REPRODUCTION OF MAGNETICALLY RECORDED SIGNALS 



1161 



method if images, this solution can be used to find the fields which exist 

 when the medium is under an ideaHzed reproducing head of permeability /x. 

 Also, the free space solution may be of use in evaluating the effect of self 

 demagnetization since the demagnetizing field is computed. 



Let the recording medium be an infinite plane sheet of thickness 5 and 

 choose rectangular coordinates so that the central plane of the medium 

 lies in the x~y plane as shown in Fig. 10. 



Let the permeability of the recording medium be unity and let the inten- 

 sity of magnetization inside it be given by 



(6) 



Fig. 10 — Coordinate system for flat tape calculations. 



This is equivalent to a volume density of "magnetic charge" given by 



p = — div / 



^ __ dh 

 dx 



- (ItIJX) cos (27rVX) 



(7) 



The problem then is to compute the field at a point (xo , So) due to this 

 charge. Consider the field at (.to , zo) due to the element f/.v dz at {x, z). This 

 element amounts to an infinitely long line of uniform charge density. The 

 field due to such a distribution is directed perpendicular to the line and 

 has a magnitude equal to twice the linear charge density divided by the 

 distance from the point to the line. 



