A planewave, incident on a panel, produces an acoustic trace wavelength that propagates along the surface of the panel. The trace wavelength excites the panel into vibration, creating structural waves within the panel that propagate. These structural waves can be purposely Bragg scattered, creating replicas of the trace wavenumber. The replicas are shifted in wavenumber precisely by the inverse of the periodic separation distance l. Hence, in principle, it should be possible to resolve the acoustic trace wavelength from one of the shifted replicas of the panel's response. The incident angle can then be ascertained from the replicated trace wavelengths.