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MIT Stealth Startup Charges Up Wireless Power Competition
gthuang88 writes: Wireless charging of electronics is an old concept, but there's a new player in the competition between companies like WiTricity, Energous, and tech giants Apple, Samsung, and Qualcomm. A new spinout from Dina Katabi's lab at MIT, called Pi, may have a new take on how to charge mobile devices at a distance. The company isn't talking yet, but Katabi's research suggests the system uses an array of coils to produce a magnetic field and detect when a device is within range, like a Wi-Fi router. The array can then focus the magnetic field on a coil attached to a phone or mobile device and induce a current to charge the battery. But it's still very early, and the field of wireless charging needs to settle on technical standards and work out its commercial kinks.
If you can magically send power like this, why not just pylon up everything, protoss style?
Mod me down, my New Earth Global Warmingist friends!
From the article itself, the device they mention has a range of "about a foot". I think it'd be pretty hard to get between the magnetic coils and the device they're charging.
work out its commercial kinks
So would that be a straight BDSM dungeon, or are we going the whole way with specialists in urolagnia, acrotomophilia and menophilia?
AFAICS the only real way to extend range is by using very a very large set of coils for the transmitter ... I'm not sure if you can do this cheaply or efficiently.
Oh yeah, magic. Everything is magic nowadays.
this isn't even remotely new technology... and it fails for a lot of reasons.
1. you still need wires because the charging transmitters need to be plugged in and they only have a limited range so you're still going to be charging in roughly the same place.
2. The efficiency hinted at in there is horrific. I think its something like 20 percent in most cases and that's on top of the AC/DC conversion. So you lose 20~30 percent converting to DC and then you lose 80 percent of of the remainder transmitting it.
3. The cost of the systems usually isn't that bad but 30~50 dollars is still 30~50 dollars.
I've decided to stop wasting my time responding to AC trolls/sockpuppets... so if you want a response from me... login.
You could still fit your hand or arm between the two though. Just because it's not possible for your entire body to touch a stove burner doesn't make it less of a safety issue.
I'll assume this technology is generally safe, but that it could interfere with medical devices or the like, which is another form of safety issue even if it's not a big deal for most people.
MRI machines are pretty safe, they have rip-your-jewelry-out-of-your-skin powerful magnets.
Magnetic fields don't hurt you
Here's a secret: the most powerful magnet on the Earth is the Earth itself.
You could charge a battery with a crystal radio. I doubt you could put in more power than the self-discharge of the battery you're trying to charge though.
Your refrigerator, washing machine, and other household appliances run on inductive motors which use a thousand watts or so to generate electromagnetic fields strong enough to pull the magnets in the motor strongly enough to move 80 pounds of water and clothes. So those are electromagnetic fields in the kilowatt range.
Charging your phone requires around five watts or so. So the power levels, the amount of electromagnetic energy, is quite small - much smaller than the difference between a large washing machine and a small one.
If you live in an apartment, your neighbors also hqve a refrigerator on the other side of the drywall, an air conditioner with a couple of large motors, etc. Not to mention wireless routers and devices, cordless phones, microwave ovens, etc. Oh, qnd you carry an electromagnetic transmitter in your pocket, one inch from your junk.
There are certain higher frequency ranges which have some risk, but these devices probably won't use those frequencies. Lower frequencies are generally better for short distance because you get the "near field", the more efficient inductive transfer rather than the less efficient radiative field.
I design near field low frequency RFID readers.
It's kind annoying to WiTricity claim they invented something (resonant charging) that the LF RFID industry has been doing for the last 30 years. ie Very HiQ coils to efficiently transmit to passive RFID tags (which also have HiQ resonant coils).
Magnetic fields can be well directed by permeable materials like ferrites, but as soon as you have to bridge the air-gap, you get 1/r^3 power loss. Can you do phased array effects like steerable antennas like the article claims? Yes, but probably not in a way that is beneficial to bridging the air-gap loss.
Here is a challenge. I give you 4 little round neodymium super magnets, and I'm going to let you rotate them into whatever static position you like, with the goal of producing twice as much magnetic attraction a distance 4x their diameter. Think you can do it?
Besides terrible efficiency you are also limited in power as described in ESTI EN 300-330-1
There is a specific allowance for magnetic near field from 119 to 135kHz of 70dBuA/m.
As for safety. These magnetic fields are fairly benign. We have thousands of these transmit at the legal limit on big 1200mmx600mm air coils, and have to our knowledge have not had an incident (ie with a pacemaker).
46137
Here's a secret: the most powerful magnet on the Earth is the Earth itself.
Ordinary bar magnets frequently have magnetic fields stronger than the earth's.
Wealth is the gift that keeps on giving.
Unless you have a conducting loop in or around your body when it fires, such as a wedding ring, or a magnets in your body, such as are found in some medical electronics, or if you've got any accidentally embedded magnets such as those swallowed by children..
http://www.npr.org/sections/he...
Or unless there is a bulky, conducting metal object in the room, such as an oxygen tank:
http://www.nytimes.com/2001/07...
I'm not suggesting that a modest hom recharger will create such risks. But please, do not extrapolate armchair physics to assume you understand the real risks of a real electromechanical device without doing the research.
Seriously, wireless on mobile is silly. It is easy enough to plug it in.
Focus should be on things like robotics, construction equipment, etc. Basically, the ability to beam energy 1 KM all the way up to 200 KM is a HUGE thing, and worth loads of money.
I prefer the "u" in honour as it seems to be missing these days.
In a time where we are trying to get away from fossil fuels, aren't allowed to build nuclear power plants, have yet to solve storage for renewables and electric plug-in cars are a thing, do you really think we should make charging our devices less efficient?
It can work if you're rich and don't mind raising world sea levels a few feet to wirelessly charge your electric car.
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Magnetic fields don't hurt you
STATIC magnetic fields don't seem to hurt you. Time-varying magnetic fields most certainly can hurt you. In addition to ionizing radiation (x-rays, gamma rays) which can obviously hurt you, plain old radio waves can too:
Radiation burns can also occur with high power radio transmitters at any frequency where the body absorbs radio frequency energy and converts it to heat.[1] The U.S. Federal Communications Commission (FCC) considers 50 watts to be the lowest power above which radio stations must evaluate emission safety. Frequencies considered especially dangerous occur where the human body can become resonant, at 35 MHz, 70 MHz, 80-100 MHz, 400 MHz, and 1 GHz.[2] Exposure to microwaves of too high intensity can cause microwave burns.
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
Yeah, because all directed energy is harmful to flesh, right?
These are magnetic fields in the range of less than those generated by your fridge, if it was harmful, everyone in the first world would already be dead.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
While Tesla did manage to transmit power wirelessly over a short distance, there is no evidence that he succeeded going further despite devoting a large part of his life to this problem.
However, we can thank Tesla for allowing us to light light bulbs from 100km... with wires. He can be considered the father of the modern power grid.
It's highly unlikely your wedding ring would happen to be just the right size to couple well with the field. If it did, it might get hot, prompting you to remove your hand from the vicinity of the charging station.
Thank you for pointing out that a small loop may not cause injury. A casual look at published guidelines shows that they say to remove _all_ metal, and some metal may be safe if designed carefully. But some guidelines accept that wedding rings, in particular, may be impossible to remove without cutting them and accept the modest risk. I'm looking particularly at this as an example:
http://www.mrisafety.com/Safet...
So you've raised a very good point, thank you for the refinement. In turn, I'll point out that not all patients in an MRI are conscious, and that not all loops are worn on the hand. There is a particular case, described at http://www.ncbi.nlm.nih.gov/pu..., where a man with a very serious head injury had a "magnetic resonance safe" pressure monitor implanted in his head. It coupled to the MRI, and the tip melted in his brain.
MRI isn't the same thing as an inductive charger. The field is much stronger in an MRI scanner, and the main field is static. There are two dangers: having metal objects pulled by the strong static main field, and heating from the varying gradient fields during scanning. Non-ferrous metal generally isn't much of a problem, but if it's easy to remove you might as well. When I started doing MRI research we emptied our pockets but went into the scanner in our regular clothes, jean rivets, zippers, whatever. You'd suggest women might want to take off underwire bras, but it wasn't insisted upon. Regulation creep now means most centres insist on subjects being stripped down to scrubs. Most piercings, dental work, etc. are okay, unless they're near the area being imaged (they can distort the images).
Inductive chargers are lower field, oscillating, and tuned to match a specific receiver coil geometry. You're unlikely to get any significant power transfer to something random like a wedding ring. Especially since the receiver coil is likely much smaller than a finger; you wouldn't want to carry something that big attached to your cell phone.
I very much agree with you. I'd not expect immediate, dangerous coupling from a relatively low intensity coupling such as a recharger might product, even if someone slept with such a device under their pillow and wore loop earrings.
It was the reasoning from viperidsenz that because MRI is safe, inductive recharging is safe that I meant to call into question. MRI, misused or accidentally mishandled, can cause injury and death. The scanners devices are not a good starting point for comparison of safety.
Federal Communications Commission (FCC) considers 50 watts to be the lowest power above which radio stations must evaluate emission safety
I wasn't aware these phone chargers would be more than 50 watts.
when you take into account the total volume of the field, its total energy is extremely large, much larger than any magnetic field generated artificially
They may be, given the horrendous loss involved and the use of directional coupling. That 50 Watt limit is not absolute, it's more of a guideline for Amateur radio stations specifically, not all emitters. Your cell phone at < 4W is also closely regulated due to its proximity to human tissue. Please refer to the FCC RF exposure site for the full regs.
RF exposure is a function of frequency, duty cycle, distance, transmitter power, and antenna gain. I have a tiny 10mW 10GHz transmitter that couples its power via WR-90 waveguide. If my math is correct, that's 3.1 mW/cm^2 at the mouth of the waveguide - WAY over the exposure limit of 1.0 mW/cm^2 at 10 GHz for uncontrolled access.
Remember, sunburns are actually RF burns.
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.