Experimental modal densities of honeycomb sandwich panels at high frequencies

The model density of a structure can be experimentally determined from the real part of its driving point admittance. Due to the impedance of the impedance head and the attachment elements, the measured admittance values can be different from the actual driving point admittance, especially at higher frequencies. A correction factor is usually applied to take into account this effect. It is seen that beyond certain frequency, the modal density of honeycomb sandwich panels obtained experimentally using this technique reduces with frequency though the theoretical estimates increase with frequency. This anomaly is investigated in this study. It is found that though the parameter of interest is the real part of the admittance, correction has to be applied considering both real and imaginary parts of the measured admittance. By doing so, it is seen that the experimental modal density values match well with the theoretical results. (C) 2000 Academic Press.