Added a note on requiring either 1mm or 2mm AustinMan/Woman models to use with dispersive material properties due to relaxation times of Debye poles.

docs/source/user_libs_austinman.rst

@@ -47,7 +47,13 @@ Package overview
     head_only_hdf5.py
 
 * ``AustinManWoman_materials.txt`` is a text file containing `non-dispersive material properties at 900 MHz <http://niremf.ifac.cnr.it/tissprop/>`_.
-* ``AustinManWoman_materials_dispersive.txt`` is a text file containing `dispersive material properties using a 3-pole Debye model <http://dx.doi.org/10.1109/LMWC.2011.2180371>`_. Note the main body tissues are described using a 3-pole Debye model, but not all materials have a dispersive description.
+* ``AustinManWoman_materials_dispersive.txt`` is a text file containing `dispersive material properties using a 3-pole Debye model <http://dx.doi.org/10.1109/LMWC.2011.2180371>`_.
+
+.. note::
+
+    * The main body tissues are described using a 3-pole Debye model, but not all materials have a dispersive description.
+    * The dispersive material properties can only be used with the 1x1x1mm or 2x2x2mm AustinMan/Woman models. This is because the time step of the model must always be less than any of the relaxation times of the poles of the Debye models used for the dispersive material properties.
+
 * ``head_only_hdf5.py`` is a script to assist with creating a model of only the head from a full body AustinMan/Woman model.
 
 How to use the models