How to represent multi-port devices such as SPDT switches on HFSS using lumped ports/lumped RLCs?

Hi folks,

I am trying to do an electromagnetic simulation on HFSS using SPDT switches that are to be used as lumped elements.

Can someone please give some insights into implementing multi-port boundary conditions or excitation using lumped RLCs or lumped ports respectively? This structure is to be exported to a circuit simulator eventually. So, drawing multiple ports is actually required so that I can replace them with the SNP file of the SPDT device in the circuit simulator. Any help will be greatly appreciated. 

Thanks in advance!

Comments

  • Peter SeranoPeter Serano Washington, DCMember
    edited May 2019

    You can do this all within AEDT. Define Lumped Port excitations where your lumped components will be (do not use LumpedRLC boundary or you will need to re-run the FEM model whenever changing the value of the lumped elements).

     

    Next, Add a new 'circuit' model to your AEDT Project. - You can now drag and drop the HFSS project into the circuit which will create a dynamic link between the circuit and FEM model. Then add in your lumped components into the schematic editor. - Here you will define the system ports, how they are driven, and the lumped component values. Next, setup a 'Linear Network Analysis' solution setup at the desired frequency/sweep and run the model. After it's solved (should take less than 30 seconds), you can right-click on the dynamically linked n-port block in the circuit editor and then click 'push excitations' - which will drive the multiple lumped ports in the HFSS model to mimic the same effect as having the lumped element(s) terminated there.

  • choudarychoudary Member
    edited September 2019

    Hi Peter,

    Thanks for informing this trick. What if I have a capacitor in my 3D model? Should I replace this capacitor (which I have defined by lumped RLC option) by lumped port ? If yes, will this not effect the results of 3D simulation? I am trying to simulate MRI birdcage coil and it has a lot of capacitors. Thanks.

  • Peter SeranoPeter Serano Washington, DCMember
    edited September 2019

    Yes - you should replace all lumpedRLC boundaries with ports in HFSS and make a linked circuit model. - Modeling MRI coils in HFSS just so happens to be my most in-depth area of expertise - what's your e-mail address? I can send you a fully working model of a birdcage coil with linked HFSS/Circuit modeling enabled for fast coil tuning...

  • choudarychoudary Member
    edited October 2019

    Many thanks Peter and sorry for the late reply. I am new to this forum and thought any reply to my comment would be forwarded to my email address but I guess this didn't happen. Anyway my email address is [email protected] I have a relevant question also: As you said, I replaced all capacitors with lumped ports and created a linked circuit model. In circuit simulation I was able to get very good return lose by introducing a tuning capacitor is series connection to the actual port (I am currently working with 1-port Birdcage coil with center/resonating frequency 64MHz). However, when I inserted back the values of capacitors and the tuning capacitor in full wave simulation, the results (S11 and impedance) do not match with the circuit simulation results. In fact I am getting bad return lose (around -5db) and that too at 65MHz. What I am skeptical about is that I created a new sub-project for full wave 3D simulation  rather than deleting/replacing the definitions of lumped ports by lumped capacitors in "port only" full wave simulation. Is this ok?  

    Can you kindly comment on this? What am I doing wrong?

    Many Thanks.

  • Peter SeranoPeter Serano Washington, DCMember
    edited October 2019

    There's no need to use LumpedRLC boundaries in the HFSS model. - After the model is solved with all ports and you have tuned the model in the circuit simulator, you can right click on the HFSS block and select 'Push Excitations' to excite the tuned condition of the circuit model into the HFSS model to view the fields.

    For me to send you the files I need you to provide me with a valid academic e-mail account.

  • choudarychoudary Member
    edited October 2019

    Thanks Peter once again. I don't see any "Push Excitation" option when I right click the block. I, however, see "Push Nominal Parameter Values". Is this the same? My university email is [email protected]

  • Peter SeranoPeter Serano Washington, DCMember
    edited October 2019

    Did you create and solve a 'Linear Network Analysis' Solution Setup in the Circuit model with the frequency sweep defined to match your HFSS model?

  • choudarychoudary Member
    edited October 2019

    Dear Peter,

    Yes I solved 'Linear Network Analysis' solution setup. I see now 'Push Excitation'. It appears that I need to do it immediately after solving.

    After push excitation I can see fields (E and H fields) in the 'ports only' version of the model. What I am wondering now is that is it possible to have a final version of 3D model with lumped capacitors as I can see in your file with title '3_phantom_only_tuned_coil_with_caps_for_validation_63p84MHz' (Thanks for sending ... it's really helping) ? I tried to create a sub-project with lumped capacitors (the values of these capacitors are taken from tuned circuit simulation) but results are not even close to the results of circuit simulation.

  • Peter SeranoPeter Serano Washington, DCMember
    edited October 2019

    @choudary - The HFSS model with ports and the linked circuit is providing you with an accurate model. There is no need to create a second model with LumpedRLC boundaries. - Unless you are running a model with a fixed lumped component (e.g., the 100 ohm resistor in a Wilkinson power diviider) then it is not recommended to use the LumpedRLC boundary.

  • kreyespakreyespa Member
    edited October 2019

    hello all, I had read your comments, and I am having the same problems about the lumped port simulation. I am trying to simulate a MRI coil with 11 capacitors and 1 feed, however when I run the design the results are not even near to be good. I tried drawing the mesh but it seems that my lumped ports are not well connected. Can you please help me with the sample you are working on, my email address is [email protected] I will greatly appreciate.   

  • Peter SeranoPeter Serano Washington, DCMember
    edited October 2019

    I sent you the MRI example files. Do not use LumpedRLC boundaries in your HFSS model. 

  • FirasFiras Member
    edited November 2019

    Dear Peter,

     

    Can you please send me the design files also ? I am trying to design an unequal Wilkinson power divider in HFSS and I want to link it to circuit for fast tuning ,but I am facing problems with defining the resistor ports in HFSS. So I will look at your design and try to understand how should I define the ports in HFSS that will be used for resistor in the circuit design.

    This is my email address : [email protected]

    I will really appreciate your help.

     

    Best Regards

  • AlexGermAlexGerm Member
    edited December 2019

    Hi Peter,

    Could you pleased share me the files for your  model of a birdcage coil with linked HFSS/Circuit modeling enabled for fast coil tuning? I'm completing a master in biomedical imaging and my current project focus on assessing RF heating for metallic implants undergoing time varying field. This would help us with the FE modelization of a our MRI Bore. It would be very appreciated.

    I'm from Polytechnique Montreal and my student email address is: [email protected]

     

    Great Regards,

  • satya4382satya4382 Member
    edited January 15

    Dear Peter,

    I have dynamically linked my HFSS design to Circuits. Have created an NMOS switch. Having a parse error at NMOS. Please help.

  • choudarychoudary Member
    edited February 6

    Hello Peter,

    After 'Push Excitation' at a single frequency (64MHz) to generate the fields in my 3D model of MRI birdcage coil, I can see the actual magnitude and phase values (HFSS --> Fields --> Edit Sources) but as soon as I change the values (magnitudes) at my 2 ports (Iport:1 and Qport:1) to scale up the power, the results get completely changed/wrong i.e. the fields (E-field, H-field) become completely in-homogeneous. The values of magnitude and Phase (after push excitation) are shown in the attached Figure. My actual ports are Iport:1 and Qport:1 which should be at 90° phase difference to create circular polarization.

    Can you kindly help me out to solve this issue? Many thanks.

    This question has also been posted here:

    https://studentcommunity.ansys.com/thread/scaling-of-power-after-push-excitation-in-mri-birdcage-coil/

  • SwadeshSwadesh Member
    edited February 7

    Hello Peter,

    I was going through this discussion which is really helpful and I am dealing with similar setup problem. Can you please share the file you mentioned with me. ([email protected])

    My Questions:

    In order to create lumped port on a substrate surface, how should I define the integration line? I am using driven modal solution. So in my design, there are port 1 and port 2, I have defined as lumped port and draw integration line with respect to  GND plane. But for  ring gap how should I create lump port and solve the cosimulation in circuit module. Your suggestion will be very helpful.

  • lakshk01lakshk01 Member
    edited May 4

    Hi Peter,

       Thanks for the helpfull hints. I am designing a surface coil array in HFSS, after the running the linear frequency

    analysis when I try to push excitation I get the following error messages

    "Failed to extract Voltage as there is no source"

    "Failed to push excitation information - Unable to extract voltage from parent solution.  You may need to analyze the circuit."

    I checked my circuit it seems correct. I did a forced analysis and it worked. I am not sure what I am doing wrong. Any ideas would be helpful.

    Also can you please share the birdcage example model, it would be really helpful.

    I am an academic HFSS user associated with NYU and my email is [email protected]

    Thanks

    Karthik

  • Hi...Suppose you are mimicking a structure in HFSS with numerous lumped ports at different spots in the structure. While HFSS doing the calculations for one lumped port, what are the properties of different ports? Do they become open circuits, or wonderful conductor planes, or something different?

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