Isotropic materials have properties that are consistent in all directions. The material property specifications are therefore simpler for such materials and are defined using matr prop elas. This creates a material that is Linear Elastic in nature.
The properties that need to be specified are density, bulk and shear moduli, longitudinal and shear attenuation, and permittivity.
Tip: Users also have the option to define material properties for elas and tisu in terms of acoustic sound speeds in the Longitudinal and Shear directions.
In OnScale, materials are more commonly defined in terms of wavespeed. To issue material properties in terms of wavespeed, the wvsp command must be used and set to 'on':
prop mat1 1000 1500 0
A more comprehensive example specified by velocities:
prop epoxy $density $vellong $velshear
or, for specification by bulk and shear moduli:
prop mat1 $density $bulkmod $shearmod
Permittivity is a single value, again as absolute permittivity:
elec epoxy $perm
Finally, attenuation must be set. This is generally specified in dB per unit distance at a given frequency, e.g., 2.5 dB/m @ 1 MHz^x. The exponent "x", which is usually between 1 and 2, indicates how the attenuation varies with frequency. Shear attenuation values are often significantly larger than longitudinal values. OnScale sets the values with:
vdmp epoxy db $freqdamp db $attlong $attenshear 1.e6 $x $dist
the polymer usually contributes significantly to attenuation in a piezocomposite.