The United States was one of the first countries to recognize the potential problems caused by electromagnetic pollution. As a result, the FCC was charged with the responsibility of promulgating rules and regulations to control and enforce limits on high frequency interference.

Figure 1 shows the current radiation limits as defined by FCC Rules Part 15, for class A (industrial) and class B (mass-market) equipment.

Figure 1

Conducted EMI can occur over a wide range of frequencies, from as low as 1MHz to several GHz. To provide protection over such a wide frequency range a number of ferrite material are available. Figure 2 shows the suppression range of each of Fair-Rite Products suppression ferrite

 Material  Optimal Suppression Range  Comments
 73 Material  1 – 25 MHz  Beads only
 75 Material  1 – 30 MHz  Snap-It™ and solid cores
 15 Material  10 – 250MHz  Customer specific applications
 31 Material®  1 – 300 MHz  Large parts only
 43 Material®  20 – 300MHz  Wide range of parts
 44 Material  20 – 300MHz  Wide range of parts
 61 Material™   200+ MHz  Wide range of parts

Figure 2 

Making the material selection is the first step in eliminating conducted EMI problems. To make this material selection it is imperative that the frequency of frequencies of the unwanted noise are known. This needn’t be an exact figure; an approximation will be sufficient.

Complex permeability will vary as a function of frequency. However, several environmental conditions will also affect these primary material parameters. The most significant ones are temperature and DC bias. In general, under conditions of high temperature and DC bias, ferrite’s suppression performance will derate. In the materials section of our website, we have published impedance derating graphs for both of these conditions.

The Curie temperature is the transition temperature above which the ferrite loses its magnetic properties. At this temperature the ferrite component is no longer performing its intended function. Once the material cools down below this temperature it will again perform as before. Fair-Rite Products publishes the Curie temperature of each of its materials under the materials section on our website.

Fair-Rite Products manufactures three classes of ferrite materials, MnZn, NiZn, and MgZn. The manganese zinc materials have low resistivities whereas the nickel zinc and magnesium zinc materials have high resistivities. For applications that use non-insulated wires or for use as connector suppression plates, a ferrite material with the highest resistivity is recommended. Fair-Rite’s 44 material is an improved 43 material® by providing both increased resistivity and Curie temperature. Components in the 44 Material NiZn material are catalog standard parts for connector plates and wound parts such as PC beads and wound beads.