Hi,
I am beginner of electrical impedance tomography (EIT), electrical capacitive tomography (ECT), etc.
I made two SUS plates to measure the impedance of my arm skin by agilent high precision LCR meter. Every measurement, I always observe that the the initial impedance is high, and it slowly decreases and saturates after a long time.
I carefully maintained the skin-electrode contact to avoid motion artifact. It was quite effective to reduce noise, but still the decreasing impedance was shown.
Also, I changed the SUS plates to Ag/AgCl electrodes. The noise was dramatically reduced, but still the start impedance looks high.
My question is why the skin impedance continuously decreases and how I can prevent or compensate the impedance instability to get a representative impedance value of the skin.
Thank you!
Seongjun
To clearly explain the situation, I placed the two electrodes at 1 cm apart on the skin (EIT case).
I also deposited 1-um-thick SiO2 on the electrodes to get capacitive electrodes, and did the same procedure (ECT case). The decreasing of the measured impedance was the same.
In fact you can use any impedance meter to measure the skin impedance All what you need is to stick two metallic probes on the skin and measure the impedance between the two electrodes by this impedance meter. There are many RLC meters that measures the impedance of the skin where it is equivalent to a parallel combination of a resistance and a capacitance. You have to press the electrodes against the skin to avoid the existence of air gaps between the electrode and the skin. You can use salty solutions to wet the electrodes. In this way you will get reproducible results.
You can also use the impedance measuring method in the paper at the given link:
Article Four Voltmeter Vector Impedance Meter Based on Virtual Instrumentation
I used this method to measure the skin impedance and it gave good results.
Best wishes
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