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Consider a cylindrical \$N52\$ magnet with mass \$m_0\$ travelling in horizontal x-axis with initial velocity \$v_0\$ in \$-x\$ to \$+x\$ direction. It passes through an copper air core solenoid on its right side. The ends of the solenoid are connected to a measuring device that measures: current, voltage and the power as the magnet approaches, enters, travels through and exits the solenoid. Alternatively we can assume a small 80% efficient electric device connected to the solenoid. Let the cumulative power generated be denoted by \$P_1\$. Let the total number of turns in the solenoid be fixed to some chosen \$N\$.

Query: How do we calculate the parameters for the magnet and the coil such that for the given velocity \$v_0\$ maximum amount of kinetic energy is converted into power in the solenoid? And what is the maximum conversion efficiency we can achieve? Solenoid and device are fixed to the ground.

For the magnet: The length\$(l)\$ and diameter\$(d)\$ of the cylindrical magnet (their ratio \$(l/r)\$) (for a fixed mass \$m_0\$)

For the solenoid: The gauge or diameter \$d\$ of the wire, the 'shape' of the \$N\$ turn cylindrical solenoid. By shape we mean that all the \$N\$ turns can be in a single layer thus resulting in a long solenoid in one extreme case or a solenoid with \$t\$ turns in each layer and \$l\$ layers such that \$N=tl\$.

From Ohm's Law \$V = IR\$. The resistance is inversely proportion to the area of the cross section of wire, thus the larger diameter would lead to lesser resistance per unit length in a wire. Moreover the inner air core diameter should be as tight as possible w.r.t. the diameter\$(d)\$ of the magnet so that maximum number of field lines pass through the solenoid as the magnet passes through it.

But I don't know how to calculate these parameters. My background is not in EE so please take that into consideration.

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  • \$\begingroup\$ What electromagnet do you refer to? A picture would be far, far better. \$\endgroup\$
    – Andy aka
    Commented Dec 31, 2022 at 11:02
  • \$\begingroup\$ @Andyaka sorry i meant magnet. there is no electromagnet! an N52 magnet is travelling on x axis with a velocity v0 from left to right and passes though a solenoid that is also placed on same axis. thats the setup. \$\endgroup\$
    – J.Doe
    Commented Dec 31, 2022 at 11:18
  • \$\begingroup\$ An N52 example magnet will differ in properties between manufacturers. Do you ask for a general answer? \$\endgroup\$
    – datenheim
    Commented Dec 31, 2022 at 12:10
  • \$\begingroup\$ please assume a generic/standard N52 for calculations. A few percentage points here or there won't matter. the link you sent seems fine too. the reason I said N52 is they seem to be the strongest permanent magnets class. \$\endgroup\$
    – J.Doe
    Commented Dec 31, 2022 at 12:36
  • \$\begingroup\$ For a given length of wire, and a given current, the coil geometry that gives the greatest magnetic field is known as a Brooks coil. Google it for the geometry. \$\endgroup\$ Commented Dec 31, 2022 at 16:35

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