Ferrite shielding materials are widely accepted as providing a simple, convenient and cost-effective solution for radio frequency interference (RFI) problems in cables and connectors. Furthermore, they accomplish both RF attenuation and suppression of unwanted high-frequency oscillations with no loss in DC or low-frequency signal strength.
Ferrishield supplies a wide variety of these products. The basic composition of the ferrite materials is a combination of ferrous oxide and one or more other powdered metals – most often manganese, zinc, cobalt or nickel. An extensive selection of shapes and sizes is available, and custom geometries may be manufactured for special situations.
There are infinite varieties of formulas and performance levels possible. Each discrete ferrite formulation results in a stoichiometric ratio which is its performance characteristic signature regarding electrical, magnetic and mechanical relationships.
The most common expression of ferrites’ performance capabilities is in terms of their permeability (μ). This property expresses the ratio of the magnitude of magnetic induction to magnetising force. The materials are normally categorised according to initial permeability (μ).
Stated most simply, the operative characteristic which makes ferrites effective in RFI/EMI suppression is their variable sensitivity to frequency. With a ferrite installed as a suppressor, lower frequencies will pass with no significant loss. But above the frequency where (tan d/μ) climbs sharply, the signal couples with the ferrite to create an impedance which is quite high compared with the rest of the circuit.
The offending RFI is thus immediately and consistently blocked out by way of impedance damping of the unwanted high-frequency signals. It is this greater resistive impedance which allows the basically passive, apparently simple material to suppress multiple signals in a variety of application situations.
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