EMC Question of the Week: June 22, 2020

Wireless Charging Circuit

Wireless charging devices, widely used for consumer devices such as phones, convey power from the transmitter to the receiver through  

  1. electric fields
  2. magnetic fields
  3. radiated electromagnetic fields
  4. electron beams


The best answer is "b". While various forms of wireless charging have been described in technical publications, commercial wireless power transfer for everything from phones to electric vehicles relies on magnetic field coupling from the transmitter to the receiver. Both the transmitter and receiver have resonant coils that act as the primary and secondary windings of a transformer. Ferrite materials help to guide and contain the magnetic flux on both sides. 

The resonant coils limit the power to a relatively narrow frequency band at a wavelength that does not allow significant radiation to occur.  Electric fields are present wherever there are voltage differences, but the electric fields do not convey any significant power.  

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