In a wireless charging system for electric vehicles, the automotive chassis may affect the magnetic fields and cause power loss. As a result, when designing a magnetic coupler the chassis should be taken into consideration. In this paper, the ferrite layer of a magnetic coupler is designed with finite element simulations in order to achieve higher efficiency. With the same volume of ferrite usage, plate-shape ferrite layer has the best performance while a net-shape ferrite layer has similar performance and allows larger ferrite thickness for the convenience of manufacture. A 3.7 kW wireless charging system with 20 cm air gap was established to verify the simulations.