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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.
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.
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.
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?
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.