 Guido Fetta later built the Cannae Drive based on Shawyer's concept as a resonant thruster with a pillbox-shaped cavity.Since 2008, a few physicists have tested their own models, trying to reproduce the results claimed by Shawyer and Fetta.Juan Yang at Xi'an's Northwestern Polytechnical University (NWPU) was unable to reproducibly measure thrust from their models, over the course of 4 years.