Part geometry

• Part Width: Nominal part width ($x$-dimension) in meters. Should be an integral multiple of Cell Size.
• Part Height: Nominal part height ($y$-dimension) in meters. Should be an integral multiple of Cell Size.
• Part Thickness: Part thickness ($z$-dimension) in meters. Required for all demag types except FastPipe and None.
• Cell Size: In-plane ($xy$-plane) edge dimension of base calculation cell. This cell is a rectangular brick, with square in-plane cross-section and thickness given by Part Thickness. N.B.: Part Width and Part Height should be integral multiples of Cell Size. Part Width and Part Height will be automatically adjusted slightly (up to 0.01%) to meet this condition (affecting a small change to the problem), but if the required adjustment is too large then the problem specification is considered to be invalid, and the solver will signal an error.
• Part Shape: Optional. Part shape in the $xy$-plane; must be one of the following:
  • Rectangle
    The sample fills the area specified by Part Width and Part Height. (Default.)
  • Ellipse
    The sample (or the magnetically active portion thereof) is an ellipse inscribed into the rectangular area specified by Part Width and Part Height.
  • Ellipsoid
    Similar to the Ellipse shape, but the part thickness is varied to simulate an ellipsoid, with axis lengths of Part Width, Part Height and Part Thickness.
  • Oval r
    Shape is a rounded rectangle, where each corner is replaced by a quarter circle with radius $r$, where $0 <= r <= 1$ is relative to the half-width of the rectangle.
  • Pyramid overhang
    Shape is a truncated pyramid, with ramp transition base width (overhang) specified in meters.
  • Mask filename
    Shape and thickness are determined by a bitmap file, the name of which is specified as the second parameter. The overall size of the simulation is still determined by Part Width and Part Height (above); the bitmap is spatially scaled to fit those dimensions. Note that this scaling will not be square if the aspect ratio of the part is different from the aspect ratio of the bitmap.

    The given filename must be accessible to the solver application. At present the bitmap file must be in either the PPM (portable pixmap), GIF, or BMP formats. (Formats other than the PPM P3 (text) format may be handled by spawning an any2ppm subprocess.)

    White areas of the bitmap are interpreted as being non-magnetic (or having 0 thickness); all other areas are assumed to be composed of the material specified in the “Material Parameters” section. Thickness is determined by the relative darkness of the pixels in the bitmap. Black pixels are given full nominal thickness (specified by the “Part Thickness” parameter above), and gray pixels are linearly mapped to a thickness between the nominal thickness and 0. In general, bitmap pixel values are converted to a thickness relative to the nominal thickness by the formula 1-(R+G+B)/(3M), where R, G and B are the magnitudes of the red, green and blue components, respectively, and M is the maximum allowed component magnitude. For example, black has R=G=B=0, so the relative thickness is 1, and white has R=G=B=M, so the relative thickness is 0.

  The code does not perform a complete 3D evaluation of thickness effects. Instead, the approximation discussed in [26] is implemented.

OOMMF Documentation Team
September 30, 2025