Active capacitive stylus and wireless charging system

An active capacitive stylus, comprising:

• a pen body, having an axial direction;
• a receiver, surrounding the pen body and used to receive a radio frequency signal, the receiver comprising an annular body, wherein the annular body has two opposite first sides and two opposite second sides, a length of each first side is greater than that of each second side, the two first sides are parallel to the axial direction, and each second side has a first radius of curvature and a second radius of curvature, the first radius of curvature being different from the second radius of curvature, wherein the first radius of curvature is greater than the second radius of curvature,
• wherein a first arc formed by the first radius of curvature is located between two second arcs respectively formed by the second radius of curvature, and the first arc formed by the first radius of curvature and the two second arcs formed by the second radius of curvature are tangential to each other;
• an insulator, located between the receiver and the pen body;
• and
• a shell, sleeved on the pen body and wrapping around the receiver,
• wherein the insulator entirely surrounds the pen body,
• wherein a length of the insulator in the axial direction is greater than or equal to that of each first side in the axial direction, and the two first sides are attached to the insulator and spaced apart to partially expose the insulator.