Direct dielectric breakdown

Direct Dielectric Breakdown. All insulating materials, including dielectric elastomers, present trade-offs between maximum applied field strength and application lifetime. In a dielectric transducer, electric field breakdown will occur as the field across the dielectric elastomer is increased. Material choices and geometry can also influence electric breakdown phenomena. For example, sharp metal edges can cause higher electric fleld concentrations and exacerbate electric breakdown. However, in dielectric elastomers, electric breakdown is often a symptom of some other type of failme rather than the cause. 

The piezoelectric response investigation also provides direct evidence that significant inelastic deformation and defect generation can occur well within the elastic range as determined by the Hugoniot elastic limit. In quartz, the Hugoniot elastic limit is 6 GPa, but there is clear evidence for strong nonideal mechanical and electrical effects between 2.5 and 6 GPa. The unusual dielectric breakdown phenomenon that occurs at 800 MPa under certain... 

ASTM D3755, 1997 (2004). Standard test method for dielectric breakdown voltage and dielectric strength of electrical insulating materials under direct voltage stress. 

The second group consists of properties that are important at very high electric field strengths, such as electric discharge, dielectric breakdown and arc resistance. They may be regarded as the ultimate electrical properties. Properties of the first group are directly related to the chemical structure of the polymer those of the second are greatly complicated by additional influences in the methods of determination. 

Until recently, little attention has been given to the dielectric breakdown strength of lead azide values reported in the literature vary from 20 to 300 kV/cm. Past studies were primarily directed to the dependence of the dielectric strength on such factors as sample thickness, density, temperature, etc. Little attention was given to the type or shape of electrode, the electrode material, or the degree of contact between sample and electrodes. Thus the measured dielectric strength was determined by the conditions of the measurement, which were usually different for each investigation. 

Dielectric breakdown The conversion of an insulating dielectric material to an electrically conductive material, typically as a direct result of high applied electric field. 

N. Heylen, Y. Li, K. KeUens, Y. Travaly, G. Vereecke, H. Volders, Z. Tokei, J. Versluijs, J. Rip, E. Van Besien, L. CarboneU, G.P. Beyer, Post-direct-CMP dielectric surface copper contamination quantitative analysis and impact on dielectric breakdown behavior, in Proc. Adv. Metall. Conf, 2008, pp. 415—421. 

A tightly structured polymer such as a crystalline polyester or a highly crosslinked polymer where the polar elements can be directly affected by the field by rotation but cannot move far from the equilibrium position does absorb energy from the field and heat to some extent. The restricted motion reduces the effect and these materials show much lower dielectric losses and generally are quite resistant to dielectric breakdown in the A.C. fields. The polyethylene terephthalate polymer films (some of the most resistant to dielectric breakdown of the commonly used plastics insulating materials), are used in a highly oriented and crystalline form which has the tightest structure and restricts molecular freedom to the maximum extent. 

The dielectric strength is the direct current voltage between two electrodes at which dielectric breakdown occurs and is an indicator of how good an insulator the material is. The voltage is increased until the material breaks down, there is an arc across the electrodes and substantial current flows. 

As indicated above, when a positive direct current is impressed upon a piece of titanium immersed in an electrolyte, the consequent rise in potential induces the formation of a protective surface film, which is resistant to passage of any further appreciable quantity of current into the electrolyte. The upper potential limit that can be attained without breakdown of the surface film will depend upon the nature of the electrolyte. Thus, in strong sulphuric acid the metal/oxide system will sustain voltages of between 80 and 100 V before a spark-type dielectric rupture ensues, while in sodium chloride solutions or in sea water film rupture takes place when the voltage across the oxide film reaches a value of about 12 to 14 V. Above the critical voltage, anodic dissolution takes place at weak spots in the surface film and appreciable current passes into the electrolyte, presumably by an initial mechanism involving the formation of soluble titanium ions. 

The resistance of most plastics to the flow of direct current is very high. Both surface and volume electrical resistivities are important properties for applications of plastics insulating materials. The volume resistivity is the electrical resistance of the material measured in ohms as though the material was a conductor. Insulators will not sustain an indefinitely high voltage as the applied voltage is increased, a point is reached where a drastic decrease in resistance takes place accompanied by a physical breakdown of the insulator. This is known as the dielectric strength, which is the electric potential in volts, which would be necessary to cause the failure of a 1/8-in. thick insulator (Chapter 4, ELEC-TRICAL/ELECTR ONICS PRODUCT). 

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