Oscillators by Means of Magnetoresistance Effect

This paper describes the application of the magnetoresistance effect to oscillators using the high mobility semiconducting compound InSb as the active element. The first stable oscillator consisted of an InSb Corbino disk in a ferrite pot core reduced to a temperature of -40°C. The frequency was 210 cps and the open-circuited ac voltage was 540 mv, peak to peak. In order to construct a stable oscillator at room temperature, the shape of the semiconductor specimen was modified to a rectangular form composed of narrow strips of InSb joined together with metallic indium. This specimen has a comparatively higher internal resistance and a more pronounced magnetoresistance effect at low magnetic flux densities. A second oscillator using this specimen as an active element in an E-form ferrite core was tested and found to operate stably at a temperature of 25°C, in a frequency range from a few cps up to 300 cps. The maximum output power available was 2.5 mw, at 70 cps. There is no heating-up time required by the oscillator and the oscillation can start immediately under certain initial conditions. The elimination of the equipment to provide the low temperature, i.e., below 0° C for the oscillator has shown that the magnetoresistance effect can be made good use of in electronic devices without requiring a complicated circuit arrangement.