Ok guys, my question is simple, how does the pressure of an electric contact influence the resistance of the human skin?
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asked Apr 2, 2018 at 15:27
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\$\begingroup\$ This mostly depends where the pressure is applied. If is applied to an area full of sweat or sebaceous glands, the pressure has much more influence than on callused skin. Just because these glands will excrete their content on pressure and make a contact of liquid between the inner areas of the body and the metal surface. \$\endgroup\$– JankaCommented Apr 2, 2018 at 15:39
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2 Answers
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Simple answer
Pressure increase contact surface area and reduces micro gap of insulation.
Salt (skin) affects conductance or inverse of resistance and pressure increases contact area to reduce resistance. Alcohol cleansed skin can raise R by 1 or 2 orders of magnitude whereas sweaty palms and fingers reduces it.
Moisture affects dielectric (up to 80x) capacitance with again squeezing out the air gaps in fingerprints to increase capacitance where water is 80x more than air but dry skin is more like 10x.
Pressure affects increases both conductance and capacitance. such that RC=T product is pretty constant.
Touch Capacitance sensors are more consistent among humans unless extreme dry skin but resistance is more sensitive but wider variance. Both need calibration.
Medical patch electrodes use a low galvanic response insulation dielectric jelly with silver particle conductor in the adhesive to improve signal to noise ratio of heart or brain wave electrodes.
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\$\begingroup\$ Thanks a lot for this answer.Hope that you'll have an happy easter! \$\endgroup\$ Commented Apr 2, 2018 at 16:13
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\$\begingroup\$ We did. 4 generations incl. 8 kids and 1 dog for dinner. now on the lighter crazy side of Easter re-enactment youtube.com/watch?v=K87FvxMsuG8#action=share \$\endgroup\$– D.A.S.Commented Apr 2, 2018 at 16:42
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Contact resistance will decrease with time as well as with increasing pressure and current, as regions of true contact increase with these factors as discussed here. However, as your question refers more specifically to contact with human skin, issues of oxide layers and surface roughness features, which dominate electrical contact resistance at most contacts, are perhaps less relevant.
