Technical Tools & References

Rod Permeability Calculator
Evaluating open magnetic structures such as rods and bobbins is less clear cut than closed magnetic structures. Since the majority of the field is not contained within the core, the initial permeability of the material has a greatly reduced influence on the inductance of the wound assembly therefor, the permeability of the material is more difficult to evaluate. The purpose of this tool is to aid in being able to identify and cross reference the material a rod type core is made out of. This tool will calculate effective permeability (µrod) of the rod-type core in question when the following values are entered: rod diameter, rod length, number of turns wrapped around the diameter of the rod, length of the winding (measured in the same direction as the length of the rod), and the measured series inductance of the wound rod. The tool will calculate a rod permeability value which can be used comparatively against the accompanying chart to find a best fit material.
Toroid Permeability Calculator
The main characteristic differentiating Fair-Rite’s material grades is initial permeability. This is the inductive portion of the complex permeability of a material measured specifically at 10kHz with a flux density of less than 10 gauss (sinusoidal excitation). Calculating the initial permeability on the sample in question is the most reliable way to get an approximation of its material grade. To evaluate the permeability, you will need insulated wire and some way to measure inductance with a 10kHz sinusoidal signal (in a pinch 1kHz-100kHz will yield a similar number for most materials). This tool will calculate the permeability of a toroidal type core when the following values are entered by the user: three critical mechanical dimensions (outer diameter, inner diameter, part height), the number of passes through the aperture of the core, and the measured series inductance of the wound core. The resulting permeability number can then be matched up to a ferrite material by comparing the mi value published. Keep in mind the having an exact match to a published mi Value is unlikely due to material variation and measurement equipment differences.
Bobbin Calculator
Utilization of bobbin ( spool or drum) cores is a simple and cost effective way of designing a power inductor. This calculator makes use of standard bobbins in Fair-Rite's # 77 material - so frequency is limited to about 10 MHz, depending on the winding. Maximum possible NI is 750 Ampere-Turns, maximum current is 15 Amps ( using AWG# 10) and minimum wire gauge is AWG# 30. The user enters target inductance and maximum operating current : the first thing the calculator does is selects a minimum wire gauge based on 700 cir-mils/Amp ( 2.8 Current Density. Then the calculator estimates number of turns required and selects the smallest size bobbin core capable. Uncoated bobbins, magnet wire and 90% copper fill ratio are assumed.
April 01, 2022
On the Air from ARRL
How to Wind a Toroid

Fair-Rite presents this information from the March/April 2022 issue of On the Air with express written permission from ARRL. No further distribution is permitted.

April 20, 2022
Dr. Min Zhang
Structure Resonances: Ways To Identify, Locate, and Fix EMI Issues

This article reviews work on structure resonances and their EMI impact. Methods to identify and locate structure resonances were presented, challenges were discussed, and fixes suggested using practical examples.

January 01, 1970
Product Overview

Take a look at a complete listing of Fair-Rite’s different product categories in both Suppression and Power/Inductive. Read along to find out what product is perfect for ‘Your Signal Solution’

January 01, 1970
Fair-Rite Partners with EMC Compliance Labs
Our flagship kit for Compliance labs. Contains our most popular Snap-Its in our 75 material, 31 material, 43/44 material,  and  61 material – along with EMC reference guides.
April 13, 2021
Dave LeVasseur, NØDL, and Gary “Joe” Mayfield, KKØSD
Easy to Build Balun Project Using Fair-Rite Products Cores

Construct an easy-to-build choke balun for use on the amateur radio bands that covers 160 through 10 meters and uses a Fair-Rite Products FR31 core.

November 03, 2020
The One Stop-Shop For Ferrite Product Manufacturing

Founded in 1952, Fair-Rite Products Corp. is one of the most prominent ferrite manufacturers in the United States. The organization handles the entire process of ferrite core manufacturing, from developing and procuring original raw materials to quick-turn prototyping to large-scale global manufacturing.

April 01, 2016
Tony Brock-Fisher, K1KP
Can Home Solar Power and HAM Radio Exist?

Rooftop photovoltaic panels have become popular during the past few years but present challenging EMI issues.  The attached article describes a methodology to mitigate the interference they create using Fair-Rite Products FR31 suppression cores.

July 10, 2020
Determining the Material of a Ferrite Core

Ferrites are offered in a wide variety of material grades and geometries to suit different applications. Often, a particular geometry may be offered in multiple material grades. In order to find a suitable replacement; Sometimes it is necessary to evaluate a ferrite core to determine what type of material it was made out of. There are many distinguishing characteristics separating different ferrite material grades but, the main material characteristic is initial permeability. This paper explains how to evaluate a core for initial permeability along with a simplistic surface resistance test. These two characteristics can give a good estimation for the material grade and type of a ferrite.

February 11, 2020
Study of Test Wire Location and Compensation for Impedance Measurements

Test wire is used for measuring the impedance of ferrite suppression cores can have significant impact on measurements. In this paper we will discuss how the test wire location within the ferrite core aperture will affect results. Click below to see the different results that are shown with and without vector subtraction of the complex impedance of test wire.

January 22, 2020
Effect of Lead Length on Ferrite Impedance

At frequencies above 200MHZ, fixturing and lead length has a significant impact on measured impedance making comparisons difficult between manufacturers. Fair-Rite Products impedance test methods employ the shortest possible lead length and appropriate fixtures in order to provide consistent impedance data that is accurate and repeatable.

For Fair-Rite’s video on this check out our Youtube video HERE!

March 14, 2019
High Frequency Mini Power Kit-80 Material Pamphlet

Featuring our NEWEST material “80”” is the focus in this High Frequency Power Material kit containing various sizes of toroids, EQ and I cores to DELIVER your DESIGN. Fair-Rite’s new 80-material! Our latest addition, this Manganese-Zinc ferrite has been tuned to operate in SiC and GaN switching power supplies with a stable temperature response for designs up to 5 MHz.

March 14, 2019
High Frequency Mini Power Kit-79 Material Pamphlet

Our newest High Frequency Power Material kit contains various sizes of toroids, EQ and I cores for designers to test how 79 Material will perform in their design. Fair-Rite’s 79-material product line continues to expand and include new geometries for power supply designs. With operating frequencies up to 1 MHz, this material is optimized for minimal losses at elevated temperatures.

August 28, 2018
Bill Kazlauskas
Determining the Effects of DC Bias on Round Cable EMI Suppression Cores

This document provides the appropriate information to allow a user to determine the effects on impedance of a Round Cable EMI Suppression core in the presence of differential mode currents.

March 08, 2018
Aaron L.F. Stein; Phyo Aung Kyaw; Jesse Feldman-Stein; Charles R. Sullivan
Thin Self-Resonant Structures with a High-Q for Wireless Power Transfer

The high-Q achievable by self-resonant structures increases the range and efficiency of wireless power transfer (WPT). However, to date implementations of this structure have been thick, which limits their practical implementations. In the attached paper, they explore the design of thin self-resonant structures. Looking into a computationally efficient 2-D optimization algorithm is proposed to design thin resonant structures and illustrate the trade-offs in the design, and a new magnetic core shape is proposed which shapes the magnetic field lines to be parallel to the conductive layers and reduces current crowding.

February 23, 2018
High Frequency Power Materials

In response to demands for High-Frequency Power Materials is growing rapidly, Fair-Rite Products has developed a new line of High Frequency Power Magnetics as we continue to be Your Signal Solution®. We now offer materials that can operate up to 25 MHz with minimal power loss and temperature dependence. Click below to find out how our new Power Materials can be Your Signal Solution®.

February 14, 2018
James Montgomery
Identifying Unknown Fair-Rite Round Cable Snap-Its

If you have a Fair-Rite Snap-It in hand, but are not sure of the material or part number, you may still be able to identify it! Since all ferrite materials are the same color and multiple materials use the same case (which only shows the part number if it was in a kit), determining the part number can be difficult. This article explains the process to determine the part number of a Fair-Rite Snap-It.

February 06, 2018
Fair-Rite Products Corp.
Fair-Rite Machining Capabilities

Fair-Rite has state-of-the-art equipment to provide you with quickturn prototypes for proof of concept before committing to production tooling. This allows our customers to quickly evaluate their design, experiment with different variations and determine the final product while maintaining their development schedule and budget.

April 06, 2017
HF Mini Power Kit (for 67 material)

Fair-Rite’s HF Mini Power Kit (for 67 Material) contains various sizes of toroids, EQ and I cores for designers to test how 67 Material will perform in their design. Optimized for power applications between 5 MHz and 25 MHz, 67 Material is suitable for high-frequency switching power supplies where low core-loss and a stable temperature response are imperative for a successful product. This pamphlet, which comes with the kit, contains vital information regarding 67 Material and the included parts. To request a kit, please contact your local sales representative or request a sample today!

April 05, 2017
Aaron L.F. Stein; Phyo Aung Kyaw; Charles R. Sullivan from Thayer School of Engineering at Dartmouth College
High-Q Self-Resonant Structure for Wireless Power Transfer

The range and efficiency of wireless power transfer systems are limited by the quality factor of the transmit and receive coils used. Multi-layer self-resonant structures have been proposed as a low-cost method for creating high-Q coils for highfrequency wireless power transfer. In these structures thin foil layers are separated by a dielectric material in order to form a capacitance that resonates with the inductance of the structure, while also forcing equal current sharing between conductors. In order to reduce winding loss, these structures are made with foil layers much thinner than a skin depth, which makes the layers of the structure extremely difficult to handle. In this paper, we present a modified self-resonant structure in which the layered conductors are made from standard PCB substrates with no vias. The PCB substrates provide an inexpensive way to handle thin conductive layers, and the modified self-resonant structure ensures that the poor dielectric properties of the PCB substrates do not impact the quality factor of the structure. The modified self-resonant structure makes it feasible to achieve advantages similar to litz wire, but at multi-MHz frequencies where effective litz wire is not commercially available. Experimental results show that the structure has a quality factor of 1177 at 7.08 MHz, despite only being 6.6 cm in diameter. The quality factor normalized by the diameter is more than 6.5x larger than other coils presented in the literature.

July 30, 2015
By Rachael Parker, Vice President of Fair-Rite Products Corp.
75-material for Low-Frequency EMI Suppression Demystified

Ferrites are ceramic components that can be used to suppress electromagnetic interference (EMI) in certain applications. This paper will discuss the basic properties of solid round ferrite cores, the impact an air-gap can have on the performance of these cores, and special considerations. In particular, this paper focuses on the use of 75-material in low-frequency suppression applications since its permeability is relatively high compared to other soft ferrites used for this purpose, making the effect of an air-gap much greater.

February 17, 2016
Fair-Rite Products Corp.
Automotive Flyer

Electronics are profoundly changing the automotive industry as the Internet of Things (IoT) and mobile connectivity become more prominent in our vehicles. Electronic content in cars has steadily increased, and this trend is only expected to accelerate. However, with the adoption of technology comes an increase in EMC, power and signal integrity issues. Coupled with growing concerns over robustness and safety, automakers are forced to strike a balance between cost, performance, and quality.

March 07, 2014
By Henry Ott Consultants
Ferrite Cores For Low-Frequency EMI Cable Suppression

Ferrite cores (chokes) provide an inexpensive, and effective, way of coupling high-frequency resistance into a cable in order to reduce the  common-mode current, and hence the radiation (or pickup) from the cable. They are commonly used  on mouse, keyboard, video, and other peripheral cables connected to personal computers, as well as on power supply cables when a device is powered from an external transformer (wall-wart) or power supply. The ferrite core acts as a one-turn common-mode choke, and can be effective in reducing the conducted and/or radiated emission from the cable, as well as suppressing high-frequency pick-up in the cable. Basically ferrites can be thought of as high-frequency resistors, with little or no impedance at low-frequencies or dc. Ferrite cores are most effective in providing attenuation of  unwanted noise signals above 10 MHz. The figure below shows a ferrite choke on a USB cable.


For low-frequency cable emission problems, typically below 10 MHz, ferrite chokes have not been very useful, since their impedance is too low, at these frequencies, to be effective. I have always wished  for a similar, simple low-frequency solution to cable emission/susceptibility problems. My wish finally has been granted.

Recently Fair-Rite Products Corp. introduced a new low-frequency, Type 75, ferrite material optimized for EMI suppression in the 200 kHz to 30 MHz frequency range. This material has an impedance peak in the 1 to 2 MHz range. Information on the new Type 75 ferrite cores is included in Fair-Rite’s  17th edition catalog.

For example,  part number 2675540002 (9/16″ OD,  1/4″ ID , and 1-1/8″ long core) has a peak impedance of  160 Ω at about 1.6 MHz as shown below.


Type 75 ferrite cores can be especially useful in reducing emission problems in the 500 kHz to 10 MHz frequency range, across which the impedance of the above ferrite is greater than 80 Ω..

The impedance of  ferrite cores can be further increased by using multiple turns. However, this also increases the inter-winding capacitance and degrades the high-frequency performance of the choke. Since the Type 75 material is intended for low-frequency use, this increase in capacitance is less of an issue, and two to five turns can be used with very little, if any, detrimental effect. The same 2675540002 core discussed above has an impedance of 1,400 Ω at 1.3 MHz when three turns are used, and an impedance of almost 4,000 Ω when five turns are used, see below. A three turn choke using this core will have an impedance greater than 500 Ω from 300 kHz to 20 MHz.


Even at 150 kHz, the low-end of the FCC/CISPR conducted emission measurement range, the three turn configuration has an impedance of approximately 250 Ω, and the five turn configuration has an impedance of approximately 700 Ω. Therefore, by using multiple turns high impedances can now be obtained at these low-frequencies.

Both smaller and larger cores are available from Fair-Rite. Type 75 cores ranging from 3/8″ to 1-1/4″ OD (7/32″ to 3/4″ ID) are listed in the Fair-Rite catalog. At present only solid cores are available, but snap-on split cores should also be available later this year. Snap-on cores are convenient for troubleshooting, and can be easily applied as an after-the-fact fix to cables. Since the manganese-zinc (MnZn) Type 75 cores are slightly conductive (resistivity, ρ = 3×10^2 Ω-cm), care should be taken that they do not touch any live electrical terminals.

Give the new Fair-Rite Type 75 material a try for your low-frequency emission/susceptibility cable problems. You might be pleasantly suppressed with the results.

February 07, 2015
Fair-Rite Products Corp.
Cable Cores for EMI Suppression

With an assortment of materials to suppress frequencies from 100 kHz into the GHz range, Fair-Rite has the spectrum covered.

January 02, 2015
Fair-Rite Products Corp.
75 Material Snap-Its

Once again, Fair-Rite Products Corp. is the first to introduce an innovative solution to the electronics industry! Our new 75 material is now available in Snap-It form so you can quickly find a solution to your low-frequency noise issues. Providing enhanced impedance between 150 kHz and 10 MHz, this material is superior to any other product available on the market and delivers twice the impedance at 1 MHz.

August 01, 2007
By Carole Parker, President of Fair-Rite Products
Specifying a Ferrite for EMI Suppression

Our past article (see “How to Choose Ferrite Components for EMI Suppression,” Conformity, June 2002) was intended to help design engineers optimize the performance of ferrite materials by analyzing the effects of frequency, field strength, temperature and core geometry. In our ideal world, safety (including effect on environment), quality and performance are paramount.


August 01, 2002
By Fair-Rite Products Corp.
How to Choose Ferrite Components for EMI Suppression

The following pages will focus on Soft Ferrites used in the application of electromagnetic interference (EMI) suppression. Although the end use is an important issue and some applications are mentioned, this technical section is not intended to be a design manual, but rather, an aid to the designer in understanding and choosing the optimum ferrite material and component for their particular application. Ferrite suppressor cores are simple to use, in either initial designs or retrofits, and are comparatively economical in both price and space. Ferrite suppressors have been successfully employed for attenuating EMI in computers and related products, switching power supplies, electronic automotive ignition systems, and garage doors openers, to name just a few

January 08, 2011
Fair-Rite Products Corp.
Use of Ferrites in Broadband Transformers

In many transformer designs ferrites are used as the core material. This article will address the properties of the ferrite materials and core geometries which are of concern in the design of low power broadband transformers. Broadband transformers are wound magnetic devices that are designed to transfer energy over a wide frequency range. Most applications for broadband transformers are in telecommunication equipment where they are extensively used at a low power levels.


February 12, 2015
Fair-Rite Products Corp
Flexible Ferrite Sheets

Fair-Rite’s Flexible Ferrite Sheets provide the benefits of soft-magnetic materials, while freeing you from their mechanical constraints! These materials are composed of NiZn to provide high-volume resistivity and high insertion-loss over a broad frequency range. Available in six material grades and four standard thicknesses as thin as 0.13mm, these RoHS compliant sheets come “scored” in a 2mm x 2mm rectangular grid.