Back scattering and Inductive coupling for RFID readers and tags

Hi,

Inductive coupling is a method of transmitting data between tags and readers in which the antenna from the reader picks up changes in the tag?s antenna. Am I true?

Backscattering is also a method of communication between passive tags (ones that do not use batteries to broadcast a signal) and readers. RFID tags using backscatter technology reflect back to the reader radio waves from a reader, usually at the same carrier frequency. The reflected signal is modulated to transmit data.

I am very confused with the above statements.
Passive tags absorbs energy from the reader, powers up the ciruitary and then communicates with reader.
What is the method of communication/technology used for data transmission in LF, HF, UHF and micrwave range?

If I am not wrong, inductive coupling and backscattering are two differnt technologies for data transmission. Then how are the above statements true?
Please correct me if I am wrong at any point.

-shaikss.

In a short, back scattering describes best the passive tag to reader communication for UHF and microwave frequencies while load modulation applies to LF and RF (13.56 MHz) RFID. The basic difference is relation of wavelength to antenna/coupler coil dimensions and reader-tag distance.

Thanks Fvm.
You mean to say that backscattering applies to UHF and microwave range whereas load modulation is used at LF and HF range. Can you please explain in detail?

At lower frequencies, wavelength is higher and so antenna dimensions will be more.
How are we compensating on the small antenna? I agree that antenna gain will be small. But the size of the antenna depends on other factors other than gain.
Some elaborate explanation is needed.
I have few more queries..... Are Readers/tags frequency dependent? If not, then how do the readers/tag communicate at specific part of the spectrum LF/HF/UHF/microwave?
Where do we use frequency tuning?
Where is the filtering of specific range implemented? As readers continuously emits energy and tags absorbs only a minute part of the energy, how do the tag know to absorb only that part of the emitted energy? It happens if some filtering is used. So, where do the filtering concept come into the picture?


-shaikss

At LF and HF the reader and tag antenna have a magnetic near field coupling because of the small antenna size and the large wavelength. And the antennas here are often coils. The tag and the reader can be seen as an air transformer. Look at this picture: ../imgqa/eboard/Antenna/rf-eeujbrhb52k.jpg, the two tags with the coils are HF/LF tags.


At UHF the system operates in the far filed. Here often dipole antennas are used for the tags, in the picture a folded is used as an antenna.


The working frequency of a reader/tag is determined by the antenna and the analog front-end. There are different systems for the different frequencies.

Surely. But I didn't want to retell the profound literature, that can be found at many places in the internet. I'm not aware of your RF engineering background. Most of your questions can be answered referring to general AC magnetic respectively electromagnetic field properties and aren't specific to RFID, I think.