# Application Gallery

The Application Gallery features COMSOL Multiphysics® tutorial and demo app files pertinent to the electrical, structural, acoustics, fluid, heat, and chemical disciplines. You can use these examples as a starting point for your own simulation work by downloading the tutorial model or demo app file and its accompanying instructions.

Search for tutorials and apps relevant to your area of expertise via the Quick Search feature. To download the MPH-files, log in or create a COMSOL Access account that is associated with a valid COMSOL license. Note that many of the examples featured here can also be accessed via the Application Libraries that are built into the COMSOL Multiphysics® software and available from the File menu.

### 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.

### Small-Signal Analysis of an Inductor

If an inductor's magnetic material is nonlinear, then the inductance depends on the current passing through it. This model consists of an inductor with a nonlinear magnetic core, where the small-signal inductance is simulated as a function of current. The model also investigates how the small-signal inductance depends on the DC current.

### Modeling a Capacitive Position Sensor Using FEM

This tutorial model explains how to extract lumped matrices by means of the *Stationary Source Sweep* study. The capacitance matrix of a five-terminal system is used to infer the position of a metallic object similar to real-world capacitive position sensors. The example illustrates the use of FEM, which is supported by the *Electrostatics* interface. When FEM is used, a volumetric mesh of a ...

### 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/)".

### Axisymmetric approximation of 3D Inductor

Inductive devices experience capacitative coupling between conductors at high frequencies. Modeling this phenomenon requires that you describe electric fields that have components both parallel with and perpendicular to the wire. This consideration might lead to the conclusion that a 3D model is always necessary to model the phenomenon, even if the coil is a helix, which is actually not the ...

### Magnetotellurics

Magnetotellurics is a method for estimating the resistivity profile of the Earth's subsurface using the natural electromagnetic source provided by the ionosphere. This model was defined by Zhdanov et al. in a study published in 1997. In this article, various scientific groups compared software performance on the same models. This is the model called COMMEMI-3D-2, which has become one of the ...

### Contact Impedance Comparison

The contact impedance boundary condition is meant to approximate a thin layer of material that impedes the flow of current normal to the boundary, but does not introduce any additional conduction path tangential to the boundary. This example compares the contact impedance boundary condition to a full-fidelity model and discusses the range of applicability of this boundary condition.

### Iron Sphere in a 13.56 MHz Magnetic Field

An iron sphere is exposed to a spatially uniform, sinusoidally time-varying, background magnetic field. The frequency of the field is so high that the skin depth in the sphere is much smaller than the radius. At such high frequencies it is possible to model only the fields and induced currents on the surface of the sphere, thus avoiding the need for solving for the fields within the volume of ...