As a widely-acknowledged truth, the interval of human tissue, the breathing activity, and the body motion work together to change the relative position of the antenna. This knowledge, with detailed examination, is going to bring significant change to the transmission efficiency in the implementation of human wireless power transfer. This paper focused on the relationship of the transfer efficiency with lateral distance, vertical distance and angular (around the center and along the edge) misalignment. A new formula, which serves to connect the geometrical parameters both with the self-resonance frequency and with the Q-factor of the printed circuit board antenna, was given. Furthermore, the paper gave a significant analysis of the efficiency with lateral distance change, vertical distance change and two kinds of angular misalignments using finite element method. The experimental results showed that in the situation of vertical distance change and angular (along the edge) misalignment, the transmission efficiency drops rapidly with the displacement of antenna. However, in the situation of lateral distance change and angular (along the edge) misalignment, there were a high-efficiency distance—the lateral misalignment ≤40% of the length of the width in the lateral misalignment; and a high-efficiency angle—angular around the center misalignment ≤30º in the angular misalignment. Within the ranges, a high-efficiency space (HES) is formed in the implantable WPT system utility, and the transmission efficiency drops rapidly when the antenna is beyond the HES. This paper can provide a practical application to the antenna design and specific implementation in human implantable WPT system.
