Patent ID: 7835679

Claim:
A heating device comprising: a magnetic field generating unit that generates a magnetic field; and a heating/rotating unit disposed so as to oppose the magnetic field generating unit, and having n (n≧2) metal layers which satisfy the following conditions (a), (b), (c) and include at least a heat generating layer, which is electromagnetically induced by the magnetic field to generate heat, and a supporting layer which supports the heat generating layer, wherein the magnetic field generating unit includes a first magnetic core and a second magnetic core such that the first magnetic core is arranged inside the heating/rotating unit and the second magnetic core is arranged outside the heating/rotating unit: (a) a total thickness t of the metal layers is greater than or equal to 30 μm and less than or equal to 200 μm; (b) the following formula (1) and formula (2) are satisfied: the total thickness t of metal layers<(δ1+δ2+δ3+ . . . +δ n ) formula (1) thickness tn of nth metal layer<δn formula (2) where δ is a surface skin depth of metal, surface skin depths δ 1 , δ 2 , δ 3 , . . . , δn of a first layer, a second layer, a third layer, . . . , an nth layer are δ 1 =503√(ρ 1 /f×μ 1 ), δ 2 =503√(ρ 2 /f×μ 2 ), δ 3 =503√(ρ 3 /f×μ 3 ), δn=503√(ρn/f×μn), ρn is a specific resistance of each metal layer, f is a frequency of a signal at the magnetic field generating unit, and μn is a relative permeability at room temperature of each metal layer; and (c) the following formula (3) is satisfied: 1 /R ≦(1 /R 1+1 /R 2+1 /R 3+ . . . +1 /Rn ) formula (3) where R is expressed as a ratio of specific resistance value to thickness as R=ρ/t, R 1 =ρ 1 /t 1 , R 2 =ρ 2 /t 2 , R 3 =ρ 3 /t 3 , and Rn=ρn/tn, wherein the metal layers include a protective layer which protects the heat generating layer, and wherein the supporting layer and the protective layer are formed of a metal which is different than the heat generating layer, and all of the metal layers are non-magnetic metals and used as non-magnetic materials.