Effect of scanning direction on amplitude of reﬂ ected pulse ......impulse radar wave with the...

© 2010 Macmillan Publishers Ltd. 1742–8262 Journal of Building Appraisal Vol. 6, 1, 21–33

www.palgrave-Journals.com/jba/

Scientifi c Review

Effect of scanning direction on amplitude of refl ected pulse radar from steel bar Received (in revised form): 7 th May 2010

Raktipong Sahamitmongkol is a researcher at the Construction and Maintenance Technology Research Center (CONTEC), Sirindhorn International Institute of Techonology (SIIT) and National Metals and Materials Technology Center (MTEC), Thailand. Dr Raktipong achieved his PhD from the University of Tokyo in September 2005 and currently focuses on the inspection of reinforced concrete structure using non-destructive tests as well as other techniques relating to the maintenance of concrete buildings and structures.

Correspondence: Raktipong Sahamitmongkol , Construction and Maintenance Technology Research Center (CONTEC), Sirindhorn International Institute of Technology, Thammasat University and National Metal and Materials Technology Center, Klong Nueng, Klong Luang, Pathumthani, Thailand .

ABSTRACT The relationship between the amplitude of the refl ected response of Ground-Penetrating Radar pulse and the scanning angle is experimentally investigated. It is found that amplitude of a refl ected radar wave increases when the size of rebar increases and changes with scanning direction. The amplitude of refl ected radar wave from a rebar with specifi c size is maximized if scanning direction is perpendicular with the axis of reinforcing bar. Empirical formulation for the relationship between size of rebar and amplitude of refl ected wave is proposed based on the experimental result. The method can be modifi ed and applied for the detection of reinforcement arrangement as well as to measure the size of reinforcement in the actual reinforced concrete structure. Journal of Building Appraisal (2010) 6, 21 – 33. doi: 10.1057/jba.2010.11

Keywords: amplitude ; GPR ; radar ; scanning direction ; size of rebar

INTRODUCTION In an inspection of reinforced concrete (RC) structure, detection of reinforcing bars is usually conducted for many possible reasons, for instance, to measure size of rebar, to determine actual thickness or to count the actual number of rebar in the RC element. Some non-destructive testing (NDT) such as half-cell potential measurement or ultrasonic pulse velocity measurement also requires the information about the location of reinforcing bars for an effective inspection.

Ground-Penetrating Radar (so-called GPR) is the term applied to NDT technique that employs radio wave, whose frequency is generally in the range of 10MHz to 3GHz, to detect the invisible interface between objects with different electromagnetic properties. By detecting such interface, the buried metallic objects or delaminations can be identifi ed ( ACI, 1998 ). The GPR is one of the techniques extensively employed to detect reinforcing bars in concrete structure.

The detection of reinforcing bars in RC structure by GPR is generally conducted by rolling an antenna across a surface as it is repeatedly transmitting radar pulse into the


Sahamitmongkol

subsurface. Once the transmitted radar pulse strikes reinforcing bars, a portion of the pulse is refl ected back to the antenna. The real time plot of the scanned subsurface profi le can be immediately created after the measurement by the present GPR equipment and the location of reinforcing bar can then be determined. In addition, the travel time of refl ected radar pulse is commonly a single parameter in the analysis. Therefore, researches about application of GPR in the inspection of RC structure mostly focuses on the modeling of electromagnetic properties of concrete in different conditions ( Halabe et al , 1993 ; Rhim and B ü y ü k ö zt ü rk, 1998 ; Laurens et al , 2002 ; Davis and Huang, 2003 ; Sahamitmongkol et al , 2006 ). Current application of GPR in the inspection of RC structure is still not capable of determining the direction of rebar. There is currently no available information about the feasibility of GPR to check the direction of reinforcement. Therefore, this study aims to investigate characteristics of the radar especially amplitude of radar wave refl ecting from rebar with different sizes and different scanning angles.

ELECTROMAGNETIC WAVE PROPAGATION AND IMPORTANT PARAMETERS

Electromagnetic wave propagation and refl ection The electromagnetic can propagate without any medium. It can propagate through the vacuum at the speed of light. However, once it hits any material, its wavelength and hence speed changes and some part of the wave refl ects. The speed of electromagnetic wave in the new medium and the refl ection ratio is dependent on the electromagnetic properties of the materials.

The propagation of electromagnetic wave is governed by Maxwell equations.

Maxwell ’ s Equations

∇ × = − ∂∂

−��

��

EH

tm …… Maxwell Faraday Equation

∇ × = ∂∂

+ −��

��

HE

tJe …… Maxwell Ampere Equation

J E� ��

= s ⋅ where E

�� : Electric fi eld strength (potential gradient); H

�� : Magnetic fi eld strength;

J�

: Current density; � : Magnetic permeability (Henry / m); � : Complex permittivity (farad / m); � : Conductivity.

Combining equations (1) – (3), we get

∇ = ∂∂

+ ∂∂

22

2E

E

t

E

t

��

me s

By solving equation (4) for one-dimensional wave propagation along the x -direction (along unit vector i

� ) in non-magnetic medium with a relative magnetic permeability of unity

E j E i kx t��

= ⋅ ⋅ −[ ]0 exp ( )v

(1) (1)

(2) (2)

(3) (3)

(4) (4)

(5) (5)

Effect of scanning direction on amplitude of refl ected pulse radar

© 2010 Macmillan Publishers Ltd. 1742–8262 Journal of Building Appraisal Vol. 6, 1, 21–33 23

where E 0 : Initial amplitude of electric fi eld; j�

: Unit vector in a plane perpendicular to the direction of wave propagation; i: −1 ; k is complex wave number which describes the behavior of wave and can be related to complex permittivity ( � ), wavelength and wave velocity and as follows:

k k ikR I r= + = =w m e w m e e0 0 0 where � : Angular frequency (rad / s); � 0 : Permeability of vacuum and non-magnetic material = 4 � × 10 − 7 Henry / m; � 0 : Dielectric permittivity of vacuum = 8.854 × 10

− 12 farad / m; � r : Relative complex permittivity (farad / m).

The real part of the wave number determines the wave length of electromagnetic wave. The wave length of electromagnetic wave is thus equal to 2 � / k R and the wave velocity is � / k R , respectively. The imaginary part of wave number k I is commonly referred as the attenuation coeffi cient.

For highly conducting medium (that is, � � / � � > > 1)

k kR I= =vm s0

2

For slightly conducting medium (that is, � � / � � < < 1)

kR = ′v m e e0 0

kI = ′s m

e e20

0

Refl ection and refraction of electromagnetic wave The electromagnetic can propagate without any medium and it can propagate through the vacuum at the speed of light. However, once it hits any material, its wavelength and hence speed changes and some part of the wave refl ects. By Fresnel equations and Snell ’ s laws, amplitude refl ection coeffi cient is expressed as follows:

n

n

c

c

k

ki

t

R

R

2

1

1

2

2

1

= =( )( )

=sin

sin( )

qq

Snell’sLaws

Rn n

n n

Rn

TEi t

i t

TMt

=−+

=

1 2

1 2

1

cos( ) cos( )

cos( ) cos( )

cos( )

q qq qq

and

−−+

n

n ni

t i

2

1 2

cos( )

cos( ) cos( )( )

qq q

Fresnel Equations

where n 1 and n 2 are refl ective index of the 1st and 2nd medium; � i and � t are angle of incidence and angle of transmission, respectively; c 1 and c 2 are wave velocity in the 1st and 2nd medium; k R 1 and k R 2 are wave numbers of the 1st and 2nd medium; R TE is an

(6) (6)

(7) (7)

(8) (8)

(9) (9)

(10) (10)

(11) (11)


Sahamitmongkol

amplitude refl ection coeffi cient when electric fi eld is perpendicular to plane of incidence (perpendicular polarization); R TM is an amplitude refl ection coeffi cient when electric fi eld is perpendicular to plane of incidence (perpendicular polarization).

By considering specifi c case where perpendicular polarization takes places with an incident angle of 90 ° , refl ection coeffi cient can be derived as follows:

Rk k

k kTER R

R R

=−+

1 2

1 2

From equations (8), (9) and (12), the refl ection coeffi cient when electromagnetic wave hits conductive medium is almost − 1 which indicates a complete refl ection with 180 ° phase change.

Polarization and scattering of electromagnetic waves Polarization of electromagnetic wave describes its magnitude and direction of the electromagnetic fi eld as a function of time and space. When the time varying electromagnetic fi elds vary sinusoidal, polarization may be classifi ed as linear, circular or elliptical. If the vector that describes the electric fi eld as a function of time is always directed along a straight line, the fi eld is ‘ linearly polarized ’ . If the vector sweeps out a circle, it is referred to as circular polarization, it is ‘ circular polarized ’ . The ‘ elliptical polarization ’ is referred to the more general polarization pattern of the electromagnetic waves.

The electric fi eld of a wave traveling in the z direction can be described by two orthogonal components as follows:

E z t E t zx xoz

x( , ) cos( )= − −−e a w b f

E z t E t zy yoz

y( , ) cos( )= − −−e a w b f

For an electromagnetic wave to have linear polarization, the time-phase difference

between the two components must be

Δf f f p= − = =y x n n 0 1 2 3, , , ,…

Most commercial GPR antennas are dipole or bow-tie antennas that radiate linearly polarized energy with the majority of the radiated electric fi eld oriented along the long axis of the dipole or bow-tie. A complete polarization mismatch using dipole antennas results when the scattered fi eld and polarization of the receive antenna are both linearly polarized and oriented at right angle to each other.

When electromagnetic wave hits a cylindrical object, it refl ects and scatters. Scattering properties of the cylindrical object are strongly polarization-dependent. In order to describe scattering from cylindrical object, two linearly independent basis vectors are necessary. Normally, the vector oriented along the long axis of the cylinder (E parallel or transverse-magnetic (TM)) and the other vector oriented orthogonal to the long axis of the cylinder (E perpendicular or transverse-electric (TE)) are chosen. TM polarization is achieved when the long axis of the transmit and receive dipole antennas are oriented parallel to the long axis of the target cylindrical object while TE polarization is achieved when the antenna axes are oriented orthogonal to the long axis of the cylinder. Analytical

(12) (12)

(13) (13)

(14) (14)

(15) (15)



descriptions of the scattering of electromagnetic wave from cylindrical bodies are available elsewhere ( Ruck et al , 1970 ; Balanis, 1989 ).

EXPERIMENTAL PROGRAM

Rebar and installation The response radar waves refl ecting from reinforcing bars with different sizes (RB6, RB9, DB12, DB16, DB20 and DB25) were measured. Wood case with the size of 1000 × 1000 × 200 mm made from 15-mm thick plywood was used as a base for reinforcing bar ( Figure 1a ). The lateral sides of the case were cut to make an opening with the size of 100 × 800 mm at the middle of each side so that reinforcing bars could be inserted into the wood case and the position of rebar can be adjusted easily.

GPR instruments The GPR machine is Komatsu IRS-150 ( Figure 1b ) with a co-pole antenna of which the long axes oriented perpendicular to the scanning direction. The machine emits the impulse radar wave with the pulse duration of 1 ns and the mean frequency of 1GHz. The topographic image of refl ected wave is automatically plotted after the measurement. The shape of refl ected wave at each position can then be taken from the image.

Experimental procedure The steel bars of certain sizes namely RB6, RB9, DB12, DB16, DB20 and DB25 were installed at the middle of the wood case. The directions described by angles corresponding to axis of rebar were marked on the top surface of wood case. The measurement was conducted in 12 directions, that is, 10, 15, 20, 30, 40, 45, 50, 60, 70, 75, 80 and 90 degree to the axis of the rebar (hereinafter, scanning angle). GPR scanning was accomplished by moving the antenna on the top of the box along the marked directions. The GPR response was measured fi ve times for each direction. The result from the test was analyzed to investigate the effect of scanning angle and size of rebar on the refl ected radar wave.

EXPERIMENTAL RESULTS

Response of refl ection of pulse radar from rebar Figure 2a shows the example of response of radar signal measured from the scanning with different scanning angles. The refl ected radar wave can then be calculated by subtracting the measured radar responses with the response when there is no rebar. The absolute refl ected radar wave can then be calculated as shown in Figure 2b .

The results obviously illustrate that magnitude of the refl ected radar wave is larger when the angle between scanning direction and axis of rebar is larger and is maximum when the angle is 90 ° . This reduction of the magnitude of refl ected radar wave may result signifi cantly from the effect of polarization on signal scattering. When the scanning angle is 90 ° , the transmitted radar signal have a TM polarization to rebar while, when the scanning angle is 0 o , the polarization is a TE one. Figure 3 gives a description of the direction of long axis of dipole antenna and polarization pattern at different scanning angles. Since the steel bar acts similarly to the metallic cylinder, it gives stronger backscattered signal to the TM polarization ( Radzevicius and Daniels, 2000 ).


Sahamitmongkol

Amplitude of refl ected radar The amplitude is measured as the difference between maximum peak and minimum peak of the absolute refl ected radar wave (see Figure 4a and equation (16)). The amplitudes of refl ected radar wave obtained from different sizes of rebar and different scanning angles are summarized in Table 1 . Figure 4a clearly shows that the larger amplitude of refl ected radar wave were obtained in the case of larger size of rebar and the refl ected wave from same rebar has larger magnitude when the scanning is larger.

Reflected Amplitude = −Amp Ampmax min (16) (16)

Figure 1: Experimental equipment. ( a ) Wood case for installation of reinforcing bars; ( b ) GPR Instrument (Komatsu IRS-150).



where Amp max is maximum signal in refl ected radar wave (2nd Peak); Amp min is minimum signal in refl ected radar wave (3rd Peak).

In order to explicitly illustrate effect of scanning direction, normalized amplitude defi ned in equation (17) was plotted against the scanning angle as shown in Figure 4b

Normalized AmplitudeReflected Amplitude

Reflected Amplitude =

@@ 90o

FORMULATION FOR AMPLITUDE OF REFLECTED RADAR PULSE The refl ection and scattering of the radar pulse from rebar is complicated since the amplitude of refl ected radar wave is mainly dependent on the geometry of the object. The refl ection of radar wave from rebar cannot be calculated only by the conventional wave refl ection theory because the antenna emits the radar wave with the conical propagation range and reinforcing bar refl ects only a portion of radar pulse emitted from

(17) (17)

0

50

100

150

200

250

Time (ns)

Am

plit

ud

e

Angle = 30Angle = 60Angle = 90

-50

-40

-30

-20

-10

0

10

20

30

40

50

Time (ns)

Am

plit

ud

e

Angle = 30Angle = 60Angle = 90

Maximum Peak

Minimum Peak

0 654321

0 654321

Figure 2: Radar response refl ected from DB16 measured in different directions. ( a ) Response before subtraction; ( b ) response after subtraction.


Sahamitmongkol

the antenna and the interface of rebar is not a smooth plane but rather a cylinder-like plane with complex shape of surface with lugs. Although the polarization of radar pulse on the scattering of the radar pulse must be also considered.

Instead of theoretical analysis which may result in a complicated formulation, the author ’ s goal is to establish empirical formulation which is more practical. Figure 4b illustrates that relationship between normalized amplitude with scanning angle is almost same for all size of reinforcing bar and implies that the effect from scanning angle and the effect from size of rebar on the refl ected amplitude is independent of the other and can be separately considered in most cases.

Effect of scanning angle The amplitude of refl ected radar signal is minimum and maximum when scanning angle is 0 o and 90 ° , respectively ( Figure 4 ). The effect from the scanning on the amplitude of refl ected radar signal can be estimated by the following empirical formula:

b aangle = sin2

where � angle is a factor representing effect of scanning angle on the maximum amplitude and � is scanning angle (angle between scanning direction and axis of reinforcing bar).

Equation (18) is proved suffi ciently accurate for most cases except when size of rebar and scanning angle is relatively small. A signifi cant discrepancy between approximation (equation (18)) and the actual amplitude is noticeable (see Figure 4b ). The discrepancy implies that the refl ection mechanism changes in such case. Although the polarization of the transmit radar wave becomes almost TE when the scanning angle is suffi ciently small,

(18) (18)

Figure 3: Transverse-magnetic and transverse-electric polarization. ( a ) Direction of long axis of dipole antenna; ( b ) polarization pattern at different scanning directions.



the area of rebar can still refl ect a certain amount of radar energy back to the receiver because the distance between antenna and rebar is not so large. The refl ecting mechanism dominates the radar response than the backscattering which is dominant in the case of

0

10

20

30

40

50

60

70

80

90

100

Scanning Angle (α)

Ref

lect

ed A

mp

litu

de

RB6

RB9

DB12

DB16

DB20

DB25

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Scanning Angle (α)

No

rmal

ized

Am

plit

ud

e an

d β

angl

e

RB6

RB9

DB12

DB16

DB20

DB25

Larger discrepancy at small scanningangle (especially for small rebar)

βangle (Equation 21)

0 908070605040302010

0 908070605040302010

Figure 4: Relationship between scanning angle and amplitude of refl ected wave. ( a ) Before normalization; ( b ) normalized amplitude and � angle .

Table 1 : Amplitudes of refl ected radar wave

Size of rebar

Scanning angle ( � , degree)

10 15 20 30 40 45 50 60 70 75 80 90

RB6 4.8 6.8 8.4 18.8 30.0 34.8 38.8 51.0 58.6 60.2 63.8 65.4 RB9 4.8 4.8 9.2 19.2 30.4 38.0 44.8 56.2 65.8 68.2 68.5 69.0 DB12 8.8 9.2 10.4 19.6 35.6 41.8 52.6 63.0 73.0 77.4 78.2 77.8 DB16 12.2 5.6 10.0 20.4 37.6 46.6 53.4 67.0 79.0 81.8 84.6 87.4 DB20 8.8 14.8 9.6 23.2 41.0 47.4 55.4 68.2 79.8 81.4 85.8 89.0 DB25 11.2 18.4 19.0 24.8 37.4 51.4 56.2 68.2 81.0 85.0 90.2 93.4


Sahamitmongkol

large scanning angle. An obvious illustration is given in Figure 5 in terms of correction factor which is determined as the ratio between normalized amplitude ( Figure 4b ) and � angle (equation (18)).

Correction FactorNormalized Amplitudeb

bcorrection angle( ) =

Figure 5a shows that the correction factor can be as high as 4.5 when the scanning angle is 10 ° but is almost 1 when the scanning angle is greater than 30 ° . Figure 5b shows the relationship between correction factor and size of the reinforcing bar. At the same scanning angle, larger rebar tends to give higher correction factor because it provides bigger refl ecting area at the same depth. The correction factor can be estimated by the

(19) (19)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Angle (Degree)

Co

rrec

tio

n F

acto

r

RB6

RB9

DB12DB16

DB20

DB25

Large Discrepancy atsmall scanning angle

Est. (10 Degree)

Est. (15 Degree)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Size of Rebar

Co

rrec

tio

n F

acto

r

10 Degree

15 Degree

20 Degree

Est. (10 Degree)

Est. (15 Degree)

0 908070605040302010

0 30252015105

Figure 5: Relationship between correction factor and scanning angle. ( a ) Correction factor at different angles; ( b ) Correction factor for different sizes of rebar.



following formula (equation (20)). The minimum value of correction factor is 1 which represents the case that TM polarization dominates the response so that the refl ected wave becomes negligible when reinforcing bar is suffi ciently large or the scanning angle is not small.

b f acorrection = − +0 082 0 326 5 46 1. . . � where � is a nominal diameter of reinforcing bar (mm) and � is scanning angle (degree).

Relationship between sizes of rebars and refl ected amplitude Figure 6 shows the relationship between refl ected amplitude and the size of rebar when the scanning angle is 90 ° . The data plotted in Figure 6 are the measured data corrected by the effect of scanning angle discussed in the previous section. The amplitude of the corrected amplitude increases when the size of rebar increases because larger size of rebar increases the refl ection interface and can be expressed by the following equation:

Reflected Amplitude = =A Bf f45 384 0 2331. .

where A and B are the constants and should be modifi ed properly for the application in the fi eld.

According to the formulation, the amplitude of refl ected radar wave can be estimated by the following formula:

Reflected Amplitude = b b fangle correctionBA[ ]

Figure 7 shows the verifi cation of the proposed formula with the measured amplitude. The calculated value is within 10 percent of the measured value.

(20) (20)

(21) (21)

(22) (22)

Amplitude = 45.384φ0.2331R2 = 0.8482

0.0

20.0

40.0

60.0

80.0

100.0

120.0

Size of Rebar

Co

rrec

ted

Am

plit

ud

e

Amplitude vs Size of Rebar

Estimation

0 30252015105

Figure 6: Relationship between correction factor and size of rebar.


Sahamitmongkol

DISCUSSION Although the direction of rebar can be easily presumed in conventional RC element such as beams and columns, the determination of rebar can be a complicated task in some specifi c cases. One example is to determine the direction of prestress tendon in irregular-shaped fl oor or slab. With the knowledge obtained from this study, the GPR can be effectively applied to determine the direction of the reinforcement at any location by simply changing scanning angle at a specifi c location. The direction that gives maximum amplitude is perpendicular to the axis of the reinforcement.

When the determination of size of reinforcement is the main objective of inspection, the relationship proposed in this study should be carefully modifi ed because the amplitude of refl ected radar wave in the real RC structure is affected by many other parameters, for instance, dielectric constant of concrete, conductivity of concrete and moisture condition, and so on.

If the objective is just to compare the size of rebar in one location to the rebar in another location in the same structure which has a same cover thickness, the information may be simply achieved by comparing amplitude of refl ected radar. The larger amplitude of refl ected radar pulse indicates a larger size of rebar.

If quantitative determination of size of reinforcing bars is necessary, many additional considerations must be taken into account. In the RC structure, the refl ected radar wave must travel through interfaces between concrete and air. Therefore amplitude of refl ected wave is actually dependent on not only size of rebar but also cover thickness, dielectric properties of concrete and moisture; the calibration test is therefore necessary in such cases.

CONCLUSION Based on experimental investigation, it is evident that the amplitude of refl ected radar wave increases when the size of reinforcement increases. It was also proved that the angle between scanning direction and axis of reinforcement affects the amplitude of refl ected radar wave as well. The amplitude of refl ected wave is largest when the angle is 90 ° . This knowledge is benefi cial to the inspection of reinforcement in RC building. Testing

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Calculated Amplitude

Mea

sure

d A

mp

litu

de

0.0 100.090.080.070.060.050.040.030.020.010.0

Figure 7: Verifi cation of proposed model.



procedures can be programmed to check the alignment of reinforcing bars or to compare the size of reinforcing bars in the same structure. The empirical relationship between amplitude of refl ected radar response and the scanning angle was proposed so that it can be applied to obtain information about direction of rebar as well as to make a comparative study on size of reinforcing bars.

REFERENCES American Concrete Institute (ACI) . ( 1998 ) Nondestructive Test Methods for Evaluation of Concrete in Structures .

ACI228.2R-98 .

Balanis , C . A . ( 1989 ) Advanced Engineering Electromagnetics . New York: Wiley .

Davis , J . and Huang , Y . ( 2003 ) Determination of Dielectric Properties of In-situ Concrete at Radar Frequencies .

Proceedings of International Symposium on Non-Destructive Testing in Civil Engineering 2003 (NDT-CE 2003);

16 – 19 September, Berlin, Germany: BAM and DGZfP .

Halabe , U . B . , Sotoodehnia , A . , Maser , K . R . and Kausel , E . A . ( 1993 ) Modeling the electromagnetic properties of

concrete . ACI Materials Journal 90 (6) : 552 – 563 .

Laurens , S . , Balayssac , J . P . , Rhazi , J . and Arliguie , G . ( 2002 ) Infl uence of concrete relative humidity on the amplitude

of ground-penetrating radar (GPR) signal . Materials and Structures 35 : 198 – 203 .

Rhim , H . C . and B ü y ü k ö zt ü rk , O . ( 1998 ) Electromagnetic properties of concrete at microwave frequency range . ACI

Materials Journal 95 (3) : 262 – 271 .

Ruck , G . T . , Barrick , D . E . , Stuart , W . D . and Krishbaum , C . K . ( 1970 ) Radar Cross Section Handbook . New York:

Plenum .

Sahamitmongkol , R . , Kato , Y . and Uomoto , T . ( 2006 ) Effect of mix proportion and cover thickness on electromagnetic

properties of concrete measured by radar method . Proceedings of the 2nd ACF International Conference; 20 – 21

November, Bali, Indonesia: Asian Concrete Federation, pp. MRC145 – 154 .

Radzevicius , S . J . and Daniels , J . J . ( 2000 ) Ground penetrating radar polarization and scattering from cylinders . Journal of

Applied Geophysics 45 : 111 – 125 .

Effect of scanning direction on amplitude of reflected pulse radar from steel barINTRODUCTIONELECTROMAGNETIC WAVE PROPAGATION AND IMPORTANT PARAMETERSElectromagnetic wave propagation and reflectionReflection and refraction of electromagnetic wavePolarization and scattering of electromagnetic waves

EXPERIMENTAL PROGRAMRebar and installationGPR instrumentsExperimental procedure

EXPERIMENTAL RESULTSResponse of reflection of pulse radar from rebarAmplitude of reflected radar

FORMULATION FOR AMPLITUDE OF REFLECTED RADAR PULSEEffect of scanning angleRelationship between sizes of rebars and reflected amplitude

DISCUSSIONCONCLUSIONReferences

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