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
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