• Coil Inductor With Ferrite Core

In electronics, a ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed. It is used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent eddy currents). Because of their comparatively low losses at high frequencies, they are extensively used in the cores of RF transformers and inductors in applications such as switched-mode power supplies, and ferrite loopstick antennas for AM radio receivers.

Ferrite Core Inductor: These types of inductor use ferrite core. Ferrite is a material with high magnetic permeability made from the mixture of iron oxide (ferric oxide, Fe 2 O 3) & a small percentage of other metals such as nickel, zinc, barium, etc. Inductor ferrite core losses. One major parameter of interest to the electronic engineer using ferrites in inductors is the core losses they exhibit and their. Targeted to specific applications, each software package offers a core. Applications: There are some important applications of ferrite core inductor which are given below. Ferrite core inductors can be used as the ferrite rod antenna for medium wave (MW) receivers. It can be used at high and medium frequencies. The ferrite core inductors is used for power transformers work in the low frequency range (1.

Ferrites[edit]

Ferrites are ceramic compounds of the transition metals with oxygen, which are ferrimagnetic but nonconductive. Ferrites that are used in transformer or electromagneticcores contain iron oxides combined with nickel, zinc, and/or manganese compounds. They have a low coercivity and are called 'soft ferrites' to distinguish them from 'hard ferrites', which have a high coercivity and are used to make ferrite magnets. The low coercivity means the material's magnetization can easily reverse direction without dissipating much energy (hysteresis losses), while the material's high resistivity prevents eddy currents in the core, another source of energy loss. The most common soft ferrites are:

• Manganese-zinc ferrite (MnZn, with the formula Mn_aZn_(1-a)Fe₂O₄). MnZn have higher permeability and saturation levels than NiZn.
• Nickel-zinc ferrite (NiZn, with the formula Ni_aZn_(1-a)Fe₂O₄). NiZn ferrites exhibit higher resistivity than MnZn, and are therefore more suitable for frequencies above 1 MHz.

For applications below 5 MHz, MnZn ferrites are used; above that, NiZn is the usual choice. The exception is with common mode inductors, where the threshold of choice is at 70 MHz.^[1]

As any given blend has a trade off of maximum usable frequency, versus a higher mu value, within each of these sub-groups manufacturers produce a wide range materials for different applications blended to give either a high initial (low frequency) inductance, or lower inductance and higher maximum frequency, or for interference suppression ferrites, a very wide frequency range, but often with a very high loss factor (low Q).

It is important to select the right material for the application, as the correct ferrite for a 100 kHz switching supply (high inductance, low loss, low frequency) is quite different from that for an RF transformer or ferrite rod antenna, (high frequency low loss, but lower inductance), and different again from a suppression ferrite (high loss, broadband)

Applications[edit]

Coil Inductor With Ferrite Core

There are two broad applications for ferrite cores which differ in size and frequency of operation: signal transformers, which are of small size and higher frequencies, and power transformers, which are of large size and lower frequencies. Cores can also be classified by shape, such as toroidal cores, shell cores or cylindrical cores.

The ferrite cores used for power transformers work in the low frequency range (1 to 200 kHz usually) and are fairly large in size, can be toroidal, shell, or shaped like the letters ‘C’, ‘D’, or ‘E’. They are useful in all kinds of electronic switching devices – especially power supplies from 1 Watt to 1000 Watts maximum, since more powerful applications are usually out of range of ferritic single core and require grain oriented lamination cores.

The ferrite cores used for signals have a range of applications from 1 kHz to many MHz, perhaps as much as 300 MHz, and have found their main application in electronics, such as in AM radios and RFID tags.

Ferrite rod aerial[edit]

Ferrite rod aerials (or antennas) are a type of small magnetic loop (SML) antenna^[2][3] very common in AM radiobroadcast bandtransistor radios, although they began to be used in vacuum tube ('valve') radios in the 1950s. They are also useful in very low frequency (VLF) receivers,^[4] and can sometimes give good results over most of the shortwave frequencies (assuming a suitable ferrite is used). They consist of a coil of wire wound around a ferrite rod core (usually several inches longer than the coil, but sometimes over 3 feet long^[5]). This core effectively ‘concentrates’ the magnetic field of the radio waves^[6] to give a stronger signal than could be obtained by an air core loop antenna of comparable size, although still not as strong as the signal that could be obtained with a good outdoor wire aerial.

Other names include loopstick antenna, ferrod, and ferrite-rod antenna. 'Ferroceptor'^[7] is an older alternative name for a ferrite rod aerial, particularly used by Philips where the ferrite core would be called a 'Ferroxcube' rod (a brand name acquired by Yageo from Philips in the year 2000). The short terms ferrite rod or ‘loop-stick’ sometimes refers to the coil-plus-ferrite combination that takes the place of both an external antenna and the radio’s first tuned circuit, or just the ferrite core itself (the cylindrical rod or flat ferrite slab).

See also[edit]

References[edit]

1. ^'Learn More Ferrites - Magnetics®'.
2. ^'page5'.
3. ^'Very Weak Signal Reception with Small Magnetic Loop Antenna'.
4. ^'The Creative Science Centre - by Dr Jonathan P. Hare'.
5. ^05-25-2012, DB8MW. 'A Joy Stick Antenna Experiment by DB8MW'.
6. ^'Ferrite Rod Antenna :: Radio-Electronics.Com'.
7. ^Service manual from Philips Radioplayer: Model BZ456A

A ferrite bead or ferrite choke is a passive electric component that suppresses high-frequency noise in electronic circuits. It is a specific type of electronic choke. Ferrite beads employ high-frequency current dissipation in a ferrite ceramic to build high-frequency noise suppression devices. Ferrite beads may also be called blocks, cores, rings, EMI filters, or chokes.^[1][2]

Overview[edit]

Ferrite beads prevent electromagnetic interference (EMI) in two directions: from a device or to a device.^[1] A conductive cable acts as an antenna – if the device produces radio-frequency energy, this can be transmitted through the cable, which acts as an unintentional radiator. In this case the bead is required for regulatory compliance, to reduce EMI. Conversely, if there are other sources of EMI, such as household appliances, the bead prevents the cable from acting as an antenna and receiving interference from these other devices. This is particularly common on data cables and on medical equipment.^[1]

Large ferrite beads are commonly seen on external cabling. Various smaller ferrite beads are used internally in circuits—on conductors or around the pins of small circuit-board components, such as transistors, connectors and integrated circuits.

Ferrite beads are used as a passivelow-pass filter, by converting RF energy to heat, by design.(Contrast this with inductors, which by design do not convert RF energy to heat, but rather offer a high impedance to RF.)

The geometry and electromagnetic properties of coiled wire over the ferrite bead result in an impedance for high-frequency signals, attenuating high-frequency EMI/RFI electronic noise. The energy is either reflected back up the cable, or dissipated as low-level heat. Only in extreme cases is the heat noticeable.

A pure inductor does not dissipate energy but it produces reactance that impedes the flow of higher frequency signals. This reactance is commonly referred to simply as impedance, although impedance can be any combination of resistance and reactance.

A ferrite core or bead can be added to an inductor to improve, in two ways, its ability to block unwanted high frequency noise. First, the ferrite concentrates the magnetic field, increasing inductance and therefore reactance, which impedes or ‘filters out’ the noise. Second, if the ferrite is so designed, it can produce an additional loss in the form of resistance in the ferrite itself. The ferrite creates an inductor with a very low Q factor.^[3] This loss heats the ferrite, normally by a negligible amount. While the signal level is large enough to cause interference or undesirable effects in sensitive circuits, the energy blocked is typically quite small. Depending on the application, the resistive loss characteristic of the ferrite may or may not be desired.

A design that uses a ferrite bead to improve noise filtering must take into account specific circuit characteristics and the frequency range to block. Different ferrite materials have different properties with respect to frequency, and manufacturer's literature helps select the most effective material for the frequency range.^[3][4]

Ferrite beads are one of the simplest and least expensive types of interference filters to install on preexisting electronic cabling. For a simple ferrite ring, the wire is simply wrapped around the core through the center, typically five or seven times. Clamp-on cores are also available, which attach without wrapping the wire: this type of ferrite core is usually designed so that the wire passes only once through it. If the fit is not snug enough, the core can be secured with cable ties or, if the center is large enough, the cabling can loop through one or more times. (Note, however, that although each loop increases the impedance to high frequencies, it also shifts the frequency of the highest impedance to a higher frequency.) Small ferrite beads can be slipped over component leads to suppress parasitic oscillation.^[3]

Surface-mount ferrite beads are available. These are soldered into a gap in the printed circuit board trace, just like any other surface-mount inductor. Inside the bead component, a coil of wire runs between layers of ferrite to form a multi-turn inductor around the high-permeability core.^[5]

See also[edit]

References[edit]

1. ^ ^abcVanhoenacker, Mark (November 1, 2012). 'What Is That Little Cylinder on My Computer Wire?'. Brow Beat blog. Slate. Retrieved 2012-11-03.
2. ^'What are the bumps at the end of computer cables?'. HowStuffWorks. InfoSpace LLC. April 1, 2000. Retrieved 21 April 2015.
3. ^ ^abcCarr, Joseph J. (2002). RF Components and Circuits. Newnes. pp. 264–266. ISBN978-0-7506-4844-8.
4. ^Crowell, Benjamin. 'Simple Nature'. Retrieved 21 April 2015.
5. ^Ferrite Bead Inductors - Radio-Electronics.com

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