This paper proposes the optimized design of a wireless energy harvesting device (EHD), by means of an evolutionary optimization method. An important component in energy harvesting technique is rectenna. In this paper, Electromagnetic coupling to transmission line terminated by a non-linear load (e.g. rectifier) is considered as rectenna and in order to increase the power density harvested from radiated field, the field-to-wire coupling must be maximized. Hence, an optimization algorithm called Genetic Swam Optimization (GSO) is applied. This procedure is developed in order to increase the lifetime of a wireless sensor network by scavenging RF energy available in the environment.