### I. Introduction

### II. Methods

### 1. Configuration of the Skin Model

_{e}, σ

_{d}, σ

_{s}for the epidermis, dermis and subcutaneous tissue were 0.13 S/m, 0.26 S/m, 0.52 S/m respectively. The skin model structure was 80 mm in width and 24 mm in height. The distance between the current electrodes (I+, I-) was 60 mm, and that between the reference electrode (V-) and the measurement electrode (V+) was 26 mm. The depth of each tissue layer was 2 mm for the epidermis and 4 mm for the dermis. Electrode width was 4 mm and height was 2 mm.

### 2. Skin Model Theory

**J**is the current density (defined as the current crossing a given surface in A/m

^{2}).

**σ**is the conductivity in s/m.

**ρ**is the charge density in C/m

^{3}.

**ε**is the permittivity of the medium, and ▽.

*A*is the divergence of vector A.

**J**at any point is the sum of a source term

**J**and an ohmic term

_{s}**σE**:

**I**

_{v}is a source term (in A/m

^{3}). The source term

**I**

_{v}is zero everywhere, except at the location of the sources. This equation is nearly identical to the Poisson equation derived from eq. (2) for dielectric media:

*I*, ε → σ, the solution to the Poisson equation for dielectric media can then be used to obtain the current in volume conductors.

_{v}**I**, the potential and current at any point can be easily derived. By spherical symmetry, the current density

**J**at a point

**P**located at a distance

**r**from the source is equal to the total current crossing a spherical surface with radius

**r**

**u**

_{r}is the unit radial vector, and r is the distance between the electrode and the point of measurement. The electrical field is then obtained from eq. (3):

### III. Results

_{1}represents the resistance of internal tissue, the R

_{2}model the resistance of external tissue, and C represents the electrode/tissue interface and constant phase element model. The equivalent circuit that describes the impedance of skin consists of a CPE with Z

_{CPE}=Y

^{-1}(jω)

^{-α}, where α is related to the fractal dimension of the skin's surface and can be regarded as a measure of the roughness of the skin's surface, ω is the angular frequency, and Y is the admittance of the CPE. Values of the chosen components were determined via a non-linear least-squares fit to the equivalent circuit using the Z-view program. Results of this fit are shown in Figure 5 and Table 1. This electrical impedance model was fitted and developed in comparison with our model for measurement of skin impedance. We obtained accurate results from our developed electric model.