# Goofy gadget, falsified by SCIENCE!

RCA (which is not the old and reputable company I remember, but has gone out of business and its name sold to anyone with the right amount of cash) recently announced a device called the Airnergy harvester, which supposedly simply soaks up the RF energy emitted by WiFi devices in the neighborhood and uses it to charge portable batteries. Wow, what an idea…but a moment’s thought makes it clear it can’t work. My local wireless router simply can’t be pumping out that much energy, or it would an awesomely wasteful device, and there can’t be that much power floating free in every few cubic inches of my home. Fortunately, one of the commenters at that site did the math and made it explicit. Don’t you just love math? It’s so powerful and so handy.

Here’s some math. Long story short, by my calculations, 100% efficiency and absorption at 5 feet away from a 100mW home router, (reasonable figures), it would take 34.5 years to charge that blackberry battery.

It’s not a Dyson Sphere, so you only get the power that hits the antenna.
Surface of a sphere = 4pir^2, r = 60″ (5 feet).
Surface area of a 5′ sphere = 45,216 square inches.

The device appears about 2″ x 3″ = 6 square inches.
The device then picks up, best case, 0.000133 of the power out from the router, which is 100mW, so.. 0.0133mW

If you leave it there for 24 hours, 0.0318 mWh are stored.
According to Will’s battery, it has ~4,000 mWh capacity.

So, it would take 12,579 days, or 34.5 years, to charge your blackberry battery once, presuming 100% absorption, no losses.

I call BS. Even adding up all the laptops, cell phones, routers, portable phones, everything, all the noise in the RF spectrum that could hit that device, I don’t see it charging the internal battery even in a week.

Ah, reality.

For a dose of unreality, though, read through the comments there. The earliest are all fast explanations of the lack of plausibility of the device, and then what happens? It alternates between clueless dopes saying, “Awesome! I want one of those!” and exasperated skeptics saying, “Read the comments up top, it can’t work!”

1. #1 Glen Davidson
January 13, 2010

If there were enough RF energy to power anything, our brains would be seriously overheated.

Much as I’d like to blame ID on such a deleterious onslaught of radio energy, I seriously doubt that’s the problem.

Here’s thought: Solar cell. It harvests a common form of radiation that has an actually significant amount of energy available–during the daytime, anyhow.

Glen D
http;//tinyurl.com/mxaa3p

January 13, 2010

maybe it picks up divine vibrations

3. #3 Nerd of Redhead, OM
January 13, 2010

Reminds me of the Mythbusters studying “free energy” devices. Yes, they could receive “free” RF power. But, there wasn’t enough power gathered to do anything useful, other than to make the test meter move. Nothing like a reality check before one buys something.

4. #4 Sastra
January 13, 2010

Pseudoscience always falls apart in the math. It’s a language with no ambiguity — and all forms of pseudoscience (including religion) rely on fuzzy analogies and superficial similarities which seem to connect one thing to another. Math — and science — instead seek clarity.

5. #5 Autumn
January 13, 2010

The great bit is that the device contains a battery. So I imagine the battery that comes with the device is simply a good, strong battery that will be able to recharge a couple of other batteries, and by the time the customer wonders why the device’s own battery isn’t magically recharging, the manufacturer has moved on.

6. #6 destlund
January 13, 2010

No, no, no people! You’re ignoring the dent. Obviously the dent isn’t just a stupid, ugly design kludge to make the device look “different.” It’s a funnel. It’s probably got a tiny wormhole or something at the bottom of it that somehow sucks all RF radiation within several square kilometers into the device to power it. Or something.

7. #7 Stuart
January 13, 2010

It’s ‘MathS‘… apart from that you’re correct

8. #8 murtagh
January 13, 2010

I do have to wonder about the motive here. Surely they can’t actually have expected that no one would figure this out prior to their beginning sales, and selling such a device would open them up to charges of fraud. So why float the pretense out there?

January 13, 2010

Nipper is rolling around in his little doggie grave.

10. #10 fauxrs
January 13, 2010

So a USB device that supposedly sucks power out of the air when its physically connected directly to a power source?

color me skeptical, how about maybe it doesnt suck power out of the air but just takes it straight out of the PC its plugged into

11. #11 tdc.udel
January 13, 2010

We speak American in these here parts, Stuart.

12. #12 mothra
January 13, 2010

Not only math, but also vocabulary. Scientific jargon reveals something, religious jargon hides something- commonspeak= kind, sciencespeak= species, religi-speak= bariman; Commonspeak= wafer, sciencespeak= wheat flour, religi-speak= Eucharist, commonspeak= donation, sciencespeak= voluntary tax, religio-speak= offering/ tithe.

13. #13 Glen Davidson
January 13, 2010

If all you damn materialists would let ID become science, though, it would work.

Or anyway, if you said otherwise we’d get to prosecute you for jinxing the magic.

14. #14 Bride of Shrek OM
January 13, 2010

Oh great, so with all those nasty radiation thingummy waves floating out there I now have to not only wrap my head in tinfoil when I go out but now also my mobile phone.

15. #15 Stuart
January 13, 2010

@tdc.udel…yeah and that word grates.

Do American schools have lessons called ‘Mathematic’?

16. #16 nathan.pozderac
January 13, 2010

At least they could have come up with a better name…it just sounds like someone is mispronouncing “energy.”

17. #17 Bill Dauphin, OM
January 13, 2010

18. #18 The Other Ian
January 13, 2010

Reposting here the comment I just posted there:

The analysis ignores an important detail: reflection. If you put the device 5 feet from a hotspot, it’s not just going to receive the energy from a 6 square inch cone, but also from waves bouncing off the walls, floor, ceiling, etc. In the extreme case, if you put it inside a black box with a hotspot, it should receive about 50% of the energy (the other 50% would simply be reabsorbed by the hotspot). That’s 50 mW, so the battery would take about 80 hours to charge, assuming 100% efficiency.

Are you going to be able to run a blackberry off this device alone? No way. But it may not be as impractical as it appears at first glance.

19. #19 raven
January 13, 2010

WTH!!!! Next you will be telling me perpetual motion machines are impossible.

There is BTW, a thriving industry build around perpetual motion machines. They even have their own science journal, Infinite Energy. Evey once in a while, a company goes public on the pink sheet stock exchange with a free energy device.

It’s all questionable though. Someone once tried to trade me a perpetual motion machine for my cold fusion power plant. Not a good exchange.

20. #20 Darren Garrison
January 13, 2010

Awesome! I want one of those!

21. #21 co
January 13, 2010

Just to add to Stuart’s dilemma, the American “math” precedes the British “maths” by about 60 years, at least according to the OED.

22. #22 joel.mueller
January 13, 2010

@Stuart –

Do British schools have a “Healths” class?

23. #23 zer0
January 13, 2010

http://www.ted.com/talks/lang/eng/eric_giler_demos_wireless_electricity.html

Wireless power for realsies is almost here. But I highly doubt this device does anything.

24. #24 X. Wolp
January 13, 2010

It is possible to power a crude simple radio with radio waves alone
Anything bigger might be a problem

Curiously enough, extracting power from radio waves was outlawed in Germany for decades. A rather useless law indeed.

January 13, 2010

To The Other Ian: What are your walls made from? Do you live in a Faraday cage? There cannot be very much wifi signal bouncing off the walls, because if there were, then the Wifi on your laptop would only work if it was in the same room as the transmitter and had no walls in the way. This is clearly not how it works. The majority of the signal passes through your walls.

26. #26 Naked Bunny with a Whip
January 13, 2010

Do American schools have lessons called ‘Mathematic’?

We have “math lessons” and “math classes” and “math books”, at least informally.

27. #27 Bill Dauphin, OM
January 13, 2010

Stuart:

Do American schools have lessons called ‘Mathematic’?

No, but by what logic do you preserve the final s when abbreviating mathematics? It’s not as if it’s a countable noun, and the abbreviation must therefore preserve the plural marker. Math is a perfectly comprehensible abbreviation; maths, on the other hand, sounds like you’re talking about something plural, such as multiple subdisciplines within mathematics (e.g., non-Euclidian geometry and vector calculus… [shudder!]).

Y’all have funny ideas about the whole singular/plural thing anyway: When you name a collection of people, like a sports team, for instance, after the place it comes from, you treat that as a plural noun (Chelsea have a match tomorrow.) while we ‘murricans take the much more sensible approach of treating it as singular (Dallas has a playoff game this weekend.). See if you can do something about fixing that, won’t you?

;^)

28. #28 Glen Davidson
January 13, 2010

Do American schools have lessons called ‘Mathematic’?

Do British schools teach you to write 500 Ns as an abbreviation for 500 Newtons?

That said, or asked, the fact is that maths is closer to the usual for abbreviating plurals–that is to say, if it is truly considered to be a plural. With Mathematics usually thought to be more of a collective word for a subject or class–at least in America–leaving off the “s” from the abbreviation seems appropriate enough. Not consistent language, just conforming with how most conceive of “math.”

Right now a number of forums (or should I write “fora”?) I visit flag spellings like “realize” as a misspelling, so perhaps we’ll end up writing “maths,” “tyre,” and “aluminium,” eventually.

29. #29 Fred The Hun
January 13, 2010

Stuart @7

I do have to wonder about the motive here. Surely they can’t actually have expected that no one would figure this out prior to their beginning sales, and selling such a device would open them up to charges of fraud. So why float the pretense out there?

I think you totally underestimate human stupidity and gullibility the Youtube link below might convince you otherwise though.

In May 2006, The Sunday Business Post reported that Steorn was a former dot.com business which was developing a microgenerator product based on the same principle as kinetic energy generators in watches, as well as creating e-commerce websites for customers. The company had also recently raised about ?2.5 million from investors and was three years into a four year development plan for its microgenerator technology.[9] Steorn has since stated that the account given in this interview was intended to prevent a leak regarding their free energy technology.[10]

In August 2006, Steorn placed an advertisement in The Economist saying that they had developed a technology that produced free, clean and constant energy.[4] They admitted that this amounted to a violation of the principle of conservation of energy[2] but said their technology, which would be available for license under the brand name “Orbo”,[13] had already been found to work by eight independent scientists and engineers.[14] Steorn said that none of these scientists was willing to publish their results for fear of becoming embroiled in a controversy[14] and declined to name them, citing mutually binding non-disclosure agreements.[14]

They are currently conducting (no pun intended) public trials on Youtube

30. #30 joel.mueller
January 13, 2010

There are many words that are the same whether they are plural or singular. For example: sheep, salmon, aircraft, deer, series, species, scissors, zucchini.

And math. If for no other reason, the “ths” sound is awkward to make. We say “fishes” instead of “fishs” for similar reasons – the extra syllable makes the word easier to pronounce.

31. #31 The Other Ian
January 13, 2010

@Steven,

There cannot be very much wifi signal bouncing off the walls, because if there were, then the Wifi on your laptop would only work if it was in the same room as the transmitter and had no walls in the way. This is clearly not how it works. The majority of the signal passes through your walls.

Wrong. If you’ll take a look at this chart, you’ll see that most sturdy construction materials block at least half the signal. Even a simple cubicle wall causes an 18 dB attenuation. Fortunately, the signal doesn’t have to go straight through. It can also go around — again, reflection. It’s also possible to run into problems where a reflected signal results in interference.

Now, I don’t know how much signal is reflected and how much is simply absorbed. It is a factor, however.

32. #32 v.rosenzweig
January 13, 2010

Plurals don’t necessarily make sense. I was reading an article in Science about a (claimed) new supernova precursor. The authors were using SN to abbreviate “supernova,” and then wandered back to the classics to pluralize that as SNe. Sure, supernova–> supernovae, but that sort of acronym is thoroughly modern, and at some point, OK, supernova, but if it’s SN the plural is either SN (a la the N for newton above) or SNs (because this is English). As a friend of mine put it years ago, dealing with similar things, the language English Latin not is.

33. #33 Ted Powell
January 13, 2010

This is just a test, to see whether my name shows up correctly as Ted Powell, or as 6p0120a7cabaae970b. In either case, clicking on it should lead to a (minimalist) profile page.

34. #34 SteveM
January 13, 2010

Many RFID tags power themselves off the radio signal that queries them for their ID. But this is a very low power signal that only transmits a short range. There are also remote weather sensors that power themselves from the radio signal that queries them. But these devices do not contradict the calculations that this device is claiming to harvest much more energy than appears to be available.

35. #35 Glen Davidson
January 13, 2010

“Sheep” and “deer” are originally (strong?) neuter plural Old English words, and now keep the original lack of change for plural forms.

“Species” is a latin neuter, and so also does not change form from single to plural. That’s where we’re holding to the latin as we do with “bacteria” for the plural of “bacterium.” “Series” may be similar, I’m not sure.

Oddly, the abbreviation of “species” is often pluralized to “spp.” More convenient, but not consistent language.

“Scissors” is a plural.

Not sure about the rest. I’d repeat that the main reason for our using “math” is how we think of it, rather than sticking to the original concept of “mathematics” truly being about a number of separate issues.

36. #36 nitramnaed
January 13, 2010

Where’s Tesla when you need him!

January 13, 2010

“Math” is not a plural noun and not a singular noun. It’s a mass noun, like “sand” or “pudding” or “water”, that is neither singular nor plural because it refers to a continuous quantity you con’t count with integers. In order for a noun to be pluralizable, it has to refer to something with discrete countability – the most important aspect of which is the ability to distinquish between having one of them versus having two of them. If you can’t distinguish between one of them versus two of them, then there’s no difference between the singular and the plural forms. Anyone claiming the British style of making it look like a plural is more correct than the American style of using it as a mass noun needs to be able to answer the following questions sensibly: “How many maths did you learn?” “At what point did you learn your second math, such that you could start using the word ‘maths’ instead of ‘math’?”

The reason “math” is neither plural nor singular in American usage is because you can’t count how many “maths” you have because it does not refer to a discrete countable thing.

January 13, 2010

@The Other Ian.
If what you claim is true, then closing the door on my bedroom so there is no longer a reflected path for the signal to take should degrade the wifi signal since then I’m only getting it bleeding through solid material and none of it is from reflections. But that isn’t what happens. The signal is just as strong either way, which proves that I’m getting it from bleed-through and not from reflection.

39. #39 David Marjanovi?
January 13, 2010

Do American schools have lessons called ‘Mathematic’?

Where actually does that stupid s come from??? I’ve always wondered, because it’s just not there in other languages, which have an ordinary singular instead (often ending in -a).

if it’s SN the plural is either SN (a la the N for newton above)

Just my 2 ¢s.

40. #40 Michelle R
January 13, 2010

Very failish. And it does indeed remind me of the Mythbusters episode.

41. #41 Ell Vee
January 13, 2010

@ #30

The extra syllable in “fishes” is inserted because in English, we don’t like pronouncing two palatals in direct sequence. This doesn’t apply to maths because “th” is a dental. We would never say “bathes” for instance. I’m sure nobody actually cares though…..

42. #42 Free Lunch
January 13, 2010

I wonder if the Portuguese bemoan how Brazilians speak Portuguese or Spaniards despair of the language spoken in Mexico, Argentina, Chile or elsewhere in Latin America.

43. #43 The Other Ian
January 13, 2010

“Species” is a latin neuter, and so also does not change form from single to plural.

Actually, it’s a 5th-declension feminine noun.

44. #44 destlund
January 13, 2010

“perhaps we’ll end up writing “maths,” “tyre,” and “aluminium,” eventually.”
Sounds dandy to me; for some reason I’ve always written “colour” and “grey,” and didn’t get castigated for it until college for some reason. As a testament to my own mathematical ignorance, I thought the very title of the Look Around You episode, “Maths,” was hilarious until I found out people actually used the pluralized abbreviation. It’s sort of the one thing I can agree Americans are not backwards on (though being left-handed, I rather like our toll booth situation).

45. #45 rob
January 13, 2010

@theOtherIan

your reflection modification argument doesn’t really matter.

the original calculation said 100 mW was the emitted power for the wifi. he then showed about ~0.01 mW could be absobed and got 35 years for the recharge time.

if we assume that all the 100 mW got absorbed, which is an unrealistic upper limit, then the charge time would be reduced to about .35 years, or about 4 months to charge.

in the best case scenario of 100% abosorption of the wifi signal, it still takes a ridiculously long time to charge.

46. #46 David Marjanovi?
January 13, 2010

“Sheep” and “deer” are originally (strong?) neuter plural Old English words, and now keep the original lack of change for plural forms.

Did they once have a plural ending -e, as preserved in German, which then fell off?

“Species” is a latin neuter, and so also does not change form from single to plural.

Nonononono. If it were neuter, its plural would (except rare exceptions) end in -a. Like series, it’s feminine and belongs to the E declension; like for all E declension words, the singular and the plural are identical in the nominative.

Oddly, the abbreviation of “species” is often pluralized to “spp.”

That’s normal for Latin abbreviations. Anatomists abbreviate musculus as M. and its plural, musculi, as Mm.. Also pp. for “pages” ? singular pagina, plural paginae.

47. #47 tdc.udel
January 13, 2010

I was joking about maths, hence the “these here parts.” While we’re on it though, do any Americans conceive of mathematics as plural? I would never consider describing geometry as a mathematic.

48. #48 DaveL
January 13, 2010

Obviously there’s no way a handheld-sized antenna is going to harvest enough energy from a 100mW point source even at modest distances.

If only there were some other commonly available source of radiant energy, along with some way to harvest it.

49. #49 Glen Davidson
January 13, 2010

Did they once have a plural ending -e, as preserved in German, which then fell off?

All I can say is that I don’t know of it being that way.

“Species” is a latin neuter, and so also does not change form from single to plural.

Nonononono. If it were neuter, its plural would (except rare exceptions) end in -a. Like series, it’s feminine and belongs to the E declension; like for all E declension words, the singular and the plural are identical in the nominative.

Thanks for the correction.

Oddly, the abbreviation of “species” is often pluralized to “spp.”

That’s normal for Latin abbreviations. Anatomists abbreviate musculus as M. and its plural, musculi, as Mm.. Also pp. for “pages” ? singular pagina, plural paginae.

Hm, I wonder how that started?

50. #50 alysonmiers
January 13, 2010

Screw the “gather energy from the air” bullshit; that’s NEVER going to be efficient. Even if someone creates a machine that gets the job done, the resources are still far too limited and diffuse; everyone will be competing for the same chunk of energy in the air. What I need is a sticker or implant or some kind of device that will draw energy directly from my body to charge electronic devices. Save on your electricity bill and burn calories at the same time! Alleviate the energy crisis AND the obesity crisis! Even my little bit of pudge could power a netbook, easy.

51. #51 Larry
January 13, 2010

So how much electricity does a charger use to charge the battery of your cell phone or iPod? My guess would that it would cost much less than a nickel. At \$40 (plus S&H) a pop for one of these units, you’d need to charge about 800 batteries using the regular charger before you’d begin to realize any financial benefit. I’m pretty sure that, long before you reach that level, you’d have already decided that its a p.o.s. and had stuck it in the bottom drawer somewhere.

52. #52 David Marjanovi?
January 13, 2010

being left-handed, I rather like our toll booth situation

?

The extra syllable in “fishes” is inserted because in English, [sic] we don’t like pronouncing two palatals in direct sequence.

Well, s isn’t a palatal, and sh isn’t really one either… Try “sibilants”.

We would never say “bathes” for instance.

This is where the infamous English spelling system comes in. There is indeed a word bathes, the 3rd person singular present of the verb bathe… but it’s pronounced very differently, though it does contain a fricative sequence just like baths.

I wonder if the Portuguese bemoan how Brazilians speak Portuguese or Spaniards despair of the language spoken in Mexico, Argentina, Chile or elsewhere in Latin America.

Austrians bemoan all the time how German is spoken in Germany… =8-)

53. #53 The Other Ian
January 13, 2010

@Steven,

If what you claim is true, then closing the door on my bedroom so there is no longer a reflected path for the signal to take should degrade the wifi signal since then I’m only getting it bleeding through solid material and none of it is from reflections. But that isn’t what happens. The signal is just as strong either way, which proves that I’m getting it from bleed-through and not from reflection.

What signal meter are you using? If you’re just looking at the number of bars you get, realize that one bar typically represents approximately 10 decibels, whereas the attenuation caused by a wooden door is only about 4-6 decibels (from the chart) — enough to matter for the purpose we’re talking about, but not necessarily enough to register on your laptop. And if your signal is strong enough to begin with, it may take more than 10 decibels of attenuation to get below 5 bars.

54. #54 Peter G.
January 13, 2010

Who designed it? John Galt?

55. #55 DaveL
January 13, 2010

What signal meter are you using? If you’re just looking at the number of bars you get, realize that one bar typically represents approximately 10 decibels, whereas the attenuation caused by a wooden door is only about 4-6 decibels (from the chart) — enough to matter for the purpose we’re talking about, but not necessarily enough to register on your laptop. And if your signal is strong enough to begin with, it may take more than 10 decibels of attenuation to get below 5 bars.

It hardly matters. What we’re talking about here is the equivalent of someone proposing to light up a stadium with the light from their cell phone screen. We point out that’s insane and you interject with “well, there would be some light reflected from the seats…”?

56. #56 David Marjanovi?
January 13, 2010

If only there were some other commonly available source of radiant energy

Nnnnnot that it’s really necessary, but… the link doesn’t work. ðŸ™‚

57. #57 The Other Ian
January 13, 2010

the original calculation said 100 mW was the emitted power for the wifi. he then showed about ~0.01 mW could be absobed and got 35 years for the recharge time.

if we assume that all the 100 mW got absorbed, which is an unrealistic upper limit, then the charge time would be reduced to about .35 years, or about 4 months to charge.

No, 100 mW = 0.01 mW x 10000, not 0.01 mW x 100. At 100 mW, it would take 0.0035 years, not 0.35 years.

More simply, at a rate of 100 mW, how long does it take to accumulate 4000 mWh? It’s just 4000 mWh / 100 mW = 40 h.

58. #58 recovering catholic
January 13, 2010

Way way way OT, but this article confuses me. If a sea slug is stealing chloroplasts so it can photosynthesize, why does it also have to be able to manufacture its own chlorophyll???

http://www.msnbc.msn.com/id/34824610/ns/technology_and_science-science/#storyContinued

59. #59 https://me.yahoo.com/a/SaqGVG0xvJEQVwURVamS3DTCdvov0BLhXK1jOsYPPJQ-#b4893
January 13, 2010

Sounds pretty much like the way things go in a Ray Comfort Food Blog entry, if you ask me.

MikeM

60. #60 Peter G.
January 13, 2010

@47 “I would never consider describing geometry as a mathematic.” Most mathematicians would disagree.

61. #61 DaveL
January 13, 2010
62. #62 https://me.yahoo.com/a/SaqGVG0xvJEQVwURVamS3DTCdvov0BLhXK1jOsYPPJQ-#b4893
January 13, 2010

By the way, I maintain that nothing surpasses the inanity of the Moller Skycar.

You’ll have to perform your own web search to find their site. I’m not going to bother to include a link, in spite of having their address memorized.

Oh, and by the way, there’s also many blogs for free energy devices. It’s the pendulum-based ones that usually cause me to chuckle most.

MikeM

63. #63 destlund
January 13, 2010

being left-handed, I rather like our toll booth situation

?

In the US, toll booths are on the left side of the vehicle. I get to use my dominant hand to throw coins in the hopper. On the whole, American traffic laws are a poor example of American backwardness, though, since only the UK and a smattering of other countries (Australia, India, etc.) still use left-hand traffic.

64. #64 The Science Pundit
January 13, 2010

Come on! You guys are just arguing semantic. ðŸ˜›

65. #65 rob
January 13, 2010

@the other ian:

ugh. apparently i can’t divide. but, hey, what’s a factor of a 100 or 10,000 amongst friends.

in any case, 40 hours is still too long.

66. #66 Blind Squirrel FCD
January 13, 2010

“Math” is not a plural noun and not a singular noun. It’s a mass noun, like “sand” or “pudding” or “water”, that is neither singular nor plural because it refers to a continuous quantity you con’t count with integers

Like bacon, I suppose.

BS

67. #67 SirBedevere
January 13, 2010

Let’s look on the bright side: If anyone buys one of these things it’ll pretty much demolish the notion that humans were “intelligently” designed. ðŸ™‚

68. #68 speedweasel
January 13, 2010

Can we please find another OM for Sastra?

Every time I go to make a contribution to a thread, I read down the page a little and that guy (girl?) has already articulated my thoughts, far better than I ever could have.

And those are just the ones that I could have come up with myself, there’s a continuing whole-other-level of insightful and profound comments from Sastra on topics I have no idea about. It happens in almost every thread.

Nice.

69. #69 Lars
January 13, 2010

The Science Pundit win the thread.

70. #70 Blind Squirrel FCD
January 13, 2010

alysonmiers @50

What I need is a sticker or implant or some kind of device that will draw energy directly from my body to charge electronic devices.

That’s being worked on to power implanted medical devices. I believe they were oxidizing glucose with some sort of fuel cell.

BS

71. #71 Andyo
January 13, 2010

The Other Ian #57

No, 100 mW = 0.01 mW x 10000, not 0.01 mW x 100. At 100 mW, it would take 0.0035 years, not 0.35 years.

More simply, at a rate of 100 mW, how long does it take to accumulate 4000 mWh? It’s just 4000 mWh / 100 mW = 40 h.

It doesn’t matter if his calculation was wrong, and by the way what you posted was also posted by one of the math people there.

Dave L a couple of posts above you has it right. Also, whatever is reflected is subject to the inverse-square law not only once (when it left the transmitter) but twice (when it bounces off walls).

72. #72 mpatter
January 13, 2010

You say: The reason “math” is neither plural nor singular in American usage is because you can’t count how many “maths” you have because it does not refer to a discrete countable thing.

Actually, I doubt there’s any reason at all. Languages pick up new tics as the way we speak drifts over time. Nobody sat down one day and made up the Big Ol’ Book of American English.

I’m stunned that this gets reduced to nationalism, and I can’t believe that people reading a blog about evolution reckon that dialects and languages just popped out of the sky one day.

73. #73 Joffan
January 13, 2010

Joel @30

If for no other reason, the “ths” sound is awkward to make.

That sounds like a good reason to use “maths” to me – we don’t want to make English too easy or everyone will be speaking it…

I suggest next week’s language wrangle should be a motion to drop the superfluous “of” often inserted after “off”.

Anyhoo… how did we get that far off-topic? I guess specious claims about energy are common enough that we don’t need to spend too much time laughing at them. However I’ll just note a transcription error (in the original comment) where a result that should be “0.318mWh” is typed as “0.0318mWh”. The correct value was subsequently used though.

74. #74 rprcvl
January 13, 2010

David,

It’s from the French “les mathématiques” and traces back to the Latin neuter plural “mathematica” which traces back to the greek “??????????” or “all things mathematical”

75. #75 The Other Ian
January 13, 2010

@DaveL,

It hardly matters. What we’re talking about here is the equivalent of someone proposing to light up a stadium with the light from their cell phone screen. We point out that’s insane and you interject with “well, there would be some light reflected from the seats…”?

Jeez, talk about distortion of scale. We’re talking about powering a device that uses at most a watt, using one or more 100 mW sources. Clearly, the power of 10 WiFi transmitters, if collected and delivered efficiently, would be sufficient to power a Blackberry. I’m pretty sure that 10 cell phones would not even come close to lighting a stadium.

@rob,

Yeah, 40 hours is probably too long to be used as a sole power source, and I think that 40 hours is an very generous estimate. At best it’s a spare battery that can be used once a week or so and that you don’t have to remember to recharge. And even then, as others have pointed out, it will never pay for itself in saved energy costs — after 250 uses, I figure it will have generated about 1 kWh, which costs about 0.10 USD.

76. #76 joel.mueller
January 13, 2010

And now, time for sport…

77. #77 Joffan
January 13, 2010

speedweasel @68

Sastra was awarded a Molly early on, in November 2007.

78. #78 Paul Murray
January 13, 2010

“It’s not a Dyson Sphere, so you only get the power that hits the antenna.”

That strikes be as being very likely to be wrong. Antennas are … mathematically interesting. Radio waves have “size” – they are not a stream of points.

79. #79 DaveL
January 13, 2010

Clearly, the power of 10 WiFi transmitters, if collected and delivered efficiently, would be sufficient to power a Blackberry.

The heart of the problem is that the basic physics of flux density make it patently impossible to “collect and deliver” the energy from Wifi transmitters efficiently. At any distance greater than the reach of a typical power cord only a tiny fraction of the power is even incident upon the receiver. To further the analogy, a few cell phones might provide adequate illumination for a single seat, but try to spread that energy across the stadium..

80. #80 Andyo
January 13, 2010

The Other Ian,

How do 10 WiFi transmitters “if collected and delivered efficiently” (whatever that means) are sufficient to power a blackberry? You mean, if you just plug the phone directly to the transmitter AC adapter? In what super far-fetched (but still possible) real scenario would that be true?

40 hours is unachievable. Whenever you convert energy there is loss, and to add to that loss, there’s the inverse-square law. You could not get even close to 100 mW from a 100 mW transmitter in the most real-world “ideal” conditions.

Besides if you tried all this, you’d pretty much have to buy a Wifi router exclusively for this purpose, and leave your phone always VERY close to it, and why would anyone do that? There’s much better power options available if you’re doing something like that.

81. #81 Brownian, OM
January 13, 2010

speedweasel @68

Sastra was awarded a Molly early on, in November 2007.

Why, over a year ago we were discussing how to recognise the pharyngula-hai like Sastra and Cuttlefish among us, including Calamari Clusters with Sides of Tzatziki.

Now I get hungry whenever I read one of their posts.

82. #82 realinterrobang
January 13, 2010

“Math” would have happened even if “maths” had been the North American standard pronunciation, because we are nuts about ease of articulation here, and that “ths” at the end of a word is hard to say.

For those of you with most British accents, it’s about as hard for us to pronounce as it is for you to pronounce “drawing” with a glottal stop in the middle of it (as in drah’ing) rather than your more standard R-that-comes-from-nowhere (as in droring). Shame you don’t have a real schwa; it does come in handy. And I wave my fully rhotic dialect in your post-vocalic-R-less faces!

83. #83 Brownian, OM
January 13, 2010

I understand that mundane concepts such as time lose their meaning when the human mind is exposed to sabbatical, but now that it’s been brought up, you should probably let us find out who won the November Molly and let us vote for December’s sometime soon, PZ.

84. #84 The Other Ian
January 13, 2010

To further the analogy, a few cell phones might provide adequate illumination for a single seat, but try to spread that energy across the stadium..

Yes, obviously any attempt to use this device from across a stadium would fail, as would any attempt to harvest solar energy from the Kuiper belt. Like I said, you’re talking about a completely different scale here.

85. #85 hznfrst
January 13, 2010

Glen (#35), species is a Latin 5th declension noun, which are all feminine except for dies and meridies, which are sometimes masculine. Neuter nouns do not have identical singular and plural nominative forms.

86. #86 DaveL
January 13, 2010

Yes, obviously any attempt to use this device from across a stadium would fail, as would any attempt to harvest solar energy from the Kuiper belt. Like I said, you’re talking about a completely different scale here.

There is no scale that allows you to get 100% of the radiant energy from the access point. At even 3m a 10cm x 15cm device only occupies about 0.01% of the solid angle seen from the access point.

That’s about 10 times more solid angle than a 0.5 square meter seat at 50m. So yes, the stadium example is a bit of an exaggeration, but it’s orders of magnitude more realistic than capturing anything close to 100% of the radiant energy from an access point with one of these devices.

87. #87 hznfrst
January 13, 2010

By the way, as Blind Squirrel said in #66, collective or mass nouns are not countable, and the way to tell is if you can use ‘fewer’ in front of them: you can have more or less bacon, but not more or fewer bacon, for example (fewer bacons maybe if you’re talking about varities, but then it’s a different word).

Unfortunately, this fine point is often lost on the masses who blithely say ‘less people’ instead of ‘fewer people’, and I have the luxury of worrying about it because my house hasn’t just collapsed on me in an earthquake.

88. #88 alysonmiers
January 13, 2010

Blind Squirrel @70:

That’s being worked on to power implanted medical devices.

FUCKING AWESOME. It’ll only be a matter of time before I will be unstoppable!

January 13, 2010

If it were a much bulkier device I’d believe that it can make use of the ambient 60Hz radiation from power lines. If it was meant to operate near the overhead 500KV lines I’d even believe it can charge a Blackberry battery in a reasonable amount of time. However, such a device would still cost an awful lot more than a simple solar panel (but of course it will run day and night – so long as you’re near those very high voltage lines).

90. #90 hznfrst
January 13, 2010

Good one, realinterrogang!

91. #91 The Other Ian
January 13, 2010

@Andyo,

How do 10 WiFi transmitters “if collected and delivered efficiently” (whatever that means) are sufficient to power a blackberry? You mean, if you just plug the phone directly to the transmitter AC adapter? In what super far-fetched (but still possible) real scenario would that be true?

I said if the power of the transmitters were collected and delivered efficiently, not the transmitters themselves. By that I simply mean any scheme you can imagine that intercepts most of that power and delivers it directly to the blackberry.

40 hours is unachievable. Whenever you convert energy there is loss, and to add to that loss, there’s the inverse-square law. You could not get even close to 100 mW from a 100 mW transmitter in the most real-world “ideal” conditions.

Yes, it’s unachievable. Maybe you missed the post where I guesstimated a week at best. As for the inverse square law, it’s less relevant within an enclosed, reflective space. The inverse square law is due to the dissipation of energy as it propagates, but in an enclosed space, there is only so much space to dissipate into.

Think of fiber optics — the inverse square law does not apply because the light cannot escape the narrow channel that guides it.

Besides if you tried all this, you’d pretty much have to buy a Wifi router exclusively for this purpose

Why? What’s wrong with the one I have?

and leave your phone always VERY close to it

No, just the charger. The phone would only have to be near it during the intervals when you’re charging it from the internal battery, which as the CES demo shows, only takes half an hour or so.

There’s much better power options available if you’re doing something like that.

Agreed. I never claimed this thing was practical.

92. #92 The Other Ian
January 13, 2010

There is no scale that allows you to get 100% of the radiant energy from the access point. At even 3m a 10cm x 15cm device only occupies about 0.01% of the solid angle seen from the access point.

This is the same point that my initial post was meant to refute, which means we’ve come full circle.

January 13, 2010

Just to add to SteveM #34: Many RF tags are powered by a high frequency tuned loop; essentially a tuned air core transformer – this is in addition to any other transceiver which may be used to interrogate the device – many devices just transmit a fixed code in a certain band of frequencies or simply resonate at a fixed frequency when powered, so it’s not strictly true that they are powered by the radio signal which interrogates them (unless you consider the power source as the “interrogating signal”).

94. #94 Stuart
January 13, 2010

Blimey, i opened a can of worms didn’t I?

Next time I’ll complain about time-based americanisms such as ‘thru’ or ‘through’ instead of ‘to’ or ‘until’… and the ommission of the word ‘on’ in US news speak
ðŸ™‚

Anyway, inverse aquare law

95. #95 Andyo
January 13, 2010

The inverse-square law is very relevant still. The walls only bounce off a small proportion, and on top of that, every time the signal bounces off the law is applied again, from the point on the wall it bounced off.

96. #96 The Other Ian
January 13, 2010

Okay, I’ve changed my mind. This thing is clearly a scam.

What convinced me? The optimal reception for a wireless network is about -10 DBm (http://en.wikipedia.org/wiki/DBm), or 0.1 mW. To be generous, let’s assume you’ve got 4 other devices on your network, and the charger gets power from those as well. That’s 0.5 mW. To charge a 4000 mWh battery will take 8000 hours, or 333 days, under ideal conditions.

Will this work at a convention like CES, with hundreds or even thousands of transmitting devices in the vicinity? Maybe. Will it work at home? Not on your life.

97. #97 DaveL
January 13, 2010

This is the same point that my initial post was meant to refute, which means we’ve come full circle.

Which means you missed the point of my original refutation. Having now established that the stadium analogy isn’t all that far off, we can now consider the light incident upon a seat due to light reflected off other surfaces… resulting in very little difference.

98. #98 Twin-Skies
January 13, 2010

At least this device looks like it’d work:

99. #99 The Other Ian
January 13, 2010

100. #100 timgueguen
January 13, 2010

This gizmo makes me think of the nonsense found in the world of audiophiles. One of the more amusing outfits fleecing them is Machina Dynamica, which produces such nonsense products as the Clever Little Clock and Brilliant Pebbles.

101. #101 davep
January 13, 2010

The thing might “work” but not in any useful way.

I’m guessing that it can be recharged by the USB cable. That’s the real way the internal battery is recharged.

I’m guessing that even the RCA people know that it doesn’t really work.

The whole point of the “wifi charging” is PUBLICITY, which, it did very well.

The demonstration doesn’t demonstrate anything useful since it did not demonstrate how the energy got into the battery.

It is disappointing that so many people believed the claim without taking any time to think about it.

102. #102 Andyo
January 13, 2010

Scales don’t matter much here. Make it a small room then. Same thing applies, whatever bounces off the wall from the cell phone light is all but inconsequential. You could probably get away with it if you placed the phone inside a 1-foot cube with white walls.

103. #103 The Other Ian
January 13, 2010

@Twin-Skies,

No, I think we have to call shenanigans on that one as well. It doesn’t say how much power the oven draws, but if it uses 60 W, then I calculate it would take 20 minutes to heat a cup of water to boiling, assuming 100% efficiency. Typical microwave ovens only operate around 60-70% efficiency, although they claim to be doing some novel thing with “a combination of mobile phone radio frequencies” (which is suspicious in itself — last I checked, mobile phones don’t cook our brains), so maybe they’re getting more than that. And if it draws more than that, it would be a significant drain on the computer’s PSU.

104. #104 amphiox
January 13, 2010

Hmm. 40h isn’t that ridiculously unreasonable. 40h means leaving your Blackberry beside your WiFi transmitter overnight charges up a substantial fraction of your battery. (Though of course you could just plug it into the wall outlet instead)

But, putting aside the impossibility of it for a moment, taking this hypothetical 100% absorption people have been musing about, wouldn’t that scenario mean that the WiFi transmitter ceases to work as a WiFi transmitter? (if 100% of its output is absorbed then it can’t transmit anything, can it?)

So then any hypothetical increase in the efficiency of this device to any significant fraction of the signal, means an inverse fall in the power of the signal available for its original purpose, WiFi, no?

105. #105 amphiox
January 13, 2010

re#50:

In Sawyer’s “Neanderthal Parallax” science fiction series, the posited alternate-dimension Neanderthal civilization has a portable PDA-type device (which pretty neat advanced AI) powered by a mini-hydroelectric generator powered by blood flow in the user’s carotid artery (it’s a permanent, implanted device, if I remember correctly).

One potential unforeseen drawback of such human body powered devices would be that, if you started overusing your electronic toys too much, you might end up increasing your food bill!

Or, more scarily, perhaps you might fail to notice the small, imperceptible, but continuous drain on your biological energy stores, and die of starvation.

And of course, once you attach AI to these devices, why, it’s just one step from a Matrix-style machine takeover.

106. #106 The Other Ian
January 13, 2010

But, putting aside the impossibility of it for a moment, taking this hypothetical 100% absorption people have been musing about, wouldn’t that scenario mean that the WiFi transmitter ceases to work as a WiFi transmitter? (if 100% of its output is absorbed then it can’t transmit anything, can it?)

Right. But suppose you have two devices near each other (why have a wireless network with nothing on it?), and the charger absorbs 50% of the transmission of each. A 50% power loss is only a 3 dB reduction, which is hardly noticeable for purposes of communication.

107. #107 bignose.pip.verisignlabs.com
January 13, 2010

> a moment’s thought makes it clear it can’t work.

This is a good response, where it’s true. But in the interest of skeptical inquiry, I find your moment’s thought to be rather lacking:

> My local wireless router simply can’t be pumping out that much energy, or it would an awesomely wasteful device, and there can’t be that much power floating free in every few cubic inches of my home.

Both of these are exactly the kind of argument from incredulity that we so often accuse others of.

*Why* is it impossible for your router to be awesomely wasteful? *Why* is it impossible for large amounts of power to be floating free in small spaces?

I’ve seen demonstrations of wireless power for quite powerful devices, so I am not satisfied that it’s obviously impossible to have a lot of power in apparently empty space.

And anyone who says my electronic devices are obviously not awesomely wasteful had better have a word with my wife, who feels differently.

I’m not denying that there may be good explanations for why those are impossible. But you merely assert they are obviously impossible, and I don’t find them to be so.

108. #108 Thickslab
January 13, 2010

The Other Ian replies:

Typical microwave ovens only operate around 60-70% efficiency, although they claim to be doing some novel thing with “a combination of mobile phone radio frequencies” (which is suspicious in itself — last I checked, mobile phones don’t cook our brains), so maybe they’re getting more than that.

That might have something do with the fact that mobile phones don’t output 1000 Watts of power into a reflective chamber containing our heads.

But I could be wrong – I’m just an electrical engineer.

109. #109 Thickslab
January 13, 2010

Stuart writes:

It’s ‘MathS‘… apart from that you’re correct

Do you enjoy watching BBC Sport?

110. #110 necronomikron
January 13, 2010

To be fair, it could supply a super-low-powered device…

111. #111 dawei
January 13, 2010

Himm? it seems we have our own culture war going on regarding the correct abbreviation of Mathematics, could this be a decisive split in the Atheist camp. ?Atheists go to war over an s? headline.

You guys use imperial for the calculation of the area of a sphere then relate that back to SI units for power per unit area that takes real skill, but opens doors for software program variable unit mixups that send spaceship crashing to earth sort of mishaps.

Long live metric and SI down with the imperial running dogs!

112. #112 speedweasel
January 13, 2010

speedweasel @68

Sastra was awarded a Molly early on, in November 2007.

Oh, yeah I knew he/she had one already. I meant we should award *another one* as in, 2OM. One obviously just isn’t enough.

113. #113 Nerd of Redhead, OM
January 13, 2010

Speedweasel, Sastra is a she. She, like Owlmirror, David Marjanovi?, and Cuttlefish, are deserving of all the tentacle clusters that fit on their shirts. If you poke around the archives there is a picture of her with PZ.

114. #114 F
January 13, 2010

Re: microwave ovens:

A USB hub only supplies c. 5v @ 100-500mA.

Good luck with the microwave there.

115. #115 The Other Ian
January 13, 2010

Ah, good catch. Although apparently there’s something called a Dedicated Charging Port that can supply up to 1.8 A at 5.25 V, at the cost of disabling data transfer. That’s still only 9.45 W, less than 1% of the power used by a typical microwave oven.

116. #116 KOPD42
January 13, 2010

That might have something do with the fact that mobile phones don’t output 1000 Watts of power into a reflective chamber containing our heads.
But I could be wrong – I’m just an electrical engineer.

Fair enough, but but with 5V and about 500 mA to work with, it’s going to be very hard to get 1000 watts out of a USB device. Even if that microwave is cooking with cell phone frequencies, it still has to be doing it at a much lower wattage than a standard microwave. I’m not quite ready to call shenanigans on this thing, but I won’t be surprised if it’s just a 21st century Easy-Bake oven.

January 13, 2010

Re. the inverse square law and reflections – don’t forget to integrate over the walls for each reflection, and the area of the walls to integrate over is proportional to the square of the size of the room. Mind, transmission/absorption by the walls is going to kill off the higher reflection terms pretty quickly.

118. #118 God
January 14, 2010

Nifty! I am ordering one right now. Never mind the physical laws it may break, I will just pardon Myself if I get caught.

119. #119 Twin-Skies
January 14, 2010

@TheOtherIan

So cooking is out:(

Will it at least heat up a cup of coffee, or a tupperware with pre-cooked white rice?

120. #120 The Other Ian
January 14, 2010

To heat a cup of coffee from 25C to 55C:

((8 fl oz) * (1 (g / mL)) * (30 (cal / g))) / (9.45 W) = 52.3748773 minutes

121. #121 MikeTheInfidel
January 14, 2010

All this talk about the British English invasion and nobody says a word about ‘kerb’ vs. ‘curb’? Best to kerb the changing linguistic tides, I think.

122. #122 eddie
January 14, 2010

It really annoys me how some people who really ought to know better can’t tell then from than. One or two even consistently use both wrongly.
Something ought to be done!

123. #123 Richard Eis
January 14, 2010

So, the cost of making this device far, far outweighs its return on energy saving, which it gets from another electronic device anyway.

Stupidity squared…or cubed?

124. #124 JohnnieCanuck
January 14, 2010

eddie, you’ve done it now.

Those last five words in your comment should never be spoken or written.

You never know when a politician or a bureaucrat is lurking nearby, just waiting to pass a law or create a rule in response. Then battalions of civil servants will have to be hired and someone will have to be promoted to manage them… and on and on until everyone is doing nothing much about anything that ought to be done.

There aught to be a law that makes it clear how dangerous it is to say things like that.

125. #125 idlemind
January 14, 2010

To those who claim that “reflections” make such a device feasible, consider this:

Rooms are often brightened by reflective enclosures known as “walls” coated with paint that intentionally reflects EM radiation in the 600THz range (otherwise known as visible light). But even with reflectivity far higher than most construction materials have at WiFi’s 2.5GHz, in such a room a sheet of paper at best is illuminated perhaps 2-3 times more brightly than it would be by an omnidirectional light source in the open air.

Unless your reflector is a large parabolic dish and the device just happens to be at its point of focus, reflections aren’t going to provide much gain at all compared to the several orders of magnitude you’d need to make this work.

In fact, given that the lights in a well-illuminated room will be emitting considerably more EM radiation than a WiFi unit, a solar cell would be quite a bit more effective in gathering “free” energy than an antenna…

126. #126 dnebdal.myopenid.com
January 14, 2010

@amphiox, 105:
I’ve always wondered why there’s not more support for the idea of charging electronics (at least implants – so pacemakers and the like) on some reaction that uses sugars and oxygen from the blood stream. Set it up so you get sensible waste products, and the load it would put on the system should be effectively the same as increasing physical activity a little bit. Unless I’m missing something, this should just make people eat correspondingly much more.

(I’d want to test the safety systems well, though – setting some required minimum levels of reagents would be an important start…)

Now, I’m neither a biologist nor a chemist. Do tell if there are any large obvious obstacles. ðŸ™‚

127. #127 JohnnieCanuck
January 14, 2010

My wireless router is reporting that the strongest signal it is receiving is about -20 dBm. Other computers, likewise in the same small room are being received at -60 dBm. I see no reason to expect the Airnergy device to have an antenna aperture (effective capture area) significantly larger than the routers. They are all (very) approximately isotropic.

The first, 10 microwatts, is a hefty signal for a radio receiver to work with. The second is decent for a radio, given the SNR for it is 30 db. Kind of impressive, though when you restate it as 1 nanowatt.

There is no way that even a directional antenna fitting inside that box could possibly absorb enough energy from one or a few 100 mW sources to charge a blackberry battery from 30% to full in 90 minutes.

I’m also not going to believe until I see it, that they have a diode in there working as a rectifier at one or two gigaHertz which is producing DC at battery charger voltages.

128. #128 AJS
January 14, 2010

This is not just snake oil. This is M&S extra virgin snake oil.

129. #129 mattheath
January 14, 2010

Free Lunch@42

I wonder if the Portuguese bemoan how Brazilians speak

They do. I live in Portugal. Many think their Brazilian cousins’ casual innovation in vocabulary and use of the letter “K” will be the end of lusophone civilization as we know it.

Also I’m a mathematician. I have known other mathmos insist on “mathematics are/maths are” I think some people say “physics are” and “linguists are”. I’m not really a fan of that.

130. #130 Nancy New
January 14, 2010

And I quote…
“If it can?t be expressed in figures, it is not science; it is opinion.”
Robert A Heinlein (From the Notebooks of Lazarus Long).

131. #131 lynxreign
January 14, 2010

Those of you claiming “It can’t work” are making quite a few unsupported assumptions and unwarranted substitutions.

First, substituting your home wireless router for a public WiFi hotspot is misrepresenting the power available.

Second, I can’t believe you’re stating “It can’t work” with such certainty based on nothing more than a video of a sales guy making a pitch at a show. Most of the descriptions of this type of device that I’ve read state that they’ll be drawing power from all the ambient signals. This means Wifi, cellphone tower emissions, radio, broadcast tv and more.

Third, while the guy states that they charged the battery from 30% to full in 90 minutes, it isn’t clear if he’s talking about from the stored power or from ambient power. My bet is on stored.

Fourth, even if it does take a full week to charge the battery, if it is used as an emergency charge that should be acceptable. If you’re dumb enough to let it sit at home and shield it so it only takes ambient power from your wifi signal, that’s your fault.

Fifth, when people come to my place and go to jump on my wireless router, they usually have 5 or 6 networks to choose from, as they did the last place I lived. Assuming there’s only your router in range is a bad assumption.

Do I know that any of the postulations I’ve made are correct? No. Then again, you’re basing yours on erronious interpretations or dubious sources. You might want to dial back the certainty, it’ll make it easier if you turn out to be wrong.

132. #132 rob
January 14, 2010

what kind of antenna do wifi hotspots use? i am betting some sort of directional or dipole antenna. the radiation field for these does not follow the inverse square law in the far field. in particular, for the dipole antenna in the far field it falls off as 1/r. also, the field is not spherically symmetric. the maximum field is perpendicular to the antenna, and goes to zero in the direction of the antenna.

133. #133 Nerd of Redhead, OM
January 14, 2010

Yawn, no math by lynxreign to back up his points. Just trying to raise doubt on what others have put forward. Now, where do we normally see such behavior?

134. #134 lynxreign
January 14, 2010

Nice try. Pointing out valid things other people have missed? We see such behavior in scientists. I haven’t shown you any math partly because my point is that we don’t have enough information to DO the math. Sure, I could make a different bunch of unsupported assumptions, but that’d be no more valid than the ones I’m questioning. I’m not saying it does work, I’m saying that the math shown doesn’t come close to proving anything.

You’re trying to imply I’m acting in a creationist-like fashion, but you’re the one blindly believing something based on little fact, lots of guessing and strange belief.

135. #135 SteveM
January 14, 2010

what kind of antenna do wifi hotspots use? i am betting some sort of directional or dipole antenna. the radiation field for these does not follow the inverse square law in the far field. in particular, for the dipole antenna in the far field it falls off as 1/r. also, the field is not spherically symmetric. the maximum field is perpendicular to the antenna, and goes to zero in the direction of the antenna.

No, in the far field the dipole is still a point source of radiation, just one with a directionality, but the signal strength still falls off as inverse-square. At any point twice as far from the antenna the signal becomes spread over 4 times the area. That is, whatever the size of your receiving antenna, when you move it twice as far away, the solid angle it forms to the transmitting antenna is cut in half and so the surface of that solid angle is cut in fourth. That’s worded poorly. At some distance R from the antenna, your receiving antenna forms a solid angle W to the transmitting antenna intercepting an area A of signal. That same solid angle W projected out to distance 2R now covers an area of 4A, but your reciever is still only area A so it receives only 1/4th the signal.

136. #136 rob
January 14, 2010

the math that is posted up top is an example of a Fermi problem. it takes some simplifying assumptions and does a back of the envelope calculation to get an approximate answer. usually just an order of magnitude estimate.

the example above came up with an answer in years for the recharge time. other assumptions can bring down that estimate to something on the 10’s of hours time scale. quibbling about details like reflections off walls and size of the receiving antenna and the phase of the moon are not in the spirit of the order of magnitude estimate a Fermi problem gives you.

in any case, it appears that the recharge time is likely to be too long to make it a practical product.

therefore, my feeling is that the product does not perform as advertised.

however, it is easy enough to go out and buy one and actually test it to see if it performs.

to quote XKCD: science. it works bitches!

ðŸ™‚

137. #137 AJS
January 14, 2010

“First, substituting your home wireless router for a public WiFi hotspot is misrepresenting the power available.” — no. The legal limits on ERP are the same whether the device is in use in a private residence or an industrial setting.

Light (and that includes radio waves) travels in straight lines. The energy coming from the antenna is evenly distributed over a sphere (or a portion of a sphere bounded by radii), whose total surface area is inversely proportional to the square of its radius.

This means that at 2 metres from the antenna, the field strength will be a quarter of what it was at one metre. At 3 metres, it will be 1/9 of what it was at one metre. And so on.

“Second, I can’t believe you’re stating ‘It can’t work’ with such certainty based on nothing more than a video of a sales guy making a pitch at a show. Most of the descriptions of this type of device that I’ve read state that they’ll be drawing power from all the ambient signals. This means Wifi, cellphone tower emissions, radio, broadcast tv and more.” — No. When we’ve said “It can’t work”, that’s because some of us actually understand physics.

You’d also be in trouble if you attempted to harvest power from broadcast radio and TV. The broadcasting companies don’t like that sort of thing. They turn a blind eye to crystal sets, but you’d better believe that any attempt to harvest more than a few milliwatts from their transmitters would land you in court.

“Do I know that any of the postulations I’ve made are correct? No. Then again, you’re basing yours on erronious interpretations or dubious sources. You might want to dial back the certainty, it’ll make it easier if you turn out to be wrong.” — Except we’re not wrong. This device is a crock of shit, plain and simple.

138. #138 SteveM
January 14, 2010

The energy coming from the antenna is evenly distributed over a sphere (or a portion of a sphere bounded by radii)…

…whose total surface area is inversely proportional to the square of its radius.

No, the surface area of a sphere is proportional to the square of its radius (not inversely proportional)

139. #139 SteveM
January 14, 2010

Light (and that includes radio waves) travels in straight lines. The energy coming from the antenna is evenly distributed over a sphere (or a portion of a sphere bounded by radii)

No, it is not uniformly distributed over a sphere, the type of antenna will determine how the power is distributed. And I have no idea what “(or a portion of a sphere bounded by radii)”, even means.

140. #140 SteveM
January 14, 2010

You’d also be in trouble if you attempted to harvest power from broadcast radio and TV. The broadcasting companies don’t like that sort of thing. They turn a blind eye to crystal sets, but you’d better believe that any attempt to harvest more than a few milliwatts from their transmitters would land you in court.

Exactly how would that work and how would they know? They are dumping megawatts of power into a radio signal, if I can put up an antenna and turn some of that back into electricity what is the harm? It is not like I can draw more power than they are putting out. That would be like saying putting up a solar panel under a street light makes the street light draw more power (or burn out faster).

141. #141 shatfat
January 14, 2010

Delurking to point out that RCA was gutted by Jack Welch.

A real American hero™.

142. #142 lynxreign
January 14, 2010

AJS

So are public WiFi spots broadcasting at 1 W or 100 mW? I’ve looked on-line, but can’t find it. A commenter above said 1 W, which would make the calculation quoted in the original post off by an order of magnitude.

that’s because some of us actually understand physics.

Would the “some of us” be you or SteveM?

Except we’re not wrong. This device is a crock of shit, plain and simple.

Perhaps, but I’ll wait until there’s better evidence before making up my mind. All you’ve given is a very poorly worded attempt at explaining field strength (and that’s giving you the benefit of the doubt that you’re just stating it badly) and some derision.

143. #143 destlund
January 14, 2010

matteah,

I have known other mathmos insist on “mathematics are/maths are” I think some people say “physics are” and “linguists are”.

Pretty sure you meant “linguistics.” Oh, and the mathmos will devour you.

144. #144 sasqwatch
January 14, 2010

lynxreign — it looks like 1W is a current upper limit for Wifi, though most transmitters in public places (cafe’s, airports in podunk towns like Colo Spgs) seem to be on par with normal consumer gear (~100mW).

Here’s info that limits “peak” transmitter power to 1W. I see another site selling pro Wifi gear that indicates a 4W limit in its table of conversion between dBm and W. I think this is a goof – as they don’t sell equipment above 1W, which is what I see widely reported as the FCC limit. Perhaps they meant the 4W line exceeds the stated FCC 1W limit.

Transmitting antennas in public hotspots tend to be of the omnidirectional variety, meaning a toroid shape of RF signal is being emitted… which means the discussions involving a sphere should suffice for rough calculation. It all comes down to how big your receiving antenna is, and what the RF flux density is (at the specific frequency) where that receiving antenna is.

Seems kind of silly to focus on Wifi, when there’s so much more RF out there (esp TV, radio signals) that provide so much more energy. You can follow the links here to legit articles and dissertations on harvesting very modest amounts of power from nearby TV stations, etc. http://www.rfharvesting.com/

which also mentions 4W, curiously enough. I call bullshit on Wifi harvesting for the simple reason that there’s so much more lower-freq RF out there (plus what people have been able to do with TV/radio signal harvesting is run extremely low current applications). (note all the places where you get power loss in the above article: transmission lines, converting to DC, conditioning the power).

145. #145 John Morales
January 15, 2010

146. #146 Dawshoss
January 17, 2010

Usually I like what I see posted here. But this time I gotta point out a glaring error.

Pure math isn’t science. It’s a tool which we use to help formulate scientific theorems and predictions.

It’s putting those theories to the test that’s science.

Otherwise all you have is something only a small step above armchair philosophy.

All the being said… did you… test the device?

147. #147 John Morales
January 17, 2010

Dawshoss, pure math ain’t science, but physics is.

Physics uses applied math, which is just like pure math, only applied. ðŸ™‚

All the being said… did you… test the device?

Um, it’s an USB device. It would need a special connector that disables the USB power connector to see how much charging results from RF.

More to the point, the onus is on the claimant — can you point to any such tests?