Simple problem with circular coil simulation on CST

Hi Everyone,
I am trying to simulate simple 1 turn coil to see the magnetic field created at the center of the coil on CST simulation tool. The steps I followed are as below;
- I created a single turn coil which has 10cm diameter in low frequency domain.
- Then I cut very small part of it, and added current path with 1Amp.
- I select wire crosssection radius as 1cm.
- Then complated mashing and boundry things
- Later I simulated with 20khz.
The formulation to calculate magnetic field created at the center of coil is (Uo*I)/2*r
When I take Uo as 4*pi*10^(-7), I= 1amp, and r=0.05 meters I got the result of 12.566*10^(-6)
But when I run the simulation, I see that magnetic field created at the center is 9.03*10^(-6).
I attached the simulation file, please help me to find what could be the reason having different results.
Thank you

not familiar with CST
the equation you used to find the magnetic field, UoI/2r works for a thin wire circular loop carrying DC current
not sure it applies to a fat wire
also not sure that it applies to AC
you had the simulations use a fat wire
try the simulation again with a wire cross section of 0.1 mm and DC
you might also try the simulation with a complete loop
or a two half loops, instead of a small section added up

The numbers make me wonder if the problem is confusing peak and rms value?
I'm not using CST, but I'm sure that basic field formula will give correct result under the given conditions.