parametrics,
sensitivity, and
optimization
module
ANSOFT OPTIMETRICS
™
Optimetrics, an add-on module for Ansoft’s 3D electromagnetic field
solvers, provides integrated parametrics, sensitivities, and optimization
capabilities to Ansoft’s users. Optimetrics performs parametric analysis,
sensitivity analysis, optimization, and other design studies from an easy
to use interface. Optimetrics can be used for designing high-frequency
products such as cellular telephones, antennas, and microwave circuits.
smart software for high-frequency design
Overview
Optimetrics is a smart parametrics and optimization engine that allows users to perform parametric
analysis, sensitivity analysis, optimization, and many other design studies from an easy to use
interface. The Optimetrics module drives Ansoft’s electromagnetic (EM) field solvers enabling
engineers to design electrical components using accurate EM field simulation. With Optimetrics,
dozens of design variations can be performed quickly and effortlessly, components can be
optimized, and design of experiments (DOE) studies can be automated to derive sensitivities
and uncertainties as a function of manufacturing tolerances.
Reduce your engineering and manufacturing costs and achieve a competitive advantage by using
Optimetrics. Give your design team the competitive edge that leverages the accuracy of electromagnetic simulation and the design robustness offered by Optimetrics.
Optimetrics organizes parametric simulation in a
convenient spreadsheet format. Each row represents a
separate EM simulation project and each column
identifies input parameters, output parameters, and other
calculated simulation results. Simply double click on a
row to launch the field visualization post processor.
optimetrics
Using Optimetrics With Ansoft HFSS
Ansoft HFSS is a finite element field solver
that accurately simulates 3D structures such
as transitions, filters, couplers and antennas
by computing the underlying electromagnetics. Optimetrics exploits the macro scripting
language in Ansoft HFSS for parametric
analysis and optimization. Ansoft HFSS can
record macro commands whenever the
software is run, allowing any HFSS session
to be replayed by simply rerunning the HFSS
macro file. These macros can be modified
to control the operations that HFSS performs, allowing quantities such as geometry,
materials, boundary conditions, sources and
frequencies to be varied.
Optimetrics automates the generation and
modification of macros. The user creates a
nominal problem and defines the independent
parameters to be varied. A macro editor
module automatically interprets highlighted
lines in a macro script and allows users to
define independent variables. The user then
defines dependent variables to be computed
in a parametric analysis, or the cost function
to be minimized in optimization. Dependent
variables and cost functions can be any
computed quantity in HFSS. Field values,
s-parameters, frequency response, eigenmode
data, impedance, and antenna metrics are all
available. HFSS performs the requested
computations, providing output in convenient
table format for parametric analysis or an
optimal design specification for optimization. A
report generator allows users to plot dependent
versus independent parameters for parametric
simulation and cost function and other metrics
versus cycle for optimization.
The Optimetrics macro editor virtually eliminates the
need for the user to hand-edit macro files. Macro view
mode interprets individual lines in a script; parametric
view allows users to assign input parameter variables.
Design for Manufacture
Designers of microwave components, high-frequency
packaging, and antennas search for the right combination of
geometry and materials to achieve a desired performance.
The combinations may be thought of as a multidimensional
“design space.” The engineer’s job is to find a design point
that meets design specifications for performance and
producibility. A high performance design that is also highly
sensitive to manufacturing tolerances is not robust and can be
very costly to produce.
Optimetrics automates electromagnetic simulation so engineers
can understand the topology of the design space. A parametric
analysis can be configured to systematically vary design geometry,
materials, and boundary conditions over user-prescribed
ranges. The EM field solver is used to deliver accurate results
for all instances of the design so users can plot contours of the
design space. Regions of the design space that provide high
performance and low sensitivity to manufacturing tolerances
can then be identified.
Only Ansoft provides parametric analysis prior to optimization
to reveal global design performance. By performing parametrics
first, engineers can focus on the highest performance and least
sensitive region of the design space. Designers use parametrics to get close to the right solution, then optimize to get
the maximum performance. Designs are far less likely to fall
into local minima and other inferior design space traps using
this method.
Image compliments of
Microwave Development Laboratories.
A feed network for a large planar phased array antenna
uses numerous reactive tee power dividers. Each reactive
tee provides different power division to achieve the
desired aperture distribution.
Port 1 (Input)
w=9”
h=0.4”
l=0.45”
d=0.1”
Port 3
Port 2
Design Parameter: Offset x
Operating Frequency: 10 GHz
One-parameter parametrics example of a rectangular
waveguide reactive tee power divider.
Optimization is Not Enough
This simple, one-parameter example of parametrics is a
rectangular waveguide reactive tee power divider. Input power
from port 1 is unequally divided to the two output ports
depending upon the position of the inductive septum.
Parametrics was used to vary the septum offset x. When x is
zero, the power to ports 2 and 3 is equal; as x increases, more
power travels to port 3 than to port 2 (see figure). This curve
can be used to design a reactive tee power divider. Suppose a
design requires 80% power to go to port 3. Simply locate 0.8
on the y-axis and then identify the value of offset needed
(design point 1). The slope of the line about the design point
provides sensitivity of the design to the parameter x.
What if a simple optimizer had been used and it located
design point 2 for the final design point for 80% power
division? It’s as good a solution as far as the optimizer is
concerned. But look at the slope of the curve. This design
point is more sensitive to manufacturing tolerances. Even worse,
look at s11 (the red curve trace). This new design reflects
significant power back to the generator rather than to port 2.
Design Point 1
Design Point 2
Power is divided unequally to ports 2 and 3
depending upon septum location. For 80% power
division, design point 1 is less sensitive to manufacturing
tolerances than design point 2.
Parametric Analysis
The IEEE SCC 34 Spherical Phantom model is used as a
measurement standard for designing cellular telephone
antennas to guarantee acceptable EM radiation levels. Ansoft
HFSS with Optimetrics was used to run a parametric analysis
to produce specific absorption rate (SAR) as a function of the
antenna position.
Ansoft provides the fastest solution for 3D SAR calculations
available today. Ansoft HFSS ran the IEEE SCC 34 Spherical
Phantom problem 15 times faster than published commercial
FDTD solutions.
IEEE SCC 34 spherical phantom head model in the
presence of a radiating dipole antenna. Parametric
analysis calculates the dipole s-parameters and specific
absorption rate (SAR) versus dipole location.
Optimization
This coax to waveguide adapter was optimized to achieve a
broadband match. Six geometric parameters were used as
input to Optimetrics including probe length, probe radius,
dielectric sleeve radius, reflector distance, waveguide step
height, and step length. Geometric constraints were placed
on the geometry; for example, the sleeve radius was constrained to always be greater than the probe radius.
This coax to waveguide adapter was optimized using
Optimetrics. Six independent parameters were adjusted
to achieve low wideband return loss.
Sensitivity Analysis
After Optimetrics was used to find the optimal design of the
coax to waveguide adapter, a sensitivity analysis was performed
to evaluate design robustness. Each geometric parameter was
varied slightly about the design point to determine the
sensitivity of the return loss to that parameter. This analysis
can identify the most sensitive parameters so that appropriate
tolerances may be delivered to production engineering.
Parametric analysis was used to compute the sensitivity of
the design to geometric tolerances. Sensitivity analysis
reveals the most sensitive parameters so that appropriate
tolerances may be delivered to production engineering.
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