# Resonating the coil in HFSS

1. ## Resonating the coil in HFSS

Hi,
The inductance of the spiral coil obtained is 96.0429nH. The capacitance & Resistor i have defined using lumped port is -6.1 ohm and 50 ohm.
[The calculated value of capacitor to acheive resonance at 10MHZ is 6.1 ohm]. But resonance is not acheived. The graph of S11 is attached here.

2. ## Re: Resonating the coil in HFSS

You are looking at the wrong value. If you compensate the R+jX of the inductor by a -jX of the capacitor, the resulting input impedance is the inductor series resistance. And we want that resistance to be small (high Q). So don't expect matching to 50 Ohm. The resonance is seen in phase(S11).

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3. ## Re: Resonating the coil in HFSS

Originally Posted by volker@muehlhaus
You are looking at the wrong value. If you compensate the R+jX of the inductor by a -jX of the capacitor, the resulting input impedance is the inductor series resistance. And we want that resistance to be small (high Q). So don't expect matching to 50 Ohm. The resonance is seen in phase(S11).
Thanks again Volker. How to choose R & C so as to achieve efficient power transfer. I have designed Capacitor value based on C = 1/L(2*pi*f)^2. How to get dip curve of S11. Any hint or reference?

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I think i have to derive for the circuit to extract resonance frequency. How to tune both the txer n rxer coils to acheive efficient power transfer?

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4. ## Re: Resonating the coil in HFSS

Originally Posted by Rosalinekavitha
How to choose R & C so as to achieve efficient power transfer.
The L:C ratio is important. Values need to be selected in consideration of available current to drive them, that is, to produce desired voltage swings.

Large L is associated with small current.
Small L, large current.

Large C, large current.
Small C, small current.

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5. ## Re: Resonating the coil in HFSS

S11 matching of the single coil is not use a useful parameter if you study wireless power transfer. We want to transfer the power to the pickup coil, with minimum losses in the driver coil.

Matching the single driver coil for S11=0 means that all power is dissipated in the driver coil (losses) which makes no sense.

6. ## Re: Resonating the coil in HFSS

Thanks for all your responses. I have extracted inductance value from im(z(1,1)) from hfss and calculated Capacitance value using resonant frequency formula. In HFSS i have used lumped port, so current cannot be taken into account. I am trying to acheive resonance using parallel LC circuit. why S11 doesnot get converge at 10MHZ?

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7. ## Re: Resonating the coil in HFSS

Originally Posted by Rosalinekavitha
I am trying to acheive resonance using parallel LC circuit. why S11 doesnot get converge at 10MHZ?
You are missing the basics. Parallel LC is high impedance at resonance -> S11=0dB

8. ## Re: Resonating the coil in HFSS

Originally Posted by volker@muehlhaus
You are missing the basics. Parallel LC is high impedance at resonance -> S11=0dB
I am new to WPT n coils. I am trying to replica the paper[DOI 10.1109/10.1109.10.1109]. Followed the same procedure as in page 4 using HFSS.

9. ## Re: Resonating the coil in HFSS

First try to calculate the matching network, given the RL equivalent of the coil and next do a S11 simulation in a circuit simulator ( eg SPICE)

10. ## Re: Resonating the coil in HFSS

Originally Posted by Twave03
First try to calculate the matching network, given the RL equivalent of the coil and next do a S11 simulation in a circuit simulator ( eg SPICE)
S(1,1) converges around 10MHZ. Delta S has been set to 0.01 and maximum passes are set to 8. Message manager shows that adaptive passes didnot converge. When passes are set to 12 it shows Matrix solver exception: out of memory. I am using 16GB RAM.Maximum RAM limit has been set to 15,000MB in solver.It takes aroung 24hrs simulation time. Sweep has been interpolated from 1MHZ to 20MHZ.

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