The non-linear electrical properties of human skin make it a generic memristor

Pabst, Oliver; Martinsen, Ørjan G.; Chua, Leon O.

doi:10.1038/s41598-018-34059-6

Cited by 31 publications

(92 citation statements)

References 31 publications

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“…The recordings on human skin (see Figs. 2e and 2f and results in [4]) exhibited pinched hysteresis loops in which the two branches of the loop crossed the pinched point with different slopes. This can be achieved for different amplitudes, frequencies and shapes of the applied voltage and also different electrode materials (see the recording with the stainless steel electrodes in Fig.…”

Section: Methodsmentioning

confidence: 79%

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The non-linear electrical properties of silver/silver chloride electrodes in sodium chloride solution

Pabst

Anwar

Nieweglowski

et al. 2019

Journal of Electrical Bioimpedance

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An electrical measurement is non-linear when it is affected by the applied stimulus, i.e. when the measured phenomenon changes with amplitude. If pinched hysteresis loops can be observed in the voltage current representation, the underlying tissue can be classified as a memristor. Several biological memristors have been published, like human skin and apples. However, changes in the polarization impedance of electrodes may also cause pinched hysteresis loops. The question whether the reported biological memristors are real or whether the results just reflect changes in the polarization impedance arises. If the impedance of the measured object is close to or smaller than the polarization impedance of the used electrodes, the latter may dominate the measurement. In this study, we investigated the non-linear electrical properties of silver/silver chloride electrodes in a sodium chloride solution that has a similar concentration as human sweat and compared these to results from human skin. First of all, we found that silver/silver chloride electrodes in sodium chloride solution can be classified as memristors. However, the currents obtained from the sodium chloride solution are much higher than the currents recorded from human skin and there is a qualitative difference in the pinched hysteresis loops in both cases. We can conclude that the non-linear electrical measurements with silver/silver chloride on human skin are actually dominated by the skin and we can confirm that the human skin memristor really exists.

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Section: Methodsmentioning

confidence: 79%

“…Thirdly, the hysteresis loop turns into a single-valued function as the frequency goes toward infinity [3]. It has been shown that human skin is a memristor [4]. The sweat is moved by electro-osmosis [5] towards the skin surface or towards deeper skin layers dependent on the polarity of the applied voltage.…”

Section: Introductionmentioning

confidence: 99%

The non-linear electrical properties of silver/silver chloride electrodes in sodium chloride solution

Pabst

Anwar

Nieweglowski

et al. 2019

Journal of Electrical Bioimpedance

Self Cite

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“…With an electrode area of 0.785 cm2, the developed system has a density of 0.6 μA/0.785 cm2 = 0.764 μA/cm2. The study from [52] observes nonlinear electrical properties of the skin at higher excitation voltages and current levels. While this quasi-constant current circuit topology in Figure A1 may benefit by maintaining low levels of current required for linear EDA measurement, we recognize that the results from [52] suggest AC topologies may provide additional benefits’ linear operation at higher frequencies >0.1 Hz.…”

Section: Figure A1mentioning

confidence: 99%

“…The study from [52] observes nonlinear electrical properties of the skin at higher excitation voltages and current levels. While this quasi-constant current circuit topology in Figure A1 may benefit by maintaining low levels of current required for linear EDA measurement, we recognize that the results from [52] suggest AC topologies may provide additional benefits’ linear operation at higher frequencies >0.1 Hz. Alternatively, this circuit topology could be modified to measure EDA using a constant-voltage model by exchanging the positions of Rskin and Rb and adjusting the reference voltage at Vb such that the voltage drop across the skin is within the linear range of operation (0.2 V DC) suggested in [52].…”

Section: Figure A1mentioning

confidence: 99%

“…While this quasi-constant current circuit topology in Figure A1 may benefit by maintaining low levels of current required for linear EDA measurement, we recognize that the results from [52] suggest AC topologies may provide additional benefits’ linear operation at higher frequencies >0.1 Hz. Alternatively, this circuit topology could be modified to measure EDA using a constant-voltage model by exchanging the positions of Rskin and Rb and adjusting the reference voltage at Vb such that the voltage drop across the skin is within the linear range of operation (0.2 V DC) suggested in [52].

Figure A1EDA sensor amplifier.As the skin resistance changes, due to activation of the sympathetic nervous system, the voltage output at node Vaaf can be modeled as:Vaaf=RskinRb(−0.2V)+2.6V.…”

Section: Figure A1mentioning

confidence: 99%

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Design and Implementation of an Ultra-Low Resource Electrodermal Activity Sensor for Wearable Applications ‡

Pope

Halter

2019

Sensors

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While modern low-power microcontrollers are a cornerstone of wearable physiological sensors, their limited on-chip storage typically makes peripheral storage devices a requirement for long-term physiological sensing—significantly increasing both size and power consumption. Here, a wearable biosensor system capable of long-term recording of physiological signals using a single, 64 kB microcontroller to minimize sensor size and improve energy performance is described. Electrodermal (EDA) signals were sampled and compressed using a multiresolution wavelet transformation to achieve long-term storage within the limited memory of a 16-bit microcontroller. The distortion of the compressed signal and errors in extracting common EDA features is evaluated across 253 independent EDA signals acquired from human volunteers. At a compression ratio (CR) of 23.3×, the root mean square error (RMSErr) is below 0.016 μ S and the percent root-mean-square difference (PRD) is below 1%. Tonic EDA features are preserved at a CR = 23.3× while phasic EDA features are more prone to reconstruction errors at CRs > 8.8×. This compression method is shown to be competitive with other compressive sensing-based approaches for EDA measurement while enabling on-board access to raw EDA data and efficient signal reconstructions. The system and compression method provided improves the functionality of low-resource microcontrollers by limiting the need for external memory devices and wireless connectivity to advance the miniaturization of wearable biosensors for mobile applications.

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Theory and Technology of Memristive Devices

Tetzlaff

Ascoli

Wouters

2022

Wiley Encyclopedia of Electrical and Electronics Engineering

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CMOS scaling is progressively and inevitably approaching atomic boundaries. The industry is thus exploring the potential of novel disruptive nanotechnologies, based on multifunctional materials, which may allow the development of integrated circuits keeping the trend predicted by Moore in 1965 in the years to come, despite further transistor shrinking being no longer possible. Memristors, originally postulated only theoretically out of a brilliant line of thought by Chua in 1971 and identified at the nanoscale almost 40 years later, back in 2008, by a team of engineers supervised by R.S. Williams at Hewlett Packard Labs, represent the key nanotechnology of the future, enabling novel forms of computation, which are closer to the principles underlying the functionalities of the human brain, given the extraordinarily peculiar capability of these devices to sense, store, and process data in the same physical miniaturized volume. Achieving progress in memristor circuit design crucially calls for the development of synergies among researchers with different academic backgrounds. In fact, only combining the technical knowledge, acquired by memristor theoreticians, with the practical know‐how of experimenters will enable to foster progress in memristor circuit and system development in the near future. In line with this necessity, the present article is the fruit of a joint cooperation between two leading memristor research units from Germany, one based at TU Dresden, which has contributed to establish solid theoretical foundations on resistance switching memories and their circuits since 2008, and the other one based at RWTH Aachen University, which has been the leading experimental research unit on nanostructures of this kind over the same time span. This article first presents a comprehensive overview of the theory of memristors, starting off from the early achievements in the pioneering studies of their father Chua, then classifies and analyses in depth the main physical mechanisms underlying the inherently nonlinear behavior of their physical realizations, and, finally, discusses their most promising applications, from the development of new nonvolatile memories based on resistance switching phenomena to the realization of novel neuromorphic circuits, capable to mimic the complex dynamics of biological entities closer than conventional purely CMOS hardware, without leaving aside an excursus on the potential to leverage the unique features of these devices for the circuit implementation of unconventional brain‐inspired time‐ and energy‐efficient sensing and memcomputing strategies, which is a great appeal for the realization of portable light‐weight technical systems for the Internet‐of‐Things industry, especially but not only to the benefit of healthcare, well‐being, and automotive market sectors.

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The non-linear electrical properties of human skin make it a generic memristor

Cited by 31 publications

References 31 publications

The non-linear electrical properties of silver/silver chloride electrodes in sodium chloride solution

The non-linear electrical properties of silver/silver chloride electrodes in sodium chloride solution

Design and Implementation of an Ultra-Low Resource Electrodermal Activity Sensor for Wearable Applications ‡

Theory and Technology of Memristive Devices

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