#### zero_coke

##### Newbie level 6

Hello, I have a few questions on the models presented on Wireless Power Transfer by MIT and other various sources seen in IEEE journals

Q1: Can I model a 4 coil system whereby the first two are inductively coupled, the middle two are resonant coupled, and the last two are inductively coupled, using ideal air-core transformer with non-unity coupling coefficient? In Multisim I'm able to couple multiple inductors so as long as I know the primary and secondary inductances as well as mutual coupling coefficients. Can I use this to simulate my 4 coil wireless power setup?

Q2: What is the role of frequency? There are so many variables and I don't know the importance of frequency. The only thing I can think of is the FCC regulations on magnetic field strength (A/m) at different frequencies. It's 2.19 A/m up to 1 MHz, and then 2.19/f (MHz) after that which allows you less field strength at higher frequencies which I don't understand why. Also, another thing I found was that you must remain in near-field which is 0 to lambda / 4 distance. Do I even need to consider this because I'm not doing the same setup as MIT where they use self-resonant coils, I'm using LC resonant coils with lumped elements. Do I need to worry about H field strength limitation posed by FCC?

Q3: How is impedance transformation done in 4 coil resonant & inductive system? I mean, how can I transfer the load impedance from my 4th coil all the way into my 1st coil? I cannot use regular transformer ratio transformation because these are non-ideal transformers and I don't know how to do it.

The two concepts are attached as images and the journal I'm using as a reference is too. It's all explained in the journal but I don't understand maybe I'm lacking enough knowledge on circuits and AC analysis. I need to know how going from concept #1 to concept #2 improves the efficiency in the system. The only thing I can think of is, in order to achieve maximum power transfer, I should introduce 2 new coils so that when you refer the impedances to the primary you will have a closer match to the source impedance and thus more power delivered to the driving coil. Is this correct?

Thanks!

Q1: Can I model a 4 coil system whereby the first two are inductively coupled, the middle two are resonant coupled, and the last two are inductively coupled, using ideal air-core transformer with non-unity coupling coefficient? In Multisim I'm able to couple multiple inductors so as long as I know the primary and secondary inductances as well as mutual coupling coefficients. Can I use this to simulate my 4 coil wireless power setup?

Q2: What is the role of frequency? There are so many variables and I don't know the importance of frequency. The only thing I can think of is the FCC regulations on magnetic field strength (A/m) at different frequencies. It's 2.19 A/m up to 1 MHz, and then 2.19/f (MHz) after that which allows you less field strength at higher frequencies which I don't understand why. Also, another thing I found was that you must remain in near-field which is 0 to lambda / 4 distance. Do I even need to consider this because I'm not doing the same setup as MIT where they use self-resonant coils, I'm using LC resonant coils with lumped elements. Do I need to worry about H field strength limitation posed by FCC?

Q3: How is impedance transformation done in 4 coil resonant & inductive system? I mean, how can I transfer the load impedance from my 4th coil all the way into my 1st coil? I cannot use regular transformer ratio transformation because these are non-ideal transformers and I don't know how to do it.

The two concepts are attached as images and the journal I'm using as a reference is too. It's all explained in the journal but I don't understand maybe I'm lacking enough knowledge on circuits and AC analysis. I need to know how going from concept #1 to concept #2 improves the efficiency in the system. The only thing I can think of is, in order to achieve maximum power transfer, I should introduce 2 new coils so that when you refer the impedances to the primary you will have a closer match to the source impedance and thus more power delivered to the driving coil. Is this correct?

Thanks!