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

Improved inductive power transfer efficiency by use of thin ferromagnetic

composites A.E. Umenei and K.J. Turner

Outline

•  System Requirements •  Composite Design •  Composite Improvements •  Test Methods •  Results •  Conclusion

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)

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

Design of composite

•  Polymer insulation of particles •  Reduce conductivity •  Retain high permeability and Bsat •  Ease of manufacturing

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

Spherical P

articles Irregular P

articles

50 µm 50 µm

50 µm 50 µm

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

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

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

Testing Results

•  Describe the overall improvements with composite

•  Basic test procedures •  Sec inductance – analogous to BH •  Efficiency - power losses

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

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

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

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

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

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

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