pp ch7 3rded sample

8/16/2019 PP Ch7 3rdEd Sample

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From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)

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Definition of Capacitance

C o = capacitance of a parallel plate capacitor in free

space

Qo = charge on the plates

V = voltage

C o =

Qo

V


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Fig 7.1

!a* Parallel plate capacitor $ith free space +et$een the plates.

!+* s a sla+ of ins-lating material is inserted +et$een the plates, there is an eternal c-rrent

flo$ indicating that more charge is stored on the plates.

!c* The capacitance has +een increased d-e to the insertion of a medi-m +et$een the plates.


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Fig 7.6 From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)

Polari/ation charge densit0 on the s-rface of a polari/ed medi-m is related to the normal

component of the polari/ation vector.


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!a* a2l chain in the a2l cr0stal $itho-t an applied field. verage or net dipole

moment per ion is /ero.

!+* 3n the presence of an applied field the ions +ecome slightl0 displaced $hich leads to

a net average dipole moment per ion.


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Fig 7.! From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)

!a* n ac field is applied to a dipolar medi-m. The polari/ation P ! P = Np* is o-t of phase $ith

the ac field.

!+* The relative permittivit0 is a comple n-m+er $ith real !ε r 4* and imaginar0 !ε r 44*

parts that ehi+it fre5-enc0 dependence.


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Cole-Cole plots

Cole-Cole plot is a plot of ε ″ r vs. ε ′r as a f-nction of fre5-enc0, ω . s the

fre5-enc0 is changed from lo$ to high fre5-encies, the plot traces o-t a

circle if De+0e e5-ations are o+e0ed.


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Fig 7.2


!a* 6o-ndar0 conditions +et$een dielectrics

!+* The case for Et 1 = Et '.


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Fig 7.2"


Time to +reado$n and the field at +reado$n, E+r, are interrelated and depend on the mechanism that ca-ses

the ins-lation +reado$n. Eternal discharges have +een ecl-ded !+ased on 8.. Dissado and 9.2. Fothergill,

Electrical Degradation and 6reado$n in Pol0mers, Peter Peregrin-s 8td. for 3EE, :, " 1;;', p.


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Fig 7.!"


The pie/oelectric effect.

!a* pie/oelectric cr0stal $ith no applied stress or field.

!+* The cr0stal is strained +0 an applied force that ind-ces polari/ation in the cr0stal and generates s-rface charges.

!c* n applied field ca-ses the cr0stal to +ecome strained. 3n this case the field compresses the cr0stal.

!d* The strain changes direction $ith the applied field and no$ the cr0stal is etended.


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Fig 7.#2


The pie/oelectric spar generator.


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Fig 7.#7


The p0roelectric detector. >adiation is a+sor+ed in the detecting element, , $hich generatesa p0roelectric voltage that is meas-red +0 the amplifier. The second element, 6, has a reflecting

electrode and does not a+sor+ the radiation. 3t is a d-mm0 element that compensates for the

pie/oelectric effects. Pie/oelectric effects generate e5-al voltages in +oth and 6 $hich across

a and + !the inp-t of the amplifier* cancel each other.


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Fig 7.#"


!a* Parallel plate capacitor $ith free space +et$een plates $hich has +een charged to avoltage V o. There is no +atter0 to maintain the voltage constant across the capacitor. The

electrometer meas-res the voltage difference across the plates and, in principle, does no

affect the meas-rement. !+* fter the insertion of the dielectric, the voltage difference is

V , less than V o and the field in the dielectric is E less than E o.


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Fig 7.#9


2onsider a #a-ss s-rface ?-st aro-nd the right plate and $ithin the dielectric

encompassing +oth @Qfree and −Q P . ! E is the electric field.*


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Fig 7.5


!a* Polari/ation and the depolari/ing field in a spherical shaped dielectric placed

in an applied field E o

!+* Depolari/ation field in a thin rod placed in an applied field is nearl0 /ero.


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Fig 7.52


!a* The macroscopic field E is determined +0 the applied field E o and the depolari/ation field d-e

to P . !+* 2alc-lation of the local field involves maing a h0pothetical spherical cavit0S inside the

dielectric. This prod-ces polari/ation s-rface charges on the inside s-rfaceS of the cavit0. The

effects of the dipoles inside the cavit0 are treated individ-all0.


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Fig 7.56


The 8angevin f-nction.


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Fig 7.5"



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Fig 7.59


&eterogeneo-s dielectric media eamples

!a* Dispersed dielectric spheres in a dielectric matri.!+* heterogeneo-s medi-m $ith t$o distinct phases 3 and 33.

!c* Series mit-re r-le.

!d* Parallel mit-re r-le.

pp ch7 3rded sample

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