So carrying on from last time.

I know that my bias coil has 40T and it's inner diameter is 30mm and it's 1mm wire, giving a loop diameter of 31mm

on the core i get 147uH and as an air core i get 61uH

Using the calc here

http://www.eeweb.com/toolbox/coil-inductanceSo running the calcs for air i get 0.0000753 H or 75.3uH (measured 61uH) Looks good for air

with the core i get 147uH which gives me a relative permeability of about

**1.4**So next to carry out the tests here, so i wound 150Turns of wire onto the iron core.

I measured the total magnetic path length as 330mm so lc = 330mm

Area of core with diameter of 20mm = 314mm2 so Ac=0.000314

I ran the system at 10KHz to get good amplitude for VL & IL and am using Rms voltages for calcs

IL=VR/R

IL=50.3mV/10

IL=0.00503 Amps

therefore uc (absolute permeability)= VL*lc / IL * Ac * N2 * 2pi * f

uc = (78.2mv * 330mm) / ( 0.00503 * 0.000314 * 150^2 * 2pi * 10000)

uc = 0.025806 / 2232.85242

uc = 1.15574 x 10-5 H·m−1

µr = µc / µ0

µr = 1.15574 x 10-5 / 1.2566370614 ×10−6

ur = 9.197

Here's the experiment and calcs page, i did Fig 1 test circuit.

http://meettechniek.info/passive/magnetic-permeability.htmlEDIT

OK i just re did the experiment at 100Hz

IL=VR/R

IL = 52.5mv / 10

IL = 0.00525 Amps

therefore uc (absolute permeability)= VL*lc / IL * Ac * N2 * 2pi * f

uc = 14.9mV * 330mm / 0.00525 * 0.000314 * 150^2 * 2pi * 100

uc = 0.004917 / 23.3051197

uc = 2.1098 x10-4

µr = µc / µ0

ur = 2.1098 x10-4/ 1.2566370614 ×10−6

ur = 167.9

OK worked out my problem Ac wrong, so have amended my results above