Technical Flyers and Papers

Notes on Impedance Measurement

Fair-Rite measures impedance using the latest available/state of the art Impedance Analyzers from Keysight Technologies. Over the years
Keysight (formerly Agilent, formerly Hewlett Packard) has developed newer instruments, while making older models obsolete. These changes
in instrumentation have resulted in differences in Fair-Rite’s published curves, tabulated impedance values and specifications over time.

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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.

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Identifying Unknown Fair-Rite Round Cable Snap-It™ Cores

 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™.

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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.

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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.

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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.

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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.

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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.

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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.

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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 31 Material® suppression cores.

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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 31 Material® core.

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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.

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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.

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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.

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