Hardware Reference
In-Depth Information
Figure 4.4: Demagnetization curves of a bonded NdFeB magnet
The performance of magnet is also related to the temperature of the en-
vironment. Increasing the temperature leads to weakening of the
fi
eld gen-
erating capability, see Figure 4.4. In the application of permanent magnet
materials, we must let the magnet to operate in the temperature lower than
T
max
, the maximum practical operating temperatures allowed for the magnet.
The magnetic performance of the permanent magnet can be recovered when
the temperature returns to its original value if the temperature is lower than
T
max
. For the bonded NdFeB magnet, T
max
normally lies in the range from
120
◦
C to 140
◦
C.
4.1.6 Magnetic Circuit and Magnetomotive Force
Because of the complexity in the geometric and electromagnetic structures,
analyzing the magnetic
fi
eld in an electromagnetic device is normally a com-
plicated procedure. Numerical methods, e.g., the
fi
nite element method (FEM)
are often used to solve a boundary value problem de
fi
ned by Maxwell equa-
tions and boundary conditions, and expressed by magnetic potential. After
getting the discrete magnetic potential solutions, post-processing technology
is employed to make clear the global electromagnetic performance of the de-
vice. Such complicated procedure relies on special software tools. In many
cases, some simpli
fi
cations can reduce the complexity and an engineering solu-
tion can be obtained easily. Magnetic circuit method is one such method which
uses magnetic
fl
ux Φ, reluctance R and magnetomotive force F to describe the
effect of magnetic
fi
eld in the device. It can be used to analyze both linear
and non-linear magnetic
fi
eld problems, and is even applicable to the magnetic
device with complicated electromagnetic (EM) structures [69],[70],[77]. The
concept and application of magnetic circuit are explained next with the help
of two examples.
