“…However, by lacking in material internal length parameters, the simple (Grade 1) classical continuum does not always seem appropriate for representing the macroscopic behavior of these materials, taking into account the size, the orientation, and the disposition of the heterogeneities. This often calls for the need of nonclassical (generalized) continuum descriptions [8][9][10][11][12] that can be considered as 'explicitly' or 'implicitly' nonlocal models due to the presence of internal length parameters and dispersion properties in wave propagation [9,13,14]. In this framework, strain gradient, or non-local models of explicit type [15], have been presented [16][17][18], as well as models referable to micromorphic continua, in particular, the micropolar continua, that can be considered non-local models of implicit type [19][20][21][22][23][24][25][26][27].…”