▎ 摘　　要

The harmonic oscillator model is used in combination with the transfer matrix method to describe the absorption of plasmonic devices with a reflector. The model demonstrates that cornplete absorption takes place as a result of the destructive interference between the reflection from the device surface and that from the reflector. In contrast, destructive interference between the transmission and the reflection results in zero absorption. Using a metal back reflector, the absorption of a resonance mode can be tuned from complete absorption to zero absorption by changing the Fermi level of graphene, which is the result of the shifting between the two kinds of destructive interference. A stacked graphene-dielectric structure is used to solve the problem as it can create a plasmonic bandgap within the terahertz region. The phase of the reflection can be actively tuned by changing the Fermi level of the graphene in the stacking structure. Therefore, plasmonic devices with a stacked graphene-dielectric back reflector can always show strong absorption by tuning the Fermi level of the top graphene.