Wave propagation responses of porous bi-directional functionally graded magneto-electro-elastic nanoshells via nonlocal strain gradient theory

This study examines the wave propagation characteristics for a bi-directional functional grading of barium titanate (BaTiO₃) and cobalt ferrite (CoFe₂O₄) porous nanoshells, the porosity distribution of which is simulated by the honeycomb-shaped symmetrical and asymmetrical distribution functions. The nonlocal strain gradient theory (NSGT) and first-order shear deformation theory are used to determine the size effect and shear deformation, respectively. Nonlocal governing equations are derived for the nanoshells by Hamilton’s principle. The resulting dimensionless differential equations are solved by means of an analytical solution of the combined exponential function after dimensionless treatment. Finally, extensive parametric surveys are conducted to investigate the influence of diverse parameters, such as dimensionless scale parameters, radius-to-thickness ratios, bi-directional functionally graded (FG) indices, porosity coefficients, and dimensionless electromagnetic potentials on the wave propagation characteristics. Based on the analysis results, the effect of the dimensionless scale parameters on the dispersion relationship is found to be related to the ratio of the scale parameters. The wave propagation characteristics of nanoshells in the presence of a magnetoelectric field depend on the bi-directional FG indices.