Journal of Signal and Information Processing, 2011, 2, 227-231
doi:10.4236/jsip.2011.23031 Published Online August 2011 (http://www.SciRP.org/journal/jsip)
227
Optimization of the UWB Radar System in
Medical Imaging
Taoufik Elmissaoui, Nabila Soudani, Ridha Bouallegue
6’Tel Research Unit Higher School of Communications of Tunis, Sup’Com University of Carthage, Tunis, Tunisia.
Received December 18th, 2010; revised May 20th, 2011; accepted May 30th, 2011.
ABSTRACT
During the last decades, we have witnessed a widespread deployment of the ultra wide band (UWB) radar systems.
Considering a medical field, an algorithm optimizing these systems is pointed out in this contribution. Beginning with
the description of the UWB radar system, this algorithm has proved to be not only able to take a medical image of the
human body but also capable of diverting the human tissue. Moreover, we insist on the fact that this algorithm can
easily optimize different radar parameters. So, the human body layer width, the incident angle and the frequency maxi-
mizing reflection coefficient are estimated in this paper.
Keywords: UWB, Radar, Medical Image, Human Body Model
1. Introduction
The ultra wide band (UWB) technology presents many
advantages. This technology is used in many fields such
as the transmission system and the radar application. In
the literature, many studies recommend the deployment
the UWB radar in medical imaging [1-4]. In fact, these
systems consist of sending ultra short electromagnetic
pulses and analyzing the echo reflected by the human
body which is exposed to this radiation. Each human
body layer makes its proper signature in the reflected
signal. Because the human body structure has a variety of
composition and electric properties.
The UWB radar has several key advantages such as
[5]:
 The pulse has a wide frequency spectrum that can
easily cross obstacles,
 The pulse length is very short but has a very elevated
resolution,
 The short pulse leads to a little energy consumption,
 It has a good resistance to the multi-path interference,
 It allows not only the detection of a human being, but
also its positioning.
In this paper, we introduce an algorithm that optimizes
the radar system in the imaging application. In fact, the
human body characteristics vary with several parameters
like age, sex and organ composition. For this goal, we
define our proposed algorithm in the first position.
Moreover, we present the different stages of this algo-
rithm in the second position. Indeed, our radar system is
capable of estimating these parameters automatically in
an attempt to optimize the capture of the medical image.
For this reason, the UWB radar system starts by com-
puting the layer width. After that, she calculates the fre-
quency that enables us to maximize the echo strength of
each layer. Similarly, we take into consideration the spe-
cific absorption rate in order to minimize the effect of the
radar radiation. Finally, we discuss the results in the con-
clusion.
2. The UWB Radar System for a Medical
Application
The UWB radar is a system that uses an ultra wide elec-
tromagnetic pulse. The band of this device must be
greater than 25% [6]. The purpose of our system is to
capture the human body layer image. This system en-
ables doctors to diagnose the human body structure. In-
deed, it can also be used in cancer detection because it
presents electric properties different form the normal
human tissue. Similarly, UWB radar enables doctors to
control the human heart movement because the human
dilated tissue has electric properties different from the
non dilated tissue.
The bases of our radar system is sending an electro-
magnetic pulse and exploiting the several echoes re-
flected by each human body structure.
Figure 1 presents the radar system architecture that is

Optimization of the UWB Radar System in Medical Imaging 228
Receiver
Tr ansce iv er
Human body layer
Skin Fat
Figure 1. The radar architecture.
used for a medical application. We propose to use multi-
static radar in an attempt to have several copies of the
echo reflected by each human body layer on one hand,
and to assure the coverage of all the human body struc-
ture on the second hand.
Moreover, Figure 2 illustrates an algorithm that en-
ables us to optimize our radar system. The later is capa-
ble of changing its parameters automatically according to
the electric characteristics of the patient. In fact, the
width and the electric properties of each layer vary with
the age, the sex and the human body region of the patient.
For this reason, we propose to use of adaptable radar
parameters for each kind of patients. Nevertheless, the
receiver antenna positions vary only with the incident
angle and the human body layer thickness.
Our radar system must start to compute each human
body layer width in the first position. In fact, the radar
system sends an oblique incident electromagnetic wave
that will be divided into two parts: a transmitted and a
reflected part. The transmitted part crosses the first hu-
man layer and reaches the second layer and undergoes
the same division. The reflected part by the second layer
crosses the first layer and arrives at the antenna. At this
stage, our radar can compute the first layer thickness by
exploiting the antenna position.
Then, the radar system computes the incident angle
that maximizes the radar resolution in the second posi-
tion. Indeed, our system changes the incident angle and
computes the strength of the echo reflected by the human
body layer.
At this stage, our system is capable of selecting an an-
tenna that enables us to capture the echo of each layer.
After that, the radar computes the frequency that
maximizes the reflection coefficient of each layer by
changing the frequency of the incident pulse. Because the
human body electric characteristics vary with the fre-
quency of the incident electromagnetic pulse.
Subsequently, the radar compares the echo reflected
by each layer with another reference echo in an attempt
to create an image of the layer source of the reflected
electromagnetic pulse.
3. The Electric Properties of the Human
Body Layer
The UWB radar in medicine exploits the echo reflected
by each human body layer to create an image. For this
reason, we must study the interaction between the human
body layer and the incident electromagnetic pulse. Many
studies in literature model the human body layer by a
good dielectric that has a dependent electric characteris-
tic frequency [7-10]. Indeed, the propagation of the elec-
tromagnetic wave in the human body structure is deter-
mined by their electrical parameters. The permittivity of
the human body tissue is given by its molecular structure.
Moreover, the permittivity of each human body layer is a
complex quantity and it can be expressed by [7-10]:
j




 (1)
where ε′ is the relative permittivity of the biological tis-
sue and ε" is the out-of-phase loss factor associated with
Pulse generation
Comparator
Layer Image
User layer
selected
Layers frequency
computer
Layers width
calculation
Pulse generation
(refrence)
Echo
layer
f
1
12
,, n
f
ff
Figure 2. Radar algorithm.

Optimization of the UWB Radar System in Medical Imaging229
it. As such:
0




  (2)
As before, the skin depth of the electromagnetic pulse
in each human body layer can be written as follows [11]:
1
2
2
00
0
11
2
r
r
 











 





1
(3)
where:

: the wave angular frequency
0

: the free space permittivity.
0

: the free space electromagnetic permeability.

: the relative conductivity.
r

: the relative permittivity.
The conductivity of the human body layer tissue has
different values depending on their compositions and
physiological functions.
Figure 3 shows the human body us the biological
structure used in this paper.
4. Thickness Estimate of Each Layer
The first step of our radar system is the computing each
layer width. For this purpose, we use an electromagnetic
pulse with an oblique incident. According to [2], we can
estimate the antenna position that enables us to capture
the echo of each human body layer.
In our case, we place many receiver antennas that en-
able us to capture each echo reflected by the human
structure. In fact, the nearest layer of the transmission
antenna has the antenna position closest to the trans-
ceiver antenna.
Let us start by the first layer in a free space. In this
section, we presume a transmitter antenna placed in a
position P that radiates electromagnetic with an incident
angle in

equal to 45˚. We start by computing the dis-
tance that separates the radar antenna transmitter and the
skin layer. In fact, the distance can be expressed as:

1
02tan in
P


 (4)
where, P1 is the antenna position that captures the echo
reflected by layer 1.
Moreover, the skin width can be expressed as:
Figure 3. Layered at a tissue model.

21
,1
2tan
SKin
t
Pl



 (5)
Here, P2 is the antenna position that captures the echo
reflected by layer 2.
Similarly, the thickness of the muscle layer can be
written as:


312
,2
2tan
Muscl e
t
Pll


 (6)
Here, P3 is the antenna position that captures the echo
reflected by layer 3.
At this stage, we can generalize this result. The width
of each layer that composes the human body structure
can be formulated as:



12 1
,1
2tan
th ii
i
ti
ll l P




 (7)
where, Pi is the antenna position that captures the echo
reflected by the layer.
th
i
This finding enables us to compute the travel echo of
each human layer. In addition with [2] the travel time for
the layer can be expressed as:
th
i
1
1
1
ii
i
i
i
dd
ttv




 (8)
Here, di is the distance crossed by the ith echo layer
and presented by:

1
,1
2sin
i
ii
ti
l
dd



 (9)
When we examine the result given by the last equation,
we conclude that it is possible to distinguish the echo
layer by its arrival time to the receiver.
5. The Frequency of Each Layer
Our radar system exploits the echo reflected by the hu-
man body structure. On this basis, we must optimize the
reflection coefficient of each human body layer. In this
section, we try to set the frequency that enables our sys-
tem to maximize the power of the signal reflected by the
human body structure.
The reflection of each layer is dealt with [1], we out-
line briefly the results in this section. Indeed, this value is
presented by:
232 31
1
t
ii
i
TTTTTT 
 



i
(10)
where, i and i
T

present respectively the total field
transmission and the reflection by the ith layer for an in-
cident wave on the left side. They can be expressed as:
1,, 1
1,, 1
(1)(1) exp(2)
1exp(2)
i
ii iii
i
i
iiii i
rr
Trr





 
 (11)

Optimization of the UWB Radar System in Medical Imaging 230


1,, 1
1,, 1
exp 2
1exp2
i
ii iii
i
i
ii iii
rr
rr






  (12)
i, is the reflection coefficient of the i layer of a com-
ing pulse from the right.
T


1,, 1
1,, 1
(1)(1) exp2
1exp2
i
ii iii
i
i
iiii i
rr
Trr





 

(13)
,1ii
r, is the coefficient between two successive layers.
1
,1
1
ii
ii
ii
Z
Z
r
Z
Z




 (14)
Zi represents the i layer impedance
0
,
i
ri
Z
Z

 (15)
where, Z0 is the impedance of the free space.
6. The Specific Absorption Rate
The electromagnetic wave is able to penetrate in a bio-
logical structure. The interaction between the human
body layer and the incident pulse result in a complex
distribution of the local fields. This interaction is related
to the dielectric properties of the human layer and the
wave frequency. The distribution of the electromagnetic
wave in the human body is known by SAR (Specific
Absorption Rate). SAR can be expressed by [12]:
2
SAR E


 (16)
where,

is the conductivity of the tissue in Siemens/
Meter

is the mass density in kg/m3 and E is the
strength of the electric field in volts/meter.
Our goal in this section is to minimize SAR value of
each layer that composes the human body.
According to Figure 4, the SAR decreases according
to the frequency of the incident pulse. The maximum
SAR was, in all the cases, located in the muscle and lung
layer.
The density of each layer is indicated in the Table 1.
7. The Thickness Measurement of Each
Human Body Layer
To illustrate the given results in this section, we will try
to compute the human body section. In fact, we used
multi-static radar that sends an electromagnetic pulse
with an oblique incident. This signal reaches the human
body layer and comes to the radar antennas. Each echo
layer has its own way, direction and an antenna receiver.
Finally, each layer triggers its own antenna. For this rea-
son, we consider the excited antenna positions and we
compute the thickness of that layer sources of the echo
Figure 4. The SAR of each human body layer versus fre-
quency.
Table 1. Density ρ in kg/m3 of the body tissues [13].
Layer ρ in Kg/m3
Skin 1100
Fat 1100
Muscle 1041
Bone 1990
Lung 655
Table 2. Estimated antenna position and the measured
thickness of each echo layer.
Layer Skin FAT Muscle Bone Lung
Estimated
antenna
position (mm)
100 100.3572 108.3314 111.1587113.6691
Permittivity
(S/m) 35.7745.0291 49.54 16.05 44.859
Measured
thickness (mm)1.5 12 14 7 6
reflected. The permittivity of each layer used in this sec-
tion, is measured by Gabriel at a frequency equal to 5
GHz. The results are summed up in the Table 2.
8. Conclusions
The UWB and radar systems have several advantages.
This encourages us to use these inventions in several
fields including medical applications. To enhance these
advantages we propose to use the UWB radar systems in
the medical imaging field. In fact, we put the emphasis
on this manuscript on an algorithm that optimizes our
radar system. This technique makes the radar system
capable of adapting its parameters depending on the

Optimization of the UWB Radar System in Medical Imaging 231
characteristics of the tissue of the patient.
Furthermore, our UWB radar system estimates the
width of each layer and computes the frequency enabling
us to maximize the echo reflected by the human body as
exposed in the radar radiation. For example we deploy a
frequency 5 GHz and 6 GHz respectively in an attempt to
detect the echo reflected by the skin and muscle layer.
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