Design of double bowtie ring shaped slot nano-antenna and their absorption properties

In this paper, a novel nano-antenna for energy harvesting is proposed. It consists of two elements gold slab with rectangular shape and slot with double bowtie ring. The height of the slots is the same as that of the nano-antenna. Due to the slot with double bowtie ring, the free electron distribution is changed. A large number of free electrons are gathered at the edge of the slots. When the incident light reaches the contact surface of the gold and the air, the free electron resonates with the incident light. Higher order localized surface plasmon is generated Thus, a stronger localized electric field is produced on the surface of the nanoantenna. At the same time, the local electric field is enhanced by the coupling between the slots. A large amount of energy is confined to the subwavelength range of surface of the nano-antenna. As a result, the reflectivity is reduced and the absorptivity is increased. Three-dimensional finite difference time-domain method is used to analyze the nano-antenna. It is found that the average absorptivity of the nano-antenna is 71% in 400-1800nm waveband. The proposed nano-antenna shows an improvement in the harvesting efficiency over the conventional nano-antenna with rectangular shape by 32%. The maximum absorptivity of the nanoantenna is 98%. In 400 nm-1100 nm, 1200 nm-1300nm and 1500nm-1700nm wavebands, the absorptivity are over 50%. In addition, the light absorbing capability of the nanoantenna is independent of the incident light polarization state in the waveband of 400-1800 nm, and it can keep up an average absorptivity of 70% with the large incident angle varying between -60° and 60°.