Abstract
Human skin has been classified as a non-volatile memristor and it is shown that information can be stored within for at least three minutes. Here we investigate whether it is possible to store information up to 20 minutes. Furthermore, we investigate whether the information can be based on four different states, not just two (binary). We stored the information into the skin of the forehead of the test subjects under three different electrodes, which allows in principle for 64 different combinations (3 electrodes, 4 states) and one can think of numbers on the base of four. For this experiment, we decided on the numbers 1234 and 3024 (that correspond to numbers 27 and 50 in the decimal system). Writing of the different states was done by the application of DC voltage pulses that cause electro-osmosis in the sweat ducts (nonlinear electrical measurements). Based on our results, we were not able to distinguish between four different states. However, we can show that binary information storage in human skin is possible for up to 20 minutes.
Highlights
The memristor has been found to be the forth passive electrical component [1], and it connects voltage and current via the state-dependents Ohms’ law v = M(x)i, (1)with M(x) as the memristance and x as the vector of the internal state variables with dx⁄dt = f(x, i) · i. (2)Research interest in the memristor increased when a first realization was found in 2008 [2]
Some ions may move through the ionic pathways in the stratum corneum [12] and changes in the state-dependent resistance may be related to corresponding changes in temperature of the stratum corneum, which acts as a negative temperature coefficient thermistor [9]
With direct current (DC) pulses we affected the conductance of the skin by changing the sweat level within the sweat ducts and measured the small signal conductance for 20 minutes afterwards to see for how long the written information can be obtained
Summary
One is based on electro-osmosis in the sweat ducts [10] (sweat duct memristor) and the other one is based on the non-linear electrical properties of the stratum corneum [11], the outer skin layer which is surrounding the sweat ducts. Both mechanisms are based on the movement of ions. It has been shown that the overall human skin memristor can be classified as generic, and non-volatile [9, 14]
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