Propagation of Acoustic Waves in a Copper Wire Embedded in a Curing Epoxy

This paper investigates the propagation o f 0.8 to 5.8 MHz acoustic waves in a copper wire embedded in a curing epoxy. The acoustic amplitudes were measured as a function of time and temperature at atmospheric pressure. It was observed that the acoustic amplitude was sensitive to the epoxy state and temperature. For the initial portion of the cure cycle, the attenuation of all the acoustic modes excited in the wire increased. As the cure p rogressed, the attenuation of one mode began to decrease. The velocity of this mode was slightly less than the shear velocity of copper. The frequency of this mode is shown to be dependent on the ratio of the acoustic wavelength to the diameter of the wire. An independent measure of the shear velocity of epoxy indicates a functional dependence between it and the attenuation of the mode, which indicates the potential for measuring the acoustic p roperties of curing resins under extreme conditions such as high temperature or pressure with copper wires.