Abstract:It has been demonstrated before that human skin can be modeled as a memristor (memory resistor). Here we realize a memristor bridge by applying two voltages of opposite signs at two different skin sites. By this setup it is possible to use human skin as a frequency doubler and half-wave rectifier which is an application of the non-linear electrical properties of human skin. The corresponding electrical measurements are non-linear since these are affected by the applied stimulus itself.
“…Beside human skin, other biological memristors have been found, for example, in the Venus flytrap 14 and in slime molds 15 . There are possible applications of memristors in circuits such as for neuromorphic computing 16–18 , emulating arithmetic operations 19,20 , and for frequency doubling 21 or rectification of electrical currents 22 .Figure 1Schematic of human skin, ( a ) showing different layers, sweat glands, blood vessels and possible current pathways through the glands and the epidermis (indicated by the purple arrows). The illustration is not to scale, e.g.…”
Much is already understood about the anatomical and physiological mechanisms behind the linear, electrical properties of biological tissues. Studying the non-linear electrical properties, however, opens up for the influence from other processes that are driven by the electric field or movement of charges. An electrical measurement that is affected by the applied electrical stimulus is non-linear and reveals the non-linear electrical properties of the underlying (biological) tissue; if it is done with an alternating current (AC) stimulus, the corresponding voltage current plot may exhibit a pinched hysteresis loop which is the fingerprint of a memristor. It has been shown that human skin and other biological tissues are memristors. Here we performed non-linear electrical measurements on human skin with applied direct current (DC) voltage pulses. By doing so, we found that human skin exhibits non-volatile memory and that analogue information can actually be stored inside the skin at least for three minutes. As demonstrated before, human skin actually contains two different memristor types, one that originates from the sweat ducts and one that is based on thermal changes of the surrounding tissue, the stratum corneum; and information storage is possible in both. Finally, assuming that different physiological conditions of the skin can explain the variations in current responses that we observed among the subjects, it follows that non-linear recordings with DC pulses may find use in sensor applications.
“…Beside human skin, other biological memristors have been found, for example, in the Venus flytrap 14 and in slime molds 15 . There are possible applications of memristors in circuits such as for neuromorphic computing 16–18 , emulating arithmetic operations 19,20 , and for frequency doubling 21 or rectification of electrical currents 22 .Figure 1Schematic of human skin, ( a ) showing different layers, sweat glands, blood vessels and possible current pathways through the glands and the epidermis (indicated by the purple arrows). The illustration is not to scale, e.g.…”
Much is already understood about the anatomical and physiological mechanisms behind the linear, electrical properties of biological tissues. Studying the non-linear electrical properties, however, opens up for the influence from other processes that are driven by the electric field or movement of charges. An electrical measurement that is affected by the applied electrical stimulus is non-linear and reveals the non-linear electrical properties of the underlying (biological) tissue; if it is done with an alternating current (AC) stimulus, the corresponding voltage current plot may exhibit a pinched hysteresis loop which is the fingerprint of a memristor. It has been shown that human skin and other biological tissues are memristors. Here we performed non-linear electrical measurements on human skin with applied direct current (DC) voltage pulses. By doing so, we found that human skin exhibits non-volatile memory and that analogue information can actually be stored inside the skin at least for three minutes. As demonstrated before, human skin actually contains two different memristor types, one that originates from the sweat ducts and one that is based on thermal changes of the surrounding tissue, the stratum corneum; and information storage is possible in both. Finally, assuming that different physiological conditions of the skin can explain the variations in current responses that we observed among the subjects, it follows that non-linear recordings with DC pulses may find use in sensor applications.
“…Therefore, passive sensors are direct sensors that change their 98 physical properties, such as resistance, capacitance or inductance [16]. 99 Some applications, in which passive impedance sensors based on chaotic circuits 100 are of great interest, are: i) monitoring of skin hydration and temperature changes [15]; ii) 101 investigations of skin nonlinear properties [17]; iii) investigations related to Bioelectrical 102 Impedance Analysis (BIA) [18]; iv) optimization of bio-oscillators [19] [20]. The second 103 application suffers from low sensitivity when measuring its properties.…”
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confidence: 99%
“…These 106 artifacts (noise) change significantly the skin impedance which, in turns, cannot not 107 be separated from the total measured impedance. It is known from [17] that skin has…”
The signature of chaotic systems can be characterized either by the sensitivity of the initial conditions or by the change of its parameters. This feature can be used for manufacturing high sensitivity sensors. Sensors based on chaotic circuits have already been used for measuring water salinity, inductive effects, and both noise and weak signals. This article investigates an impedance sensor based on the Van der Pol and Duffing damped oscillators. The calibration process is a key point and therefore the folding behavior of signal periods was also explored. A sensitivity of 0.15 kΩ/Period was estimated over a range from 89.5 to 91.6 kΩ. This range can be adjusted according to the application by varying the gain of the operational amplifier used in this implementation. The development of this type of sensor might be used in medical and biological engineering for skin impedance measurements, for example. This type of chaotic sensor has the advantage of sensing small disturbances and then detect small impedance changes within biological materials which, in turn, may not be possible with other detectors.
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