- I am characterizing simple cotton textile by using the waveguide method and extracting permittivity from S parameters through Nicolson-Ross-Weir Method. At some frequencies, I am getting peaks on the negative axis side as well. What could be the possible reason of those negative values?
Dear Mr. Nasser,
we have practical only positive permeability or positive permittivity of a "normal"
material. If we have a synthetic material, like the metamaterial, then we have negative material values.
At my opinion, you have some practical measurement problems like not the best calibration or not the best place of the probe. So you have resonances and you can get a negative permittivity.
Sincerely yours
F. Gräbner
I think the NRW method can be ill conditioned so can give some unexpected results. Alternatively, the textile is a periodic structure so may have metamaterial properties, but I would make sure it isn't just sensitivity to the data before believing negative index results.
Dear . Malcolm White , Malcolm White and Preston Guynn thank you for your kind comments. From your input, I concluded that the main source of error could be:
1 Poor calibration, for your information I am Using 2 port TRL waveguide calibration method.
2 Probe position. Is there any rule for the best placement of probes.
3 The sample length, as far as I figured out that there is issue with length because I am getting the desired result on some other length than the one I have used in experiments.
Mr. Malcom, It will be interesting to check the effect of periodic structures of textile on permittivity
Regards
Noaman
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