传感器原理传感器原理 (32).ppt

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1、Principle of Sensors传感器原理压电式传感器Inductive Sensors 6.1.2 压电效应机理Mechanism of piezoelectric effect 石英晶体的坐标系石英晶体的坐标系石英晶体的坐标系石英晶体的坐标系The coordinate system of quartz crystal The coordinate system of quartz crystal X X轴（电轴）：轴（电轴）：轴（电轴）：轴（电轴）：平行于相邻棱面内夹角的等分线。垂直于此轴的面上压电效应最强。X axis(electric axis):X axis(electri

2、c axis):The bisector parallel to the angle between adjacent prisms.The piezoelectric effect is strongest on the surface perpendicular to this axis.由于石英晶体的物理特性与方向有关，因此需要在晶体内选定参考方向，这种方向叫晶体轴。规定：规定：规定：规定：采用右手直角坐标系表示晶体轴的方向。Because the physical properties of quartz crystal are related to direction,it is n

3、ecessary to select a reference direction in the crystal,which is called crystal axis.Provisions:Provisions:The right-hand rectangular coordinate system is used to express the direction of crystal axis.石英晶体的坐标系石英晶体的坐标系石英晶体的坐标系石英晶体的坐标系The coordinate system of quartz crystal The coordinate system of qu

4、artz crystal Y Y轴（机械轴）：轴（机械轴）：轴（机械轴）：轴（机械轴）：垂直于六边形对边的轴线。沿该轴方向的机械形变最明显。Y axis(mechanical axis):Y axis(mechanical axis):The axis perpendicular to the opposite side of the hexagon.The mechanical deformation along this axis is the most obvious.Z Z轴（光轴）：轴（光轴）：轴（光轴）：轴（光轴）：垂直于X、Y轴的纵轴方向。沿此轴无压电效应。Z axis(opti

5、cal axis):Z axis(optical axis):The longitudinal axis direction perpendicular to X and Y axes.There is no piezoelectric effect along this axis.石英晶体压电特性石英晶体压电特性石英晶体压电特性石英晶体压电特性Piezoelectric properties of quartz crystal Piezoelectric properties of quartz crystal 当不收外力时，正、负离子正好分布在正六边形顶角上，形成三个互成120夹角的偶极矩

6、P1、P2、P3，如图（a）所示。此时正负电荷中心重合，电偶极矩的矢量和等于零，即P P1 1P P2 2P P3 30 0。When no external force is received,positive and negative ions are distributed on the vertex angle of the regular hexagon,forming three dipole moments P1,P2 and P3 at an included angle of 120,as shown in Figure(a).At this time,the positiv

7、e and negative charge centers coincide,and the vector sum of electric dipole moments is equal to zero,that is,P P1 1+P+P2 2+P+P3 3=0.=0.组成石英晶体的硅离子Si4+和氧离子O2-在Z平面投影为正六边形排列，图中“”代表Si4+，“”代表2O2-。Silicon ion Si4+and oxygen ion O2-,which make up quartz crystal,are projected in a regular hexagonal arrangem

8、ent in Z plane.In the figure,+represents Si4+and-represents 2O2-.当晶体受到沿X方向的压力作用时，电偶极矩：X方向分量为：(P(P1 1+P+P2 2+P+P3 3)X X00Y、Z方向分量为：P P1 1P P2 2P P3 30 0 When the crystal is subjected to a pressure along the X direction,the electric dipole moment:The X direction component is(P(P1 1+P+P2 2+P+P3 3)X X 0

9、0 The components in Y and Z directions are P P1 1P P2 2P P3 30 0 X X轴：正向有正电荷轴：正向有正电荷轴：正向有正电荷轴：正向有正电荷Y Y、Z Z轴：无电荷。轴：无电荷。轴：无电荷。轴：无电荷。X Axis:Positive Charge X Axis:Positive Charge in Positive Direction in Positive Direction Y,Z axes:No charge.Y,Z axes:No charge.当晶体受到沿Y方向的压力作用时，X方向分量为：（P P1 1+P+P2 2+P+P

10、3 3）X X00Y、Z方向分量为：P P1 1P P2 2P P3 30 0 When the crystal is subjected to a pressure along the Y direction,the electric dipole moment:The X direction component is(P(P1 1+P+P2 2+P+P3 3)x x0 0 The components in Y and Z directions are P P1 1P P2 2P P3 30 0 X X轴：正向有负电荷轴：正向有负电荷轴：正向有负电荷轴：正向有负电荷Y Y、Z Z轴：无电荷

11、。轴：无电荷。轴：无电荷。轴：无电荷。X-axis:Negative Charge X-axis:Negative Charge in Positive Direction in Positive Direction Y,Z axes:No charge.Y,Z axes:No charge.当晶体受到沿Z Z方向的压力方向的压力方向的压力方向的压力作用时，无压电效应。When the crystal is subjected to pressure along the Z directionthe Z direction,there is no piezoelectric effect.压电

12、陶瓷的压电效应压电陶瓷的压电效应压电陶瓷的压电效应压电陶瓷的压电效应Piezoelectric effect of piezoelectric ceramics Piezoelectric effect of piezoelectric ceramics 压电陶瓷的极化压电陶瓷的极化压电陶瓷的极化压电陶瓷的极化Polarization of piezoelectric ceramics:Polarization of piezoelectric ceramics:当压电陶瓷不受外力压电陶瓷不受外力压电陶瓷不受外力压电陶瓷不受外力时，把电压表接到陶瓷片的两个电极上进行测量时，电压表显示为零电压表

13、显示为零电压表显示为零电压表显示为零。这是因为陶瓷片内的极化强度总是以电偶极矩的形式表现出来，即在陶瓷的一端出现正束缚电荷，另一端出现负束缚电荷。由于束缚电荷的作用，在陶瓷片的电极面上吸附了一层来自外界的自由电荷。这些自由电荷与陶瓷片内的束缚电荷符号相反而数量相等，它起着屏蔽和抵消陶瓷片内极化强度对外界的作用。When piezoelectric ceramics are not subjected to external forcepiezoelectric ceramics are not subjected to external force,when the voltmeter is

14、connected to the two electrodes of the ceramic sheet for voltmeter is connected to the two electrodes of the ceramic sheet for measurement,measurement,the voltmeter shows zerothe voltmeter shows zero.This is because the polarization intensity in ceramic wafer is always expressed in the form of elect

15、ric dipole moment,that is,positive bound charge appears at one end of ceramic and negative bound charge appears at the other end.Due to the binding charge,a layer of free charge from outside is adsorbed on the electrode surface of ceramic chip.These free charges are opposite in sign and equal in num

16、ber to the bound charges in the ceramic wafer,which play a role in shielding and counteracting the polarization intensity in the ceramic wafer to the outside world.当在陶瓷片上加一个与极化方向平行的压力加一个与极化方向平行的压力加一个与极化方向平行的压力加一个与极化方向平行的压力F F，如图，陶瓷片将产生压缩形变（图中虚线），片内的正、负束缚电荷之间的距离变小，极化强度也变小。因此，原来吸附在电极上的自由电荷，有一部分被释放，而出现

17、放电现象出现放电现象出现放电现象出现放电现象。当压力撤消后，陶瓷片恢复原状(这是一个膨胀过程)，片内的正、负电荷之间的距离变大，极化强度也变大，因此电极上又吸附一部分自由电荷而出现充电现象。这种由机械效应转变为电效应，或者由机械能转变为电能的现象，就是正压电效应。When a pressure F parallel to the polarization direction a pressure F parallel to the polarization direction is applied to the ceramic chip,as shown in the figure,the c

18、eramic chip will undergo compressive deformation(dashed line in the figure),and the distance between positive and negative bound charges in the chip will become smaller,so will the polarization intensity.Therefore,part of the free charge originally adsorbed on the electrode is released,and a dischar

19、ge phenomenon occursdischarge phenomenon occurs.When the pressure is removed,the ceramic sheet returns to its original state(this is an expansion process),the distance between positive and negative charges in the sheet becomes larger,and the polarization intensity also becomes larger,so a part of fr

20、ee charges are adsorbed on the electrode and charging occurs.This change from mechanical effect to electrical effect,or from mechanical energy to electrical energy,is the positive piezoelectric effect.当在陶瓷片上加一个与极化方向相同的电场加一个与极化方向相同的电场加一个与极化方向相同的电场加一个与极化方向相同的电场，如图，由于电场的方向与极化强度的方向相同，所以电场的作用使极化强度增大。这时，陶

21、瓷片内的正负束缚电荷之间距离也增大，就是说，陶瓷片沿极化方向沿极化方向沿极化方向沿极化方向产生伸长形变产生伸长形变产生伸长形变产生伸长形变（图中虚线）。同理，如果外加电场的方向与极化方向相反，则陶瓷片沿极化方向产生缩短形变。这种由于电效应而转变为机械效应或者由电能转变为机械能的现象，就是逆压电效应。When an electric field with the same polarization direction an electric field with the same polarization direction is applied to the ceramic chip,as s

22、hown in the figure,because the direction of the electric field is the same as the direction of polarization intensity,the polarization intensity increases due to the action of the electric field.At this time,the distance between the positive and negative bound charges in the ceramic sheet also incre

23、ases,that is to say,the ceramic sheet produces elongation the ceramic sheet produces elongation deformation along the polarization directiondeformation along the polarization direction (dashed line in the figure).Similarly,if the direction of the applied electric field is opposite to the polarizatio

24、n direction,the ceramic sheet will have shortened deformation along the polarization direction.This phenomenon of changing from electrical effect to mechanical effect or from electric energy to mechanical energy is called inverse piezoelectric effect.压电陶瓷的坐标系压电陶瓷的坐标系压电陶瓷的坐标系压电陶瓷的坐标系Coordinate system of piezoelectric ceramics:Coordinate system of piezoelectric ceramics: