REPRODUCTION OF MAGNETICALLY RECORDED SIGNALS 1171 



^ = -^TrXvIm COS M{2TR/\){2Ta/X)Ki{2wR/\)li{2Tra/\) (40) 



As X approaches infinity, Ki{2irR/\) approaches \/2'kR and Ii{2ira/\) 

 approaches ira/X so that, for very long wavelengths, equation (40) reduces to 



% = -Mmv{2'K/\){W) COS (coO (41) 



at 



This relation (which could have been derived in a much simpler manner) 

 should be useful for the experimental determination of the intensity of 

 magnetization, Im . 



SINGLE TURN OF RADIUS R 

 CONCENTRIC WITH WIRE 



WIRE OF 

 RADIUS a 



Fig. 14 — Elementary reproducing head consisting of a single turn of wire. 



Another case of some interest corresponds to a high permeability repro- 

 ducing head which surrounds the wire. In this case m is great enough so that 

 equation (36) reduces to 



" " {2TR/\)h{2TR/\)K,{27rR/\) ^^^^ 



If it is assumed, in addition, that the wire is solid so that flo = 0, then equa- 

 tions (42) and (39) give 



^ = -^TrXvIm cos (co/)(27ra/X)7i(2xa/X)//o(2Ti?/X) (43) 



dt 



Comparison between Round Wire and Flat Medium Response 



It is interesting to compare equation (43) with equation (24) to see how 

 the response characteristic of a round wire compares with that of a tape. 

 Assuming m » 1, the appropriate equation for the flat medium is 



^' = -ArWvI^ cos (coOd - e-''^"'')e-''"' (44) 



at 



