Magnetostriction Oscillators

Author: J.B. Hoag

Fig. 14 I. Elementary form of a magnetostriction oscillator

Figure 14 I shows the circuit of a magnetostriction oscillator. Here the coupling between the plate circuit and the grid circuit is accomplished through a special metal rod made of magnetic material. When its magnetization at the plate end is changed, by virtue of a change in the plate current, a physical constriction in the dimensions of the rod occurs, causing it to move inside the grid coil by an exceedingly small amount. The moving magnetism induces voltages in the grid coil which apply themselves to the grid of the tube. These in turn cause a reverse change in the plate current.

The frequency of the vibrations depends upon the natural resonant frequency of the rod, and is inversely proportional to its length. It is possible with these oscillators to produce very intense oscillations at frequencies of the order of 10,000 to 100,000 cycles per second. Since the rod is also vibrating at these frequencies, it sets up vibrations in the air. These are called super-sonics — meaning that they are above the audible limit to which the human ear can respond.