Composite Elastic Wave Waveguide

Aspects and embodiments provide a method of selecting physical characteristics of elements forming a composite elastic waveguide structure configurable to propagate an elastic wave and a composite elastic waveguide structure formed from elements having selected physical characteristics. The method comprises: selecting an elastic wave propagation speed within the composite structure; calculating, based on the selected elastic wave propagation speed, a range of values for at least one the physical characteristic of at least one of at least two elements forming the composite structure, such that propagation of the elastic wave through the combined elements of the composite material at the selected elastic wave propagation speed occurs according to a wave mode in which displacement of a surface of the composite material formed from the at least two elements is substantially zero. Aspects recognise that the propagation of elastic waves in a composite material waveguide may differ from the propagation of elastic waves in a homogeneous material waveguide. In particular, in an appropriately designed composite material, an elastic wave of may propagate through the composite structure and leave, for example, the upper surface of the composite structure substantially unmoved. Homogeneous structures do not allow for propagation of elastic waves in such a manner.