MAGNETIC-FLUX DENSITY PRODUCED BY FINITE-LENGTH TWISTED-WIRE PAIRS

Twisting a wire pair is often used to reduce the wire's low frequency magnetic flux density impinging upon spatially adjacent circuitry. Typ ically, predictions of the magnetic Bur density due to the twisted-wir e pair are based upon mathematical formulations for infinite-length wi res. In this work, expressions for predicting the quasistatic magnetic Bur density near a finite-length, current-carrying twisted-mire pair are derived. These equations are numerically integrated, and the resul ts compared with the magnetic nux density from the corresponding strai ght-wire pair, thereby yielding results useful for electromagnetic com patibility analyses. Additionally, approximate Par-zone magnetic flux density equations are developed, and their range of validity establish ed. These equations are useful for magnetic flux density estimations a t distances further removed from the twisted-wire pair than the usual ones encountered in a typical enclosure. Also, they show that the larg e near-zone reduction of the magnetic flux density magnitude obtained by twisting the wire pair, relative to thr straight-wire pair, is not available in the far-zone.