In General, the materials steel and alloy steel. -Silicon, a round magnetic permeabilities, low values are often in a State of saturation of the magnetic field the magnetic material, but these are not causing the problem. When it is used for internal cores of transformers, because it is often used in conditions that have put so much into the magnetic field. But for the various communication tools that are used in high-sensitivity detection or signaling often requires the use of a magnetic nickel-iron alloys, such as the valuable high-intensity magnetic permeabilities in conditions of low magnetic field. Composite material, metal, nickel and iron are divided into two major categories, namely breast alloy with Ni 50% and 79% Ni alloy with Ni is 50% will have a value of magnetic induction medium and high saturation values permasbilities parts alloy with Ni is 79% will have a value of satilation induction, low alloy, these are often used in audio equipment and transformers, resistors, relays, etc