A high demand for an efficient design of on-board energy devices is the need of the hour, especially for executing commanded tasks, sometimes even at the cost of compromising mission accuracy. Therefore, on-board energy gains techniques pertaining to autonomous vehicles moving in a fluid require extensive research. Recent advances in the field of energy extraction techniques show that the flapping/vibrating motion can be varied from routine propulsion technique to energy extraction process. It is realized that a flexible area type vibrating (tail or wing) structure is better for enhancing power efficiency compared with fixed area type structures, but the main disadvantage of such flexible structure is that they are effected by viscous nature of the operating fluid. The present article focuses on to develop a new approach for energy gain and recharge power pack of on-board resources from the surrounding medium. The prime purpose of the energy gain is to create an autonomous vehicle by using the variable area (perforated plate) of a vibrating structure (tail fin). The robotic fish is designed in such a way that at the point of recharge the tail fin of the robotic fish points out of water and use the surrounding fluid (air) to scavenge energy. Techniques to scavenge energy from fluid (air) such as flapping tail fin and the other technique using a rotating tail fin with a nonlinear spring are mentioned. All results discussed only for air as a surrounding medium to scavenge energy.