That article is somehow confusing. They are also using S21 for the calculation..
They are comparing the two methods against calculated values.
Interesting fixture.
Yes, indeed, you are right!
The fixture is 3d printed. I think I have saved some fusion 360 or stl files, if needed.
I've never tried the capacitive coupling method, but great to see it's working. Thanks!
For fun attempting to replicate your test except following the paper. I am using a 39pF ATC capacitor. Your couple of uH makes no sense with the 37.6MHz. Looks like we need something around 450nH. I cut one that measures 509nH. Whole setup seems to resonate around 35MHz. Close enough.
Looking at the group delay, I get roughly 2us or a Q of 217.
Yes, sorry, I have not calculated nor measured that L
, just cut a piece of wire and wrote "few uH" , so you are right.
I have also used a high quality cap from EXXELIA (
https://www.digikey.com/en/products/detail/exxelia/501CHB390FCLE/14112408)
Obviously your L has higher Q.
Re: Checking PIN diodes
This wireless method was what Copper Mountain discussed, but did not use in their experiment. Thanks for showing actual application of wireless measuring. So many questions:
What is point of break in coaxial sheath? Was break location by trial or by principle?
I'll have to study on coupling before I can appreciate other details. Thanks for showing results from both programs.
This article describes shielded and unshielded loops and also explaines the gap.
https://incompliancemag.com/article/shielded-vs-unshielded-square-magnetic-field-loops-for-emiesd-design-and-troubleshooting/The PIN Diodes I have mentioned, are fast protection diodes, used to protect the MRI receivers from high RF energy fields.
In this case they are used in so called passive detuning circuits.
I try to simplify that.. So imagine the resonator I have used in the experiment as a receiver antenna and solder two diodes antiparallel on top of the capacitor. On low voltages,
under normal receiving conditions, this diodes have a very low conductance (aprox. 50uS). So the Q factor of the loop should be high.
Not so the defective diodes, with a lower resistance that decreased the Q factor.
The diodes should get conductive only when the MRI is transmitting and the voltage is rising. So they are basically clamping the capacitor, detuning the antenna thus protecting the receiver.
Happy Easter everyone!
Cyprian