The present disclosure described devices, assemblies, apparatus and methods useful in conducting health monitoring of structures including monitoring for structural damage and liquid (e.g., water, fuel, anti-Icing fluid, moisture, etc.) Ingress in composite sandwich-type structures of mobile platforms. An exemplary method for detecting water Ingress in a structure comprises: introducing mechanical energy into the structure; sensing the mechanical energy transmitted through the structure; and determining the existence of water ingress in the structure based on the sensed mechanical energy.