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1、2.1 固体电介质的极化与损耗,2.1.1 固体电介质的极化 2.1.1 Polarization of Solid Dielectrics 2.1.2 固体电介质的损耗 2.1.2 Loss of Solid Dielectrics,2.1 Polarization and Loss of Solid Dielectrics,本节内容 Contents in this section,电介质的介电常数也称为电容率，是描述电介质极化的宏观参数。电介质极化的强弱可用介电常数的大小来表示，它与该介质分子的极性强弱有关，还受到温度、外加电场频率等因素的影响。,2.1.1 固体电介质的极化 2.1.1
2、 Polarization of solid dielectrics,固体电介质介电常数： The dielectric constant of solid dielectric:,The permittivity of dielectrics is also called capacitivity , which is a macro parameter to describe dielectric polarization. Polarization degree could be denoted by the magnitude of permittivity which is rela
3、ted to molecular polarity strength and influenced by the factors such as temperature and frequency of external electric field.,电介质的相对介电常数为,式中，D、E分别为电介质中电通量密度、宏观电场强度。,(2-1),Relative permittivity of dielectrics is,In the formula, D, E denote electric flux density and macro electric field strength in t
4、he dielectrics respectively .,平板电容器的介电常数,图2-1 平板电容器中的电荷和电场分布 (a)真空 (b)充以介质,电荷面密度,极板间真空中的电场强度,(2-2),Permittivity of plate capacitor,Strength of vacuum field between plates,Fig 2-1 charge and electric field distribution in the plate capacitor (a) vacuum (b) filled with dielectric, surface charge densi
5、ty,视频链接,真空电容器的电容量为,当极板间充以均匀各向同性的电介质时（见图2-1 (b)），在电场作用下电介质产生极化，极板上自由电荷面密度应为,(2-3),(2-4),The capacitance of vacuum capacitor is,When the plates are filled with uniform isotropic dielectrics (figure 2-1(b), polarization takes place under the electric field and free surface charge density on the plates
6、is,充以电介质后电容器的电容量为,显然，极板间充以电介质后，由于电介质的极化使电容器的电容量比真空时增加了，因此，可以用充以介质后电容量的变化来描述电介质极化的性能。,(2-5),(Capacitance of capacitor filled with dielectrics is),Evidently, after the plates are filled with dielectrics, the capacitance becomes larger compared with that in vacuum due to the dielectric polarization. So
7、 the change of capacitance could be used to describe the performance of dielectric polarization.,电容器充以某电介质时的电容量C与真空时电容量C0的比值为该介质的相对介电常数，即,是一个相对的量，叫做相对介电常数，是大于1的常数。,(2-7),The ratio of capacitance C of capacitor filled with some kind of dielectric to capacitance C0 in vacuum is the relative permittivi
8、ty namely:,which is called relative permittivity is a relative quantity, constant value, and larger than one.,根据电介质极化强度P的定义，当电介质中每个分子在电场方向的感应偶极矩为 时，则有,式中，N电介质单位体积中的分子数。,(2-10),According to the definition of dielectric polarization strength P, if every molecule has a dipole moment at the direction of
9、 electric field, then,In this formula, Nmolecule number of dielectric in the unit volume.,若作用于分子的有效电场强度为 ，则分子的感应偶极矩可以认为与 成正比，即,式中，比例常数 称为分子极化率，在SI单位制中的单位为 。,(2-11),If the effective electric field strength acting on molecule is , then it could be considered that the dipole moment of molecule is propo
10、rtional to , namely,In this formula, proportional constant is called molecular polarizability whose unit is in the SI unit system.,于是根据式（2-10）和式（2-11），可得电介质极化的宏、微观参数的关系为,亦可写成,(2-12),(2-13),Then, according to the formula (2-10) and (2-11), we could get the relationship between macro parameter and mic
11、ro parameter of dielectric polarization.,It also could be written as,上式建立了电介质极化的宏观参数 与分子微观参数 的关系 。一般来说，作用于分子上的电场强度Ei不等于介质中的宏观平均电场强度E，称Ei为电介质的有效电场或内电场。式（2-13）又称为克劳休斯（Clausius）方程。,The upper formulas establish the relationship between macro parameter and micro parameter . Generally, the electric field
12、strength Ei which is called effective electric field or internal electric field acting on the molecule is not equal to macro average electric field strength E. Formula (2-13) is also called Clausius Equation.,1. 非极性固体电介质,这类介质在外电场作用下，按其物质结构只能发生电子位移极化，其极化率为 。,Non-polar solid dielectrics,Based on its m
13、aterial structure, this kind of dielectrics could only exist electron displacement polarization under the external electric field. Its polarizability is .,如不考虑聚合物微观结构的不均匀性（高分子聚合物中晶态和非晶态并存）和晶体介质介电常数的各向异性，非极性固体介质的有效电场 （莫索缔有效电场），介电常数与极化率的关系符合克莫方程。,If we ignore the nonuniformity (crystal state and amorp
14、hous state coexisting in polymer) of polymer microstructure and anisotropy of dielectric constant of crystal state, the relationship between effective electric field of non-polar solid dielectrics, dielectric constant, and polarizability accord with Clausius-Mosotti Equation.,2. 极性固体电介质,极性固体电介质在外电场作
15、用下，除了发生电子位移极化外，还有极性分子的转向极化。由于转向极化的贡献，使介电常数明显地与温度有关。,Polar solid dielectrics,Polar solid dielectrics exist orientation polarization of polar molecules other than displacement polarization of electrons under the external electric field. Because of the contribution of orientation polarization, it makes
16、 the dielectric constant obviously related to temperature.,2.1.2 固体电介质的损耗,在电场作用下没有能量损耗的理想介质是不存在的，实际电介质中总有一定的能量损耗，包括由电导引起的损耗和某些有损极化引起的损耗，总称为介质损耗。,2.1.2 The loss of solid dielectrics,It doesnt exist such a ideal dielectric that has no energy loss under the electric field. Actually, any dielectric has some energy loss including the loss caused by conductance and polarization with loss
