Conclusions

Coupled wave propagation in a solid body is possible to describe using a unified formulation inferred from general principles. In this paper coupling between elastic and electromagnetic and thermal quantities is derived as an example; other quantities describing the dynamic state of a solid body, such as magnetic fields, can easily be included. Since fluid flow is excluded, the theory is completely linear. Using coupled conservative and constitutive equations coupled wave equations can be formulated in the time domain. Transforming in the Fourier domain leads to an eigenvalue problem, the generalized Christoffel equation. By solving this equation, wave speeds and particle motions of waves traveling in the medium can be calculated. As we see from the examples of quartz and Lead-Titanate-Zirconate, 3D slowness surface plots show significant difference in uncoupled and coupled wave propagation behavior. The fact, that boundary conditions give a major effect on coupled wave propagation needs careful consideration, and suggests that coupling phenomena can be observed not only, when measuring all coupled quantities, but also when boundary conditions are specified such that one coupled quantity is eliminated. Such a hidden variable still produces a significant coupling phenomena. This suggests that coupling phenomena could prove to be significant in potential geophysical applications such as enhanced oil recovery and detailed studies of hydrocarbonceous target zones.