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INVASIVE MICROWAVE MEASUREMENT OF SOIL ELECTROMAGNETIC PROPERTIES AND CORRELATION WITH PHYSICAL QUANTITIES
K. Clay, M. Farid, A. N. Alshawabkeh , C. M. RappaportContact Info: [email protected] [email protected] [email protected] [email protected]
This work was supported in part by CenSSIS, the Center for Subsurface Sensing and Imaging systems, under the Engineering Research Centers Program of the National Science Foundation (Award Number EEC-9986821)
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Overview of the Strategic Research PlanOverview of the Strategic Research Plan
FundamentalScienceFundamentalScience
ValidatingTestBEDsValidatingTestBEDs
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Bio-Med Enviro-Civil
ABSTRACTModeling detailed spatial distributions and dynamics of the soil properties in
the inherently inhomogeneous subsurface requires extensive site
characterization.
Characterizing this variability with conventional methods is invasive and thus,
time consuming, costly, and subject to a large degree of uncertainty due to
lack of densely populated sampled insitu measurements thus the need for
none or less invasive techniques.
It is known that the propagation of electromagnetic waves through a material
is dependent on the electrical and magnetic properties of the material. These
properties are dielectric permittivity, electrical conductivity and magnetic
permeability. There is also need for correlation of measured EM properties to
physical and mechanical properties of the soil.
Most of these parameters are frequency dependent thus broad band
frequency dielectric permittivity and conductivity is vital.
INTRODUCTIONMicrowave measurements refer to electromagnetic measurements conducted
at frequencies in the micro wave region. This region lies between 300MHz
and 300GHz.
In the electromagnetic spectrum for frequency and wavelength, the position of
microwaves lies between radio waves and infrared. This region is bounded at
the long-wavelength end by the radio wave region, and at the short-
wavelength end by the infrared region.
The interaction of microwaves with materials and structures is best described
in terms of waves. Therefore microwave measurements such as amplitude
and phase measurements of transmitted or reflected waves by the specimen,
will contain information about internal flaws, material composition, structure,
density, porosity, homogeneity, orientation, state of cure, and moisture
content, as well as the geometry of the specimen. The fact that microwaves
are sensitive to such a large number of material properties leads to a number
of possible applications.
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PLANE WAVE PROPAGATION IN LOSSY MEDIA
The propagation properties of an electromagnetic wave such as its phase velocity up and wavelength, are governed by the angular frequency w and the three constitutive parameters of the medium:To examine wave propagation in a conducting medium, we return to the wave equation give by
22
w ww
fw
ww
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LOW-LOSS DIELECTRIC AND GOOD CONDUCTOR
When the medium is called a low-loss dielectric and when
the medium is characterized as a good conductor.
For a low-loss dielectric,
For a good conductor
,1
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SOILBED FACILITY AND LABORATORY MEASUREMENT SYSTEM
The SoilBED testing facility has dimensions of 150 cm width by 120 cm depth by 275 cm length (5 ft x 4 x 9 ft).
The longitudinal walls of the facility are made of reinforced concrete while the transverse walls and the gate to the small injection trench are made of 3.8 cm (1.5 in) thick acrylic sheets.
The facility is filled with sand as the homogeneous and isotropic soil media.
The laboratory measurement system is an Agilent 8714ES RF Network Analyzer (NA) and a computer for data acquisition using a Microsoft Excel based system.
A NA is an instrument which measures the complex transmission and reflection characteristics of two-port devices in the frequency domain for the frquecy range 300kHz-3GHz.
Its connected to connected to a 12 channel Agilent 87050ES multiport test set on which 12 co-axial cables are connected.
LABORATORY SETUPAntenna set up 1: Antennas on top of each other (Vertical Plane)
Antenna set up 2: Antennas in the same horizontal plane
FREQUENCY DEPENDENCE OF EM PROPERTIES
The relative permittivity of the sand does not show significant frequency dependencewhatever the water content is. There is significant frequency and water content dependence of the electrical conductivity
THEORETICAL BACKGROUND OF MEASUREMENTS AND DATA PROCESSING
In this analysis, the problem is modeled as a plane wave boundary value problem which leads to a number of algebraic equations that can be solved for the relative permittivity and conductivity. We have restricted our study to the complex permittivity because most materials of geophysical interest are nonmagnetic, while conductivity is incorporated in the complex permittivity.
We can deduce that the differential phase is equal to: j(ωt-βz)= j(β(z+dz) -βz)
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DETERMINATION OF THE CONDUCTIVITY
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0.4 0.6 0.8 1 1.2 1.4 1.6-35
-30
-25
-20
-15
-10
-5
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5Variation of unwrapped differential phase with frequency
dP in
radia
ns
24681012
0.4 0.6 0.8 1 1.2 1.4 1.6-80
-60
-40
-20
0
20A plot of the unwrapped phases for 6", 12" and differential
dP in
radi
ans
0.4 0.6 0.8 1 1.2 1.4 1.60
0.2
0.4
0.6
0.8
1
A plot of the Conductivity profile for the sand
Frequency (GHz)
612dP
612
EFFECT OF EXPERIMENTAL PROCEDURES ON RESULTS
To investigate the impacts of saturating and draining on the relative permittivity, phase measurements for saturating cycles were done.
1 2 3 4 5 6 721.8
21.85
21.9
21.95
22
22.05
22.1
22.15
Saturating cycles
Variation of Relative permittivity with saturating cycles
Average
1 1.5 2 2.5 3 3.5 419.7
19.8
19.9
20
20.1
20.2
20.3
20.4
20.5
20.6
20.7
Saturating cycles
Variation of Relative permittivity with saturating cycles
Average
Cycle
Distance from Transmitter
8" 12" 16" Average
1 23.367 21.465 20.742 21.858
2 23.071 21.556 20.846 21.824
3 23.577 21.617 20.838 22.01
4 23.664 21.611 20.858 22.044
5 23.706 21.675 20.83 22.07
6 23.664 21.635 20.813 22.037
7 23.738 21.645 20.835 22.073
INTRUSIVE MICROWAVE MEASUREMENTS FOR DENSITY INFERENCEThe relative permittivity of saturated sand and dry density were determined at differentlevels of compaction. The relative permittivity was then plotted against the dry density, porosity and void ratio.
Average dry density (g/cm3)
Relative Permittivity
Porosity Void ratio
1.397333333 23.61080.473 1.118
1.682514286 19.56220.365 1.7465
1.723433333 18.36990.3495 1.8835
1.748466276 16.92310.34 1.9395
1.755708403 16.59170.3375 1.981
0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.216
17
18
19
20
21
22
23
24
Frequency (GHz)
Rela
tive
Perm
ittiv
ity
Frequecy dependence of the Relative Permittivity for the different Dry Densities
D1D2D3D4D5
D1D2D3D4D5
16 17 18 19 20 21 22 23 241.35
1.4
1.45
1.5
1.55
1.6
1.65
1.7
1.75
1.8A plot of Dry density against Relative Permittivity
Relative Permittivity
Den
sity
(g/c
c)
16 17 18 19 20 21 22 23 240.32
0.34
0.36
0.38
0.4
0.42
0.44
0.46
0.48A plot of Porosity against Relative Permittivity
Relative Permittivity
Poro
sity
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 216
17
18
19
20
21
22
23
24A plot of Void ratio against Relative Permittivity
Relative Permittivity
Void
ratio
ONGOING WORK•Design of a reliable 2D setup•Collection of phase and transmission data from the 2D setup•Validation of the 2D FDFD model using using 2D setup data.
REFERENCES•Blitz, Jack. “Electrical and magnetic methods of nondestructive testing” Bristol ; Philadelphia : A. Hilger, 1991.•Ida, Nathan. “Microwave NDT” Dordrecht ; Boston : Kluwer Academic, c1992.•Ida, Nathan.” Engineering electromagnetics” New York : Springer, c2000.
