1. 2.3. Nonlinear Electrical Phenomena
Nonlinear Inductance
An Electronic Oscillator (the Van der Pol Equation)

2. Nonlinear Inductance
Iron core inductor
Kirchhoff's law

4. 2.3.2. An Electronic Oscillator (the Van der Pol Equation)
Limit cycle: A periodic motion to which the system approaches irregardless of the initial conditions.
All electronic oscillator circuits display limit cycles.
van der Pol equation :

5. X > 1: damping is purely dissipative.
X < 1: "damping" term amplifies.
Oscillator can be self-excited.
X = const ( 1) : limit cycle.
Tunnel Diode Oscillator:
Example 2-3.nb nb

6. Self-sustained oscillations occur whenever a periodic motion is coupled to an energy source.
Tacoma Narrows Bridge (1940)