螺旋线-word文档制作.doc

(b)
(a)
R1
M1
R

i1
L1
●
●
●
iN
RN
L2
MN
i
L

FIGURE Lumped circuit model for eddy gradient coil (a) and each eddy-current conductor (b) are modeled as LR currents result from mutual inductance Mk between the gradient coil and each eddy-current mutual inductance allows a current i in the gradient coil to induce current ik in the eddy-current conductor produces a magnetic field proportion to ik+ (Adapted from Van Vaals and Bergman 1990;Jehenson et .)

Rd

a
d


c
-
rt
+
r
R
-
R1
+

b
PS
gradient coil
>>
PE
(δ＝1)
computer


PS
Z0 - coil
>>
PE
(δ＝0)
. (a) Preemphasis circuit (for one exponential term).The high-pass RC filter generates an exponentially decaying signal with adjustable time constant (p1=RC) and relative amplitude(V1=(r/rt)(R1/Rd)).Summation of the signal to the input step function produces the desired pulse RC filters with different time constants and gains can be added in parallel to generate direct path d should only exist in the preemphasis for the gradient coil,not for other coils like the Z0 coil.(b) General circuit computer provides the input f