Oscillation

Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes is used to be synonymous with oscillation. Oscillations occur not only in physical systems but also in biological systems and in human society.
The simplest mechanical oscillating system is a mass, subject to the force of gravity, attached to a linear spring. The system is in an equilibrium state when the weight of the mass is balanced by the tension of the spring. If the system is displaced from the equilibrium, there is a net restoring force on the mass, tending to bring it back to equilibrium. However, in moving the mass back to the equilibrium position, it has acquired momentum which keeps it moving beyond that position, establishing a new restoring force, now in the opposite sense and this time due to gravity. The time taken for an oscillation to occur is often reffered to as being the oscillatory period.
The specific dynamics of this spring-mass system are described mathematically by the simple harmonic oscillator and the regular periodic motion is known as simple harmonic motion. In the spring-mass system, oscillations occur because, when at the static equilibrium displacement, the mass has kinetic energy which is converted into energy stored in the spring at the extremes of its path.

Voltage-controlled crystal

A voltage-controlled crystal oscillator (VCXO) is used when the frequency of operation needs to be adjusted by a relatively small amount, or when exact frequency or phase of the oscillator is critical, or, by applying a varying voltage to the control input of the oscillator, to disperse radio-frequency interference over a range of frequencies to make it less objectionable. Typically the frequency of a voltage-controlled crystal oscillator can only be varied by a few tens of parts per million (ppm), because the high Q factor of the crystals allows only a small "pulling" range of frequencies to be produced.
A temperature-compensated VCXO (TCVCXO) is normally used so that temperature does not alter the piezoelectric effect, thereby causing frequency drift due to heat buildup inside of a transmitter.

crystal oscillator

A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters.
Using an amplifier and feedback, it is an especially accurate form of an electronic oscillator. The crystal used therein is sometimes called a "timing crystal". On schematic diagrams a crystal is sometimes labeled with the abbreviation XTAL.

Backward wave oscillator

A backward wave oscillator (BWO), also called carcinotron or backward wave tube, is a device that is used to generate microwaves and terahertz radiation. It consists of a vacuum tube that provides 1 mW to 50 mW of power. Some types can produce frequencies in a range of 200 GHz to 1.1 THz. It sustains the oscillations by reflecting the traveling wave backwards against the beam. It is derived from the traveling wave tube. It has two main subtypes, the M-type (M-BWO) and O-type (O-BWO). Carcinotrons are used as powerful and stable microwave sources. Due to the good quality wavefront they produce, they find use as illuminators in terahertz imaging.
It is an amplifier with a wide tuning range. The electron gun generates an electron beam that passes through a slow-wave structure. The generated electromagnetic wave moves in the direction opposite to the direction of the electrons. The output signal is coupled out near the electron gun

Self inducing oscillations

Some systems can be excited by energy transfer from the environment. This typically occurs where systems are embedded in some fluid flow. For example, the phenomenon of flutter in aerodynamics occurs when an arbitrarily small displacement of an aircraft wing (from its equilibrium) results in an increase in the angle of attack of the wing on the air flow and a consequential increase in lift coefficient leading to a greater displacement before, at sufficiently large displacements, the stiffness of the wing dominates to provide the restoring force that enables an oscillation.

Coupled oscillations

The harmonic oscillator, and the more complicated systems for which it stands as a simple model, has a single degree of freedom. More complicated systems have more degrees of freedom, for example two masses and two springs. In such cases, energy is converted between the respective inertias of each degree of freedom and the several restoring forces in the system. This leads to a coupling of the oscillations of the individual degrees of freedom. For example, two pendulum clocks mounted on a common wall will tend to synchronise. The apparent motions of the individual oscillations typically appears very complicated but a more economic, computationally simpler and conceptually deeper description is given by resolving the motion into normal modes

Electronic oscillator

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave.
A low-frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform between 0.1 Hz and 10 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.