A New spaced coil only had enough homemade litz for 3.25 Turns though
Was the turn spacing equal to the wire thickness? 49.4-45.9=3.5 45.9-42.5=3.4 bandwidth 6.9MHz
Measured like this? Q = 45.9/6.9=6.65 Not that much change really
The Q might be dominated by other circuit components, e.g. the capacitor or leads. Also made a Bias coil 40 Turns of 1mm wire, 22 turns first with 18 turns on top, 2cm wide, measured inductance is 48uH, now this measured inductance on the core has me worried, there seems to be something amiss . I am using this calculator to design my coil's magnetic field, for iron I should be using a relative permeability of 200 and that's how i arrived at 40 turns for 0.5T field strength but according to the same calculator my measured inductance should be 8mH
According to this, the permeability of 99.8% iron should be around 5000. Now if i put a relative permeability of 1 into the calculator instead of my cores 200 i get roughly the measured inductance, but then my magnetic field strength is only 0.002T which is way too low, so i am currently not sure whats wrong here
The Eddy currents in a conductive core can decrease the measured permeability. Check if the measured permeability changes drastically with the frequency of inductance measurement. Negative strong frequency dependency suggests, that the Eddy currents in the core are repelling the AC magnetic filed created by the inductance meter. It agrees with my measured inductance, so this begs the question why is my bias coil behaving as if there's no core present??
Eddy currents or measurement error is all I can think of. Eddy currents repel the magnetic field (or freeze it). Especially the Eddy currents in the steel bracket because it has lager dimensions than the rod. In other words why does my core appear to have the same permeability of free space, is it because the coils inner diameter is 1cm bigger than the outer diameter of my core.
No. Try putting a piece of ferrite inside that coil and see if the inductance shoots up. Ferrites do not support Eddy currents. Also Eddy currents do not exist at DC so you can expect that the constant magnetic field developed in the core/rod at DC will be radically different from an AC field. I've increased the winding diameter to 30mm to allow for a heater on top of the core.
That's good. Larger coils immerse the rod in a more homogeneous field towards their center. See the picture below:
« Last Edit: 2016-02-07, 12:25:07 by verpies »
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