Hi,here is a video showing an air core coil ,with a short duration high current pulse applied. the hammering noise is the contraction and relaxation of the coil due to the strong magnetic field.The flashing red light is a magnetic pulse detector,like a logic probe,only for magnetic fields.The pictures are the coil and the detector, I believe the vibration in the tpu is caused by a short duration high current pulse.
Well done CP2012....I have done some similar testing looking to recreate vibration. The next step would be to try the same test with a non-inductive winding instead of a solenoid winding. Also a tall thin structure would allow more free play of the vertical wires than a tightly wound solenoid. Looking at the cross section cutaway of the SM17, It looks to me that SM is using a loopback winding for low inductance....hence all the glue and outer ring at the base where a few tie wraps would have sufficed to hold the whole thing to the base. Look closely at the cutaway, the windings do not appear to turn the square corners of the lower block. In his early designs, SM used lamp cord in a bifilar fashion for low inductance. Why lampcord? If you twist two ends together and pulse the opposite two ends, you have a nice uniform non-inductive path. Parallel currents flowing in opposite directions always cause repulsion between the wires, regardless of the polarity of the energizing current. In a loopback winding you go down one side and back up the same side, repeating this on the inside and outside of the TPU, never making complete solenoid style turns around the TPU.
This creates a non-inductive wind, but you get repulsion effects between the loops. This is a very different construction technique than bifilar out of phase windings. A non-inductive wind will make better use of the risetime of a sharp pulse, peak current limited only by the DC resistance of the wire as the inductance is minimal. This is my next area of research.
« Last Edit: 2010-12-11, 14:26:40 by ION »
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