Barkhausen noise[ edit ] When an external magnetizing field through a piece of ferromagnetic material is changed, for example by moving a magnet toward or away from an iron bar, the magnetization of the material changes in a series of discontinuous changes, causing "jumps" in the magnetic flux through the iron. These can be detected by winding a coil of wire around the bar, attached to an amplifier and loudspeaker. The sudden transitions in the magnetization of the material produce current pulses in the coil, which when amplified produce a sound in the loudspeaker. This makes a crackling sound, which has been compared to candy being unwrapped, Rice Krispies , or the sound of a log fire. This sound, first discovered by German physicist Heinrich Barkhausen , is called Barkhausen noise. Similar effects can be observed by applying only mechanical stresses e.

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There are two types of approaches to generate sine waves Using resonance phenomena This can be implemented with a separate circuit or using the non linearity of the device itself By appropriately shaping a triangular waveform. Multivibrator is a circuit which generate non sinusoidal wave forms such as square, triangular, pulse e.

Oscillators are circuits which generates sinusoidal wave forms. Multi vibrators are basic building blocks in function generators and nonlinear oscillators whereas oscillators are basic building blocks in inverters. Often feedback network consists of only resistive elements and is independent of frequency but amplifier gain is a function of frequency.

At that frequency overall gain of system is very large theoretically infinite. Noise at the input of amplifier consists of all frequencies with negligible amplitudes.

For all frequencies other than the oscillator frequencies the amplifier gain will not be enough to elevate them to significant amplitudes. But at that frequency where oscillator oscillates it provides very large gain and the amplitude of corresponding sine wave will be limited by the nonlinearity of the active device. The frequency of oscillation depends mostly on few circuit parameters such as passive elements such as resistance, inductance, and capacitance e.

The principle cause of drift of these circuit parameters is temperature. Therefore compensation measures should be taken for balancing temperature induced variations. Leave a Reply Your email address will not be published.


oscillators-Barkhausen criterion

It consists of the capacitor and an inductor. The capacitor is already charged and connected to an inductor with the switch between them. When the switch is open, nothing will happen. When the switch is closed the charge stored by the capacitor will start discharging, and the electrons will start flowing in the circuit.


Barkhausen effect


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