Signedon front panel: PIERCE / MAGNETOSTRICTION OSCILLATOR / GENERAL RADIO CO / CAMBRIDGE, MASS
FunctionThis is a device that can produce a very stable frequency output, which can serve as the basis for a very accurate clock or as a standard for the frequency of radio emitters. It is a very innovative, unique design that uses the phenomenon of magnetostriction--the expansion and contraction of metals when magnetized--as the source of the oscillations.
The problem of accurate timekeeping and the production of stable radio frequencies was central to the development of radio, and when this oscillator was made there was only one other way of producing stable high frequencies, quartz oscillators (also partly developed by G.W. Pierce), which were the subject of an intense patent dispute. This magnetostriction oscillator works on an altogether different principle.
It consists of a standard oscillating circuit (LC) composed of an inductor coil and a variable capacitor, connected to an amplifier whose output oscillates at the same frequency and feeds back into the oscillator. The key elements of this system are two inductor coils that would be connected to the circuits through the opening on top of the box, one before, and one after amplification. Through these coils passes a long metallic rod. This rod changes its length in the presence of a magnetic field, and has a specific natural frequency of oscillation that depends on its material and geometry. Crucially, it also creates a magnetic field when expanding and contracting that can feed back into the circuit. If one adjusts the radio oscillator's frequency to coincide with the rod's oscillation frequency, the output is very strong and stable.
In addition to radio uses, its output could be connected to a clock motor for very accurate timekeeping.
This device was built by General Radio on order from G. W. Pierce, and is another version of instrument RS1313.
Primary SourcesThe device is described, including a picture, in George W. Pierce, "Magnetostriction Oscillators," in Proceedings of the Institute of Radio Engineers Vol. 17, No.1 (January, 1929).
ProvenanceProbably from the Department of Physics, Cruft Laboratory, Harvard University.