Patent ID: 6942741

Claim:
A yoke for use in voice coil magnetic circuits formed from an iron alloy strip having a gage of 0.1 to 5 mm and a magnetic field strength variation within the strip of 0 to 10 Hz, the strip being made of an iron alloy consisting essentially of, in percents by weight, 0.0001 to 0.02% of C, 0.0001 to 5% of Si, 0.001 to 0.2% of Mn, 0.0001 to 0.05% of P, 0.0001 to 0.05% of S, 0.0001 to 5% of Al, 0.001 to 0.1% of O, 0.0001 to 0.03% of N, 0.1 to 10% of Co, 0.02 to 10% of Cr, 0.01 to 5% in total of at least one alloying element selected from the group consisting of Ti, Zr, Nb, Mo, V, Ni, W, Ta and B, and the balance of Fe and incidental impurities, and having a saturation magnetic flux density of 1.7 to 2.3 Tesla, a maximum relative permeability of 1,200 to 22,000 and a coercive force of 20 to 380 A/m, and the yoke being free of a corrosion resistant metal coating on its surface.