selfexcited

Selfexcited (often written as self-excited or self-excitation) describes systems in which sustained oscillations are generated and maintained by internal feedback mechanisms rather than continuous external forcing. The phenomenon appears in electronic circuits, mechanical structures, aeroelastic systems, and fluid-structure interactions. In many cases, an initial disturbance or noise triggers the oscillation, which is then sustained by the system’s own energy transfer.

In electronic engineering, self-excited oscillators rely on positive feedback to regenerate a signal. A loop gain near or above unity with the correct phase condition causes the circuit to begin oscillating; nonlinearities then limit the amplitude, producing a stable limit cycle. Classic self-excited oscillator topologies include RC phase-shift, Colpitts, Hartley, and Clapp configurations, realized with transistors, tubes, or operational amplifiers. They differ from forced oscillators that require an external periodic drive.

In mechanics and aeroelasticity, self-excited vibrations occur when energy from a steady source, such as a fluid flow or rotating machinery, is transferred to a vibrating mode via feedback, without a periodic external force. Examples include flutter and buffeting in aircraft structures, galloping of aerodynamically unstable bodies, or stick-slip friction-induced vibrations. These phenomena can be disruptive, causing fatigue or noise, but are also exploited in some musical mechanisms and sensing concepts.

Analytically, self-excited systems are treated with nonlinear dynamics and stability analysis. The onset of oscillation is explored with criteria from linear theory, while nonlinear models reveal limit cycles and amplitude stabilization. Design concerns aim to suppress unwanted self-excited oscillations or, when useful, to harness them in oscillators or sensing devices.