Fig.1
Schematic of (a) the four-electrode EIS probe with a sense (1), guard (2), second inject (3) and first inject (4); (b) the electrodes of the probe and the stripped skin comprising living epidermis and dermis; and (c) the reduced model consisting of dermis with the living epidermis and electrodes reduced to boundary conditions.
Tab. 1
Skin thickness (mean value ± standard deviation) at the volar forearm for epidermis, stratum corneum and dermis. Some measurement techniques are: Confocal Microscopy (CM), Confocal laser scanning microscopy (CLSM), Optical coherence tomography (OCT), Transepidermal water loss (TEWL), Confocal Raman spectrometer (CRS) and Ultrasound (US).
| ED (μm) | Subj | Age | Measurement | Source |
|---|---|---|---|---|
| 73.54±2.84 | 10 | 23 - 47 | CM | [12] |
| 89±9 | 15 | 19 - 24 | CLSM | [13] |
| 71.8±10 | 30 | 21 - 35 | OCT | [14] |
| 102±7.4 | 5 | 20 - 35 | OCT | [15] |
| 66.39±5.82 | 19 | 20 - 29 | OCT | [16] |
| 65.1±8.9 | 8 | 31 - 37 | OCT | [17] |
| SC (μm) | ||||
|---|---|---|---|---|
| 12.9±3.8 | 6 | 25 - 31 | TEWL/Stripping | [18] |
| 12.3±3.6 | 6 | 33.2±3.1 | TEWL/Stripping | [19] |
| 9.58±0.8 | 10 | 23 - 47 | Reflectance CM | [12] |
| 10.4±3.2 | 13 | 18 - 25 | CLSM | [20] |
| 22.6±4.33 | 14 | 23 - 49 | CRS | [21] |
| 18±3.9 | 14 | 28 - 50 | CRS | [22] |
| 10.4±0.9 | 9 | 23 - 55 | OCT | [22] |
| 13.07±2.12 | 19 | 20 - 29 | OCT | [16] |
| 18±2 | 2 | 23 - 25 | CRS | [23] |
| DE (mm) | ||||
|---|---|---|---|---|
| 1.02±0.10 | 44 | 21 - 30 | US 20MHz B scanner | [24] |
| 1.00±0.13 | 20 | 15 - 76 | US 20MHz B scanner | [25] |
| 1.02±0.21 | 17 | 16 - 50 | Biopsy | [26] |
| 0.85±0.11 | 5 | 26 - 74 | US 22 MHz B scanner | [27] |
Tab. 2
Dimensions and material parameters.
| Current detection width, w1 | 1 mm |
| Ceramic width, w2, w4, w6 | 0.15, 0.15, 1.9 mm |
| Guard width, w3 | 0.3 mm |
| Secondary inject width, w5 | 0.5 mm |
| Primary inject width, w7 | 0.5 mm |
| Living epidermis thickness, hLE | 61 μm |
| Dermis thickness, hDE | 1.0 mm |
| Inject voltage, V0 | 0.05 V |
| Depth setting, α | 0.1, 0.58, 1 |
| Electrical permittivity in vacuum, | 8.85 x10-12 Fm-1 |
| ɛ0 [28] |
Fig. 2
The mean (depth 1 ●; depth 5 ■] and standard deviations (error bars) for the (a) magnitude and (b) phase of the experimentally measured impedances. The fitted mean resistivity and relative permittivity and their standard deviations can be found in (c) and (d) respectively for the living epidermis (♦) and dermis (▼); the fitted equations, Eqs. 7-8, are shown as lines. In (e) and (f), the validation set for depth setting 3 is shown for the experiments (●) and model predictions (lines).
Tab. 3
Coefficients for the conductivity and relative permittivity of the skin layers for 1 kHz to 1 MHz.
| j | ||
| 0 | 1.6306×10-2 | -2.3922×10-2 |
| 1 | -3.3591×10-1 | 5.5919×10-1 |
| 2 | 2.7019×100 | -5.2033×100 |
| 3 | -1.0667×101 | 2.4090×101 |
| 4 | 2.0531×101 | -5.6056×101 |
| 5 | -1.3260×101 | 5.7328×101 |
| j | ||
| 0 | -1.0475×10-2 | -2.5399×10-1 |
| 1 | 2.2902×10-1 | 5.5554×100 |
| 2 | -1.9609×100 | -4.7903×101 |
| 3 | 8.2439×100 | 2.0330×102 |
| 4 | -1.7209×101 | -4.2527×102 |
| 5 | 1.4687×101 | 3.5741×102 |