Explaining the Birdcage Coil Theory

I'm trying to simulate a birdcage coil for this I need a little bit more ideas about the theoretical part of that coil. I will describe what i mean i already understood and maybe you can give me the last input to break through to a better level of understanding.

So in my opionon it works like that:

1.
The Birdcage coil consists of a number of sections which are designed as an Low-Pass, High-Pass or Band-Pass. So the number of the rungs is identical to the number of sections. Each of this section produces a Phase Shift of the current flow through the rungs. The goal is to approximate a cos or sin-distribution over the "surface" of the coil (for the homogenous transverse B-Field). The overall Phase has to be N*2*3,14 and in this case you have resonance. But at which frequency?
Do you use the lumped elements to bring it to a specific frequency?
Where I can something about to caculate them?
Is THIS independent from the number of ports or did it only work if you use a minimum nuber of two ports?

2.
Now you can use two ports with a 90° phase shift to get a circular polarized field. In my simulation that works fine. But now the question: is there a difference between using this two ports and a two-channel coil?
What about the concept of multi-channel coils? Are there more Ports to get a more homogenous B-Field or is this another concept?

I hope somebody is able to give me another input. Maybe this sounds a little bit confusing but I think it's just because I'm not sure how to bring all this ideas together!

thx

birdcage theory

Hi,I enter the field of the RF coil using in MNR a few days before. There doesn't seem to be many people do the work of this aspect. And so few people know birdcage coils here.
I think the capacitance isn't necessary for tuning coil, and so many people use capacitance to tune. There may be following two reasons:
First, the coils have the characters of high inductance, so we can tune it thorough using capacitance in series or using inductance by parallel connection. But using capacitance in series is more easy to achieve, so most people tune by this way.
Second, the kinds of capacitance is more than inductance.

Re: Birdcage Coil Theory

hiii

In birdcage coils the tuning and matching to resonant frequency is done by varying the capacitance. i tuned a chlorine coil to 88.32 resonant frequency and it was designed for 900 mhz magnet. but the problem i face with my chlorine coil is that they seem to pick up radio signals that are transmitted at 88.9 MHz..may be if anyone could help me to avoid the signals..i tried sheilding the coil with aluminum foil sheet and it helped to reduce the signal interference.but i'm looking for a better way to avoid the radio signals

Birdcage Coil Theory

Hello Malathy1947,

Did you verify the functioning of your balun/cable traps so that you don't get interference from CM to DM conversion?

The best cables "lose" their screening when you have common mode to differential mode conversion. It is bad you can't use ferrite absorbers.