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A wireless power transfer experiment suitable for senior physicsundergraduates that operates between 3 and 4 MHz is described and demonstratedin detail. The apparatus consists of a pair of identical resonant coils thatcan be moved relative to one another. A signal generator circuit is inductivelycoupled to the transmitting coil using a single loop of wire. Likewise, asingle loop of wire couples the receiving coil to a load impedance. A matchingcircuit was used to tune the impedance of the system of coupled resonators tomatch the 50-$\ohm$ output impedance of the signal generator. A low-cost vectornetwork analyzer was used to characterize the system performance as thedistance between the pair of coils was changed. When the distance between thetransmitting and receiving coils was small, a double resonance emerged. Thefrequency difference between the pair resonances was inversely proportional tothe distance between the coils. After the system was fully characterized, itwas operated with up to 20 W of incident power. Our measurements revealed that,at weak coupling, the fraction of the incident power lost to radiationincreases linearly with the distance between the coils. Finally, we were ableto transmit enough power to dimly light a 60-W incandescent light bulb.

Non-radiative mid-range wireless power transfer: An experiment for senior physics undergraduates