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Mechanistic multilayer model for non-invasive bioimpedance of intact skin

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Fig. 1

Schematic of skin layers.
Schematic of skin layers.

Fig. 2

Schematic of skin comprising n layers and a circular EIS probe with m electrodes.
Schematic of skin comprising n layers and a circular EIS probe with m electrodes.

Fig. 3

Schematic of a 4-electrode probe and skin modeled as a three-layer entity.
Schematic of a 4-electrode probe and skin modeled as a three-layer entity.

Fig. 4

The mean magnitude (▲) and phase (•) from the experimental EIS measurements [9] with the error bars indicating one standard deviation. The lines are the predicted counterparts from the approximate semi-analytical solution, where (–) represent a thickness of 14 μm SC and (- -) denotes a thickness of either 11 or 17 μm. These values for the thickness of SC correspond to the mean and ± one standard deviation.
The mean magnitude (▲) and phase (•) from the experimental EIS measurements [9] with the error bars indicating one standard deviation. The lines are the predicted counterparts from the approximate semi-analytical solution, where (–) represent a thickness of 14 μm SC and (- -) denotes a thickness of either 11 or 17 μm. These values for the thickness of SC correspond to the mean and ± one standard deviation.

Fig. 5

The individual currents, Ik, in terms of their (a) real and (b) imaginary parts for the numerical solution of the complete model (symbols) and the corresponding analytical counterpart (lines), for I4 (★), I2 (▲), I1 (■) and I3 (▼).
The individual currents, Ik, in terms of their (a) real and (b) imaginary parts for the numerical solution of the complete model (symbols) and the corresponding analytical counterpart (lines), for I4 (★), I2 (▲), I1 (■) and I3 (▼).

Fig. 6

The absolute value of the potential distribution at 1 MHz for n=3 and m=4: The numerical solution of the full set of equations for SC (a), VS (c), and AT (e); and approximate semianalytical solution for SC (b), VS (d) and AT (f).
The absolute value of the potential distribution at 1 MHz for n=3 and m=4: The numerical solution of the full set of equations for SC (a), VS (c), and AT (e); and approximate semianalytical solution for SC (b), VS (d) and AT (f).

Base-case dimensions and material parameters for the 4-electrode probe and 3 skin layers (n=3, m=4). (The outer radius of the skin is only used in the numerical solution for verification purposes.)

Current detection width, w11 mm[2]
Ceramic width, w2, w4, w60.15, 0.15, 1.9 mm[2]
Guard width, w30.3 mm[2]
Secondary inject width, w50.5 mm[2]
Primary inject width, w70.5 mm[2]
Outer radius of the probe, R4.5 mm[2]
Outer radius of the skin, Rskin20 mm
Stratum corneum thickness, h314 μm[11]
Viable skin thickness, h21.2 mm[11]
Adipose tissue thickness, h11.2 mm[11]
Inject voltage, V00.05 V[2]
Depth setting, α0.1[2]
Electrical permittivity in vacuum, ε08.85 ×107 Fm-1[12]