High-Power Thermal Analysis

using

HFSS and ANSYS Mechanical Integration

Martin Vogel, PhD

Product Management Team

Why couple simulators for electro-magnetics and multi-physics?

Courtesy of

Electronics produce heat, which can cause malfunctions.

Existing Electromagnetics – Multiphysics Links

Electromagnetic simulators:

HFSS, Q3D Maxwell SIwave

ANSYS Mechanical

Thermal Solvers

ANSYS ICEPAK

cooling of

electronics

ANSYS FLUENT

Thermodynamics

and fluid flow

ANSYS Mechanical

Stress Solver

Raytheon high-power connector

Co-axial Glass + Micro-strip Metal

cable Kovar trace housing

Before turning power on

Courtesy of

Co-axial pin connecting to microstrip trace

Soon after turning power on

Courtesy of

Excessive heat has destroyed the connector.

HFSS has been “data integrated” with Workbench

Analyze the model in HFSS

Pin connecting to trace

Easy to link to thermal simulators

Add boundary conditions for convection and cooling.

Natural convection

Cooling on bottom face

Outline of thermal model

Temperature exceeds 300 deg C in kovar.

Link thermal to structural analysis

Resulting schematic

Deformation up to 22 µm

Stress mostly in inner conductor

Improve the design.

• Kovar, responsible for the high temperatures, has been replaced by a different metal.

• Temperatures may still be high, which Teflon cannot handle. Accurate analysis

wanted.

• Use the two-way thermal coupling to account for temperature-dependent materials.

Why two-way thermal?Teflon loss tangent increases with temperature. Run-away effect possible.

Glass transition

Two-way thermal link

Solve EM model at initial temperature.

Send electromagnetic

loss to thermal simulator.

Determine temperatures.

Send temperatures back to EM model.

Material parameters change.

Solve EM model with

new temperatures.

ΔT < threshold?

Done

NoYes

Two-way thermal analysis: Final temperatures with normal Teflon

EM Power Losses as function of two-way thermal iteration

Volume Loss in normal Teflon

Surface Loss on metals

Volume Loss in low-loss Teflon

Temperatures as function of two-way thermal iteration

Tmax Normal Teflon

Tmax Low-Loss Teflon

Tmin Normal Teflon

Tmin Low-Loss Teflon

Two-way thermal analysis:

Final temperatures with low-loss Teflon