XIX Sympozjum Srodowiskowe PTZE - materialy.pdf

XIX Sympozjum PTZE, Worliny 2009
THE POSSIBILITY OF ELECTRIC AND MAGNETIC
PARAMETERS MEASUREMENTS OF NON-SOLID
MATERIALS IN COAXIAL LINES
Roman Kubacki, Leszek Nowosielski, Rafał Przesmycki
Military University of Technology, Warsaw, Poland
With the increasing of quantity of devices emitting of the electromagnetic radiation there is a
need to develop and introduce into practice materials and techniques to protect against
unwanted radiation. This is important for EMC purposes as well as for people protection
against the harmful radiation. The ideal absorber should have low reflectivity and high value
of absorption of the incident electromagnetic energy. There are many possible way to obtain
minimal value of reflected power, eg. pyramidal layer surface or λ/4 thickness of the layer.
Unfortunately, such structures operate correctly rather at higher (microwave) frequencies. At
frequencies lower than 10 MHz there is a need to develop another materials or technique to
reduce reflection coefficient with good parameters of absorption. Such materials should have
not only electric but also magnetic parameters. Monolithic ferrite materials guarantee good
absorption properties, however in many practical use such solid form of absorber can not be
introduce. There is a need to developed much flexible form of substrate. For such form of
materials waveguide or coaxial methods of measuring are not practical. The important thing
also is to assess electric and magnetic parameters of components of the substrate, which are
mainly in powder form.
The method describe in the paper allows to measure complex relative permittivity εr and
permeability µr of non solid (mainly powder) substrate in wide band of frequency – from few
tens kHz till few GHz. The technique of measurement has been based on method developed
for coaxial transmission line where solid material under test must have toroidal form. In
proposed method substrate under test is inserted into coaxial line between two plastic walls as
is showed in Fig.1 and values of electric and magnetic parameters of measured powder
substrate are extracted in mathematical evaluation
measured powder
plastic walls
from measured data of whole sample.
Fig. 1. The sketch of coaxial line with a simple of material under test
Mathematical evaluation which allows to extract
electromagnetic data of measured powder substrate
from measured data of whole sample has been derived
on the base of scattering parameters describing twoport
networks as is presented in Fig. 2.
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