In this paper near-cut-on Guided Resonances (GR) are generated in a composite structure using an array of piezoelectric transducers. A GR is a type of high-order uni-directional wave mode, guided between the finite boundaries of a periodic waveguide's cross-section. Near their cut-on frequency, these waves often exhibit high chromatic dispersion and spatial decay, which compromise their potential use for wave-based inspection and Structural Health Monitoring (SHM) of advanced composite or metamaterials. A custom GR actuator is designed to achieve an accurate shape appropriation of the predicted 3D Floquet-Bloch solutions in a 3m-long sandwich structure. An original wave conversion phenomenon is then exploited to generate almost non-dispersive selected GR pulses near their cut-on frequency. Full wavefield measurements are conducted in time-domain using Laser Doppler Velocimeter to provide new insights on the GR near-cut-on scattering effects in the low vibroacoustic bandwidth.