SoundMods wrote:
It just dawned on me! The word I was trying to remember regarding this whole coil issue was Hysteresis.
By definition:
When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. It must be driven back to zero by a field in the opposite direction. If an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retraceability of the magnetization curve is the property called hysteresis and it is related to the existence of magnetic domains in the material. Once the magnetic domains are reoriented, it takes some energy to turn them back again. This property of ferrromagnetic materials is useful as a magnetic "memory". Some compositions of ferromagnetic materials will retain an imposed magnetization indefinitely and are useful as "permanent magnets". The magnetic memory aspects of iron and chromium oxides make them useful in audio tape recording and for the magnetic storage of data on computer disks.
That is one of the reasons where in most situations an air core inductor is superior to one using a magnetic core. Air has no hysteresis. If the inductance value needed is so large that an air core inductor is impractical then using a premium magnetic core inductor such as the ERSE SuperQ series that I used in the eggs will help. The core is made of many very thin sheets of magnetic material which reduces eddy currents in the material compared to a solid slug and extends frequency response. Also, air will not saturate like a magnetic core when subjected to very large signals. It is always a trade off.