Estimation of dynamic paramaters for viscoelastic materials by longitudinal vibration testing using pulse method
In this paper, two methods based on longitudinal vibration testing of a thin bar are proposed for measuring the dynamic parameters of the viscoelastic materials in a wide frequency region. First, an inverse method by FEM based on resonance measurement is presented, in which the measured response of longitudinal vibration is asymptotically approached by the forward calculated response from the finite element computation, then the dynamic parameters can be obtained. Second, an improved wave propagation measurements based on free end longitudinal vibration signal is described. In which the dynamic parameters in the frequency range of 1kHz to 5kHz are calculated from the vibration velocity ratio between the long bar and the short bar.
Resonant acoustic determination of elastic moduli
A long rod of circular or elliptical cross section can be selectively excited in the torsional, longitudinal, and flexural resonant modes using a single pair of electrodynamic transducers consisting of coils glued to each end of the bar and placed in the field of a magnet. The elastic moduli of the material can be simply determined to high accuracy by measuring the resonance frequencies of these modes and the mass and physical dimensions of the rod. Since the longitudinal and flexural modes both yield values for the Young’s modulus, the system has a built‐in redundancy that makes the interpretation of the data more robust. The large signal amplitudes make automated measurement of the temperature dependence of the moduli simple through the use of a phase‐locked loop to track the change in the resonance frequency with temperature.
Investigations of dielectric gratings using electrodynamic models based on volume integral equations
Eigenmodes of planar and cylindrical dielectric gratings (DGs) and electromagnetic wave scattering from multiplayer DGs are investigated. The DG characteristics are calculated using numerical-analytical solution of integral equations (IEs).