As discussed in Section 1.4, to reduce the losses caused by eddy currents in the core, the magnetic circuit usually consists of a stack of thin laminations. Two common types of construction are shown schematically in Fig. 2.1. In the core type (Fig. 2.1 a) the windings are wound around two legs of a rectangular magnetic core; in the shell type (Fig. 2. lb) the windings are wound around the center leg of a three-legged core.Silicon-steel laminations 0.014 in thick are generally used for transformers operating at frequencies below a few hundred hertz. Silicon steel has the desirable properties of low cost, low core loss, and high permeability at high flux densities (1.0 to 1.5 T).The cores of small transformers used in communication circuits at high frequencies and low energy levels are sometimes made of compressed powdered ferromagnetic alloys known as ferrites.