The common plasma waveguide system can not be widely used due to its complex structure, limited available band and poor tunability.A simple metal-insulator-metal (MIM) waveguide composed of double semi-ring cavities (DSR) is proposed. The finite element method (FEM) is used to simulate the structure, and the transmittance and sensing characteristics are studied by adjusting geometric parameters and refractive index. It is shown that two typical Fano resonances can be produced, which can be regulated independently by cavity size and coupling distance.It can be found that discrete energy plays a leading role in the formation of Fano resonances, and the maximum refractive index sensitivity and figure of merit are 1 260 nm/RIU and 17 473 RIU-1 respectively. In addition, four Fano resonances and semi-independent control can be realized by adding resonance cavity to DSR structure. Due to the advantage of simple construction and the ability to generate multiple Fano resonances with high transmittance, good tunability and high sensitivity,the DSR can be used in the fields of filters, switches, sensors.

surface plasmon polaritons; metal-insulator-metal waveguide; multiple Fano resonances; sensor