Lecture 8: Introduction to Hybrid FEM IE 2015.0 Release ANSYS HFSS for Antenna Design 1 2015 ANSYS, Inc.
Hybrid FEM-IE Solution Using HFSS and HFSS-IE Advantages of Hybrid Solution Leverage the strength of both Finite Element (HFSS) and Integral Equation (HFSS-IE) methods in a single problem Conformal and discontinuous air region to minimize solution volume required for FEM solution IE solution used to solve for field propagation through free space and conductors outside of FEM volume, no volume mesh required IE solution can overlap with FEM solution (i.e. currents are continuous from one solution domain to another) FEM Only Solution Hybrid FEM-IE Solution IE Solution FEM Solution 2 2015 ANSYS, Inc. Surface current on metal block solved with IE
Invoking the Hybrid Finite Element-Integral Equation Solution The Hybrid FEM-IE Solution The hybrid FEM-IE solution is invoked with special boundary conditions in an HFSS design type called FE-BI and IE-Regions A hybrid solution can contain FE-BI boundary conditions and/or IE-Regions. Finite Element Boundary Integral (FE-BI) Similar concept as an ABC or PML, boundary condition that truncates the FEM solution volume with infinite free space Applied to an air volume that surrounds a geometry Unlike ABC or PML, FE-BI can be any arbitrary shape, and any distance from radiator The IE solution on the outer boundary also allows for discontinuous FEM solution spaces For example 2 antenna s separated by a distance could be solved using 2 separate air boxes surrounding each antenna with FE-BI applied to each airbox Applying Model exterior as HFSS-IE domain when setting up a Radiation Boundary Condition Hybrid Solution Process FEM Solution in Volume IE Solution on outer surfaces and IE Regions IE-Regions Assigning an object as an IE-Region When an object is assigned as an IE-Region, the IE solver will be used to solve for currents on the surface of this object FEM Solution Iterate IE Solution on Reflector and Outer Surface of Airbox 3 2015 ANSYS, Inc.
Hybrid Finite Element-Integral Equation Hybrid Solution Using Finite Element Boundary Integral Hybrid FEM-IE significantly reduces required computer resources Large air volume inside of radome is removed from the FEM solution Air volume is required if using PML or ABC Discontinuous solution space made possible using FE-BI FE-BI applied to 2 separate air boxes around - Airbox conformal to radome Airbox conformal to horn antenna IE solution is used to solve for fields between FEM domains 26 GHz RAM Elapsed Time PML 259G (DDM) 840min 19143 λ³ 2860 λ³ FEM-IE Surface FE-BI 64G 205min FEBI shows 4.1x speedup factor and 75% less RAM 4 2015 ANSYS, Inc. PML FEM-IE
Hybrid IE-Regions Metal objects that are outside of the FEM solution volume can be directly solved using the integral equation solution Removes the need for air box to surround metal objects Fully coupled FEM and IE domains Reflector Analysis with Hybrid FEM-IE solution Blockage due to feed FE-BI: Applied to outer surface of airbox. FEM solution of horn inside of airbox IE Region: Applied to reflector Hybrid solution of reflector fully couples the solutions of the FEM and IE Domain 5 2015 ANSYS, Inc.
Hybrid IE-Regions: Interior Dielectrics Not only can metal objects that are exterior to the FEM solution be solved using a hybrid solution, but also models with uniform dielectrics interior to the FEM solution volume When a model contains a uniform dielectric inside of an FEM volume, the integral equation solver can solve for the surface currents only on the surface of the dielectric, forgoing the need to solve for the fields directly inside of the dielectric Solution Type RAM (GB) FEM Only 20 Hybrid FEM-IE 6.2 Hybrid solution uses ~70% less RAM than FEM only solution FEM Solution Hybrid FEM-IE Solution Dielectric ε r = 4 Metal ❷Metallic IE-Region ❶Dielectric IE-Region 6 2015 ANSYS, Inc.
Hybrid FEM-IE Solution with Overlapping Domains Advanced hybrid FEM-IE solution allows FEM and IE domains to overlap Useful in situations where the FEM and IE domains are not physically separated Currents will be continuous across domains Region of overlap should be placed at least λ/4 away from an antenna element Co-site Analysis Reflector Analysis FEM Solution for Antenna Elements FEM-IE IE Solution for metallic fuselage IE-Region 7 2015 ANSYS, Inc.
Hybrid FEM-IE Solution: Examples 60λ Full Wave, Accurate Solution in 37G RAM, 3.2 hours FE-BI applied to conformal Airbox 10x RAM reduction over FEM only solution Beam Waveguide Antenna IE Domain FEM DDM FEM-IE 15x RAM reduction over FEM only solution IE-Region 3 8 2015 ANSYS, Inc.
IE-Regions: Boundary Condition Setup IE Solution Applied to Metal outside of air box and dielectric inside of air box IE-Regions can be applied to metal or dielectric objects inside of an HFSS Design Metal Objects Typically exterior to air box region with FE-BI outer radiation boundary or Internal to dielectric IE Region Dielectric Objects Must be interior to air box region Assignment: Select Object Select the menu item HFSS > IE Regions > Assign As IE Region Air Volume truncated with FE-BI radiation boundary condition 9 2015 ANSYS, Inc.
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