Wireless Energy Transfer

Radiated Power ?
The energy is transferred with a pure magnetic field, not to be confused with radio waves. The effective radiated power, responsible for radio, is determined with the product of the electric- and the magnetic field-components which are perpendicular in polarisation and 90 degrees out of phase. The electric field is kept as low as possible, far below the RF-radiation limits for industrial equipment. Such a magnetic field can be generated with antenna coils much smaller than the wavelength, with a low feed-impedance, balanced and eventually shielded.

Operation
Electric power is coupled from transmit-coil to receive-coil by pure inductive coupling. The very low coupling-factor compared to other transformers is compensated by the resonance with a high Q-factor in the receive-coil. This coil should be precisely tuned, which can be a problem in mass-production.
Outputvoltage is rectified and regulated, making the power independent of fieldstrength and mistunig.

Range ?
The power from the magnetic field is only available within a limited distance around the antenna. This distance is determined with its dimensions and shape. Outside this range the fieldstrength will decrease rapidly with distance in the 3rd or 4th power, as long as the effective radiated power is zero.

Some applications :

• Wireless Lamps, a funny example for demonstrating RF-energy
• Battery Chargers:
  Oxidized contacts, bad cables or tiny connectors do decrease the discharge efficiency of batteries in portable equipment. Inductive charging makes use of fixed (PCB-mounted) batteries possible. They can be charged without placing in a charger or connecting with cables. The charge antenna can be PCB mounted too, so the portable equipment needs no power cable at all.