Wouldn't this just decrease the reception for rf devices? Isn't it just stealing power from the system to power other devices?
this post was submitted on 26 Jul 2024
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No more than any random objects.
Think of it like a solar panel. Yes, it blocks light from things behind it, but it doesn't suck light from nearby.
That's interesting! I thought that if you for example have a 50w RF transmitter, taking 40w from it would make it act as a 10w one for the other devices around it.
Thx for the explanation :3
It you could build a 40w antenna sure, but it’d basically have to be a dome surrounding the transmitting one at that point.
it's called an antenna. That's its job.
This ain't free at all it's more like stealing electricity with extra steps. Though if it does not degrade wifi or radio signal I'm up for it be used aside from just wasting away.
Tale as old as time. And guess what will happen? Wifi signal strength will go down.
how exactly? What will physically happen?
Any receiving antenna is basically an energy harvesting device. Usually, it is specially designed to harvest just enough energy to actually receive the signal in order not to weaken the field. In the 2.4GHz spectrum, where WiFi and BT are at home, a sender is limited to 10mW of power. The more power energy harvesting devices draw from this field, the less will be available for other devices to actually receive the information.
Technically, an electromagnetic field of a frequency f will induce an alternating current in an antenna of length lambda/2 (or lambda/4 or even lambda/8, with less power received the smaller they get and lambda=wavelength=speed of light/frequency) that the receiver can "take out" at the antennas mid point and feed it into an amplification circuit.
Wouldnt the effect be very local? How far could the harvester affect the field? But i suppose it would be quite annoying if multiple people used something like that in densely populated area.
https://en.m.wikipedia.org/wiki/Rectenna
What they've done here is use the very old existing rectenna technology and new types of nanoscale rectenna arrays to capture very low energy radio waves without an external antenna. We're taking -20 dBm or 10 μW.
In the end, I welcome any rectenna advances because if we ever build an efficient optical rectenna it'll blow photovoltaics out of the water by efficiency. Optical rectennas are like fusion power in just how revolutionary they would be to our energy economy.
Agreed, this is the future Nikola Tesla wanted, and it's not some wild eyed crack pottery but what he was actually working on in Colorado.
Dang that's actually a super interesting concept. Thanks for the wikipedia link!
I know of companies who have already tested and tried this our years ago, didn't read the article but doesn't seam very new to me
Definitely not new. This is how RFID tags work. They harvest energy from the transmitter to power the circuitry in the tag to send back a response.
Tap-to-pay on credit card chips, too.
Not new indeed. Kinda reminds me of old Nextel phones that you would put a little LED on the antenna and it would blink from the EMI when sending and receiving data.
Those were cool!
And low-power really means low powered... Like... milliamps. If you fed an RFID chip directly, you'd need to supply about 1 mW depending on the specific chip... 1 milliwatt...
In order to feed that chip with a transmitter you feed up to 2W. So up to 99.95% losses... It's NOT economical for any other device that isn't super low power.
Hell Qi charging is just as bad. Qi2, newest and greatest... Which you basically have the devices touching only get up to 80% at absolute best efficiency numbers. Every mm you add, drops that number significantly.
None of this is going to enable "battery free" for basically anything that any consumer would care to be battery free. And honestly I wish we wouldn't pump the airwaves with all sorts of garbage just because it enabled the most minimal amount of "convenience" for things that never needed to be convenient to begin with.
No radio expert here, but would'nt this at some point interfere with the transmissions if deployed at a large scale?
My guess is only in the sense that those radio waves, instead of reflected, they will be absorbed as energy. Partially.
In no way is this a discovery.
This is what crystal diode radios are from the '40s.
Some guy built one in Japan, it's basically just a thousand transceivers in a box hooked up to a USB port harvesting radio/wifi signals.
Here's a guy using them to make light:
It's super cool, but not a discovery.
This would be neat for a bunch of passive IoT buttons. No need for a piezo to generate power, good for a couple presses at a time, just simple stuff like that.
I wonder if it could power a sensor. Something like a soil dampness or thermometer, where you only need a few updates per day. Could be pretty cool for passive monitoring applications.
Charge up a capacitor and allow a single button press to send a radio signal. Or maybe have enough power to send a WiFi signal.
You're right, that would be the preferred application atm.
I remember making a crystal diode radio with my dad as a kid. You can still buy kits for those.
From Radio Shack?!
A friend of mine was working on a car chassis and that thing suddenly started to receive radio. You could faintly hear it coming from the chassis and not from somewhere else. We thought we were going crazy. Touching the chassis made it go away.
When I was a kid, I got a stereo system for my birthday one year alongside two big speakers. The speakers, if they stayed powered while the stereo was off, would receive faint traces of radio signal. So round midnight when the house is quiet I could always hear faint voices, just barely loud enough to hear, but quiet enough to make you wonder if you're really hearing it. Nearly scared the dick off me, I thought my parents gave me a haunted stereo. No, turns out it was just haunted by the ghosts of local AM radio.
Haha, that's so cool.
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