A comprehensive micromechanical model for the analysis of a smart composite piezo-magneto-thermoelastic thin plate with rapidly-varying thickness is developed in the present paper. A rigorous three-dimensional formulation is used as the basis of multiscale asymptotic homogenization. The asymptotic homogenization model is developed using static equilibrium equations and the quasi-static approximation of Maxwell's equations. The work culminates in the derivation of a set of differential equations and associated boundary conditions. These systems of equations are called unit cell problems and their solution yields such coefficients as the effective elastic, piezoelectric, piezomagnetic, dielectric permittivity and others. Among these coefficients, the so-called product coefficients are also determined which are present in the behavior of the macroscopic composite as a result of the interactions and strain transfer between the various phases but can be absent from the constitutive behavior of some individual phases of the composite material. The model is comprehensive enough to allow calculation of such local fields as mechanical stress, electric displacement and magnetic induction. In part II of this work, the theory is illustrated by means of examples pertaining to thin laminated magnetoelectric plates of uniform thickness and wafer-type smart composite plates with piezoelectric and piezomagnetic constituents. The practical importance of the model lies in the fact that it can be successfully employed to tailor the effective properties of a smart composite plate to the requirements of a particular engineering application by changing certain geometric or material parameters. The results of the model constitute an important refinement over previously established work. Finally, it is shown that in the limiting case of a thin elastic plate of uniform thickness the derived model converges to the familiar classical plate model.

A comprehensive micromechanical model for the analysis of a smart composite piezo-magneto-thermoelastic thin plate with rapidly varying thickness is developed in Part I of this work. The asymptotic homogenization model is developed using static equilibrium equations and the quasi-static approximation of Maxwell's equations. The work culminates in the derivation of general expressions for effective elastic, piezoelectric, piezomagnetic, dielectric permittivity and other coefficients. Among these coefficients, the so-called product coefficients are determined which are present in the behavior of the macroscopic composite as a result of the interactions between the various phases but can be absent from the constitutive behavior of some individual phases of the composite structure. The model is comprehensive enough to also allow for calculation of the local fields of mechanical stresses, electric displacement and magnetic induction. The present paper determines the effective properties of constant thickness laminates comprised of monoclinic materials or orthotropic materials which are rotated with respect to their principal material coordinate system. A further example illustrates the determination of the effective properties of wafer-type magnetoelectric composite plates reinforced with smart ribs or stiffeners oriented along the tangential directions of the plate. For generality, it is assumed that the ribs and the base plate are made of different orthotropic materials. It is shown in this work that for the purely elastic case the results of the derived model converge exactly to previously established models. However, in the more general case where some or all of the phases exhibit piezoelectric and/or piezomagnetic behavior, the expressions for the derived effective coefficients are shown to be dependent on not only the elastic properties but also on the piezoelectric and piezomagnetic parameters of the constituent materials. Thus, the results presented here represent a significant refinement of previously obtained results.

We show that for the spherical model of the brain, the part of the neuronal current that generates the electric potential (and therefore the electric field) lives in the orthogonal complement of the part of the current that generates the magnetic potential (and therefore the magnetic induction field). This means that for a continuously distributed neuronal current, information missing in the electroencephalographic data is precisely information that is available in the magnetoencephalographic data, and vice versa. In this way, the notion of complementarity between the imaging techniques of electroencephalography and magnetoencephalography is mathematically defined. Using this notion of complementarity and expanding the neuronal current in terms of vector spherical harmonics, which by definition provide the angular dependence of the current, we show that if the electric and the magnetic potentials in the exterior of the head are given, then we can determine certain moments of the functions which provide the radial dependence of the neuronal current. In addition to the above notion of complementarity, we also present a notion of unification of electroencephalography and magnetoencephalography by showing that they are governed respectively by the scalar and the vector invariants of a unified dyadic field describing electromagnetoencephalography.

Unit-cell based finite element models are developed to completely characterize the role of porosity distribution and porosity volume fraction in determining the elastic, dielectric and piezoelectric properties as well as relevant figures of merit of 3-3 type piezoelectric foam structures. Eight classes of foam structures which represent structures with different types and degrees of uniformity of porosity distribution are identified; a Base structure (Class I), two H-type foam structures (Classes II, and III), a Cross-type foam structure (Class IV) and four Line-type foam structures (Classes V, VI, VII, and VIII). Three geometric factors that influence the electromechanical properties are identified: (i) the number of pores per face, pore size and the distance between the pores; (ii) pore orientation with respect to poling direction; (iii) the overall symmetry of the pore distribution with respect to the center of the face of the unit cell. To assess the suitability of these structures for such applications as hydrophones, bone implants, medical imaging and diagnostic devices, five figures of merit are determined via the developed finite element model; the piezoelectric coupling constant (K t ), the acoustic impedance (Z), the piezoelectric charge coefficient (d h ), the hydrostatic voltage coefficient (g h ), and the hydrostatic figure of merit (d h g h ). At high material volume fractions, foams with non-uniform Line-type porosity (Classes V and VII) where the pores are preferentially distributed perpendicular to poling direction, are found to exhibit the best combination of desirable piezoelectric figures of merit. For example, at about 50% volume fraction, the d h , g h , and d h g h figures of merit are 55%, 1600% and 2500% higher, respectively, for Classes V and VII of Line-like foam structures compared with the Base structure.