Dielectric materials, electrical properties

Pradhan, D.K., R. Choudhary, andB. Samantaray, Studies of dielectric and electrical properties of plasticized polymer nanocomposite electrolytes. Materials Chemistry and Physics, 2009.115(2) 557-561. 

The dielectric constant is concerned with the electrical properties of a material. The dielectric constant for a solid is a 3 x 3 matrix with different components according to the Cartesian axes. These elements are given by ... 

Electrica.1 Properties. The bulk electrical properties of the parylenes make them excellent candidates for use in electronic constmction. The dielectric constants and dielectric losses are low and unaffected by absorption of atmospheric water. The dielectric strength is quoted for specimens of 25 p.m thickness because substantially thicker specimens cannot be prepared by VDP. If the value appears to be high in comparison with other materials, however, it should be noted that the usual thickness for such a measurement is 3.18 mm. Dielectric strength declines with the square root of increasing... 

Applications. For use as a gaseous dielectric, other specific properties are needed in addition to high breakdown strength, and a compromise must be made between electrical and mechanical requirements. Desirable properties include low toxicity, thermal stabiUty toward materials of constmction. 

Electrical Insulation. The substitution of a gas for part of a soHd polymer usuaUy results in large changes in the electrical properties of the resulting material. The dielectric constant, dissipation factor, and dielectric strength are aU generaUy lowered in amounts roughly proportional to the amount of gas in the foam. 

Two parallel plates of conducting material separated by an insulation material, called the dielectric, constitutes an electrical condenser. The two plates may be electrically charged by connecting them to a source of direct current potential. The amount of electrical energy that can be stored in this manner is called the capacitance of the condenser, and is a function of the voltage, area of the plates, thickness of the dielectric, and the characteristic property of the dielectric material called dielectric constant. 

For coaxial cables, the following electrical properties related to the dielectric constant of the core material and the dimensions determine the quaUty of the signal impedance, capacitance, attenuation, crosstalk, and time delay and velocity of propagation. 

R. Bartnikas, "Engineering Dielectrics Vol. II A—Electrical Properties of SoHd Insulating Materials Molecular Stmcture and Electrical Behavior," ASTM Special Technical Publication 783, 1983, Chapts. 1—5, pp. 3—515. 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

Semiconductors (qv) are materials with resistivities between those of conductors and those of insulators (between 10 and 10 H-cm). The electrical properties of a semiconductor determine the hmctional performance of the device. Important electrical properties of semiconductors are resistivity and dielectric constant. The resistivity of a semiconductor can be varied by introducing small amounts of material impurities or dopants. Through proper material doping, electron movement can be precisely controlled, producing hmctions such as rectification, switching, detection, and modulation. 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

Barium titanate has widespread use ia the electronics iadustry. Its high dielectric constant and the ease with which its electrical properties can be modified by combination with other materials make it exceptionally suitable for a variety of items, ie, miniature capacitors (see Ceramics as electrical materials). 

Dielectric Constant, Power Factor and Structure 111 Table 6.1 Typical electrical properties of some selected plastics materials at 20°C... 

Electrical Properties Traditionally plastics have established themselves in applications which require electrical insulation. PlFt and polyethylene are among the best insulating materials available. The material properties which are particularly relevant to electrical insulation are dielectric strength, resistance and tracking. 

Capacitance (C) is the property that describes the quantity of electricity that can be stored when two conductors are separated by a dielectric material. The unit of capacitance is the farad. The capacitance of two equal-area, conducting parallel plates (see Figure 2-64) separated by a dielectric is given by... 

The early development of modern plastic materials (over a century) can be related to the electrical industry. The electronic and electrical industry continues to be not only one of the major areas for plastic applications, they are a necessity in many applications worldwide (2,190). The main reasons is that plastic designed products are generally basically inexpensive, easily shaped, fast production dielectric materials with variable but controllable electrical properties, and jn most cases the plastics are used because they are good insulators (Chapter 5, ELECTRICAL PROPERTY). 

A number of areas in which plastics are used in electrical and electronic design have been covered there are many more. Examples include fiber optics, computer hardware and software, radomes for radar transmitters, sound transmitters, and appliances. Reviewed were the basic use and behavior for plastics as an insulator or as a dielectric material and applying design parameters. The effect of field intensity, frequency, environmental effects, temperature, and time were reviewed as part of the design process. Several special applications for plastics based on intrinsic properties of plastics materials were also reviewed. 

The moisture content of a plastic affects such conditions as electrical insulation resistance, dielectric losses, mechanical properties, dimensions, and appearances. The effect on the properties due to moisture content depends largely on the type of exposure (by immersion in water or by exposure to high humidity), the shape of the product, and the inherent behavior properties of the plastic material. The ultimate proof for tolerance of moisture in a product has to be a product test under extreme conditions of usage in which critical dimensions and needed properties are verified. Plastics with very low water-moisture absorption rates tend to have better dimensional stability. 

FIG. 1 Schematic representation of the operation of the scanning polarization force microscope (SPFM). An electrically biased AFM tip is attracted toward the surface of any dielectric material. The polarization force depends on the local dielectric properties of the substrate. SPFM images are typically acquired with the tip scanning at a height of 100-300 A. (From Ref. 32.)... 

Dielectric analysis (DEA) measures the electrical properties of a material as it is subjected to a periodic electric field under various conditions. This technique provides quantitative information on the capacitance and conductance of the ma-... 

Poly(tetrafluoroethylene) (PTFE), which is also known by DuPont s trade-name Teflon, is a solid at room temperature and has a dielectric constant in the range of 2.00-2.08, while its monomer, tetrafluoroethylene, is a gas at room temperature. PTFE is exceptionally chemically inert, has excellent electrical properties and outstanding stability, and retains its mechanical properties at high temperatures. The problem with PTFE is that it is not processable. A family of commercial polymeric materials known as Teflon AF is believed to be a... 

The main objective of the work to be described here is to design and synthesize new organic dielectric materials, and to develop new techniques to deposit these materials as thin, thermally stable films with very low dielectric constants, for use as ILDs. New dielectric materials must not only possess proper electrical, thermal, and mechanical properties but should also minimize or eliminate the use of solvents in this era of concern for environmental pollution. 

Polystyrene can be exceptionally crosslinked, leading to a tough and transparent material with improved electrical and thermal properties used as a dielectric material. Table 4.34 displays examples of crosslinked polystyrene properties. The data cannot be used for designing. 

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