HF120 Element Description

HF120 is a high-frequency brick element which models 3-D electromagnetic fields and waves governed by the full set of Maxwell's equations in linear media. It is based on a full-wave formulation of Maxwell's equations in terms of the time-harmonic electric field E (exponent jωt dependence assumed). A companion tetrahedral element, HF119, has similar full-wave capability. See HF120 in the Theory Reference for ANSYS and ANSYS Workbench for more information on Maxwell's equations and full-wave formulations, respectively.

HF120 applies to the full-harmonic and modal analysis types, but not to the transient analysis type. It is defined by up to 20 geometric nodes with AX DOF on element edges and faces and inside the volume. The physical meaning of the AX DOF in this element is a projection of the electric field E on edges and faces, as well as normal components to the element faces.

A first order or second order element option is available for the hexahedral and prism-shaped elements using KEYOPT(1). The pyramid-shaped element is only available as a first order element. The first order element has one AX DOF on each edge. The first order hexahedral element has a total of 12 AX DOFs.

The second order hexahedral element has two AX DOFs on each edge, four AX DOFs on each face, and six AX DOFs inside the volume for a total of 54 DOFs {2(12 edges) + 4(6 faces) + 6 (1 volume)}.

The first order prism and pyramid elements have a total of 9 AX and 8 AX DOFs, respectively. The second order prism element has a total of 42 DOFs {2(9 edges) + 4(5 faces) + 4(1 volume)}.

HF120 Input Data

Figure 120.1: "HF120 Geometry" shows the geometries, node locations, and the coordinate system for the element. The element supports three geometric shapes: a hexahedral (brick) shape defined by twenty geometric nodes with degeneracies to prism and pyramid shapes.

The only unit system supported for high-frequency analysis is the MKS unit, where the free-space permeability MUZERO = 4π x 10^-7 H/m and the free-space permittivity PER0 = 8.854 x 10^-12 F/m (see the EMUNIT command).

KEYOPT(4) provides options for the element formulation. KEYOPT(4) = 0 activates the normal full-wave formulation, which solves for the total field. KEYOPT(4) = 1 activates the perfectly matched layers (PML) formulation, which absorbs the field at the open boundary or at the port of a waveguide. KEYOPT(4) = 2 activates the scattering formulation, which is only required in the regions of a domain receiving a reflected wave from an imposed soft source magnetic field excitation (BF,,H option).

HF120 requires two sets of material constants; that is, relative permeability and permittivity tensors (in the element coordinate system if any). To specify a diagonal relative permeability tensor use the MURX, MURY, and MURZ labels on the MP command. Use the TB,MUR and TBDATA commands to specify the terms of an anisotropic permeability matrix. To specify a diagonal relative permittivity tensor use the PERX, PERY, and PERZ labels on the MP command. Use the TB,DPER and TBDATA commands to specify the terms of an anisotropic permittivity matrix.

You can specify an optional diagonal resistivity tensor (inverse of the conductivity tensor) using the RSVX, RSVY, and RSVZ labels on the MP command. To specify the terms of an anisotropic electric current conductivity tensor or anisotropic magnetic current conductivity tensor use TBDATA and TB,CNDE or TB,CNDM, respectively.

For an isotropic lossy material, you can define the lossy characteristics of the material by either the electric loss tangent (MP,LSST) or magnetic loss tangent (MP,LSSM). To calculate a specific absorption rate (SAR), you must input a mass density using the DENS label on the MP command.

To define nodal constraints on geometric nodes, use the D command. With the D command, the Lab variable corresponds to the only degree of freedom AX and the VALUE corresponds to the AX value. AX is not the x component in the global Cartesian coordinate system. In most cases, the AX value is zero, which corresponds to a perfect electric conductor (PEC) or "Electric Wall" (tangential component of   = 0) condition. If both end nodes and the mid-node on an element edge are constrained, DOFs on the edge are also constrained. Similarly, if all edges on an element face are constrained, DOFs on the face are also constrained. The DOFs based on volume are not constrained. If you leave the nodes on a surface unspecified, the boundary assumes a perfect magnetic conductor (PMC) or "Magnetic Wall" condition (tangential component of H¯ = 0).

To define constraints on lines and areas, use the DL and DA commands, respectively. The Lab variable corresponds to the degree of freedom AX and the Value1 corresponds to the AX value.

Node and Element Loads describes element loads. You can specify an exterior waveguide port, surface impedance boundary conditions, infinite boundary surface flags, and Maxwell surface flags on the element faces indicated by the circled numbers in Figure 120.1: "HF120 Geometry" using the SF and SFE commands or on the solid model using the SFA command. You can use the infinite boundary surface flag for a radiating open boundary in lieu of PML elements. You should use the Maxwell surface flag to determine an equivalent source surface for near and far field calculations performed in POST1.

To define surface loads on areas of the model, use the SFA command.

You can apply current density, magnetic field, and electric field body loads to the finite element model using the BF and BFE commands or to the solid model using the BFK. BFL, BFA, and BFV commands. To specify a interior waveguide port, use the BF and BFA commands.

You can input the temperature (for material property evaluation only) body loads based on their value at the element's nodes or as a single element value (BF and BFE commands). In general, unspecified nodal values of temperatures default to the uniform value specified with the BFUNIF and TUNIF commands. Element heat loss (JHEAT) may be made available for a subsequent thermal analysis with companion elements. (See the description of the LDREAD command.)

Upon initiation of the solution calculations (SOLVE), the solid model loads and boundary conditions transfer automatically to the finite element model.

HF120 Solution Considerations

To choose the modal or full harmonic analysis type, issue the ANTYPE command.

In a harmonic analysis, the ANSYS program performs a complex solution and computes two sets of results data: real and imaginary. The measurable field quantities can be computed as the real step with a cosine time change and the imaginary set with a sine time change. You can set the frequency of the time change via the HARFRQ command. The measurable power terms and Joule losses are computed as rms (time-average) values and are stored with the real data set. You can choose a solver via the EQSLV command (the ICCG or sparse solvers are recommended).

For modal analysis, choose a frequency shift point just below the anticipated eigenfrequency of interest (via the MODOPT command). Select an upper end frequency as well. Use the Method argument to choose the Block Lanczos solver (the default). To visualize the electric and magnetic field modes, use the MXPAND command to expand the mode shapes.

"HF120 Input Summary" summarizes the element input. Element Input in the Elements Reference provides a general description of element input.

HF120 Output Data

The solution output associated with this element is in two forms:

The element output direction is parallel to the element coordinate system (if any). Solution Output in the Elements Reference provides a general description of solution output. See the Basic Analysis Guide for ways to view results.

Table 120.1: "HF120 Element Output Definitions" uses the following notation:

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates the item can be accessed by the Component Name method [ETABLE, ESOL]. The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, Y indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and a - indicates that the item is not available.

Table 120.3: "HF120 Item and Sequence Numbers" lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table in this manual for more information. The following notation is used in Table 120.3: "HF120 Item and Sequence Numbers":

HF120 Assumptions and Restrictions

HF120 Product Restrictions

There are no product-specific restrictions for this element.