The Existence of Low Loss Lamb Modes in Highly Attenuative Media

A great deal of work on Lamb waves has been devoted to their application to materials which are assumed to be elastic and hence have negligible material attenuation (see e.g. [1–2]). However for materials such as polyethylene, the assumption of elasticity may be invalid as the amplitude of the Lamb waves will decrease with propagation distance, a phenomenon not accounted for in the elastic treatment. From a dispersion curve point of view, the interest lies in determining whether the inclusion of attenuation will greatly change their characteristics. In most, if not all, circumstances the bulk shear wave attenuation for any given material is considerably larger than that for the bulk longitudinal wave. Given that Lamb waves can be modelled by the superposition of such bulk waves, it is believed that the shear wave attenuation will be the dominant factor on the character of the dispersion curves.