The Ultra Wide Band Radar System Parameters in Medical Application

In this work, an Ultra Wide Band (UWB) radar system is proposed in an attempt to take a medical image of each human body layer. In fact, this system consists of sending an electromagnetic pulse and analyzing the echo reflected by the human body tissue. In order to realize this system, the parameters which enable us to optimize the functionality of our radar are computed. Indeed, we fixed a frequency range, incident angle, pulse repetition frequency, the power and the antenna deployed by the UWB radar system in medicine. As well as, a human body model is presented in order to have practical results.


Introduction
There have been growing interests in recent years' research the Ultra Wide Band (UWB) technology and radar system.The radar is built in a wide variety and for a large number of different applications.In the early years, Radar system was limited to military and a few civil applications like navigation and vehicle speed detection.
Nowadays, the Radar system is used in many applications such as in the GPR (Ground Penetration Radar).In this paper, the UWB radar system is to be used in a medical application.In fact, it is possible to employ this system to take a medical image of the human body.Moreover, this image enables doctors to diagnose the human body in an attempt to detect anomalies like cancer.
To meet such an aim, the system UWB radar block diagram is suggested and used in a medical image in the first section.Then, the parameters of the UWB radar system in medicine are fixed, in the second section.In fact, a human body model as used in this application is presented.Similarly, the reflection and transmission coefficients of each human body layer for two types of incidence (normal and oblique) are computed.Moreover, the frequency range used by our system is fixed in the third section.Then, the travel time put by each human body echo is estimate.Besides, the pulse repetition frequency needed in this application is calculated.While in the fourth section, the antenna deployed by our radar is designed.Furthermore, the antenna position needed to capture each echo reflected by the human body structure is computed.Finally, the results in the conclusion are discussed.

The UWB Radar System
The UWB radar system uses radiated and reflected electromagnetic waves to detect, locate and identify a certain target.
A UWB radar system offers many benefits over continuous wave radars [1]: • Due to a very high down-range resolution, a target can be precisely located; • A large bandwidth allows a better separation between targets and a clutter; • It possesses a good immunity against a multipath interference, which is very strong within buildings and collapsed buildings; • Multiple targets can be resolved.Moreover, this system can be used in the medical application.In fact, the electromagnetic pulses generated by the UWB radar are able to explore human body.Then, the human body layer has got electric characteristics which make differentiate between each echo reflected by the human body structure.
Our UWB radar system consists of sending an electromagnetic pulse and listens to the echo reflected by each human layer.For this reason, it is possible to take a photo of each human body layer after analyzing his reflected pulse.
In this part, a generic radar block diagram is to be proposed.
Figure 1 shows the radar system block diagram.For the normal incidence of the electromagnetic pulse, the same antenna for both radiation and reception is used.But, for the oblique incident an antenna for each human body layer is used and the antenna position must be studied.
Then, this proposed system presents many advantages better than other medical imaging systems used until now such as:  Contrast X-rays  Computerized tomography scanning  Magnetic resonance imaging (MRI)  Positron emission tomography  Radionuclide scanning  Single photon computerized tomography  Ultrasound and X-rays All these technologies suffer from many disadvantages.Most of them need to expose human body to the strong electromagnetic radiation for long time that presents a potential damage to the cell.This can strengthen the risk of cancer in patient's later life.In the same vein, the repeated use of this kind of system is not safe for the human health.However, the UWB radar system uses an ultra short pulse that minimizes the electromagnetic effect.Similarly, it has a very high image resolution and a good capacity of penetration in the human body biological structure.And, the UWB radar imaging is very fast compared to all other systems.For example the MRI processes can take 30 minutes.
In addition, this system is not expensive like MRI system.Nonetheless, the technique of the realization of this equipment is not complicated akin to other systems.
Although the UWB radar is a new system for medical application it tends to ignore other techniques in the future.

The Human Body Model
Each human body layer can be presented by a good di- electric with certain characteristics that vary according to the frequency of the incident wave [2][3][4][5].Moreover, the permittivity of the human body structure is complex and can be expressed by [2][3][4][5]: where   is the relative permittivity of the biological tissue and   the out-of-phase loss factor associated with it such as in: The permittivity is increased with the frequency in all the layers of the human body.But the conductivity is decreased with the frequency [1].
The propagation constant of each human body layer can be written as y j     ; where the attenuation constant  and propagation constant  can be written as follows [6]: where:  : The Angular frequency 0  : The Free space permittivity.The skin depth  is given 1  by as follows [6]: In this case, the human body can be modeled by a multilayer good dielectric that is composed of planar layers skin, fat, muscle, bone and lung tissue.The human body model is shown in Figure 2.

Normal Incidence
When the normal incident electromagnetic wave encounters a boundary, it will be subdivided into reflected and transmitted parts.The total field that is reflected by the layer can be expressed by [1]: where i and i represent, respectively, the total field transmission and reflection by the layer for an incident wave from the left they can be expressed by [1]: The reflection coefficient of the electromagnetic wave by the interface interlayer i/i+1 is given by [7]: Here, i presents the impedance of the i th layer is written as [7]: The total field transmission by the i th layers for an incident wave from the right can be expressed by [1]: The reflection coefficient of i/i+1 interface is mentioned (11) The total electromagnetic field transmission by the i th layer is represented by [1]:

Oblique Incidence
The same for the oblique incidental pulse, it will be divided into parts reflected and transmitted.In Order to examine the reflection and transmission coefficients, the electromagnetic wave must be decomposed into parallel and perpendicular parts.The total reflected and transmitted field will be the sum of the two parts.

The Perpendicular Polarization
in the following expression by [8]: The transmission coefficient of i/i+1 interface can be presented by [8]: where: in  : The Incident angle.The reflection coefficient of i/i+1 in the following expression by [9]: The transmission coefficient of i/i+1 interface can be presented by [8]:

The Frequency Range
ity (EMC) and the elecith all frequency.In The electromagnetic compatibil tromagnetic interference (EMI) must be considered as the UWB radar system design to elude the potential interference problem.Moreover, our radar system is used in the medical application (indoor).Then, the FCC allocated frequency ranges from 3.1GHz to10.6GHz to UWB system.The emission limit for the system imagining and indoor system is limited to -41.3DBm The radar system can be operated w this part, a frequency range that enables us to optimize our UWB radar system in medicine applications is to be fixed.In accordance with the previous section, the human body is composed of many parallel layers.This encourages us to choose a frequency range that discards the mutual influence of the layer that composes the human body.
According to [1], the mutual layer influence in the fre ing the pa B system that im quency range 4GHz-6GHz can be neglected.Actually, our goals consist of designing and fix rameters of the UWB radar in medicine.For this reason, the condition of the UW poses the fractional bandwidth FB which must be greater than 0.25 must be respected [9].
where: The Brewster angle m has an FB greater or equal to 0.4 that respects the UWB system definition.

The Incidence Angle
The reflection and transmissio quantities.Then, these values depend on the frequency and incidence angle.For this reason, an angle that enables to maximize both coefficients reflection and transmission is to be found.In fact, the angle that optimizes the reflection coefficient is the critical angle.Moreover, the angle that maximizes the transmission coefficient is the Brewster angle.When examined the results presented by Gabriel in [3-5,10], can prove that the electric characteristic of the human body layer are changed slightly according to the frequency in the 4 GHz -6 GHz frequency range.
Whe ation, a study of the parallel polarization case can be proposed.In fact, they have the same critical angle.Besides, the Brewster angle perpendicular polarization doesn't have a solution.

The Brewster An
In this part, the condition un efficient for parallel polarization will disappear is examined, the set b / /  is set up equal zero; that is The reflected echo is exploited by our radar system in or cedure is repeated and used in a der to make the human body layer photo.For this motive, interest must be given to the incident angle that enables us to optimize the reflection coefficient better than the transmission coefficient.In the next subsection, the incident angle is to be computed and made capable to maximize the echo of each human body structure.

A Critical Angle
In this case, the same pro perpendicular polarization.
pression for the critica The ex l angle c  is the same angle as that for a perpendicular polarizat n as given by [8]: When the Equation ( 21) is examined, the critical angle th f the Reflected Echo of In lected angle is equal at exists only if the wave propagates from a denser to a less dense layer is confirmed.With this intention, it is possible to compute the critical angle only for both layers which are Skin and Bone layer.But for the other human body layer, it is more interesting to use a normal incidence because the maximum of the reflection coefficient exists with this kind of incidence.In fact, Figure 3 illustrates that the incident angle must be greater than 8.05° for the Skin layer.Moreover, Figure 4 shows that for the Bone layer, we must use an incident angle greater than 18.4°.

The Return Time o the Human Body Layers
addition to the Snell law, the ref to the incident angle.Then, the receptive antenna and transceiver antenna must be in the same position in an attempt to capture the reflected echo.For this reason, the same antenna is used for reception and emission.In that case, the reflected echo of each human body layer is discerned by the arrival time at the receiver.Now, the travel   The ec ace twice, for this reason, the echo time travel t 1 can be expressed by: where C is the speed of light in the free space and d 1 is 0 the distance crossed by the echo reflected by the Skin layer.It can be expressed by.
For the second layer, the echo crosses the layer of t fr he ee space twice as well as the second layer with this intention, the time put by this echo can be expressed by: where: Which can be generalized by: where: is the velocity into the i th layer.
d i is written as: he oblique incidence is [2].In fact, the distance travelled by t ca The case of t studied deeply in he echo of the layer n be expressed by:

Pulse Repetition Frequency (PRF)
The PRT (Pulse Repetition Time) is the time fro beginning of one pulse to the beginning of the ne The Pulse Repetition Frequency (PRF) is the number of radiation pulses issued by our UWB radar in one sec e PRF is mentioned in the following expression by: Our target is to fix parameters of tem in medicine.In an attempt to realize th PR characteristics but also in the width.This ge in the UWB radar.ity of the Skin layer is better than the perthe free space.Then, a normal incident is the UWB radar sysis system, the F must be determined.In fact, the PRF is to be used in attempt to distinguish the several echo reflected by the human body.
The human body layers are different not only in terms of the electric nerates a variety of the echo travel time.On this basis, a PRF is to be computed for each human body layer.In order to illustrate results, a frequency equal to 5 GHz is used for two reasons: • The mutual influence is discarded in this frequency.• 5 GHz is the central frequency of our frequency range used

Skin
The permittiv mittivity of used in an attempt to capture the Skin image.e that separates our layer).
The travel time of the echo reflected by the skin layer is equal to In an attempt to detect the Skin e PRF equal or less than 3GHz.ittivity of the Skin layer is better than the perf the Fat layer.Then, we use an Oblique inci-cho, we must use a

Fat
The perm mittivity o dental pulse in an attempt to capture the Skin image.
According to section 6 an Incident angle greater than 8.05° can be used.In our case, an incident angle equal to 45° is chosen in an attempt to illustrate practical results.The travel time put by the Fat layer echo can be expressed by: The skin echo travel time is equal to the PRF should be equal or less than 1.9098 GHz eason and like the Skin layer, the permituscle layer is better than the permittivity of 523.6071ps.Then,

Muscle
For the same r tivity of the M the Bone layer, a normal incident pulse must be used.Consequently, the travel time of the Muscle skin layer can be expressed by: where: v 3 : the wave velocity in the Muscle layer The echo travel time of the bone l 1.0357 103 ps.For this reason, a PRF less or equal to 0.
the last layer of our human body model used r.Then, the Lung echo crossed all previous ayer is equal to 96556GHz is used.

Lung
The Lung is in this pape layers time twice.Moreover, the Lung permittivity is greater than the Bone permittivity.For this reason, a normal incidence is used.The echo travel time of the Lung layer can be presented by

The Antennas
Our Radar system mu receive electromagnet ducer between the system and the free space.Moreover, the antenna is an important parameter for a good result.
In this section, the antenna employed by the UWB radar system is designed.In fact, the antenna must be radi ed in 4 GHz -6 GHz frequency range.The central frequency of our system is equal to 5 GHz.
In our case, a patch circular antenna that has a radius equal to 8.17 mm is used.Figure 7 show our antenna.This antenna has a return loss equal to -17 DBI at a frequency of 5GHz.
Figure 8 present the pattern radiation at 5 GHz.
In an attempt to optimize our ra tenna position must be found.
For the Skin, Muscle and Lung layers, normal incidence is used.For this reason, the sam ceive an electromagnetic pulse is exploited.But, for the Fat and Bone layer, an oblique incidence is used.In this case, the antenna position is computed for each layer.
Table 1 illustrates the emplacement of the receiver's antenna of each echo layers for an oblique incidence lsion in  = 45° and a normal incidence at a frequency   • An Oblique inc Bone layers.Furthermore, a particular study accorded to the reflection and transmission coefficie Moreover, our radar system uses a unique Pulse Frequency Repetition (PRF) for each human body layer.Similarly, an antenna's position that enables us to capture

0:
The Free space electromagnetic permeability. : The Relative conductivity of the human body layer.r  : The Relative permittivity of the huamn body layer.
 : The Permittivity respectively of i th layer and i+i 2 arallel Polarization interface is mentioned th lay 4.2. .The P er.
) H f = the high frequency L f  = the low frequency If we use the frequency range 4 GHz -6 GHz, our syste n coefficients are complex n the obtained result in [8] is taken into consider gle der which the reflection co-18)

Figure 3 .
Figure 3. Critical angle of the Fat layer.

Figure 4 .
Figure 4.The Critical angle of the Bone layer.

Figure 5 .
Figure 5.An outside distance crossed by each echo of th

1
Skin c v  nce crossed by the echo reflected byThe velocity into the Skin layer[11].
into the Fat layer.d 3 the dista e Muscle layer and it is given by: nce crossed by the echo reflected by th

Figure 6 .
Figure 6.Outside, the distance d i crossed by the layer at an oblique incident.echo

4
time of the bone 6.1267 10 3 ps.Therefore, a PRF less or equal to 0.16322 G st deploy an antenna to radiate and ic pulse.The antenna is the trans-

Figure 8 .
Figure 8.The three-dimensional of the pattern radiation at 5 GHz.
we must carefully choose the characteristics of t radar system.In fact, th dar sy m eploys a 4GHz-6GHz frequency range.Then, this sysinds of incidences: • A Normal incidence for the Skin, Muscle and Lung idence that is equal to 45°for the Fat, nts.the echo reflected by the human body tissue is computed.his paper, a ne dar

Figure 7 .
Figure 7.The return loss of the antenna.