>> If you had a permeable core that could saturate > So, if I understand it (or something, anyway), an air core inductor/ > antenna would be preferred, as the intention is to radiate energy, > not lose it in a solid core ? Not directly related to what I said. I was commenting on the effect of a permanent magnet on the system. The desired result is a coil of adequate Q and this may be achieved with or without an additional core material BUT most systems which transfer substantial power do so using a core. This may be ferrite or may be powdered iron depending on frequency. The IPT (I'll call them" organisation has various reference coil designs freely available and the uChip App Note I have referenced several times discusses many coil designs. > As for the transfer itself, say I make two identical air-core inductors/ > antennae, spatially in parallel. If one is driven resonantly, the other > should be a matching receiver ? Both should be resonant and at the same frequency. They do not need to be mechanically identical. For a TX inductor I used 100 metres of TPS mains wiring driving. Assume 2 core and drive phase and neutral as a current loop with far end shorted. Resonate. Receivers were Ferrite U cores with a winding on cross bar (could have been anywhere on core) and a resonating capacitor. In this case TPS had outer sheath removed at desired pickup points and conductors separated enough for one ferrite leg to fit between. That was demo only - multi station working system can have conductors spaced as required. Your system wants an across air gap transfer so facing flat coils is better. Look at photos of MIT 2 metre plus transfer to get a 'big picture' view :-). FWIW (very little) "my" 1999 US patent is here Please not to blame me for typical patentese and nasty diagrams at rear and I don't know where the 555 timers came from :-). I did all the power transfer and signalling stuff. Others did warehousing stuff. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .