Group 7 Report (Module 11 for group 7).pptx

Module 11

1. GROUP INFORMATION GROUP : 7 TOPIC: ELECTRICAL PROPERTIES AND DIELECTRICAL BEHAVIOR MEMBERS : Elevado, Edgar Jr. M. (1 st Presentor ) Espinosa, Joemary C. (2 nd Presentor ) Florendo, Justin (3 rd Presentor ) Ganal , Ceejay (4 th Presentor ) Jervoso , Frence Jarvy (5 th Presentor )

2. ELECTRICAL PROPERTIES AND DIELECTRICAL BEHAVIOR MODULE 11

3. OHM’S LAW Georg Simon Ohm – German physicist who discovered the law, named after him, which states that the current flow through a conductor is directly proportional to the voltage and inversely proportional to the resistance V=IR w here: V = Voltage (V) I = Current (A) R = Resistance (Ω)

4. OHM’S LAW

5. OHM’S LAW Ohm’s Law Triangle

6. OHM’S LAW Problem 1: What is the voltage in a circuit if the current is 2mA and the resistance is 1000 Ω ? Answer: 2V

7. OHM’S LAW Problem 2: What is the current in a circuit if the voltage is 2 V and the resistance is 1000 Ω ? Answer: 2mA

8. OHM’S LAW Problem 3: What is the resistance in the circuit if the voltage is 2 V and the current is 2mA? Answer: 1000 Ω

9. ELECTRICAL RESISTIVITY Electrical resistivity is a fundamental property of a material that measures how strongly it resists electric current. Its unit is Ωm . where: R = Resistance = Resistivity of the material L = Length of Conductor A = Cross Section Area

10. ELECTRICAL RESISTIVITY Resistance formula Unit for Resistivity Resistivity formula

11. ELECTRICAL RESISTIVITY

12. ELECTRICAL CONDUCTIVITY Electrical conductivity is the measure of the amount of electrical current a material can carry or it's ability to carry a current . It is the reciprocal of electrical resistivity. Its unit is . where : = Resistivity of the material σ = electrical conductivity  

13. ELECTRICAL CONDUCTIVITY

14. Current   density   is the product of electrical conductivity and electric field intensity. Also, it is the ratio of current per unit area of cross section perpendicular to flow in a region through which an electric current is flowing . where : J = Current Density σ = Electrical Conductivity E = Electric Field Intensity CURRENT DENSITY Where: I = Current A = Specimen Area Note : E = Where: V = Voltage difference between two points l = Distance separating the two points  

15. CURRENT DENSITY

16. CLASSIFICATIONS OF SOLID MATERIALS CONDUCTORS Metals have conductivities on the order of SEMICONDUCTORS Semiconductors have intermediate conductivities ranging between to INSULATORS Insulators have low conductivities ranging between to Note: Insulation can fail in a variety of ways, if voltage gets too high and exceeds the " breakdown voltage " electrons will get excited to the point where they break out of their stable orbit, current will then pass through the material and often destroy the insulator.  

17. ELECTRIC CURRENT An electric current results from the motion of electrically charged particles in response to forces that act on them from an externally applied electric field.

18. ELECTRIC CURRENT Within most solid materials a current arises from the flow of electrons, which is termed electronic conduction. For ionic materials, a net motion of charged ions is possible that produces a current; such is termed ionic conduction .

19. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS Free electrons – ( negatively charged) electrons that are in random continuous motion and participate in the conduction process. However, when connected to a battery, these free electrons will flow opposite to the direction of the electric field instead of random motion. With E lectric Field No Electric Field

20. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS Hole – ( positively charged) found in semiconductors and insulators. Once an electron travels, a hole is created. A hole is considered to have a charge that is of the same magnitude as that for an electron, but of opposite sign ( 1.6x C ).  

21. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS Fermi L evel – named after the Physicist, Enrico Fermi . Fermi level is t he highest energy level that an electron can occupy at the absolute zero temperature 0K .   It lies between the valence band and conduction band because at absolute zero temperature the electrons are all in the lowest energy state .

22. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS Fermi energy – is the value of the Fermi level at absolute zero temperature 0K or (−273.15 degrees Celsius, or -459.67 Fahrenheit) . It is also the maximum kinetic energy an electron can attain at 0K . Fermi energy is constant for each solid.

23. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS Band gap – the distance between the valence band of electrons and the conduction band. It r epresents the minimum  energy that is required to excite an electron up to a state in the conduction band where it can participate in conduction. The size and existence of this band gap allows one to visualize the difference between  conductors, semiconductors, and insulators.

24. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS There are four possible band configurations: Partially Filled Bands (metals/conductors) Overlapping Bands (metals/conductors) Semiconductors - narrow band gap (< 2 eV ) note: eV = electron Volt - more electrons excited across band gap d. Insulators - wide band gap (> 2 eV) - few electrons excited across band gap

25. a b c d

26. ELECTRON MOBILITY Electron Mobility – characterizes how quickly an electron can move through a metal or semiconductor when pulled by an electric field. In other words, it is simply the frequency of scattering events. It is represented by .

27. ELECTRON MOBILITY When a conductor is connected to a voltage source, an electric field is applied. As a result, a force is brought to bear on the free electrons ; as a consequence, they all experience an acceleration in a direction opposite to that of the field , by virtue of their negative charge .

28. ELECTRON MOBILITY Free electrons ( negative charge ) move in opposite direction of that of the electric field when a conductor is connected to a voltage source.

29. ELECTRON MOBILITY The scattering of the free electrons will depend on the property of a material . A semiconductor virtually behaves like an insulator at low temperatures . However, at room temperature , some free electrons cross over to the conduction band giving little conductivity to the semiconductor In insulators ,  f ree  electrons  cannot freely move due to very low conductivity . The scattering phenomenon is manifested as a resistance to the passage of an electric current. Several parameters are used to describe the extent of this scattering, these include the drift velocity and the mobility of an electron .

30. ELECTRON MOBILITY Drift velocity - The drift velocity represents the average electron velocity in the direction of the force imposed by the applied field.

31. ELECTRON MOBILITY Drift speed of electrons is less when compared with its speed in random motion (no electric field). With E lectric Field No E lectric Field

32. ELECTRON MOBILITY Formula for Drift Velocity: where: = drift velocity ( ) = electron mobility ( ) = electric field ( )

33. ELECTRON MOBILITY

34. ELECTRON MOBILITY Formula for conductivity (with electron mobility): where: = electrical conductivity = number of free electrons = absolute magnitude of electrical charge = electron mobility ( )

35. ELECTRON MOBILITY

36. ELECTRICAL RESISTIVITY OF METALS

37. ELECTRICAL RESISTIVITY OF METALS

38. ELECTRICAL RESISTIVITY OF METALS MATTHIESSEN’S RULE — for a metal, total electrical resistivity (p) equals the sum of thermal, impurity, and deformation contributions. P = Pthermal + Pimpurity + Pdeformation

39. ELECTRICAL RESISTIVITY OF METALS

40. INFLUENCE OF TEMPERATURE For the pure metal and all the copper–nickel alloys shown in Figure 12.8, the resistivity rises linearly with temperature above about 200C.

41. INFLUENCE OF TEMPERATURE Formula for Thermal Resistivity: Where: = Thermal Resistivity & = Constants for each metal = Temperature Note : Thermal resistivity is dependent on temperature so they are directly proportional with each other.

42. INFLUENCE OF IMPURITIES Impurities will distort the crystal lattice, hence impeding the drift velocity. Therefore , the electrical resistivity increases as impurities in a conductor increase.

43. INFLUENCE OF IMPURITIES Formula for additions of a single impurity that forms a solid solution: Where: = Impurity Resistivity = composition-independent constant that is a function of both the impurity and host metals. = impurity concentration ci in terms of the atom fraction (at %/100) Formula for a two-phase alloy consisting of α and β phases , a rule-of-mixtures expression may be utilized to approximate the resistivity as follows : Where: V ’s and ρ ’s = represent volume fractions and individual resistivities for the respective phases

44. INFLUENCE OF PLASTIC DEFORMATION Plastic deformation increases the electrical resistivity of a material as a result of increased numbers of electron-scattering dislocations .

45. INFLUENCE OF PLASTIC DEFORMATION The effect of deformation on resistivity is also represented in Figure 12.8.

46. SEMI CONDUCTIVITY Electrical conductivity of the semiconducting materials is not as high as that of the metals. The electrical properties of these materials are extremely sensitive to the presence of even minute concentrations of impurities .

47. SEMI CONDUCTIVITY Two types of semiconductors: Intrinsic Semiconductors are those in which the electrical behavior is based on the electronic structure inherent in the pure material. Extrinsic Semiconductors Electrical characteristics are dictated by impurity atoms

48. INTRINSIC SEMICONDUCTORS

49. INTRINSIC SEMICONDUCTION IN TERMS OF ELECTRON AND HOLE MIGRATION Hole is an electric charge carrier with a positive charge , equal in magnitude but opposite in polarity  to the charge on the electron

50. INTRINSIC SEMICONDUCTION IN TERMS OF ELECTRON AND HOLE MIGRATION

51. INTRINSIC SEMICONDUCTION IN TERMS OF ELECTRON AND HOLE MIGRATION e e e

52. NUMBER OF CHARGE CARRIERS

53. ESTIMATING CONDUCTIVITY

54. CHARGE CARRIERS IN INSULATORS AND SEMICONDUCTORS

55. INTRINSIC SEMICONDUCTORS: CONDUCTIVITY VS. TEMPERATURE

56. INTRINSIC VS. EXTRINSIC CONDUCTION

57. EXTRINSIC SEMICONDUCTORS: CONDUCTIVITY VS. TEMPERATURE DOPING Doping - is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties

58. EXTRINSIC SEMICONDUCTORS: CONDUCTIVITY VS. TEMPERATURE

59. SEMICONDUCTOR DEVICES Semiconductor device (or Solid-state device) - is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. It's Conductivity lies between conductors and Insulators Diodes Transistors

60. SEMICONDUCTOR DEVICES Advantages of semiconductor devices: small size, low power consumption, and no warmup time

61. THE p-n RECTIFYING JUNCTION Allows flow of electrons in one direction only (e.g., useful to convert alternating current to direct current ) P stands for Positive , which means the semiconductor is rich in holes or Positive charged ions N stands for Negative and N-type semiconductors have Negative charged ions or in other words have excess electrons

62. THE p-n RECTIFYING JUNCTION Allows flow of electrons in one direction only (e.g., useful to convert alternating current to direct current ) P stands for Positive , which means the semiconductor is rich in holes or Positive charged ions N stands for Negative and N-type semiconductors have Negative charged ions or in other words have excess electrons

63. THE p-n RECTIFYING JUNCTION

64. PROPERTIES OF RECTIFYING JUNCTION

65. THE TRANSISTOR Transistor – also called as “ transfer-resistor ”, is a small electronic component with two main functions: 1. Switch circuits on and off 2. Amplify signals Two major types of transistor: Junction (or bimodal) transistor Metal-oxide-semiconductor field-effect ( MOSFET )

66. THE TRANSISTOR Switch circuits on and off Amplify Signals

67. DIELECTRIC BEHAVIOR Dielectric  is another word for insulator . A dielectric material is one that is electrically insulating (nonmetallic) and exhibits or may be made to exhibit an electric dipole structure; that is, there is a separation of positive and negative electrically charged entities on a molecular or atomic level . When a dielectric is placed between the plates of a capacitor, it increases its capacitance

68. CAPACITANCE Capacitance – is the ability of a component or circuit to collect and store energy in the form of an electrical charge . Current does not pass through capacitors. It's the electrons attraction of the inverted flow, so there is not real electron flow inside the capacitor .

69. CAPACITANCE There are three formulas for finding the capacitance : Where: C = capacitance (Farads, F) Q = charge ( Coulumbs , C) V = the voltage applied across the capacitor A = represents the area of the plates l = the distance between the plates = the permittivity of a vacuum (8.85 x F/m ) ε = the permittivity of this dielectric medium (greater in magnitude than )  

70. CAPACITANCE Formula for relative permittivity (or dielectric constant ): Where: = relative permittivity or dielectric constant = the permittivity of a vacuum (8.85 x F/m) ε = the permittivity of this dielectric medium (greater in magnitude than )  

71. The dielectric constant is one material property that is of prime consideration for capacitor design . The values of a number of dielectric materials are contained in Table 11.2  

72. FIELD VECTORS AND POLARIZATION Dipole = di + pole Di = two Pole = rounded object Electric Dipole – is pair of point charge with equal magnitude and opposite in sign separated by a distance Electric Dipole Moment (p) – is a measure of the separation of positive and negative   electrical charges  within a system. A vector that is directed from negative to positive . Where: q = magnitude of each dipole charge d = distance of separation between them

73. FIELD VECTORS AND POLARIZATION In the presence of an electric field, which is also a vector quantity, a force (or torque) will come to bear on an electric dipole to orient it with the applied field; The process of dipole alignment is termed polarization. Electric Field No Electric Field

74. FIELD VECTORS AND POLARIZATION Again, returning to the capacitor, the surface charge density D (also called dielectric displacement ), or quantity of charge per unit area of capacitor plate (C/ ), is proportional to the electric field E . When a vacuum is present, then the constant of proportionality being . Furthermore, an analogous expression exists for the dielectric case ; that is ,  

75. TYPES OF POLARIZATION There are four types of polarization: Electronic Polarization Ionic Polarization Orientation Polarization Space Charge Polarization

76. TYPES OF POLARIZATION 1. Electronic Polarization Electronic polarization may be induced to one degree or another in all atoms. It results from a displacement of the center of the negatively charged electron cloud

77. TYPES OF POLARIZATION 2. Ionic Polarization Ionic polarization occurs only in materials that are ionic . An applied field acts to displace cations (+ charge) in one direction and anions (- charge ) in the opposite direction , which gives rise to a net dipole moment.

78. TYPES OF POLARIZATION 3 . Orientation Polarization Orientation polarization results from a rotation of the permanent moments into the direction of the applied field . It is found only in substances that possess permanent dipole moments .

79. TYPES OF POLARIZATION 3 . Orientation Polarization The total polarization P of a substance is equal to the sum of the electronic, ionic , and orientation polarizations ( Pe , Pi, and Po, respectively), or

80. TYPES OF POLARIZATION 4. Space Charge Polarization Also called ‘Interfacial’ or  space charge polarization  occurs when there is an accumulation of charge  at an interface between two materials or between two regions within a material because of an external field.

81. FREQUENCY DEPENDENCE OF THE DIELECTRIC CONSTANT Relaxation Frequency – The frequency at which the  dielectric loss factor reaches a maximum , for a dielectric material that has no static ( d.c. ) conductivity and that is subjected to an alternating electromagnetic field. Dielectric Loss – is the absorption of electrical energy by a dielectric material that is subjected to an alternating electric field. A low dielectric loss is desired at the frequency of utilization .

82. FREQUENCY DEPENDENCE OF THE DIELECTRIC CONSTANT Silicone rubber is usually a good choice for a buffer layer due to its very low dielectric loss  factor , high  dielectric constant, good mechanical properties, high  dielectric strength, and durability after many welds .

83. DIELECTRIC STRENGTH Dielectric Strength also known as “ breakdown strength ”, represents the magnitude of an electric field necessary to produce breakdown.

84. DIELECTRIC STRENGTH Dielectric Breakdown – happens when very high electric fields are applied across dielectric materials which may suddenly excite large numbers of electrons to energies within the conduction band. As a result, the current through the dielectric by the motion of these electrons increases dramatically ; sometimes localized melting , burning , or vaporization produces irreversible degradation and perhaps even failure of the material.

85. DIELECTRIC STRENGTH If Voltage exceeds 250V Maximum Working Voltage: 250V Melted Capacitor Burnt Capacitor

86. DIELECTRIC MATERIALS A number of ceramics and polymers are used as insulators and/or in capacitors . Many of the ceramics, including glass, porcelain, steatite, and mica , have dielectric constants within the range of 6 to 10 (Table 11.2).

87. DIELECTRIC MATERIALS These materials also exhibit a high degree of dimensional stability and mechanical strength . Typical applications include power line and electrical insulation , switch bases , and light receptacles . Power line and electrical insulation Lightbulb socket switch base Light receptacles

88. DIELECTRIC MATERIALS The titania (TiO2) and titanate ceramics, such as barium titanate (BaTiO3) , can be made to have extremely high dielectric constants , which render them especially useful for some capacitor applications .

89. DIELECTRIC MATERIALS The dielectric loss is increased by the following factors: 1 . high frequency of the applied voltage 2 . high value of the applied voltage 3 . high temperature 4 . humidity

90. OTHER ELECTRICAL CHARACTERISTICS OF MATERIALS Ferroelectricity The group of dielectric materials called ferroelectrics exhibit spontaneous polarization – that is, polarization in the absence of an electric field. Electric dipoles in a Ferroelectric material with no electric field Electric dipoles in a Ferroelectric material with electric field

91. OTHER ELECTRICAL CHARACTERISTICS OF MATERIALS 2. Piezoelectricity Piezoelectricity is also called as “ pressure electricity .” It’s polarization is induced and an electric field is established across a specimen by the application of external forces . Examples of Piezoelectric Material Piezoelectric materials include titanates of barium and lead, lead zirconate (PbZrO3 ), ammonium dihydrogen phosphate (NH4H2PO4 ), and quartz. Buzzer Piezo plate

92. End of presentation. Thank you!