Changes
*Wire Currents
A volume current group is characterized by the three components of the current density vector, Jx, Jy and Jz, having units of A/m<sup>2</sup>. You learned about volume current sources in Tutorial Lesson 4. Under a volume current group, you can draw any solid geometric objects such as box, cylinder, cone, <i>etc</i>. A wire current is used to approximate a current filament, that is a current source flowing through a line or curve with a specified finite radius. A wire current group is characterized by its total current (I) having units of Amperes. In [[EM.Ferma]], only line and polyline objects can support wire currents. Under a wire current group, you can define any curve geometric object. However, before running a magnetostatic simulation, the program warns that all the curve object will be polygonized and replaced with polyline objects.
Since the governing differential equations only recognize the volume current density '''J''', and not I, as a valid source, [[EM.Ferma]] takes the linear current along a wire current source and converts it to a volume current density defined as
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The definition of the three coordinate functions X(t), y(t) and z(t) also involves variables like "major_rad", "minor_rad", "height", <i>etc</i>. which you saw earlier in the variables dialog. To preserve the parameterization of your solenoid object, you should change its properties from the variables dialog rather than directly from its property dialog.
{{Note| CubeCAD's curve generator always creates polyline objects. Unlike ordinary polylines that are characterized by their node sets, the ones created by the curve generator are characterized by mathematical expressions or Python functions.}}
== Building & Analyzing a Toroidal Coil ==
You may want to start a new blank project for this part of the tutorial lesson. You are going to create the geometry of a toroidal helix coil using one of [[EM.Cube]]'s convenient wizards. To do so, click on the <b>Coil Wizard</b> [[Image:CoilWizardIconx.png]] button of the Wizard Toolbar or select the menu item '''Tools → Component Wizards → Toroidal Coil'''.
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The geometry of a toroidal helix coil with a circular cross section appears at the center of the project workspace, and its name is added under a new group item called "WIRE_CURRENT" in the navigation tree. The wire current group has the same properties as in the last part.
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Open the property dialog of your coil object and examine the definition of toroidal helix coil in Curve Generator. The parameter "major_rad" determines the major radius of the torus. The cross section of this curve in a generalized super-quadratic curve with two horizontal and vertical radii: "minor_rad_h" and "minor_rad_v". The parameter t varies from zero to 2π. For this project, you reduced the value of the variable "step" to 0.0025 to create a smoother polyline.
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<td> [[Image:Ferma L5 Fig24B.png|thumb|left|640px|The properties of the toroidal helix coil shown in CubeCAD's curve generator.]] </td>
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