Biomedical Engineering Reference
In-Depth Information
instruments for magnetic measurements have been devel-
oped based on the ponderomotive method; among them are
pendulum, torsion and beam magnetic balances and balances
using an elastic ring. h e method is also used in measuring the
magnetic susceptibility of liquids and gases and the intensity
of magnetization of ferromagnets and magnetic anisotropy.
•
Bridge and Potentiometer Methods:
h ese methods are
used for determination of magnetic properties and are
mainly used for measurements in variable i elds over a wide
frequency range. h ey are based on measurement of the
parameters (inductance
L
and resistance
R
) of an electric
circuit containing the ferromagnetic samples being studied.
h ey make possible determination of the relationships
B(H
)
and
J(H
) and the components of complex magnetic perme-
ability and complex reluctance in variable i elds, as well as
magnetization-reversal losses.
•
Wattmeter Method:
h is is the most common method for
measuring magnetization-reversal losses, which is used if
the change in magnetic induction versus time is of the sinu-
soidal type. In this method a wattmeter is used to i nd the
total power in the circuit of a coil used to reverse the magne-
tization of a sample. h e wattmeter method is standardized
in testing electrical steels.
•
Calorimeter Method:
h is method is used over a wide fre-
quency range and is an absolute method for measuring losses
in ferromagnetic materials. It makes possible measurement
of losses for any mode of changes in the intensity of a mag-
netic i eld or in magnetic induction, and also under complex
conditions of magnetization. In essence, the rise in tempera-
ture of the sample and the surrounding medium during
magnetization by a variable magnetic i eld is the measure
of energy losses. Calorimetric magnetic measurements are
conducted using methods of mixing and heat input and also
using l ow calorimetry.
•
Neutron Dif raction Methods:
h e
“magnetic structure” of
ferromagnets and antiferromagnets may be studied using
methods of neutron dif raction, which are based on the
phenomenon of magnetic scattering of neutrons that arises
as a result of interaction between the magnetic moments
of a neutron and the magnetic moments of particles of a
substance.
