Characteristic Parameters of a Coaxial Cable
Electrical cables, also called transmission lines, are used everywhere in the modern world to transmit both power and data. These cables carry electromagnetic energy, but instead of dealing with the full complexity of the electromagnetic fields, they are more commonly classified according to parameters such as capacitance, inductance, and impedance. In this model of a coaxial cable, we ...
Optimizing Coils
Several different approaches to optimizing a ten-turn axisymmetric coil are presented. First, the current in each turn is adjusted with the objective of having a uniform magnetic flux density along the centerline. Second, the currents are adjusted to minimize power dissipation with a constraint on field minimum at a point. Third, the currents are adjusted to minimize the gradient in the ...
Electromagnetic Plunger with Stopper
This is a transient model of an electromagnetic plunger with stopper restricting the linear motion. The model consists of a magnetic core, nonmagnetic guider, multi-turn coil, nonmagnetic stopper/blocker, and magnetic plunger attached to the spring and damper at the far end. The electromagnetic force on the plunger due to the transient current in the coil is calculated using the Maxwell stress ...
Iron Sphere in a 60 Hz Magnetic Field
An iron sphere is exposed to a spatially uniform, sinusoidally time-varying, background magnetic field. The frequency of the field is low enough such that the skin depth is larger than the radius of the sphere. A reduced field formulation is used to impose the background field. Two approaches for solving this problem are shown. The induced currents in the sphere and the perturbation to the ...
Magnetically Permeable Sphere in a Static Magnetic Field
A sphere of relative permeability greater than unity is exposed to a spatially uniform static background magnetic field. Two formulations are used to solve this problem, and the differences between these are discussed. The field strength inside the sphere is computed and compared against the analytic solution.
A Geoelectrical Forward Problem
The classical forward problem of geoelectrics (includes electrical resistivity tomography, ERT and earlier techniques as vertical electric sounding, VES) is the calculation of potentials at a given set of electrodes (M,N) while current is injected at other electrodes (A,B) into the ground. Typically the physical domain (earth) is unbounded to the sides and the bottom because of which one needs ...
An RFID System
RFIDs are used in a multitude of applications such as tracking or identifying consumer products and their packaging. An RFID system consists of two main parts: A tag or transponder with a printed circuit-board (PCB) antenna A reader unit with a larger RF antennaThe reader antenna generates an electromagnetic field that energizes a chip (IC-circuit) inside the tag. The electromagnetic field ...
External Material, AC/DC Module, General HB/BH relation
The AC/DC magnetic interfaces now support material models defined in external C code. A new way to specify user-defined material models is included in COMSOL Multiphysics version 5.2. You can now access external material functions, written in C code, which have been compiled into a shared library. By writing a wrapper function in C code, you can also use material functions written in another ...
Tubular Permanent Magnet Generator
This tutorial shows how to model the tubular permanent magnet generator in 2D axisymmetry. The generator consists of a modular stationary stator and moving/oscillating slider. The stator is made of three-phase multiturn windings and an iron core. The slider is made of permanent magnets and iron spacers. The open circuit voltage in the three-phase stator windings due to the periodic motion of the ...
Applying a Current-Voltage Switch to Models
This example exemplifies how to model the switching between current and voltage excitations in *Terminal* boundary conditions. A more detailed description of the phenomenon and the modeling process can be seen in the blog post "[Control Current and Voltage Sources with the AC/DC Module](https://www.comsol.com/blogs/control-current-and-voltage-sources-with-the-acdc-module/)".
