Abstract
An electrical measurement is non-linear when the applied stimulus itself affects the electrical properties of the underlying tissue. Corresponding voltage-current plots may exhibit pinched hysteresis loops which is the fingerprint of a memristor (memory resistor). Even though non-linear electrical properties have been demonstrated for different biological tissues like apples, plants and human skin, non-linear measurements as such have not been defined, yet. We are studying the non-linear properties of human skin systematically and initiate non-linear measurements on biological tissues as a field of research in general by introducing applicable recording techniques and parameterization. We found under which voltage stimulus conditions a measurement on human skin is non-linear and show that very low voltage amplitudes are already sufficient. The non-linear properties of human skin originate from the sweat ducts, as well as, from the surrounding tissue, the stratum corneum and we were able to classify the overall skin memristor as a generic memristor. Pinched hysteresis loops vary largely among subjects; an indication for the potential use in biomedical sensor applications.
Highlights
When a constant low-frequency sinusoidal voltage of high amplitude (e.g., 13 V) is applied to human skin[1], the shape of the measured current differs from sinusoidal
The human skin memristor as previously described[17] must be labelled more precisely as a “sweat duct memristor”, since there is a second, non-linear mechanism that originates from the stratum corneum[18], which may be modelled as a memristor itself
Sinusoidal, triangular and non-periodic voltage stimuli were applied with six different frequencies (0.05 Hz to 2.5 Hz) each to verify whether human skin is a memristor and under what voltage stimuli conditions a measurement becomes non-linear
Summary
When a constant low-frequency sinusoidal voltage of high amplitude (e.g., 13 V) is applied to human skin[1], the shape of the measured current differs from sinusoidal. A measurement on any memristor is non-linear as soon as its inner state is affected by the applied stimulus. Sinusoidal (with amplitudes of 0.4 V, 0.8 V, and 1.2 V), triangular and non-periodic voltage stimuli were applied with six different frequencies (0.05 Hz to 2.5 Hz) each to verify whether human skin is a memristor and under what voltage stimuli conditions a measurement becomes non-linear.
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