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Electrical Field in Materials
Published in Ahmad Shahid Khan, Saurabh Kumar Mukerji, Electromagnetic Fields, 2020
Ahmad Shahid Khan, Saurabh Kumar Mukerji
Figure 8.2b illustrates a current in the distributed form over a surface of a conductor of finite length and breadth. This current is confined to a vanishingly small thickness. This distributed form of the current is referred to as surface current density. It is denoted by letter K, which is taken as a vector quantity. This current density may be uniform or non-uniform and is measured in ampère per meter (A/m). At a given point P on the surface, the surface current density is defined as follows:K=deflimΔL→0ΔIΔLa
Nuclear Magnetic Resonance
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Superconducting magnets on NMR spectrometers consist of a solenoid wound with superconducting wire, which comprises the fundamental design of every high-frequency NMR magnet [24]. The superconducting elements of the wire are a niobium-titanium alloy (NbTi) embedded in a copper matrix and produce field strengths up to 9.4 T (400 MHz). The copper is used because it has high resistance compared to the superconductor that is carrying the current. Higher m agnetic fields, 11.7 T (500 MHz) and above, use niobium-tin (Nb3Sn) alloy wire. This alloy has the flexibility and tensile strength to allow precise winding into a solenoid form and is more expensive due to its brittle nature making it difficult to wind relative to the NbTi wire. Hence, strength of the magnetic field is determined by the current density contained in the superconducting coil. The higher the current density, the higher is the magnetic field. Commercially produced superconducting magnets have 1H Larmor frequencies ranging from 100 to 1000 MHz.
Medium Voltage Phase Overcurrent Feeder Protection
Published in Ramesh Bansal, Power System Protection in Smart Grid Environment, 2019
Martin J. Slabbert, Raj Naidoo, Ramesh Bansal
Resistance in terms of Ohm’s law is defined as voltage (V) divided by current [31]. Ohm’s law take a holistic view on a conducting material. This means that the current passing through a conducting material is dependent on the potential difference between the two ends of the conducting material and then the resistance of this conducting material between the two ends. If the length of the material increases, the resistance will increase. The resistance is thus proportional to the length (L) of the conducting material. When the effect of current within a material conducting the current is considered, it can be defined in terms of resistivity (ρ) [31]. The resistivity of a conducting material can be calculated by dividing the electric field (E) with the current density in a vector format [31]. Current density has units of ampere per square meter. Thus, if the area (A) of the conducting material is increased, the resistivity will decrease if the electric field is kept constant. Conductivity (σ) is a measure of how good the conducting material is (e.g., wood vs. gold as a conductor) and this is the reciprocal of the resistivity [31]. Resistivity is dependent on the type of material used in the conductor and resistance is a property of the conductor itself [31]. The link between resistance and resistivity is defined by Equation (6.13) [31,33,34]. () R=ρLA
Effect of electro-codeposition parameters on particle incorporation in Ni-CrAlY(Ta) coatings
Published in Materials and Manufacturing Processes, 2021
Current density is one of the most important process parameters in conventional electroplating, which not only governs the coating deposition rate but also affects the coating quality. For electro-codeposition, the relationship between current density and particle incorporation varies, depending on the characteristics of particles, the type of metal matrix, and other process parameters such as agitation.[10,23] In some cases (e.g., Cr in Ni,[24] SiC in Ni,[25] etc.), the quantity of incorporated particles increase or decrease monotonically with the current density. In other cases (e.g., Ni-W/diamond[26] and Cu-SiC[27]), when the current density is increased, one or multiple peaks of particle incorporation have been observed.
Investigation of electrodeposited copper layer with island twinning structure on Zr substrate
Published in Surface Engineering, 2023
Meysam Karimi, Ali Hadipour, Masoud Araghchi, Amir Razazzadeh
In the copper electroplating process on zirconium substrate, zirconium is used as the cathode and copper as the anode. Inert anodes such as platinum and graphite can also be used. A conductive solution containing copper ions is also used as the ion transfer medium for the formation of the copper layer. The copper layer will be made in a solution containing the copper ions (copper sulfate) using the reduction of copper ions on the zirconium substrate. Due to the very negative standard potential of zirconium, as soon as it is placed in the plating solution, an oxide layer is quickly formed on it. Despite this layer, the formation of the copper layer becomes complicated [10,12–16]. On the other hand, the difference in the FCC structure of copper (Face Centered Cubic) and the HCP structure of zirconium (Hexagonal Close-Packed) causes physical changes in the copper layer such as atomic order, lattice strain, etc. Therefore, plating parameters will play an important role in copper coating properties. One of the most important parameters is the current density. In most studies, the optimal current for copper plating is 0.5–6 A/dm2. By increasing the coating current density, due to the increase in the speed of anodic and cathodic reactions, hydrogen gas molecules can form on the cathode and transfer into the coating so, the possibility of forming microscopic cracks will increase. On the other hand, with the increase in coating current density, the crystallite size decreases, and the hardness of the material increases. Therefore, there will be an optimal current density to create a copper layer according to the type of substrate [10,12,17–18].
Numerical and outdoor experimental study on active snow melting of conductive rubber composites in roads
Published in Road Materials and Pavement Design, 2023
Shuanye Han, Haibin Wei, Boyu Jiang, Hongwei Wang, Jinhao Chen
The snow melting energy is provided by an external power source. The power supply is controlled by a transformer to ensure a stable voltage. The current density at the electrically insulated position can be calculated as follows (COMSOL, 2016): where is the current density, A/m2.