Wireless charging is commonly divided into two types. One of the wireless charging types is a magnetic induction type and the other is a magnetic resonance type. Both of these types work on near field technology, i.e., the electromagnetic field dominates the region close to both the PTU and the PRU. The magnetic induction type includes two coils which are very close to each other, generally within a range of a few millimeters to a few centimeters. The magnetic resonance type includes two resonant coils, which are generally separated in a range of a few centimeters to a few meters, operating at the same resonant frequency, are strongly coupled, and thus a high charging efficiency is achievable.

As illustrated in FIG. 1A, a wireless charger 11 includes an induction coil antenna 12. The wireless charger 11 senses the presence of a mobile device (target device) 13 for charging on a flat surface of a charger base 14. The induction coil antenna 12 creates an alternating electromagnetic field from within the wireless charger 11, and a second induction coil (not shown) in the mobile device 13 takes power from the alternating electromagnetic field and converts the power back into electric current to charge a battery in the mobile device 13 or to provide direct operational power to the mobile device 13. However, the design of a coil antenna in existing wireless chargers usually suffers from a non-uniformity of the magnetic field issue, especially at an edge region of the induction coil antenna 12. This issue is problematic since an unevenly distributed magnetic field over the charger base surface 14 greatly impacts the charging efficiency, particularly in a negative way.