Noise reduction in magnetic modulators by using two frequency excitation

In the second harmonic type magnetic modulators, the origin of noise is thought mainly to be from Barkhausen jumps. In this paper we describe one method of noise reduction. By using two frequency excitation, one (f1) at about 3 kHz, and the other (f2) higher by several hundred kHz, we observed considerable decrease of noise, about 1/10 of that of ordinary magnetic modulators with one frequency excitation. The mechanism of noise reduction was explained by solving the equation of wall motion when passing through the potential barriers in magnetic cores. The results obtained from our experiments are as follows. 1) At optimum frequency, decrease of noise is maximum. 2) With application of second high frequency excitation f2, signal to noise ratio increases. 3) The larger the amplitude of second frequency excitation, the lower the noise. 4) The effect of second frequency excitation on long time drift is small. The excitation source of f2may be a conventional one, and the distortion of its waveform is not a serious condition.