(a) Elastic waveguide with a graded array of resonators of increasing height. Since the zero-group velocity mode is met at the edge of the Brillouin Zone, after a certain amount of time the input wave is reflected. While the wave propagates, the amplitude and the wavelength decrease due to energy transfer between the waveguide and the resonators. This is shown in the experimental spectrogram in (b) obtained for a rainbow reflection device in the kHz range. Due to this energy transfer, this mechanism is useful to harvest energy in the resonators. Contrary to rainbow reflection, rainbow trapping is obtained through a symmetry broken array, where an accidental degeneracy is lifted, resulting in zero group velocity modes within the first Brillouin zone. This allows to reduce reflections and to increase the energy available inside the array for harvesting.