139 - Power Transmission Analysis Using Magnetic Resonance Phenomena
Recently, magnetic resonance is gaining attention as a new type of wireless transmission technology. Magnetic resonance differs from conventional types of electromagnetic induction transmission that are widely used today in that the axes of the transmission and receiving coils do not need to be aligned and in that it allows efficient transmission at a distance of several meters. A design for the coil geometry and circuit that is optimized for the frequency being used is necessary to make the transmitting and receiving sides resonate and thus transmit power.
It is very difficult to use measurement to visualize how magnetic field is being generated, and is therefore transmitting power, in the space between the transmitting side and the receiving side. Reproducing the power transmission state using analysis can help with designing optimized coils.
This Application Note presents how to confirm the power transmission efficiency and the magnetic flux density distribution.
Power Transmission Efficiency
Graphs of power transmission efficiency for varying distances between the transmission and receiving coils are shown in figures 1 and 2.
From fig. 1, it is apparent that with distances between the coils of 200 to 275 mm, there are peaks to each side of the resonance frequency of 17.5 MHz, at which a transmission frequency of nearly 100% is achieved. With a distance between the coils of 300 mm, there is one consolidated peak equal to the resonance frequency. Fig. 2 shows that with distances between the coils of 325 to 400 mm, power transmission efficiency does not reach 100% even at its peak, meaning reduced efficiency. Therefore, it can be said that the optimal distance for power transmission at a resonance frequency of 17.5 MHz is around 300 mm.
Magnetic Flux Density Distribution
Fig. 3 shows magnetic flux density distributions (amplitude) for 17.0 MHz, 17.5 MHz, and 18.0 MHz with distances between transmission and receiving coils of 200 mm, 300 mm, and 400 mm.
The figure makes it clear that, for each distance between transmission and receiving coils, magnetic flux density is larger near the receiving coil at a frequency with good power transmission efficiency. The size of the magnetic field can also be displayed in JMAG.