Table 3.

Tissue conductivity values for six tissue types. White matter, gray matter, bone and skin values were sourced from the literature for measurement frequency up to 20kHz [13] and within the range of reported values in typical volume conductor models [29]. Bone conductivity (combined) was computed as $\sigma =\sqrt{{\sigma }_{can}\cdot {\sigma }_{cor}}$ where σ_can was cancellous bone and σ_cor was the average of cortical bone conductivity reported in the reference. Isotropic white matter conductivity was simulated using the formula $\sigma =\sqrt{{\sigma }_l\cdot {\sigma }_t}$ where σ_l was longitudinal and σ_t was transverse conductivity.

Tissue types	σ (S/m)	Reference
White matter	1.2×10−1(trans.) 1.2 (long.)	Geddes and Baker (1967) [29]
Gray matter	1.0×10−1	Gabriel et al. (1996) [30]
Cerebrospinal fluid	1.8	Baumann et al. (1997) [31]
Skin	4.3×10−1	Holdefer et al. (2006) [32]
Bone	21.4 ×10–3 (cancellous) 5.52 × 10–3 (cortical) 10.9 × 10–3 (combined)	Akhtari et al. (2000) [33]
Air	2.5×10−14	Huang (2019) [24]