From (32) and the preceding discussion, we conclude that a reasonable choice of the functional form for dynamic permability is
(43) |
Figure 1 shows that all these choices give very similar behavior in the complex plane. The function looks much like a semi-circle centered at the point (1/2,0) and having radius 1/2 in all cases. But this observation is only exactly true for the case P = 0. For that case it is also true that the relationship between and the polar angle in the complex plane is given exactly by . For the other values of P, this relationship holds approximately true for and , but deviations become substantial in all cases for higher values of , as is observed in Figure 2.
fivemodels
Figure 1 lustration of the behavior in the complex plane of five model functions for of the form found in Eq. (43) for the different values of P = 0, 0.25, 0.4, 0.5, 1. Note that the case P=0 is exactly a semi-circle of radius 1/2 centered at the point (1/2,0) in the complex plane. |
angledeg
Figure 2 Polar angle in degrees in the complex plane of points of five model functions of the form found in Eq. (43) for the different values of P = 0, 0.25, 0.4, 0.5, 1 (see Figure 1). Note that the case P=0 is exactly a semi-circle of radius 1/2 centered at the point (1/2,0) in the complex plane, and for this case . All other cases are observed to deviate from this behavior. |
fivemodsre
Figure 3 Illustration of the behavior of the real part of five model functions for different values of P = 0, 0.25, 0.4, 0.5, 1 as a function of the argument .Note that the real part of the dynamic permeability is essentially flat for a wide range of the smaller frequencies, but then falls off rapidly as the frequency approaches the resonance frequency from below. |
fivemodsim
Figure 4 Illustration of the behavior of the imaginary part of five model functions for different values of P = 0, 0.25, 0.4, 0.5, 1 as a function of the argument .Note the main region of the deviation (half maximum and above) lies approximately in the range ,which is just slightly over one decade in width. |
Figure 3 shows that the real part of the dynamic permeability is essentially flat for a wide range of the smaller frequencies, but then the function falls off rapidly as the frequency gets close to the resonance frequency . Figure 4 shows that all the action occurs over six decades of frequency and the main region of the deviation (half maximum and above in the imaginary part) lies approximately in the range , which is just slightly over one decade in width.