[TowerTalk] VSWR Heating in Chokes and Baluns

[jimlux]

On 9/3/20 11:14 AM, David Gilbert wrote:
> 
> Can anyone point me to a technical reference that discusses dielectric 
> heating (not magnetic flux related) due to high VSWR in the ferrite core 
> of a balun or common mode choke?
> 

As it happens, i've been looking at stuff like this over the past week, 
for some work on dielectrically loaded wire antennas (how do you make a 
receiving dipole 100m long that works from 10kHz to 100 MHz, without 
having multiple lobes)

What you want to do is look for references on dielectric losses in high 
frequency switching power supplies.




----
The Ferroxcube handbook (FXC_HB2013.pdf) has some discussion on epsilon 
measurements - Resistivity and epsilon r both vary with frequency. (0.5 
ohm meters at 1 MHz for MnZn, er of 1E5 at 1 MHz, both falling with 
frequency)

There's a discussion on page 173 with some plots, and more on page 884 
with discussion about EMI suppression materials (where you combine the 
two loss mechanisms)
----

Here's a paper analyzing chokes as a transmission line, and deriving the 
4 parameters (G,R,L,C) and calculating losses using that model.

http://www.jpier.org/PIERC/pierc88/03.18071405.pdf

----
http://www.die.ing.unibo.it/pers/grandi/papers/mag99.pdf

is a paper where they develop a small signal model for a ferrite core 
transformer - the dielectric losses in the core are considered.

---

https://digital-library.theiet.org/content/journals/10.1049/el_19991161
Dielectric loss analysis of toroid MnZn ferrite core
JunZhu 1 ; Chek FokFoo 1 ; P. Hing 1

looks interesting but I've not been able to download it yet.
"Two types of relaxation polarisation are combined to analyse the 
frequency spectrum of the complex permittivity of MnZn ferrite. The 
dielectric loss of the toroid core has been calculated based on this 
polarisation model. Results show that the dielectric loss accounts for 
25% of the total loss in the megahertz region."


----

Here's a paper that analyzes one case.

http://web.mst.edu/~marinak/files/my_publications/Papers/Ferrite_05508393.pdf

Complex Permittivity and Permeability
Measurements and Finite-Difference Time-Domain
Simulation of Ferrite Materials
Xu, et al.

2010 IEEE Trans EMC


Characterization of MnZn ferrite materials and finite element method for 
MnZn ferrite core loss calculations

https://vtechworks.lib.vt.edu/handle/10919/42895

Not sure this one really is what you want.. but take a look at the abstract