Overview
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Recently, the magnetic resonance type of transmission is gaining attention
as a wireless transmission technology. Magnetic resonance allows transmission
very efficiently from a distance of several meters and the axes of the
transmission end and receiving end of the coils do not need to be aligned,
which differs from the conventional electromagnetic induction type transmission
that is widely used today. Investigating the coils via analysis is advantageous
because an optimal design for the coil geometry and circuit for the frequency
to use is necessary to transmit from the transmission coil to the receiving
coil using resonance.
This example presents the use of a magnetic resonance analysis to obtain
the transmission efficiency and magnetic flux density distribution for
the magnetic resonance by changing the distance between the coils. |
Power Transmission Efficiency
The power transmission efficiency when the distance is changed between
the transmission and receiving coils is indicated in Fig. 1 and Fig. 2.
The results indicated in Fig. 1 show a power transmission efficiency of
almost 100 % at the two peaks on each side of the resonance frequency of
17.5 MHz at a distance of 200 mm to 275 mm between the coils. There is
a single peak with the same frequency at a distance of 300 mm between the
coils. The results indicated in Fig. 2 show the efficiency decreasing with
a transmission efficiency of less than 100% even at the peaks at a distance
of 325 mm to 400 mm between the coils. Therefore, the appropriate distance
of the power transmission for a resonance frequency of 17.5 MHz is approximately
300 mm. |
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Magnetic Flux Density Distribution
The magnetic flux density distribution (amplitude) for 17.0 MHz, 17.5 MHz,
and 18.0 MHz at a distance of 200 mm, 300 mm, and 400 mm between the transmission
and receiving coils are indicated in Fig. 3, Fig. 4 and Fig. 5.
The magnetic flux density is larger around the receiving coil at the frequency
that has a better power transmission efficiency for each distance between
the transmission and receiving coils. Furthermore, the intensity of the
magnetic field can be displayed in JMAG.
The amplitude, B, is defined as follows: |
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