Application of Soft-hard Magnets

8/10/2019 Application of Soft-hard Magnets

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Chapter 12: Applications of Soft Magnets

1. Losses

2. Materials

3. Static Applications

4. Low-frequency Applications

5. High-frequency Applications

Comments and corrections please:[email protected]


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Further reading

C.W. Chen,Magnetism and Metallurgy of Soft Magnetic Materials, Dover: 1983An excellent monograph which contains a wealth of detailed and reliable information on almost every aspect of soft magnets.


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Ni-Fe/Fe-Co (heads)

Fe-Si

Fe-Si (oriented)

Ni-Fe/Fe-Co

Amorphous

Others

Others

Alnico

Sm-CoNd-Fe-B

Hard ferrite

Co- Fe 2O 3

(tapes, floppy discs)

CrO2 (tapes)

Iron (tapes)

Co-Cr (hard discs)

Soft ferrite

Others

Iron

Soft

Magnets

HardMagnets

MagneticRecording

Magnet applications; A 30 Bmarket


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Figure 12.1 Hysteresis in a soft magnetic material. B(H)

and J(H) are indistinguishable in small fields.

Minimal hysteresis.

High polarization

Largest possible permeability

B = 0rH

102< r

< 106

r

B 0M)


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skin depth

Bd= 0r

H

Electrical steel; = 0.5 m, r = 10,000

s= 0.36 mm at 50 Hz; s= 3.6 m at 500 kHz

rdecreases with increasing frequency; 106 to 102


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Pan

f

Phy

Pan

P/f

Phy

Ped

Hysteresis loss per cycle is the area of the

B(H) loop

H

Reduction of eddy-current losses by lamination

Figure 12.2 Total loss per cycle showing the three

contributions

1. Losses

1/n2


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t

d

H

Figure 12.3 Pry and Bean model for movement of uniformly-spaced domain walls.

Currents are induced in the vicinity of the walls, as shown by the dashed lines.

Reduces to zero as d/t 0


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Figure 12.4 Total loss per kg for permalloy at differentfrequencies. Thickness is 350 m

Figure 12.5 Progress during the 20th Century.

a) Losses in transformer cores

b) Initial static permeability

Losses are double in a rotating field.


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12.1.2 High-frequency losses.

Complex permeability = - i

h= h0exp it

b= b0exp i(t-) real parts are h(t), b(t)

= (b/h) exp -i

= (b/h) [cos - i sin]

Re(h) is the time dependent flux density

b(t) = h0[cost + sint] Losses are proportional to

Quality factorQ = / = cot

Loss angle


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A Fourier integral

The Fourier components are

General time-dependent response

Real and imaginary parts of are related via the Kramers-Kronig relations

Rate of energy dissipation P= h(t) db(t)/dt = h02cost (- sint + cost) sc=0, c2=1/2

P = (1/2)h02

Losses are +ve, hence the - sign in the defn


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Hs

h

M

Msm

Precession of the

magnetization


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Snoeks relation


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Figure 12.6 Real and imaginary parts of the susceptibilities and . The peak is at the ferromagnetic resonance frequency


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Figure 12.7 Global market for soft magnetic materials.

The pie represents about 10 B$ per annum

12.2 Soft Magnetic Materials


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[100] roll direction

(011) plane

Goss texture of grain-oriented silicon steel

Iron-rich edge of the Fe-Si phase diagram

Figure 12.8 Losses as a function of operating inductionfor grain-oriented silicon steel

At % Si

Wt % Si

L

TC


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Figure 12.9 Frequency response of some Ni-Zn ferrites


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Figure 12.10 A laboratory electromagnet

Tapered pole pieces; 55


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Figure 12.11 Types of cores. The powder core has been

sectioned to indicate its internal structure.

Stacked laminations Tape-wound core Powder core

Ferrite E-core

12.4 Low Frequency Applications


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Figure 12.12 Two electric motor designs: a) an induction motor with a squirrel-cage winding and b) a 3/4

variable reluctance motor


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Figure 12.13 A fluxgate magnetometer. a) Schematic b) operating principle

~

V

H

H

B

Hexc


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Figure 12.14 A surface accoustic wave delay line


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a a

b b

A magnetic amplifier


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An assortment of soft magnetic components made from Finemet


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A pulse transformer

Figure 12.15 A wire loop antenna, and am equivalent ferrite rod

with a much smaller cross section.

12.5 High Frequency Applications


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Q = 0/

A C-core with an airgap

Figure 12.16 An LC filter circuit, and the pass band.


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Figure 12.17 Absorption and transmission for left- and

right-polarized radiation


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Figure 12.18 A plane-polarised wave is decomposed into the sum of two, counter-rotating

circularly-polarized waves (a) which become dephased because they propagate at different

velocities (b) through the magnetized ferrite. The Faraday rotation is non- reciprocal - independentof direction of propagation.


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Figure 12.19 A waveguide propagating a TE01mode. Filling the upper half with YIG

magnetized vertically absorbs the microwaves for one direction of propagation, but not the

other.

YIG


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Figure 12.20 A four-port circulator a) illustrates the principle, b) shows the sense of

propagation and c) is the logic table.antennareceiverloadtransmitter.

0100

0010

0001

1000

In out

45


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A resonant microwave filter. The device transmits a

signal in a narrow frequency range, around the

ferromagnetic resonance frequency of the YIG sphere.

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Application of Soft-hard Magnets

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