Calculate the compressibility material properties of a scatterer's tissue or shell (kappa)

Usage

kappa(interface1, interface2)

interface1: Dataframe object containing density (kg/m^3) and sound speed (m/s) values for a boundary/interface (1)
interface2: Dataframe object containing density (kg/m^3) and sound speed (m/s) values for a boundary/interface (2)