85W. I'd guess around 6 dB-ish (WAG) for directivity. Various reports and beam plots can be found here:


      They definitely try to do some beamforming to target differing locations however I think they have skewed this design to be very 'focused' at 50cm straight ahead.

      Would be interesting to see your results!