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![Page 1: Improved inductive power transfer efficiency by use of ... · PDF fileImproved inductive power transfer efficiency by use of thin ferromagnetic composites A.E. Umenei and K.J. Turner](https://reader036.vdocument.in/reader036/viewer/2022070607/5aabd90b7f8b9ac55c8c5f75/html5/thumbnails/1.jpg)
Improved inductive power transfer efficiency by use of thin ferromagnetic
composites A.E. Umenei and K.J. Turner
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Outline
• System Requirements • Composite Design • Composite Improvements • Test Methods • Results • Conclusion
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Inductive Power Transfer Systems
• 100 – 200 kHz • Low Power Level Transfer
Inductive Coupling • Tight size constraints (0.3 mm
max) • DC magnets commonly in
systems (75 - 150 mT at material surface)
• Parasitic materials common (batteries, metal casing, etc)
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Typical Ferromagnetic Materials
• Core loss @ 100 – 200 kHz
• Conductivity of materials
• Saturation Magnetization (Bsat)
Material Resistivity (µΩcm) Bs (T) Purified Iron* 10 2.15
Grain-oriented Fe-Si 47 2 MuMetal 62 0.65
Ferroxcube 3 100000000 0.25 *0.05% impurity
[1]
[1] Progress in Materials Science 44 (1999) 291-433 [2] Ferromagnetism by Richard Bozorth
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Design of composite
• Polymer insulation of particles • Reduce conductivity • Retain high permeability and Bsat • Ease of manufacturing
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Design of composite, cont.
• High purity iron powder – Irregular particles (fig. a)
50 – 200 µm diameter – Spherical particles (fig. b)
1 – 5 µm diameter
• Epoxy Binder – Powdered Epoxy – 1 – 3 % resin by weight
b
a
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Spherical P
articles Irregular P
articles
50 µm 50 µm
50 µm 50 µm
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5.80
6.00
6.20
6.40
6.60
6.80
7.00
7.20
7.40
7.60
7.80
8.00
1 2 2.5 3
Binder Content (wt%)
Seco
ndar
y In
duct
ance
in S
tack
(uH
)
35 TSI
40 TSI
45 TSI
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30 TSI Pressure 10 µm
30 TSI Pressure 10 µm
40 TSI Pressure 10 µm
40 TSI Pressure 10 µm
Surface of plate
Break surface of plates
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Resistivity (µΩcm)
1
10
100
1000
10000
100000
1000000
1E+07
1E+08
1E+09
1E+10
1E+11
1E+12
1E+13
Purified Iron* Grain-oriented Fe-Si MuMetal Composite** Ferroxcube 4
* 0.05% impurities **Fulton data Source data: Ferromagnetism by Bozorth
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Testing Results
• Describe the overall improvements with composite
• Basic test procedures • Sec inductance – analogous to BH • Efficiency - power losses
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0
5
10
15
20
25
30
35
0 20 40 60 80 100 120 140
Magnet Strength (mT)
Seco
ndar
y In
duct
ance
(uH
)
FINEMET 0.3 mm
FINEMET 0.6 mm
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0
5
10
15
20
25
30
35
0 20 40 60 80 100 120 140
Magnet Strength (mT)
Seco
ndar
y In
duct
ance
(uH
)
FINEMET 0.3 mm
FINEMET 0.6 mm
Ferrite 0.7 mm
Ferrite 0.5 mm
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0
5
10
15
20
25
30
35
0 20 40 60 80 100 120 140
Magnet Strength (mT)
Seco
ndar
y In
duct
ance
(uH
)
FINEMET 0.3 mm
FINEMET 0.6 mm
Ferrite 0.7 mm
Ferrite 0.5 mm
Amorphous 0.23 mm
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0
5
10
15
20
25
30
35
0 20 40 60 80 100 120 140
Magnet Strength (mT)
Seco
ndar
y In
duct
ance
(uH
)
FINEMET 0.3 mm
FINEMET 0.6 mm
Ferrite 0.7 mm
Ferrite 0.5 mm
Amorphous 0.23 mm
Composite 0.6 mm
Composite 0.3 mm
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5W Output, 75mT Magnet Strength
56.0%
58.0%
60.0%
62.0%
64.0%
66.0%
68.0%
70.0%
72.0%
0.3 0.6
Thickness (mm)
Syst
em E
ffic
ienc
y
CompositeFINEMETFerrite
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5W Output, 150mT Magnet Strength
56.0%
58.0%
60.0%
62.0%
64.0%
66.0%
68.0%
70.0%
72.0%
0.3 0.6
Thickness (mm)
Syst
em E
ffic
ienc
y
CompositeFINEMETFerrite
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Conclusions
• High Saturation Magnetization and permeability required
• Reduced conductivity through isolation of iron powder
• Increase manufacturability through high pressure compaction
• Increased performance for thin applications with high magnetic field