FWIW, here are some test results of measurements between two parallel flat pancake coils that are connected in a bucking mode
Are these coils connected electrically in parallel or serial "bucking mode" ? that is, the flux on the inside of each coil is going in the same direction as depicted in the drawing below.
But the flux produced by one coil is called the H-flux. The amount of flux lines penetrating a given area of a perpendicular 2D plane is the magnetic flux density - often just called the H-field or B-field * after interaction with a ferromagnetic. The direction of the H-field is not parallel to the plane that serves to measure its density - it is perpendicular. The vectors denoting the flux and flux density are parallel by definition so there is something wrong with your drawing. Please, draw the direction of the electric current flowing in these coils and how they are connected (I cannot read that from the photo). Also, please mark the printed side of the PCBs, so I can see from the edge-on view how they are oriented to each other. I assume that these two PCB coils are identical and single-sided. (pls confirm). * In equations, the letter "B" is often used to denote magnetic flux density, regardless of the origin of that flux (i.e. coil, magnet).Each coil measures 65.2uH and the aid inductance is 170.6uH and the buck inductance is 89.5uH so the calculated k = .31 . These values are confirmed by Lbuck = ((1-k)*2)*(L1*L2)^1/2 = 89.9uH and
Laid = (1-((1-k)/2))*4*(L1*L2)^1/2 = 170.82uH.
That makes sense but I still do not know how these coils are connected electrically. The first pix and scope shot shows the position of the sense coil parallel to the flat coil with the resulting current measurement of 40.34ma rms at resonance.
The second pix and scope shot show the position of the sense coil 90 degrees to the flat coil with a current measurement of 1.235ma rms and is slightly off resonance.
Please decrease the frequency an order of magnitude, so the measurement is not deceived by capacitive coupling. My conclusion, which of course is subject to correction, is that the H field is on axis with the axis of the flat coils or at a right angle to the coil plane while the coil flux is bucking
It's an interesting challenge, then ! [H-field] ...and in the same direction across the face of each coil.
Measured when the coils are together or separate ? Also, in this context, does "across the face" mean parallel to the plane of the coil ?
« Last Edit: 2020-07-24, 21:52:47 by verpies »
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