Flatwire in an inductor design is much more efficient than using roundwire. The reason for this will be explained in the next six slides. In general, it can be said that the whole amount of losses of an inductor are created by copper losses and core losses. The copper losses depend on resistance, both DC and AC. While the DC resistance is a stable value, the AC resistance is frequency dependent and based on the Skin and Proximity Effect. The AC-resistance will increase with an increase of the frequency. Core losses will not be discussed here as the wire type has no influence on the core losses.