Hi, Recently I received a RFID chip to open company's door when entering office building.
It is very easy to carry and use like a key.
I would like to know whether it contains a battary or not.
If there is no battary in it, how can a circuit work running with Radio Frequency?
Weng
No battery. The circuit scavenges the energy in the RF signal, rectifies it and uses that to power the circuit. Sort of like a crystal radio set.
Hi Ray, It is really a marvelous invention!!!
Who is the inventor?
Weng
No telling.
The idea might be uncovered just by observation. When in Berlin the big TV Tower was opened a lot of small gardens where nearby. All of them did not have electric power supply - but at night one could see light bulbs there. They drew energy from the field with a cable - a "long antenna".
Nicola Tesla wanted to transport energy by via a radio field. He constructed his famous "Tesla Coil" witch transformed AC to ultra-high voltage (with almost no current). I have seen a Tesla coil producing light strike of over 50cm length - more than 50kV. I touched this strike (with a screw driver to avoid to burn my hand) and felt a small prickle in my lower arm. With this Tesla Coil it was possible to carry a Neon Lamp that was glowing (no wires). And this was the idea of Tesla: He wanted to transport the energy by air.
13,5MHz RFID tags operate with inductive coupling. Therefore the observer of the inductivity could be named as the inventor. -> Joseph Henry, Michael Faraday.900MHz RFID operate with resonant coupling - the idea of a radio. Marconi could be named as inventor.
Ok - this was the direction from the interrogator to the tag. Backward communication is done by drawing more or less energy from the field (switching on/off a load). Who could be named here? - I don't know.
Ralf
Is that generally true? I had imagined that communication from the tag would be easier by controlling the level of one or more harmonics re-radiated from the tag.
- Brian
I wonder how long it'll be before folks get flamed on usenet for not wikipeding before posting? :-)
Know how an AC power transformer works ?
The power going in doesn't have to be a fixed frequency, it can be modulated a little. The secondary coil may have a switchable shunt across it. Combine them into a communications system.
Increase the distance till they are quite separate and the secondary coil can be quite small and embedded on a Si chip as coils surrounding the chip or on a carrier pcb. Still power transmitted in the primary can reach to some degree the secondary and be rectified, stored and the local logic can both detect variations in the received power frequency (data input) and shunt the secondary coil (data output) and that can be detected by the power transmitter as changes in the impedance of the primary coil. Datarates of 1MBps or so even 20 years ago in close proximity.
Well thats as I understood it 15yrs ago, I guess it finally cought on. I once developed the smart idea of storing music albums on a compressed ROM chip and using RF as the means to both power and read/play the music out. At the time the Rom would have only been 64MBits, 1GByte Flash & MP3 was more than a decade later.. This would have made the device contactless and fully protected from scratching etc unlike the CDs we still have today.
John Jakson transputer guy
Alot of good stuff there but not exactly drive by reading.
So what would you call someone that hasn't pre wiki'ed up on something.
If we all went to wikipedia first, we could dissolve the news groups right?
Hi John, Good points! I sense, rightly or wrongly, you have a little nervousness about Wikipedia, and I share that. Who's to know what motivation someone has had for posting stuff there? I usually use Wikipedia to get a start on what to Google when I'm new to a subject. So, if I had no idea how RFID worked, I'd start at Wikipedia. Then do a few Google searches, and probably end up at somewhere like
I am a little behind the curve and have heard of some fights over corrections, still it seems a good place to start for safe subjects.
Thats what I would do too, sometimes, not as often if I just want to jump right in to a favourite topic. Tthe RFID topic kept getting posted in c.a where it really was a total nuisance, shame about that group getting hammered into useless.
Bye
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