A Shifted-Beam Method for Near-Field Wireless Power Transfer using Parasitic Arrays

Optimizing near field (NF) wireless power transfer (WPT) to ensure maximum power transfer efficiency (PTE) is essential for a number of applications such as radio-frequency identification (RFID) and device charging. A new WPT method using a parasitic array is proposed, inspired by a shifted-beam (SB) wave interference technique for field focusing. The SB method is implemented for target distances between $\mathbf{1}\lambda$ and $\mathbf{2}\lambda$ at 2.4 GHz $(\lambda=12.5\ \text{cm})$ , which lie roughly in the radiative NF. PTE from the SB method is compared with results from a uniformly excited array of similar length, as well as a phase optimization (PO) method based on conjugate-phase (CP) focusing. The transmit $(\mathrm{T}_{\mathrm{x}})$ system is implemented as an array of center-fed dipoles, with a $\mathbf{0.48}\lambda$ non-excited dipole used as the receive $(\mathrm{R}_{\mathrm{x}})$ element. The results show an enhancement of PTE compared to the baseline uniform array, and in some cases the PO array. The simplicity of the SB method makes it an advantageous design choice.