In-situ Measurement of Electromagnetic properties of
The (EM) characterization of materials is
of interest to a variety of research areas including the
detection of buried objects. Conventional measurement
techniques were focused on measuring only the complex
permittivity of the material under test while their magnetic
properties (permeability) were assumed to be unity. Recent
interests on characterizing permeable materials, such as
volcanic soil, make measurement of both the permittivity (ε*)
and the permeability (μ*)
of material equally important for accurate and reliable
interpretation of data and cost effective detection and
classification of buried targets.
In order to measure the electromagnetic properties of the
materials at microwave frequencies, the
reflection/transmission methods are required to estimate
both complex permittivity and permeability over broadband
frequency ranges. Beside the conventional off-line
(laboratory) measurement method,
in-situ method of material
characterization complex is essential to extract accurate
material characteristics without disturbing material’s
environmental properties. Our group has recently developed a
in-situ and broadband probe (40
MHz – 1 GHz) for material characterization including both
the complex permittivity and permeability measurements .
The probe design uses two sections of multi-conductor TEM
transmission lines and unique post processing algorithm for
the determination of both
from S-parameters measurements. The
in-situ probe development (see
Fig. 1) involves the design of junctions and transitions to
achieve good impedance matching throughout the system. Using
numerical simulation, the number and diameter of the outer
conductors were optimized to minimize radiation losses and
undesired higher mode. Prototype probe was manufactured and
experimentally tested to evaluate its performance. Broadband
In-situ probes which can cover up to 10 GHz or
lower to 100 KHz are being designed and their prototype will
be manufactured and tested.
|Fig. 1. (a) Two sections of
coaxial probe are joined across the undisturbed soil
section of interest, (b) Photograph of the developed
prototype of the in-situ probe.
Deliverables & milestones
Simulation of the multi-conductor TEM transmission
line and optimize the configuration.
Development of the post-processing and calibration
algorithm and their verification using simulation.
Prototypes of multi-conductors TEM waveguide and
transient structure to verify the simulation results.
Separate prototype will be constructed to cover
different frequency bandwidth.
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