【正文】 21 邊界與端口設置 電子科技大學 賈寶富 22 Boundary/Excitations Overview ? Why are They Critical? ? For most practical problems, the solution to Maxwell?s equations requires arigorous matrix approach such as the Finite Element Method (FEM) whichis used by Ansoft HFSS. ? The wave equation solved by Ansoft HFSS is derived from thedifferential form of Maxwell?s equations. ? For these expressions to be valid, it is assumed that the field vectors are: ? singlevalued, ? bounded, and have a ? continuous distribution (along with their derivatives) ? Along boundaries of media or at sources, ? Field vectors are discontinuous ? Derivatives of the field vectors have no meaning ? Boundary Conditions define the field behavior across discontinuous boundaries 23 Boundary/Excitations Overview 24 Boundary/Excitations Overview 25 HFSS Boundary List ? Perfect E and Perfect H/Natural ? Ideal Electrically or Magically Conducting Boundaries ? ?Natural? denotes Perfect E ?cancellation? behavior ? Finite Conductivity ? Lossy Electrically Conducting Boundary, with userprovided conductivity and permeability ? Impedance ? Used for simulating ?thin film resistor? materials, with userprovided resistance and reactance in ??/Square ? Layered Impedance ? Screen Impedance ? Radiation ? An ?absorbing boundary condition,? used at the periphery of a project in which radiation is expected such as an antenna structure ? Symmetry ? A boundary which enables modeling of only a subsection of a structure in which field symmetry behavior is assured. ? “Perfect E” and “Perfect H” subcategories ? Lumped RLC ? Master and Slave ? ?Linked? boundary conditions for unitcell studies of infinitely replicating geometry (. a slow wave circuit an antenna array) ? PML (Perfect Match Layer) 26 邊界條件定義的覆蓋 27 HFSS Boundary Descriptions: Perfect E and Perfect H/Natural ? Parameters: None ? Perfect E is a perfect electrical conductor* ? Forces Efield perpendicular to the surface ? Represent metal surfaces, ground planes, ideal cavity walls, etc. ? Perfect H is a perfect magic conductor ? Forces Hfield perpendicular to surface, Efield tangential ? Does not exist in the real world, but represents useful boundary constraint for modeling ? Natural denotes effect of Perfect H applied on top of some other (. Perfect E) boundary ? ?Deletes? the Perfect E condition, permitting but not requiring tangential electrical fields. ? Opens a ?hole? in the Perfect E plane Perfect E Boundary* Perfect H Boundary ‘ Natural? Boundary larperpendicuE? continuousE? parallelE?*NOTE: When you define a solid object as a ?perf_conductor? in the Material Setup, a Perfect E boundary condition is applied to its exterior surfaces!! 28 Perfect E應用實例 29 Perfect H應用實例 210 Perfect H for 2D Aperture (I) ? Monopole Over a Ground plane Perfect H Surface Interior to the Problem Space Behaves Like an Infinitely Thin 2D Aperture Perfect H 211 Perfect H for 2D Aperture (II) ? Small Hole Can be “Cut” in infinitely Thin Septum Between the Upper and Lower Guide Using a Perfect H Surface at the Hole Perfect H 212 Finite Conductivity ? 趨膚深度 1=f? ? ? ?213 DC versus AC 214 HFSS Boundary Descriptions: Finite Conductivity ? Parameters: Conductivity and Permeability ? Finite Conductivity is a lossy electrical conductor ? Efield forced perpendicular, as with Perfect E ? However, surface impedance takes into account resistive and reactive surface losses ? User inputs conductivity (in siemens/meter) and relative permeability (unitless) ? Used for nonideal conductor analysis* Finite Conductivity Boundary gattenuatinlarperpendicuE ,?215 HFSS Boundary Descriptions: Impedance ? Parameters: Resistance and Reactance, ohms/square (??/ ) ? Impedance boundary is a direct, userdefined surface impedance ? Use to represent thin film resistors ? Use to represent reactive loads ? Reactance will NOT vary with frequency, so does not represent a lumped ?capacitor? or ?inductor? over a frequency band. ? Calculate required impedance from desired lumped value, width, and length ? Length (in direction of current flow) ? Width = number of ?squares? ? Impedance per square = Desired Lumped Impedance ? number of squares EXAMPLE: Resistor in Wilkenson Power Divider Resistor is mils long (in direction of flow) and 4 mils wide. Desired lumped value is 35 ohms. squar eNRRNlu m p eds h eet /40875.35 ??????216 HFSS Boundary Descriptions: Layered Impedance ? Parameters: Surface Roughness。 Layer。 Thickness/Type。 Materials ? 用于定義多層均勻材料組成的邊界。如在某種涂敷吸波材料散射特性的計算中，可以使用這種邊界。 217 218 HFSS Boundary Descriptions: Radiation ? Parameters: None ? A Radiation boundary is an absorbing boundary condition, used to mimic continued propagation beyond the boundary plane ? Absorption is achieved via a secondorder impedance calculation ? Boundary should be constructed correctly for proper absorption ? Distance: For strong radiators (. antennas) no closer than ?/4 to any structure. For weak radiators (. a bent circuit trace) no closer than ?/10 to any structure ? Orientation: The radiation boundary abso