Final Report_491

American University of Sharjah
Electrical Engineering Department
3-D MICROWAVE SCANNING
SYSTEM
Senior Design II Report
ELE 491 Senior Design II
Student(s) Names & IDs:
Mariam Altunaiji 36898
Taha Al-Anee 41161
Kunal Dialani 45069
Syed Saad Bokhari 46324
Supervised by:
Dr. Nasser Qaddoumi Dr. Amer Zakaria
Semester
Spring 2015

3-D M ICROWAVE SCANNING SYSTEM - Senior Design I Report Rev 1.1
Page ii
ABSTRACT
The idea behind this project is to generate microwave images through a 3D scanning system.
Microwave imaging is one of the Non-Destructive Evaluation (NDE) technique; it is a
technique used to determine the properties of a material without affecting the material
physically. This progress report contains cumulative work of Senior Design I and II. This
project is a continuation of a pre-existent design of a microwave scanning system. The
project is about designing and utilizing a scanner that is moving in three dimensions. This
scanner uses microwave radiation to scan the objects to determine their properties. The sensor
that is attached to the scanner will obtain 3D data; that is a multiple layers of 2D images.
Then, the data will be merged in Matlab to produce one 3D image. In Senior Design I, the
system’s hardware issues were fixed and a code to run the system was designed in LabView.
In Senior Design II, data was collected via a DAQ in LabView and exported to a text file.
This text file was then opened and plotted in Matlab in 3D. Furthermore an issue of noise in
the data was investigated and various solution were implemented.

Page iii
TABLE OF CONTENTS
ABSTRACT.............................................................................................................................II
TABLE OF CONTENTS .....................................................................................................III
LIST OF FIGURES ................................................................................................................V
LIST OF TABLES ................................................................................................................ VI
GLOSSARY..........................................................................................................................VII
1 INTRODUCTION..............................................................................................................1
1.1 PURPOSE .........................................................................................................................1
1.2 MOTIVATION...................................................................................................................1
1.3 SCOPE .............................................................................................................................1
1.4 LITERATURE REVIEW......................................................................................................2
1.5 ASSUMPTIONS AND DEPENDENCIES ................................................................................3
2 REQUIREMENTS SPECIFICATIONS..........................................................................4
2.1 TECHNICAL SPECIFICATIONS...........................................................................................4
2.2 DESIGN SPECIFICATIONS.................................................................................................4
3 DESGIN ..............................................................................................................................5
3.1 OVERALL SYSTEM ..........................................................................................................5
3.2 SYSTEM DECOMPOSITION ...............................................................................................6
3.2.1 User interfaces ....................................................................................................6
3.2.2 Hardware Interfaces............................................................................................7
3.2.3 Software Interfaces .............................................................................................8
4 SIMULATION AND VERIFICATION...........................................................................9
4.1 HARDWARE INTERFACE ..................................................................................................9
4.1.1 Microwave sensor...............................................................................................9
4.1.2 Waveguide..........................................................................................................9
4.1.3 Data Acquisition Device...................................................................................10
4.2 SOFTWARE INTERFACE..................................................................................................11
4.2.1 LabVIEW .........................................................................................................11
4.2.2 MATLAB.........................................................................................................13
4.3 IMPLEMENTATION AND VALIDATION ............................................................................15
4.3.1 Noise ................................................................................................................17
5 SCHEDULE......................................................................................................................20
6 CONCLUSION AND FUTURE WORK .......................................................................21

Page iv
7 APPENDIX.......................................................................................................................22

Page v
LIST OF FIGURES
Figure 1: Overall System flowchart...........................................................................................5
Figure 2 Graphic User Interface.................................................................................................6
Figure 3: Platform......................................................................................................................7
Figure 4: Motor Loop.................................................................................................................8
Figure 5: Microwave Sensor......................................................................................................9
Figure 6: Waveguide Connected to Gunn Oscillator...............................................................10
Figure 7: DAQ .........................................................................................................................10
Figure 8: X Forward Motion....................................................................................................11
Figure 9: Y Forward Motion....................................................................................................12
Figure 10: Z Forward Motion ..................................................................................................12
Figure 11: Return to Home Blocks ..........................................................................................13
Figure 12: Home Setting Blocks..............................................................................................13
Figure 13: Image at plane z=1mm ...........................................................................................16
Figure 16: 3D Image combining all z plane images ................................................................17
Figure 17: Noisy Image............................................................................................................18
Figure 18: Multiple Filters Tested ...........................................................................................19

Page vi
LIST OF TABLES
Table 1: Senior Design 1 Gantt chart.......................................................................................20
Table 2: Senior Design 2 Gantt chart.......................................................................................20
Table 3: Common waveguide designations .............................................................................22

Page vii
GLOSSAR Y
TERM DEFINITION
Near field
The region surrounding an antenna, shorter
than the Fraunhofer distance (see Appendix
A)
Gunn diode
Transferred electron device (TED), used to
emit high-frequency microwaves.
Waveguide
Hollow, metallic tube which transmits certain
electromagnetic waves

Page 1 of 26
1 INTRODUCTION
1.1 Purpose
The aim of this project is to design a three-dimensional scanning system that utilizes
microwave-imaging technology to examine the integrity of a structure. In fact, a different
group designed this project last semester, and our aim is to proceed with what they left. Thus,
one goal is to implement a functional 3D microwave scanning system. This can be achieved
by improving mechanics of pre-existing scanning system, re-designing it, and troubleshooting
the control software. The second goal is to acquire 3D data using the system’s microwave
probe. We will record multiple 2D layers and merge them as one 3D image. This process
would be done using MATLAB to obtain images of defects.
1.2 Motivation
This project is about building and utilizing a three-dimensional microwave scanner to acquire
images noninvasively for various targets. The images will be used to detect defects and
impurities within different specimen by locating their positions. In order to get the 3D
position of the defects, various data at 2D position within a plane will be measured as well as
the relative depth within the object.
The structure of the 3D microwave scanning system was designed and implement by a
different group. The pre-existing system hardware specifications were; X-band waveguide
with two 2.5 × 1.0 cm rectangular openings and a transceiver unit (source and detector)
connected to one opening of the waveguide. Waveguide motion in 2D was possible by using
a motor system with one motor in x-axis, and two motors in y-axis. However, the waveguide
could not move in the z-axis; its position can be manually adjusted in the third dimension.
1.3 Scope
The main purpose of technology is to facilitate human life and to help humans achieve their
goals. It is important to expand the range of available technology that fall under non-
destructive testing. This test is important as it insure the safety of the structures and materials
without any negative efftect on the material. One type of non-destructive testing is the
microwave non-destructive evaluation; it examines and categorizes the materials using the
microwave band of electromagnatic spectrum, ranging form 300 MHz to 300 GHz.

Page 2 of 26
Microwave radiation is more useful if the object is low-loss dielectric material which are
easier to penetrate. The importance of non-destructive testing is that its keeps the material
safe from any physical damage. The material is exposed to microwave radiation emitting
form a transceiver and the reflected wave is observed as voltage. Any sudden change in
voltage represents a defect within the material. There are numerous applications where
microwave NDE is essential, some of which are: testing for delamination’s in rocket casings,
detecting defects in rocket propellants, measuring the thicknesses of ablative shields for
reentry vehicles, detecting voids in honeycombed ablative materials, detecting inclusions and
porosity in ceramics and molded rubber, detecting surface cracks in artillery shells,
measuring moisture content in dielectric materials, and measuring density variations in
lumber [1].
Input/Output:
The primary input to the system is a Gunn diode which is operating at 10GHz. The secondary
input to the system is the length and width of the test sample. The user has to specify where
to save the file containing the DAQ data.
The output of the system is voltage from the DAQ unit and this data is saved in a text file.
The voltage is plotted as color variations within 3D space in MATLAB. The position of the
sensor is also outputted so that the location of any defect can be specified.
1.4 Literature Review
M. Pastorino. “Microwave imaging”
This book is about the microwave imaging. This book defines the microwave imaging as “a
technique used in sensing a given scene by means of interrogating microwaves”. Also, it
explain the usefulness of this technique for engineering purposes.
G. Roqueta, L. Jofre, and M. Feng, "Microwave Non-Destructive evaluation of corrosion in
reinforced concrete structures"
This source presents evidence of the non-distructive microwave imaging technique to
determine the corrosion percentage in reinforce concrete structure. This technique depends on
frequency domain measurements of the scattering signature of the concrete structure and the
thermal induction application on rebar surface.

Page 3 of 26
G. S. Schajer and F. B. Orhan, "Microwave Non-Destructive Testing of Wood and Similar
Orthotropic Materials"
This paper is about microwave non-destructive testing of wood and similar orthotropic
material. The testing in this book estimate the fiber direction, moisture destiny, and dry
density of orthotropic material.
N. Qaddoumi, R. Zoughi and A. J. Bahr, "Microwave NDE Techniques".
Dr. Nasser Qaddoumi, Associate Professor of Electrical Engineering at AUS, Dr. Reza
Zoughi, Missouri University of Science and Technology, and Alfred J. Bahr of SRI
International, wrote this paper. This paper provided information needed to implement
waveguides properly in the system.
1.5 Assumptions and Dependencies
The system is interfaced with a computer; therefore, a computer with all the necessary
software is required at all times to operate the machine. These software include National
Instruments Measurement and Automation, Kollmorgen Workbench and LabView to run the
hardware and collect data, Notepad to write data into, and finally MATLAB to process and
plot the data.
An assumption is made because the actual data collected is very noisy and distort the colors
in MATLAB. Therefore a filter in MATLAB was added to remedy the problem and color
limits were set to minimize noise. It is assumed that the data colors represent actual highs and
lows where as they are filtered out.

Page 4 of 26
2 REQUIREMENTS SPECIFICATIONS
2.1 Technical Specifications
For the 3D scanning system, there are three axes: x, y, and z.
The structure must have the following dimensions:
 Base structure: 0.4 x 0.4 m
 Scanning area: 0.3 x 0.3 m
 Frame height: 0.1 m
The x-, y- and z- axes resolutions are 0.1 mm (step size).
The step size can be altered depending on the quality of the results that need to be obtained
from the system.
2.2 Design Specifications
The system has several significant aspects to be taken into consideration.
1. High Resolution
The system needs to have small resolution so that the scanner may detect miniscule
change in the specimen. This would provide an accurate 3D image.
2. Low Cost
The system should be affordable for parties that wish to use it.
3. Weight
The less the weight of the system, the more portable will be the machine.
4. Fast and Efficient motor
Time is an important property to judge in the quality of the product. The faster and
more accurate the system the better the product will be.
5. High Stability
The system needs to be stabled to insure the quality of the reading

Page 5 of 26
3 DESGIN
3.1 Overall System
Figure 1: Overall system flowchart
 As displayed in Fig. 1, we start the sampling of the object by first setting home
position of the probe.
 The user has a choice for a fixed z position or incremental z positions. There are 2
separate codes available.
 Next the user enters the specification for the scanning process. The user sets the final
x, y and z positions in the graphical user interface (GUI).
 After the above steps are done, start scanning.
 If the z position is fixed then the z-axis motor will move to final position and then x-
axis and y-axis motors will move.
 If the z-position is incremental, then the x-axis and y-axis motors will complete their
motion and come back to ‘Home’. After that z position will increment followed by x-
axis and y-axis motors repeating their motion.
 During the above motion, the sensor will emit microwave radiations. The radiation is
reflected back by the specimen at a fixed intensity. If there is a defect the intensity
would be different.

Page 6 of 26
 The intensities at different points are recorded in a 2D matrix for a particular position
of z.
 Multiple 2D matrices at different values of z-positions will be merged together in
MATLAB to form a 3D image via recording the data in a text file.
 After the scanning is done the probe returns to the ‘Home’ position.
3.2 System Decomposition
3.2.1 User interfaces
Figure 2 Graphic User Interface
 The GUI is common to both the fixed z-position and incremental z-position programs.

Page 7 of 26
 After pressing the LabVIEW play button, we first set our origin (‘Home’) position
using the buttons shown in the GUI above. These buttons work like the keys on a
keyboard of a computer.
 Once the origin is set, the user can specify the specimen dimensions and the velocity
within which the frame will move.
 The user then needs to click the ‘Start’ button for the program scanning to start.
 Once the scanning is complete, the sensor provides data points in the form of
voltages, which will be shown in the ‘Real Matrix’.
3.2.2 Hardware Interfaces
A different group designed the hardware therefore; its specifications were fixed. The
hardware consists of three different facets.
1. Platform
Made from aluminum and it has 1 x-axis, 1 y-axis and 1 z-axis. The arrangement of
the axes are shown in figure 3. X-axis the frame movement being towards the right
and left, y-axis forward and backward and z-axis upward and downward.
Figure 3: Platform
2. Motor Loop
Motor shafts are connected to the screws on the platform. The motor are connected
to the drives which in turn are connected to the interface. The interface is connected

Page 8 of 26
to the PCI controller of the PC. The loop is completed via an ethernet cable
connecting the drive to the PC.
Figure 4: Motor Loop
3. Waveguides and Gunn Diodes
The waveguides connected to the microwave sensor to be used range from 8 to 12
GHZ; these are the X-band range for waveguide. Gunn diodes are composed of two
diodes. A 10-V DC supply voltage is applied on its terminals to power the Gunn
diodes. The transmitter emits microwave RF signals at 10.5 GHz.
3.2.3 Software Interfaces
The software to be used for this project are LabVIEW , MATLAB , NIMAX and Kollmorgen
Workbench.
 LabVIEW is the main application software for the project. LabVIEW was chosen as it
is user friendly and has blocks readily available.
 MATLAB will be used to merge the 2D matrices into a 3D image.
 NIMAX is used to test all the hardware to insure proper functioning.
 Kollmorgen Workbench is used to connect the drives with the P.C. of the computer
via the Ethernet cable.

Page 9 of 26
4 SIMULATION AND VERIFICATION
4.1 Hardware Interface
The 3D scanning system consists of four DC voltage supplies. Three DC supplies for each of
the three motors and one for the microwave sensor; however the motors will require higher
DC voltages than what the microwave sensor in order to work. The direction of rotation of
the motors depends on polarity of the connections (negative and positive terminals) of the DC
supply.
4.1.1 Microwave sensor
Figure 5: Microwave Sensor
Fig. 5 shows the microwave sensor that will be used to take images. It is a Gunn oscillator,
which consists of two parts, the Gunn diode and the diode detector. Gunn diodes provide the
ability to convert DC energy into microwave power. Gunn diodes are easy to use and they are
a relatively low cost method for generating microwave RF signals. Diode detectors operate
by detecting the envelope of the incoming signal. The operation is done by rectifying the
signal. Current is allowed to flow through the diode in only one direction, giving either the
positive or negative half of the envelope at the output. A capacitor at the output is used to
remove any radio frequency components of the signal at the output.
4.1.2 Waveguide
Diode Detector
VDC
Ground

Page 10 of 26
A waveguide is a hollow, metallic tube, which transmits electromagnetic waves via
successive reflections from the inner walls of the guide. Waveguides come in circular and
rectangular shapes but of uniform cross-section. We have used a rectangular X-Band
waveguide.
Figure 6: Waveguide connected to Gunn Oscillator
4.1.3 Data Acquisition Device
The Data Acquisition device (DAQ) is used as an intermediate between the hardware
components and software. It transfers the readings from the microwave sensor to the
computer. These readings will be the intensity of the return wave from the specimen. The
DAQ will collect information in multiple planes, which will then be merged in MATLAB to
form a 3D image.
Figure 7: DAQ

Page 11 of 26
4.2 Software Interface
4.2.1 LabVIEW
Figure 8: X forward motion
Figs. 8, 9 and 10 show the blocks responsible for the forward movement of X, Y and Z
motors. The ‘Position’, ‘Acceleration’ and ‘Velocity’ blocks aid in movement of the motors
and the ‘Read Axis’ and ‘Read Position’ aid in recording the position of the frame. The DAQ
assistant block is in the X axis, as the whole idea of the program is to jot down various points
on this axis in order to generate a matrix. The three figures below belong to both the
programs.

Page 12 of 26
Figure 9: Y forward motion
Figure 10: Z forward motion
Fig. 11 is the code for returning all the three axes to the origin. All three axes have the
position block with a final value fixed at zero. When implemented, this code moves the frame
back to the user-defined origin.

Page 13 of 26
Figure 11: Return to home blocks
Figs. 12 shows the codes that are used for setting the ‘Home’. The figure has the ‘Event
Structures’ blocks. These blocks are implemented only when their respective buttons are
clicked in the GUI. Figure 12 represents the ‘Home’ button which when pressed, defines the
origin to be that particular point on the platform.
Figure 12: Home setting blocks
4.2.2 MATLAB
clc
clear
%Read Dimensions
sample_dim=dlmread(uigetfile('*.txt','Select the MAX and MIN text
file'),'',0, 0);
x_length=sample_dim(1);
y_length=sample_dim(2);
z_length=sample_dim(3);
ll=1;
row=y_length*2;
column_deci=16.22*(x_length/10)+18.637;
column=round(column_deci);

Page 14 of 26
%Setup 3D Space
x_axis = linspace(0,x_length,column+1);
y_axis = linspace(0,y_length,row+1);
z_axis = linspace(1,z_length,z_length);
[x_grid, y_grid] = meshgrid(x_axis, y_axis);
%Read DAQ value files
data_file=uigetfile('*.txt','Select the DAQ VALUES text file');
for ii=1:z_length
sample_DAQ_transposed(:,:,ii)=dlmread(data_file,'',[ll 0 ll+row
column]);
ll=ll+row+3;
sample_DAQ(:,:,ii)=sample_DAQ_transposed(:,:,ii).';
end
%2D Plots
for xx=1:z_length
sample_DAQ_max1=min(max(sample_DAQ_transposed(:,:,xx)));
sample_DAQ_min1=max(min(sample_DAQ_transposed(:,:,xx)));
clims=[sample_DAQ_min1 sample_DAQ_max1];
sample_DAQ_filtered1(:,:,xx)=wiener2(medfilt2(sample_DAQ_transposed(:,:,xx)
,[8 8]),[8 8]);
figure;
imagesc(sample_DAQ_filtered1(:,:,xx),clims);
set(gca,'YDir','normal');
xlabel('length (mm)');
ylabel('width (mm)');
end
summin=0;
summax=0;
%3D Plot
for jj=1:z_length
sample_DAQ_max(1,jj)=min(max(sample_DAQ(:,:,jj)));
sample_DAQ_min(1,jj)=max(min(sample_DAQ(:,:,jj)));
summin=summin+sample_DAQ_min(1,jj);
summax=summax+sample_DAQ_max(1,jj);
sample_DAQ_filtered(:,:,jj)=wiener2(medfilt2(sample_DAQ(:,:,jj),[8
8]),[8 8]);
A = sample_DAQ_filtered(:,:,jj);
z1 = z_axis(jj) + 0*x_grid;
if jj==1
figure;
surface(x_grid, y_grid, z1, A.','linestyle', 'none');
caxis(clims);
hold;
else
surface(x_grid, y_grid, z1, A.','linestyle', 'none');

Page 15 of 26
hold;
end
set(gca, 'YDir','normal');
end
max=summax/z_length;
min=summin/z_length;
clims=[min max];
caxis(clims);
colormap(jet);
xlabel('length (mm)');
ylabel('width (mm)');
zlabel('height (mm)');
title('Scanned Sample');
The MATLAB code operates in 5 distinct steps
1) The dimensions of the specimen are read from a file.
2) A 3D space is created using meshgrid command.
3) The voltage readings are read from the text file and placed in matrices for each value
of z-plane.
4) Separate 2D images for every value of z-plane are plotted
5) A 3D plot with all values of z are shown.
4.3 Implementation and Validation
Figures 13, 14, 15 and 16 show the result of plotting the DAQ data in Matlab.

Page 16 of 26
Figure 13: Image at z=1mm
The defect is visible in Fig. 13 but due to scattering the image is not clear.
Figure 14: Image a z=2mm
In Fig. 14 again a defect is visible but the details cannot be made out due scattering of the
waves.
Figure 15: Image at z=3mm

Page 17 of 26
An image of the defect is clearly visible in Fig. 12 and show the defect in great detail.
Various colors show the relative depth of the defect at various locations. For this specimen,
the right depth of z of the defect is 3 mm which can be inquired from the results. In any
future readings one can simple go to 3mm and take just 1set of readings to save time.
Figure 16: 3D Image combining all z values
A 3D plot shows all of the slices of z together.
4.3.1 NOISE
One of the biggest and most unexpected issues that plagued the project was noise. We started
to troubleshoot the entire system to find the source of the noise. Following are the various
methods we tried to eliminate the noise.
1. We tested the power supply by putting its output straight to the DAQ in order to
ensure that our DAQ is working properly.
2. We made the output of the sensor go through a couple of resistors of the same
resistances by trying 10k, 100k and 2.2M Ohm resistors. Adding resistors are known
to smoothen the values.

Page 18 of 26
3. We tried using an instrumentation amplifier and a DC amplifier at the output of the
detector.
4. We also tried replacing the DAQ with another.
5. Lastly, we tried configuring the DAQ using other modes such as NRSE and RSE
configurations. We originally were using the differential mode.
We found out that none of these methods helped in eliminating the noise. The resistors were
giving the best values; the lower the resistance the better. The amplifiers were actually
amplifying the noise along with the average DC value. The values did not change much even
after we changed the DAQ. All the three configurations were giving nearly the same results.
After all the trials we narrowed down 2 possibilities, firstly that the noise originated from
within the DAQ itself and secondly that the servo motors are producing interfering magnetic
field. We have filter commands in the MATLAB program which we are using to eliminate
the noise as further testing is required to fully remove the noise.
Figure 17: Noisy image
Figure 12 shows a very noisy image of the sample defect. We applied various filters to it
before settling for one.

Page 19 of 26
Figure 18: Multiple filters tested
We eventually settled for the combination of Wiener and Median filter as it produced the best
possible result.

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5 SCHEDULE
Table 1: Senior Design 1 Gantt chart
Table 2: Senior Design 2 Gantt chart

Page 21 of 26
6 CONCLUSION AND FUTURE WORK
The scanner was designed and implemented by a different group. Our first and foremost task
was to fix all bugs in the system. The problems were divided into two parts: hardware and
software problems. Both hardware and software problem were tackled individually and one
after the other. Synchronization of Y-axes was the major issue relating to hardware.
Therefore, we modified the design to remove one of the y-axis motors. We also managed to
automate the z-axis motion, which required us to use the extra y motor and a flange; also two
separate codes for the z-axis were written. Software part of the problem included rewriting
some of the code to make it more efficient and writing new codes to complete z-axis motion;
y-, z- and x-axis return motion; generating matrices; and setting home position via LabVIEW.
Furthermore the sensor was attached to take test reading of a sample. In Senior Design II, we
focused on the imaging part of the project. The imaging part has three parts; 2D scanning, 3D
image generation and detecting defects. First 2D images are be taken at different levels of z
and then merged to form a 3D image in MATLAB. This image easily show defects under the
surface of the specimen. The scanner can also be used to determine the depth of the defect as
well. All that remains is to make the scanner as efficient, reliable and cheap as possible while
taking accurate images and to find a more permanent solution to the noise.

Page 22 of 26
7 APPENDIX
A. Formulae
Fraunhofer distance, 𝑑𝑓 =
2𝐷2
𝜆
, where λ is the wavelength and D is the
longitude/diameter of the antenna
B. Waveguide calculation
C. Waveguide designations
Waveguide
Designation
a
(in)
b
(in)
t
(in)
f
c10
(GHz)
freq range
(GHz)
WR975 9.750 4.875 .125 .605 .75 – 1.12
WR650 6.500 3.250 .080 .908 1.12 – 1.70
WR430 4.300 2.150 .080 1.375 1.70 – 2.60
WR284 2.84 1.34 .080 2.08 2.60 – 3.95
WR187 1.872 .872 .064 3.16 3.95 – 5.85
WR137 1.372 .622 .064 4.29 5.85 – 8.20
WR90 .900 .450 .050 6.56 8.2 – 12.4
WR62 .622 .311 .040 9.49 12.4 - 18
Table 3: Common waveguide designations
2 2
2mnc
c m n
f
a b
 
   
   
   
8
where 3 10 m/sc  
22
2













b
n
a
m
c

Page 23 of 26
D. User Manual for the 3D Microwave Scanning System

Page 24 of 26

Page 25 of 26
E. References
[1] P. J. Shull, Nondestructive Evaluation: Theory, Techniques, and Applications, New York:
Marcel Dekker, 2002.
[2] M. Pastorino, Microwave imaging. Hoboken, N.J: Wiley, 2010.
[3] G. Roqueta, L. Jofre, and M. Feng, "Microwave Non-Destructive evaluation of corrosion
in reinforced concrete structures," in Proceedings of the 5th European Conference on
Antennas and Propagation (EUCAP), pp. 787-791.
[4] G. S. Schajer and F. B. Orhan, "Microwave Non-Destructive Testing of Wood and
Similar Orthotropic Materials," Subsurface Sensing Technologies and Applications, vol. 6,
pp. 293-313, 2005.
[5] N. Qaddoumi, R. Zoughi and A. J. Bahr, "Microwave NDE Techniques".

Final Report_491

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