Combination Oscillations

oscillations that arise when a nonlinear system is acted on by two or more harmonic oscillations with different frequency components. The frequencies of combination oscillations are expressed as the sum or difference of the frequencies of each pair of oscillations acting on the system or of their components.

In the simplest case, when two oscillations with frequencies v₁ and v₂ act on the system, the spectrum of forced oscillations contains components with frequencies v = n₁v₁ ± n₂v₂, where n₁ and n₂ are integers. The occurrence of combination oscillation underlies most frequency conversion methods—modulation, detection, and the production of an intermediate frequency. Combination oscillations may also arise in a linear system if one of its parameters changes periodically. In this case, combination oscillations with a frequency corresponding to a linear combination of two frequencies—the acting frequency and the frequency of the change in parameter— may occur even under the influence of one harmonic oscillation. This is precisely the mechanism of combination light scattering and of the parametric excitation and amplification of electric oscillations.