Guide to ferrite beads, sleeves and cores
3.5 minutes | 17 Dec 2019
When designing electronic equipment, controlling the EMI (electromagnetic interference) in a device is necessary to protect components, and often external equipment, from damage caused by high frequency noise levels.
Electromagnetic interference (EMI) happens when one electromagnetic field interferes with another, causing distortion of both fields.
Some common causes of EMI are switching-mode power supplies, arc welders, motor bushes, and electrical contacts. All of these can be problematic, not only in the equipment itself, but in other electronic equipment in the surrounding area.
The effect of stray EMI range from subtle to disastrous. For example, power sources produce low-frequency EMI where data cabinets and electric cable enclosures are concerned. If cabling is not properly installed and protected, high voltage surges are possible, generating electrical noise. These surges can damage hardware, often corrupting data. This has the potential to disrupt business operation on many levels.
To counteract these risks, ferrite solutions are used for a range of applications – they’re even used as industrial generator parts. Ferrites are made of ceramic compounds with iron oxides integrated with nickel, zinc and manganese compounds.
Ferrite beads and cores are used in equipment design to suppress and dissipate high frequency noise levels caused by electromagnetic devices. Ferrite components are used to attenuate EMI and can be extremely effective.
Of course, using properly installed and grounded shielded cables helps suppress EMIs. However, ferrite cores may also need to be installed on cabling as well. The type of ferrite core filter used to suppress EMIs depends on several factors, including:
- Where the ferrite is used (for example, a ferrite bead inductance filter may be soldered directly to a PCB)
- When the EMI suppression is installed (for instance, a ferrite core cable EMI suppressor may be installed after the equipment is already in use)
As already mentioned, properly installed shielded power and control cables are one option to suppress damaging EMI issues. However, ferrite sleeves and ferrite beads are other useful solutions that reduce EMI output from devices. They prevent the cable from behaving as an antenna for other sources responsible for EMI and are very cost-effective solutions.
There are several ferrite material types and different ferrite core shapes and bead shapes available, each designed for a specific application. Most act as "soft magnets," meaning they only produce the magnetic properties needed to suppress stray EMIs when energised.
Ferrite core specifications are usually referred to as ferrite core relative permeability values. These values are determined by your specific application’s needs. Manufacturers will list these values, along with other necessary information in charts provided with the product specification. This information will include a ferrite core saturation table to help you calculate the ferrite material types and product that you need for your design application.
When working with ferrite bead inductor components, a ferrite bead inductance calculator is used to determine the values necessary to suppress EMIs present in the electronic components of your design.
In some applications, EMIs can be suppressed by using a ferrite core transformer design. The transformer itself is constructed by using a magnetic core in which coil (inductor) windings are made on a ferrite core component.
Before designing a transformer, check your requirement and exact application including input voltage, output voltage, current and frequency of operation.
Sleeves and cores are often used on power and control cabling on electronic and electrical devices. Sleeves are usually installed after all cabling has been attached.
For round cabling, a square plastic ferrite sleeve is often used. The core is contained in a hinged plastic casing that opens up to permit the insertion of the cable, then snaps together to secure the ferrite A5 core around the cable to suppress EMIs.
Another option is to use a ferrite sleeve suppression cored with a round plastic casing, sized to fit the cable used. Both the square and round cased ferrite cores attenuate any form of EMI emission and are often used either as a retrofit or for testing purposes when calculating ferrite core filter specifications and design requirements.
To begin choosing the correct type of ferrite core, bead, or sleeve you need for your design applications, use this handy chart.
|Your need or requirements||Type of suggested ferrite product|
|A single circuit protection on a PCB uses a single, two-lead ferrite bead|
|Protect multiple adjacent circuits on a PCP. Use a multiline suppressor bead|
|For installation on outer cables for retrofit or testing purposes, use a square plastic casing ferrite sleeve|
|For installation on round power cables, use a round plastic casing ferrite sleeve|
|For flat cables in electronic devices, use a flat cable ferrite core|
|For looping cable through and around a ferrite core with no casing necessary, use a ferrite sleeve, round, no casing|
|For automatic insertion in PCB production lines, use an axial type ferrite bead|
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Free CADs are available for most solutions, which you can download for free. You can also request free samples to ensure the solutions you’ve chosen are exactly what you need. If you’re not quite sure which product will work best for your application, our experts are always happy to advise you.