Electrical – python – Why is there no attenuation in the magnetic field at the boundary of the near field

I have used the Wikipedia FSPL formula for the farfield, and the one kindly provided by @mnsp for the near field:

• http://grouper.ieee.org/groups/802/15/pub/04/15-04-0417-02-004a-near-field-channel-model.pdf

To model the attenuation of the magnetic field across the spectrum. Low frequency magnets have a very quick attenuation by distance. For example a bar magnet easily loses it's influence after 3-4 cm. However as you increase the frequency, the attenuation is lowered, and it possibly reaches 0 right at the boundary of the near field.

In my thought experiment I have used a distance of 5 m to model this for a theoretical isotropic transmitter. The general formula is λ/(2*π) for the boundary.

So in our case we have pretty much close to 0 attenuation at 8.4 MHz, and it starts to go back up from there. Looks like this:

Here is the python3 code to remove any uncertainty how my calculations were done

import math

π  = math.pi    #pi
c0 = 299792458  #lightspeed
r = 5           #distance

#---------------------------CALCULATION---------------------------------------------------------

def FSPL(f):
 λ = (c0/f)
 k = (2 * π ) / λ

 PLANEWAVE= 20*math.log(f,10) + 20*math.log(r,10) + 20*math.log(4*π/c0,10)
 MAGNETIC  =abs(10*math.log(1/4  *  (  1/  (k*r)**2 + 1/  (k*r)**4     ) ,10))
 ELECTRIC  =abs(10*math.log(1/4  *  (  1/  (k*r)**2 - 1/  (k*r)**4 + 1/  (k*r)**6     ) ,10))

 if(r<(1/k)): #Fraunhofer Boundary
  return f,MAGNETIC,ELECTRIC  # Near Field
 else:
  return f,PLANEWAVE # Far Field

#------------------------------ITERATION--------------------------------------------------------

CYCLES=34
STEP=1
for i in range(0,CYCLES):
 print (FSPL(STEP))
 STEP=STEP*2

#------------------------------END--------------------------------------------------------------

Which begs the following questions:

• What is exactly happening between the nearfield and farfield boundary?

• Is the model theoretically accurate?