Conformity Magazine - June 2008 - (Page 53)

• Operating conditions (environment); • If high resistivity is required because of multiple turns, • The circuit impedance, source and load; • How much attenuation is required; • The allowable space on the board. The design engineer can then compare materials at the relevant frequencies for the complex permeability, heeding effects of temperature and field strength. After this, core geometry can be selected, from which the inductive reactance and series resistance can be defined. The Equations The impedance of a ferrite core in terms of permeability is given by: Z = jωµ Lo And: µ = µ' - jµ" =(µs'2 +(jµs")2)1/2 Where: µ'= real part of the complex permeability µ"= imaginary part of the complex permeability j = unit imaginary vector Lo= the air core inductance Therefore: Z = j ωLo (µ' − jµ") Equation 5 Equation 4 Equation 3 conductor pins in a connector filter plate or position in the circuit; At low frequencies, the impedance of the component is primarily the inductive reactance. As frequency increases, the inductance decreases at the same time the losses increase and the total impedance increases. Figure 4 is a typical curve of XL, Rs and Z vs. frequency for our a medium permeability material. Knowing that, the magnetic quality factor: Q = µ'/µ" = ωLs/Rs Equation 8 Then, the inductive reactance is made directly proportional to the real part of the complex permeability by Lo, the air core inductance: j ωLs= j ωLoµs' The loss resistance is also made directly proportional to the imaginary part of the complex permeability by the same constant: Rs= ωLoµs" Substituting into Equation 7 for impedance: Ζ = ωLoµs" + j ωLoµs' The impedance of the core is also considered to be a series combination of inductive reactance (XL) and the loss resistance (Rs), both of which are frequency dependent. A loss free core would have an impedance that would be given by the reactance: X = j ωLs Equation 6 A core that has magnetic losses may be represented as having an impedance: Z = Rs + j ωLs Where: Rs= total series resistance =Rm + Re Rm = Equivalent series resistance due to the magnetic losses Re = equivalent series resistance for copper losses JUNE 2008 CoNformity 53 Equation 7 http://www.captorcorp.com http://www.captorcorp.com http://www.captorcorp.com

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Conformity - June 2008 Contents Editor's Note 700 MHz Auction Raises a Record $20 Billion FCC Modifies PCS and AWS Power Limit Rules for Broadband Wireless Commission Designates Spectrum Test Bed FCC Releases Report on Wireless Competition Commission Proposes $5 Million Fine for Slamming Using EDX for Non-Destructive Detection of Lead in Consumer Products ESD Open Forum Challenges in Testing - Improving Election Security and Accuracy Part 1 Challenges in Testing - Human Body Model: The Hidden Challenges High-Speed Signal Integrity Considerations for ESD Components Focus On...EMC Components Buyer's Guide FCC Levies $2.6 Million Fine for Junk Faxes FDA Updates Guidance on its Product Review Process EU Issues Updated Energy Star Regulations EU Repeals Directive on Veterinary Electro-Medical Equipment New Product Announcements Updated Standards List for the EU's PPE Directive CPSC Announces New Effort to Keep Out Hazardous Products CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity - June 2008

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