Propagation of acoustic wave’s motion in orthotropic Cylinders of infinite length

We report, in the present work, a numerical method for investigating guided waves propagation in a homogeneous infinite cylinder composed of elastic material. This method makes use of Legendre polynomials series and harmonic function to express different displacement components which are introduced into the equation of motion. The advantage of this method is the possibility to incorporate the stress-free boundary conditions directly into the equations of motion by assuming position-dependent elastic constants and mass density. The solution of the wave equations can be reduced to an eigenvalue problem. Numerical results are presented and compared with those published earlier in order to validate our polynomial approach. For certain specific modes, dispersion curves and field profiles such as mechanical displacements, normal stresses are presented. The developed software is capable of dealing efficiently and accurately with a variety of homogeneous and inhomogeneous cylinders

Two-port network theory based thermal characterization of power module packages

For thermal analysis, power module packages can often be considered as plane multilayered systems for which it has been demonstrated that appropriate Fourier transforms associated with the two-port network theory permit to develop very efficient solutions of the static or the time dependent 3D heat flow equation. However, in practice, the thermal resistances of soldered or pasted interfaces are most often not well known. Most of these parameters are theoretically unpredictable, therefore it is of highest interest to develop an experimental procedure intended for an adequate characterization of the 3D thermal behaviour of the cooling substrates. A two-port network theoretical basis for experimental characterization of the thermal behaviour of multilayered substrates (96% Alumina, AU4G, IMS), which are classically used for power module packaging, is presented. In spite of some difficulties in setting perfectly the boundary conditions for temperature and heat fluxes, the experimental results demonstrate the validity of the characterization method, and the soughted parameters can be measured for wide ranges of spatial pulsation. Suggested improvements of the existing experimental set can give rise to an industrial measurement set intended for thermal characterization of power module packages

Mapped orthogonal functions method applied to acoustic waves-based devices

This work presents the modelling of acoustic wave-based devices of various geometries through a mapped orthogonal functions method. A specificity of the method, namely the automatic incorporation of boundary conditions into equations of motion through position-dependent physical constants, is presented in detail. Formulations are given for two classes of problems: (i) problems with guided mode propagation and (ii) problems with stationary waves. The method’s interest is demonstrated by several examples, a seven-layered plate, a 2D rectangular resonator and a 3D cylindrical resonator, showing how it is easy to obtain either dispersion curves and field profiles for devices with guided mode propagation or electrical response for devices with stationary waves. Extensions and possible further developments are also given