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From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Definition of Capacitance
Qo
Co 
V
Co = capacitance of a parallel plate capacitor in free
space
Qo = charge on the plates
V = voltage
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) Parallel plate capacitor with free space between the plates.
(b) As a slab of insulating material is inserted between the plates, there is an external current
flow indicating that more charge is stored on the plates.
(c) The capacitance has been increased due to the insertion of a medium between the plates.
Fig 7.1
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Polarization charge density on the surface of a polarized medium is related to the normal
component of the polarization vector.
Fig 7.6
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) A NaCl chain in the NaCl crystal without an applied field. Average or net dipole
moment per ion is zero.
(b) In the presence of an applied field the ions become slightly displaced which leads to
a net average dipole moment per ion.
Fig 7.9
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) An ac field is applied to a dipolar medium. The polarization P(P = Np) is out of phase with
the ac field.
(b) The relative permittivity is a complex number with real (r') and imaginary (r'')
parts that exhibit frequency dependence.
Fig 7.13
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Cole-Cole plots
Cole-Cole plot is a plot of r vs. r as a function of frequency,  . As the
frequency is changed from low to high frequencies, the plot traces out a
circle if Debye equations are obeyed.
Fig 7.17
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) Boundary conditions between dielectrics
(b) The case for Et1 = Et2.
Fig 7.21
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Time to breakdown and the field at breakdown, Ebr, are interrelated and depend on the mechanism that causes
the insulation breakdown. External discharges have been excluded (based on L.A. Dissado and J.C. Fothergill,
Electrical Degradation and Breakdown in Polymers, Peter Peregrinus Ltd. for IEE, UK, © 1992, p. 63)
Fig 7.28
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The piezoelectric effect.
(a) A piezoelectric crystal with no applied stress or field.
(b) The crystal is strained by an applied force that induces polarization in the crystal and generates surface charges.
(c) An applied field causes the crystal to become strained. In this case the field compresses the crystal.
(d) The strain changes direction with the applied field and now the crystal is extended.
Fig 7.38
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The piezoelectric spark generator.
Fig 7.42
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The pyroelectric detector. Radiation is absorbed in the detecting element, A, which generates
a pyroelectric voltage that is measured by the amplifier. The second element, B, has a reflecting
electrode and does not absorb the radiation. It is a dummy element that compensates for the
piezoelectric effects. Piezoelectric effects generate equal voltages in both A and B which across
a and b (the input of the amplifier) cancel each other.
Fig 7.47
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) Parallel plate capacitor with free space between plates which has been charged to a
voltage Vo. There is no battery to maintain the voltage constant across the capacitor. The
electrometer measures the voltage difference across the plates and, in principle, does no
affect the measurement. (b) After the insertion of the dielectric, the voltage difference is
V, less than Vo and the field in the dielectric is E less than Eo.
Fig 7.48
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Consider a Gauss surface just around the right plate and within the dielectric
encompassing both +Qfree and -QP. (E is the electric field.)
Fig 7.49
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) Polarization and the depolarizing field in a spherical shaped dielectric placed
in an applied field Eo
(b) Depolarization field in a thin rod placed in an applied field is nearly zero.
Fig 7.51
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
(a) The macroscopic field E is determined by the applied field Eo and the depolarization field due
to P. (b) Calculation of the local field involves making a hypothetical spherical cavity S inside the
dielectric. This produces polarization surface charges on the inside surface S of the cavity. The
effects of the dipoles inside the cavity are treated individually.
Fig 7.52
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The Langevin function.
Fig 7.56
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Fig 7.58
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Heterogeneous dielectric media examples
(a) Dispersed dielectric spheres in a dielectric matrix.
(b) A heterogeneous medium with two distinct phases I and II.
(c) Series mixture rule.
(d) Parallel mixture rule.
Fig 7.59
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)