4.6.1 Self-inductance arrangements From Eq (4.28)we obtian WuoA WuoA WuoA △6 S 04-0 0410 262 2(0+△)2N 26 If there is a very small air gap, that is,△δ<<δo, the sensitivity s can be further approximated as W-LoA S (429) 26From Eq. (4.28) we obtian (1 2 ) 2 2( ) 2 0 2 0 0 0 2 2 0 0 0 2 2 0 0 2            − +  = − = − W A W A W A S If there is a very small air gap, that is,     0 , the sensitivity S can be further approximated as 2 0 0 0 2 2 W  A S = （4.29） 4.6.1 Self-inductance arrangements