question about the energy in CST MWStudio

cst input power

Hi, All,

In the help document of CST, it is stated that:
"The total energy is represented by the completely stored energy amount
in the simulated structure, equally to the electric or magnetic energy:
W = We = Wm.
For the eigenmode solver the energy is equal 1 Joule, while for the
transient and the frequency solver the energy is referred to the input
power of 1 W."

my understanding is: the electric energy is always equal to magnetic energy, and the total input power is 1W.

however, how to guarantee the input power 1W? assume discrete port is used, and Gaussian pulse is used, such that the input voltage is known, but the input current may vary with the simulation. then how can we say the input power is always 1W? really confused.

another question is: is We=Wm always true? I have tried a simple dipole problem with Matlab, they are not equal actually. So did I misunderstand anything, can anybody give me any hints?

any of your suggestion or advice will be appreciated.

Added after 37 minutes:

one more question, how to record the time-domain electric energy or magnetic energy in CST? I tried, but only get the maximum energy in designated space.

no one replied me, so sad... 8O

About discrete ports: check 'Monitor voltage and current' in port options to control V and I.
About time-domain energy: total (E and M) energy during the time-domain simulation recorded in 1D-Results/Energy. This energy normalized to maximum.

Kit

Dear 'Kit-the-great',

thk you very much for your reply.

Maybe I didn't pose my question clearly, my question is: how to control the input power as 1W.

actually I know how to record discrete port voltage and current, but in CST, we can only 'record' current, not 'control' current.

As for the energy, my question is: how to record electric energy or magnetic energy separately, not the total energy.

so any idea? thks.

Hi tenderne,

in CST it input power at a port is by default 1W (peak) or 0.5 W (RMS). All field monitors /E/H-Fields, Currents. Powers, losses are normed to this 1W(peak).
Input power means the power used to excite the structure. Depending on your structure, this 1W can now be reflected back to the port,, it can be dissipated inside the structure or it can be transmitted/radiated.

The "input power" and the "accepted power" are related via the S-Parameter(s).

If you have the S-Parameter(s) you can easily calculate how much power is accepted by the structure.

does this make thinks clear?

In order to get the electric or magnetic energy can can use an electric or magnetic energy density monitor together with a 0D Results Template to integrate these monitors. You can use the 0D Template "evaluate 0D/1D/2D/3D Fields" for this purpose. This directly allows you to integrate the energy density..


F.

As I understand You can't control both I and V to control power on discrete port, only 'I or V' possible (use user-defined signal if gaussian pulse not enough). CST normed the input power to 1W on every frequency point when calculate E- and H-fields, surface current etc. Did You mean the control of total energy of gaussian pulse to 1W?
To record E and M energy try to use electric/magnetic energy power density field monitor 'specified in time with small timestep', but to calculate total power in volume You should integrate it manually.
Kit

Dear 'RFSimulator' and 'Kit-the-great',

thks a lot for your reply.

Just now I tried to restore the normalization process. In CST, the time-domain and freuqncy domain voltage and current are recorded, i.e. Vol(time), Cur(time), Vol(frequency),Cur(frequency).

Applying DFT operation to time-domain data, we can get Vol(DFT), Cur(DFT). Then 'Vol(DFT)/Vol(frequency)' and 'Cur(DFT)/Cur(frequency)' should be the original frequency-domain reference signals.

I noticed that both the reference signals are idential gaussian pulse. In other words, the frequency-domain input voltage and current are same. so the excitation of discrete port is current source, and the interal impedance actually is only a resistance, is it?

if anything wrong with my 'ratiocination', pls correct me, thks in advance. :roll:


for the recording of electric or magnetic energy, still trying, will let you know if i can find something. :lol:

regards,
tenderne

Added after 2 hours 53 minutes:

Hi, 'RFSimulator'

I tried the 0D template you mentioned, I select
'Results' -> 'Template Based Postprocessing' -> '0D Results' -> 'Evaluate Field in arbitrary Coordinated' -> '3D', 'max range', 'integral-3D'

However, only a maximum 3D energy value at a specified location is output. seems not right, i want the total electric or magnetic energy varied with time.

anyway, i will keep trying... :|