Materials
Materials properties correspond to a specific class called material. This object hosts the physical constants required to perform the field computations (either anatically or with Finite Elements technique). For the moment, two properties are inherent to a material:
The electrical conductivity \({\sigma}\) for a material in S.m. This can be a scalar value or an anisotropic property described by atensor corresponding to:
The relative dielectric permittivity, used for computation in complex (unitless).
The material class can be instantiated by hand, however we recommend for the en user to use files. The usual format is a ‘.mat’ file containing the figures. NRV comes with a list of predefined materials, and it is particularely easy to add new materials, which are both explained bellow.
To load material, the function load_material should be always used to ensure reliable code. This function adapts to each following case.
List of pre-defined materials
Some materials are predefined as routinely used materials and properties. In this case, the argument of the load_material function is the string ‘name’ of the follwing table:
Material |
Name |
scientific source and comment |
|---|---|---|
Axoplasm |
“axoplasmic_mrg” |
from reference [m1] |
non-specific bone |
“bone” |
from reference [m2] |
Cerebrospinal fluid |
“cerebrospinal_fluid” |
from reference [m3] |
Dura mater |
“dura” |
from reference [m3] |
Endoneurium |
“endoneurium_bahdra” |
figure from reference [m6], isotropic material, corresponds to no meausrement |
Endoneurium |
“endoneurium_horn” |
figures from reference [m5] |
Endoneurium |
“endoneurium_ranck” |
figures from reference [m4] |
Averaged epidurial space |
“epidural_space” |
from reference [m3] |
Epineurium |
“epineurium_horn” |
figures from reference [m5] |
Epineurium |
“epineurium” |
scientific source |
Average muscle |
“muscle” |
do not corresponds specifically to smooth, skeletal or cardiac muscle, from reference [m3] |
Perineurium |
“perineurium_horn” |
figures from reference [m5] |
Perineurium |
“perineurium” |
scientific source |
Platinum |
“platinum” |
commonly found value |
Saline solution |
“saline” |
commonly found value |
Silicone |
“silicone” |
commonly found value |
All the pre-defined material are located in a folder inside the NRV package with the path nrv/_misc/materials/.
Here is the list of exact scientific references used to write pre-defined materials:
[m1] McIntyre, C. C., Richardson, A. G., & Grill, W. M. (2002). Modeling the excitability of mammalian nerve fibers: influence of afterpotentials on the recovery cycle. Journal of neurophysiology, 87(2), 995-1006.
[m2] Kosterich, J. D., Foster, K. R., & Pollack, S. R. (1983). Dielectric permittivity and electrical conductivity of fluid saturated bone. IEEE Transactions on biomedical engineering, (2), 81-86.
[m3] Gabriel, C., & Gabriel, S. (1996). Compilation of the dielectric properties of body tissues at RF and microwave frequencies.
[m4] Ranck Jr, J. B., & BeMent, S. L. (1965). The specific impedance of the dorsal columns of cat: an anisotropic medium. Experimental neurology, 11(4), 451-463.
[m5] Horn, M. R., Vetter, C., Bashirullah, R., Carr, M., & Yoshida, K. (2023). Characterization of the electrical properties of mammalian peripheral nerve laminae. Artificial organs, 47(4), 705-720.
[m6] Bhadra, N., Lahowetz, E. A., Foldes, S. T., & Kilgore, K. L. (2007). Simulation of high-frequency sinusoidal electrical block of mammalian myelinated axons. Journal of computational neuroscience, 22, 313-326.
How to define a specific material using a .mat file?
It is possible to add new materials by defining a .mat` file. This file can be directly added in the nrv/_misc/materials/. In this case, to load the material, just the filename without the .mat extension is the corresponding loading string. It is also possible to define locally a .mat file and give the path as argument to the load_material function.
In this case, the .mat file is a simple of list of values arranged with the following keys:
name |
name of the material, important if constitutive of the nerve (perineurium, epineurium, endoneurium) |
|---|---|
source |
free comment for user purpose, not interpreted by NRV |
sigma |
electrical conductivity, if the material is isotropic |
sigma_xx |
electrical conductivity along the x-axis (longitudinal), if the material is anisotropic |
sigma_yy |
electrical conductivity along the y-axis (radial), if the material is anisotropic |
sigma_zz |
electrical conductivity along the y-axis (radial), if the material is anisotropic |
epsilon_r |
relative permittivity of the material |