Hey,

Im relatively new to simulating with CST.

I did an experiment where I placed a Probe into an alcohol solution and measured the S11 values at 2.45 GHz with an VNA. I calibrated the Probe.

I used a probe with a closed end and an open slot. I used a graduated plastic cylinder to store the alcohol inside and placed the probe in the middle of the cylinder for measurement.

With CST I designed the Probe with exact dimensions and materials and placed it in an alcohol material made up of a cylinder, roughly the same size as the real one. I placed a port at the bottom of the Probe and ran the simulation for the S11 values. The CST important settings are as follows:

• Simulation in time domain solver
• accuracy -40dB
• Meshtype-Hexahedral
• Port is facing the correct direction
• Dielectric constant of the alcohol is taken from research papers at 20°C
• The model is surrounded by Vacuum which has the same dielectric constant as air
• Frequency range is from 2 GHz to 2.9 GHz, which is also set in the VNA
• Im also reading the values at 2.45 GHz in CST.

Few things to notice while experimentally measuring S11:

• The alcohol is probably not at 20°C (yes, should have measured the temp) instead its at room Temp.
• The experiment is done in the Lab and not in a anechoic chamber.
• The Probe Cable has a SEM Connecter which the CST model lacks

In CST im getting for Methanol a value of -2.8 dB, while experimentally im getting -31 dB roughly.

I also measured experimentally for Ethanol, Butanol, DMSO and performed a simulation for them as well.

All of these alcohol compounds produce a very similar curve in CST and give similar values in the range of -2.6dB (see attached photo), while experimentally, each alcohol solution give a very different value for S11 at 2.45 GHz

Experimental values:

• Methanol: -31 dB
• Ethanol: -13.5 dB
• Butanol: -10.5 dB
• DMSO: -20 dB

CST Values:

• Methanol: -2.8 dB
• Ethanol: -2.4 dB
• Butanol: -2.5 dB
• DMSO: -2.6 dB

I can't figure out how are my CST values so different from my experimental values

Any help would be greatly appreciated.