Electro Thermal Simulation

The increasing complexity of nowadays wireless RF devices increases the demand for accurate and efficient simulations of large and complex RF designs. Identifying and predicting potential issues early in the design process saves resources, time, and money. Heat can degrade the performance and the reliability of electronic devices, thus thermal analysis plays a crucial role to determine weather the device will perform as intended to be in real operating conditions. Electromagnetic losses including the dielectric and conductor losses are one of the main heat sources and thus an accurate calculation of these losses is essential to predict the actual performance. Using ANSYS HFSS, the EM losses can be accurately calculated, which can then be imported into ANSYS thermal analysis and simulated using ANSYS Icepak CFD solver to help engineers solve the most complex thermal challenges and to predict how their designs will perform with temperature changes.

Overview

In this blog we will be using the ANSYS Electronics Desktop (AEDT) to run electro-thermal simulation of high power RF coaxial filter. ANSYS HFSS will be used to perform the electromagnetic simulation to calculate the RF dielectric and conductor losses. The RF losses will then be coupled to ANSYS Icepak CFD solver to perform the thermal analysis including conduction, convection, and radiation modes of heat transfer and calculate the temperature profile. 

Workflow

The work flow of this demo consists of the following steps:

1) Simulating the electromagnetic losses through all solids using ANSYS HFSS

2) transfer the geometry with material assignments to Icepak with the calculated EM losses

3) setup the Icepak simulation, including boundary conditions, mesh setup, and solver setup

4) simulate the Icepak design and postprocess the results

HFSS Setup

In this demo we will simulate the below RF Coaxial filter and calculate the RF conduction losses due to the finite conductivity of the materials used and the dielectric losses.

The below figure shows the S parameters plot of the filter response.

Using the filed calculator we can calculate the surface loss density on the finite conductive surfaces and the volume loss density in the lossy dielectric volumes as seen below. The input power can be modified in the Edit Sources window. In this demo the input power is set to 1W.

Icepak Setup

To create the Icepak design using the 2025R1 release,

1) right click on the HFSS design, and select Create Target Design...

2) Under the General Tab, select Target Design Type to be Icepak

3) Select the Analysis Setup

4) Under the Icepak Tab, Select Forced Convection

5) Select the Flow Speed to be 1 m/s

6) Select the Flow Direction to be +Z

This workflow will create an Icepak design with the geometry, boundary conditions, and analysis setup defined. It will also automatically link the EM losses to the right geometry.

The solution type for the Icepak analysis is Steady State with Temperature and Flow.

The defined boundary conditions are as seen below, an Inlet Velocity and Outlet Pressure.

Before starting the analysis, the mesh can be viewed. Notice the thermal simulation mesh is different than the HFSS generated mesh.

• In the mesh viewer, check the “Show” option and make sure that “Cut plane” is selected.
• In the “Define plane drop down, choose “X plane through center”
• Turn the model so that you are looking at other planes

The analysis setup for this model is as seen below. Temperature and Flow problem types with a Flow Regime of Turbulent. The radiation model is Discrete Ordinates and gravity is included. Both are necessary for natural convection. To increase the simulation accuracy, the number of iterations can be increased.

Under the “Solver Settings” tab, the user is setting initial values for the simulation equations

• Allows steady state models to converge faster
• 1 m_per_sec is set opposite to gravity (positive z direction)
• This panel, however, can be ignored if you want
• Press the “Advanced Options” to review recommended settings

After the simulation is completed. We can review the solution profile and observe the residual plot for the convergence criteria setup in the solution. 

We can also confirm that the EM losses calculated by HFSS has been mapped correctly by looking at the total mapped EM loss in the simulation profile. As seen, the total EM loss is the same as the summation of the HFSS calculated surface and volume loss densities. 

Below is the temperature profile and the velocity plot of the coaxial filter simulation.

A complete demonstration is provided in the video link below: