Kramers–Kronig analysis of polymer acoustic data

We briefly present the relationships between the acoustic velocity v and attenuation α in their exact form, while retaining the ambiguity in the magnitude of the response function. We show that some recent experimental measurements of v and α in polymers satisfy the Kramers–Kronig relations very well, while others are not as satisfactory. We demonstrate that the nearly local approximation obtained by dropping terms in (αv/ω)2 is quite inappropriate for these materials, and we point out the importance of these measurements for the experimental analysis of space charge in insulators.