Wireless Power Wiki

Wireless Power Transfer (WPT) can be implemented in many ways. The most well-known technologies in the sector today are depicted in Figure 1 and can be divided into WPT by acoustic or by electromagnetic means

Figure 1 overview of WPT

Near-field WPT is realised by a magnetic or electric field (IPT/CPT), whereas far-field WPT uses electromagnetic waves in the form of a radio frequency signal to transfer energy. Both techniques differ primarily in the distance between transmitter and receiver over which energy is transmitted. The range of near-field applications is typically limited to a few millimetres to a few centimetres, while far-field WPT extends from several metres to kilometres. Another key distinction is the alignment requirement between the transmitter and receiver. Near-field technology requires precise alignment, whereas far-field WPT does not. However, the most significant difference between the two methods lies in their efficiency.

The efficiency of the WPT system depends on the type of technique. As seen in Figure 2, the implementation methods vary strongly in efficiency. Near-field electromagnetic WPT typically achieves a higher efficiency than far-field WPT. According to the distance, the energy transfer efficiency declines exponentially with all methods. This is due to the air gap and its poor conductive properties. The inductive coupling technology attains the highest energy transfer efficiency, varying from 70% up to 90%. In the same figure can be seen that the efficiency for magnetic resonant coupling strongly declines to a range of 40-60%. In the near-field technology this WPT method is used for greater distances, going from a few centimetres up to a maximum of 5m. A summary of these near-field methods is given in Figure 3.

Figure 2 efficiency of WPT (Jawad et al., 2017, p. 8)

Figure 3 Near-field technology specifications (Jawad et al., 2017, p. 10)

References

• Detka, K., & Górecki, K. (2022). Wireless Power Transfer—A Review. Energies, 15(19). https://doi.org/10.3390/en15197236
• Jawad, A. M., Nordin, R., Gharghan, S. K., Jawad, H. M., & Ismail, M. (2017). Opportunities and challenges for near-field wireless power transfer: A review. In Energies (Vol. 10, Issue 7). MDPI AG. https://doi.org/10.3390/en10071022
• Minnaert, B. (2018). Near-Field Wireless Power Transfer for Non-Static Applications.