Coil Noise
Encyclopedia
Coil Noise is a phenomenon in electronics which produces both undesirable audible sound, and electronic noise
.
or transformers
, have a certain resonant frequency
when coupled with the rest of the electric circuit
, as well as a resonance at which it will tend to physically vibrate.
As the wire that makes up the coil passes a variable current, a small amount of electrical oscillation
occurs, creating a small magnetic field
. Normally this magnetic field simply works to establish the inductance
of the coil. However, this magnetic field can also cause the coil itself to physically vibrate. As the coil vibrates physically, it moves through a variable magnetic field, and feeds its resonance back into the system. This can produce signal interference in the circuit, and can produce an audible hum as the coil vibrates.
Coil noise can happen, for example, when the coil is poorly secured to the circuit board, is poorly damped
, or if the resonant frequency of the coil is close to the resonant frequency of the electric circuit . The effect becomes more pronounced as the signal passing through the coil increases in strength, and as it nears the resonant frequency of the coil, or as it nears the resonant frequency of the circuit. Coil noise is also noticed most often when it is in the humanly audible frequency
.
Coil noise is also effected by the irregularities of the magnetic material within the coil. The flux density
of the inductor is effected by these irregularities, causing small currents in the coil, contaminating the original signal. This particular subset of is sometimes referred to as Magnetic Fluctuation Noise or the Barkhausen Effect
. Coil noise can also occur in conjunction with the noise produced by Magnetostriction
.
are often effected by coil noise, often aggravating their users. Older Cathode ray tube
televisions are also effected. Florescent lights
are often blamed for such noise, although it is their electrical ballast
or driving circuity that actually produces the sound.
The amount of Coil Noise in a device will often seem to increase as the devices age. This can be due to many factors, but is often due to the degradation of the damping materials in the circuit. As an example, a layer of glue is often added atop coils in televisions. Over the years, this glue degrades due to age and due to the years of vibration it has been subjected to. As a result, the coil is able to move more as it vibrates, and the sound level increases.
Coil noise can be reduced by damping and can be minimized by design, but in some cases, unacceptable levels will remain. To combat this, the coils are sometimes isolated from the rest of the device. They can be placed in such a way as to absorb and contain the noise and vibration that occurs.
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
.
Description
Coil Noise is, as its name suggests, caused by Electromagnetic coils. These coils, which may act as inductorsInductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
or transformers
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
, have a certain resonant frequency
Electrical resonance
Electrical resonance occurs in an electric circuit at a particular resonance frequency where the imaginary parts of circuit element impedances or admittances cancel each other...
when coupled with the rest of the electric circuit
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
, as well as a resonance at which it will tend to physically vibrate.
As the wire that makes up the coil passes a variable current, a small amount of electrical oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
occurs, creating a small magnetic field
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
. Normally this magnetic field simply works to establish the inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
of the coil. However, this magnetic field can also cause the coil itself to physically vibrate. As the coil vibrates physically, it moves through a variable magnetic field, and feeds its resonance back into the system. This can produce signal interference in the circuit, and can produce an audible hum as the coil vibrates.
Coil noise can happen, for example, when the coil is poorly secured to the circuit board, is poorly damped
Damping
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
, or if the resonant frequency of the coil is close to the resonant frequency of the electric circuit . The effect becomes more pronounced as the signal passing through the coil increases in strength, and as it nears the resonant frequency of the coil, or as it nears the resonant frequency of the circuit. Coil noise is also noticed most often when it is in the humanly audible frequency
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...
.
Coil noise is also effected by the irregularities of the magnetic material within the coil. The flux density
Magnetic flux
Magnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
of the inductor is effected by these irregularities, causing small currents in the coil, contaminating the original signal. This particular subset of is sometimes referred to as Magnetic Fluctuation Noise or the Barkhausen Effect
Barkhausen effect
The Barkhausen effect is a name given to the noise in the magnetic output of a ferromagnet when the magnetizing force applied to it is changed...
. Coil noise can also occur in conjunction with the noise produced by Magnetostriction
Magnetostriction
Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of material's magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ...
.
Devices Effected By Coil Noise
All but the simplest devices experience some level of Coil Noise, although it is usually far too slight to be noticed or deemed problematic. Ordinarily, the noise is simply a minor annoyance. In some devices however, such as audio video equipment, Coil Noise can present a major problem if it is not minimized in design. Video CardsVideo card
A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...
are often effected by coil noise, often aggravating their users. Older Cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
televisions are also effected. Florescent lights
Fluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...
are often blamed for such noise, although it is their electrical ballast
Electrical ballast
An electrical ballast is a device intended to limit the amount of current in an electric circuit. A familiar and widely used example is the inductive ballast used in fluorescent lamps, to limit the current through the tube, which would otherwise rise to destructive levels due to the tube's...
or driving circuity that actually produces the sound.
The amount of Coil Noise in a device will often seem to increase as the devices age. This can be due to many factors, but is often due to the degradation of the damping materials in the circuit. As an example, a layer of glue is often added atop coils in televisions. Over the years, this glue degrades due to age and due to the years of vibration it has been subjected to. As a result, the coil is able to move more as it vibrates, and the sound level increases.
Reducing Coil Noise
Some steps to reducing coil noise include:- As previously mentioned, damping is a critical step towards reducing coil noise.
- Low Noise Coils are specifically produced to avoid coil noise.
- Coil noise can be reduced in some instances by changing the shape of the coil to a figure eight rather than a traditional coil shape.
Coil noise can be reduced by damping and can be minimized by design, but in some cases, unacceptable levels will remain. To combat this, the coils are sometimes isolated from the rest of the device. They can be placed in such a way as to absorb and contain the noise and vibration that occurs.