RFID chip has battary in it or not

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

Weng Tianxiang wrote:
> 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

Weng Tianxiang wrote:

> It is really a marvelous invention!!!
> 
> Who is the inventor?

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

On Fri, 05 May 2006 07:59:55 +0200, Ralf Hildebrandt
<Ralf-Hildebrandt@gmx.de> wrote:

>Weng Tianxiang wrote:
>
>> It is really a marvelous invention!!!
>> 
>> Who is the 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.

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? :-)
http://en.wikipedia.org/wiki/RFID 

Weng Tianxiang wrote:
> 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

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?

"JJ" <johnjakson@gmail.com> wrote in message 
news:1146982987.316600.228410@i39g2000cwa.googlegroups.com...
> 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 
http://www.rfidinc.com/ and ask questions on sci.electronics.design or maybe 
alt.privacy. I doubt I'd ask on comp.arch.fpga, even though I know CAF is 
the only place to be for the world's top digital engineers! :-)
As for this newsgroup, the peak level of expertise here is a lot higher than 
in Wikipedia. If only for that reason, I don't see this newsgroup going away 
anytime soon. The Wikipedia FPGA article is designed to give the absolute 
beginner a place to start from.
Just MHO!
Best, Syms. 

Symon wrote:
> "JJ" <johnjakson@gmail.com> wrote in message
> news:1146982987.316600.228410@i39g2000cwa.googlegroups.com...
> > 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 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.

> 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
> http://www.rfidinc.com/ and ask questions on sci.electronics.design or maybe
> alt.privacy. I doubt I'd ask on comp.arch.fpga, even though I know CAF is
> the only place to be for the world's top digital engineers! :-)
> As for this newsgroup, the peak level of expertise here is a lot higher than
> in Wikipedia. If only for that reason, I don't see this newsgroup going away
> anytime soon. The Wikipedia FPGA article is designed to give the absolute
> beginner a place to start from.
> Just MHO!
> Best, Syms.

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