Showing papers in "Ndt & E International in 2007"

Accuracy of pavement thicknesses estimation using different ground penetrating radar analysis approaches

Abstract: The Ground Penetrating Radar (GPR) is a Non-destructive Testing (NDT) technique, which is able to capture continuous pavement layer thicknesses data. The radar pulse propagation is a major factor for gathering the dielectric constants of pavement materials accurately. The present research focuses on the accuracy of pavement asphalt layer thicknesses estimation using GPR data analysis by employing different estimation approaches based on material dielectric properties. A comprehensive comparative analysis of GPR and asphalt-drilled cores data incorporating a variety of pavements is performed. The major findings of the detailed comparative analysis including the effectiveness of the approaches used are reported and discussed in the present paper.

Thickness measurement of non-magnetic plates using multi-frequency eddy current sensors

Abstract: A robust feature in multi-frequency eddy current (MEC) testing has been found that can be directly linked to the thickness of the plate under test. It is shown mathematically that the peak frequency of the imaginary part of the inductance change when an air-cored coil is placed next to a non-magnetic metallic plate is inversely proportional to the thickness of the plate for a given material. Experimental results indicate that this relationship also holds for a ferrite-cored U-shaped coil. In addition, this peak frequency has been shown to be relatively independent of lift-off variations. Use of this new feature provides a fast and accurate method to gauge the thickness of plates. Measurements made for a sample air-cored and ferrite U-cored coil next to copper and aluminium plates of various thicknesses verified the proposed method.

Analysis of free and forced vibration of a cracked cantilever beam

Abstract: Structures are weakened by cracks. When the crack size increases in course of time, the structure becomes weaker than its previous condition. Finally, the structure may breakdown due to a minute crack. Therefore, crack detection and classification is a very important issue. In this study, free and forced vibration analysis of a cracked beam were performed in order to identify the crack in a cantilever beam. Single- and two-edge cracks were evaluated. The study results suggest that free vibration analysis provides suitable information for the detection of single and two cracks, whereas forced vibration can detect only the single crack condition. However, dynamic response of the forced vibration better describes changes in crack depth and location than the free vibration in which the difference between natural frequencies corresponding to a change in crack depth and location only is a minor effect.

Real-time arc-welding defect detection and classification with principal component analysis and artificial neural networks

Abstract: A novel system which allows arc-welding defect detection and classification is presented in this paper. The spectroscopic analysis of the plasma spectra produced during the welding process is a well-known technique to monitor the quality of the resulting weld seams. The analysis of specific emission lines and the subsequent estimation of the electronic temperature T e profile offers a direct correlation between this parameter and the corresponding weld seams. However, the automatic identification and classification of weld defects has proven to be difficult, and it is usually performed by means of statistical studies of the electronic temperature profile. In this paper, a new approach that allows automatic weld defect detection and classification based in the combined use of principal component analysis (PCA) and an artificial neural network (ANN) is proposed. The plasma spectra captured from the welding process is processed with PCA, which reduces the processing complexity, by performing a data compression in the spectral dimension. The designed ANN, after the selection of a proper data training set, allows automatic detection of weld defects. The proposed technique has been successfully checked. Arc-weld tests on stainless steel are reported, showing a good correlation between the ANN outputs and the classical interpretation of the electronic temperature profile.

Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation

Abstract: Magnetic flux leakage (MFL) testing is widely used to detect and characterise defects in pipelines, rail tracks and other structures. The measurement of the two field components perpendicular to the test surface and parallel to the applied field in MFL systems is well established. However, it is rarely effective when the shapes of the specimens and defects with respect to the applied field are arbitrary. In order to overcome the pitfalls of traditional MFL measurement, measurement of the three-dimensional (3D) magnetic field is proposed. The study is undertaken using extensive finite element analysis (FEA) focussing on the 3D distribution of magnetic fields for defect characterisation and employing a high sensitivity 3-axis magnetic field sensor in experimental study. Several MFL tests were undertaken on steel samples, including a section of rail track. The experimental and FEA test results show that data from not only the x- and z-axes but also y-axis can give comprehensive positional information about defects in terms of shape and orientation, being especially advantageous where the defect is aligned close to parallel to the applied field. The work concludes that 3D magnetic field sensing could be used to improve the defect characterisation capabilities of existing MFL systems, especially where defects have irregular geometries.

Tool wear evaluation by vibration analysis during end milling of AISI D3 cold work tool steel with 35 HRC hardness

Abstract: In this study, the relationship between vibration and tool wear was investigated during end milling. For this purpose, a series of experiment were conducted in a vertical milling machine. An indexable CBN insert and AISI D3 cold work tool steel hardened to 35 HRC were used as material twin in the experiments. The vibration was measured only in the machining direction, which has more dominant signals than in the other two directions. The measurements were taken by using an acceleration sensor assembled on a machinery analyzer. Tool wear was measured by a toolmaker's microscope. It was observed that there was an increase in vibration amplitude with increasing tool wears. This situation was evident especially by monitoring vibration of displacement type. It was also observed that the first three multiplies of tooth passing frequency (1×, 2×, 3×) gave the best information about the tool wear. Results showed that there was no considerable increase in the vibration amplitude until a flank wear value of 160 μm was reached, above which the vibration amplitude increased significantly.

Field trials for dynamic characteristics of railway track and its components using impact excitation technique

Abstract: Assessment of condition of railway track is crucial for track design, repair, and effective maintenance operations. In-field dynamic testing in combination with track modelling represents an efficient strategy for identification of the current condition of railway track structure and its components. Field investigations for the dynamic characteristics of a railway track and its components were carried out and are presented in this paper. A non-destructive technique using impact excitation, so-called ‘modal testing’, was utilized in these trials. Integrated approach combining field measurements, experimental modal analysis, and finite element modelling to evaluate the dynamic parameters of the in situ railway track components are appended. A ballasted railway track site in Central Queensland managed by Queensland Rail (QR) was selected to perform the field tests. Six sleeper-fastening-rail assemblies were selected for dynamic testing. The frequency response functions (FRFs) were recorded by using Bruel & Kjaer PULSE vibration analyser in a frequency domain between 0 and 1600 Hz. The data obtained were best fitted using the least-square technique to determine the dynamic stiffness and damping constants of the tested track components. In addition, the experimentally determined resonance frequencies along with the dynamic properties of the track components can provide an important input for determining the maximum speed and axle load for the future track upgrades. This paper also points out on how to judge the dynamic responses (e.g. FRFs) together with the visual inspection of existing conditions from the field experience. Examples of testing results representing the deficient integrity are additionally highlighted. Based on the results, the impact excitation technique is an efficient method susceptible to the structural integrity of railway track structures.

Static and dynamic testing of bridges through microwave interferometry

Abstract: A novel microwave sensor capable of remote detection of structural displacements is experimented as geotechnical instrument for static and dynamic testing of bridges. The sensor is based on an interferometric radar providing range imaging capability and sub-millimetric accuracy range displacement measurement. Dynamic monitoring calls for sampling rate high enough for transient analysis, while static monitoring requires long-term stability. The instrument has been designed in order to provide both these features. The results of a validation campaign on a railway bridge during the final test before going into service are reported.

Pulsed electromagnetic methods for defect detection and characterisation

Abstract: The magnetic flux leakage (MFL) method has very good defect detection and location capabilities, but defect sizing capabilities, especially for sub-surface defect characterisation, are limited. The pulsed magnetic flux leakage (PMFL) technique has recently been introduced and shown to have great potential for automated defect sizing for surface-breaking defects using time-frequency signal processing techniques, but sizing of sub-surface defects has proved problematic. In this paper, pulsed magnetic reluctance (PMR), a new electromagnetic (EM) non-destructive evaluation (NDE) technique, is introduced and incorporated into a dual PMFL/PMR probe for the characterisation of surface and sub-surface defects in ferromagnetic materials. Experimental results from a comparison study of the two techniques using variety of defects analysed using time-frequency analysis show that the techniques offer complementary information, with PMFL providing defect location data and data for the characterisation of surface defects and PMR offering sub-surface defect characterisation capabilities. The work concludes that integration of these inspection techniques in the new pulsed EM probe can provide enhanced defect characterisation capabilities for flux leakage-based inspection systems using relatively simple time-frequency signal processing techniques.

Application of eddy currents induced by permanent magnets for pipeline inspection

Abstract: This paper presents an alternative to the common concentric coil method to induce low-frequency eddy currents in ferromagnetic pipe and tubes. Pairs of permanent magnets rotating around the central axis of these cylinders in proximity of the surface can be used to induce high current densities in the material that is the object of the inspection. Anomalies and wall thickness variations are detected with an array of sensors that measure local changes in the magnetic field produced by the current flowing in the material. This electromagnetic technology is being developed for pipeline inspection platforms that either crawl slowly inside a pipe to maneuver past physical barriers or are pushed by flexible rods. These devices move down the pipeline independent of the product flow, and potentially stop for detailed defect assessment. Fundamental finite element modeling analysis and experimental investigations performed during this development have led to the derivation of a first-order analytical equation for designing rotating exciters and positioning sensors. The rotating permanent magnet system has the potential for broader application because the sensor configurations can be small in physical size, allowing them to pass obstructions that currently prevent inspection using available NDE implementations.

Study on source location using an acoustic emission system for various corrosion types

Abstract: In this paper, four main types of corrosion: uniform, pitting, crevice and stress corrosion cracking (SCC) found in the petrochemical industry, were characterized and identified by Acoustic Emission (AE) analysis using their locations and extracted AE parameters. A novel low-cost AE location system based on a Field Programmable Gate Array PC (FPGA-PC) and a LOCAN 320 AE analyzer were utilized in this study. Specimens used in experiments were austenitic stainless-steel SS304. The pattern of AE signals from each type of corrosion was plotted using their location and correlation. Experimental results show the ability of our FPGA-PC system to determine corrosion locations. The correlations of AE parameters including amplitude, counts, hits and time were used to identify different types of corrosion. In addition, the characteristics of the corrosion process for each type are explained using the AE signals obtained corresponding to the source locations, together with experimental observation.

Ultrasonic surface wave propagation and interaction with surface defects on rail track head

Abstract: Electromagnetic acoustic transducers (EMATs) are non-contact ultrasonic transducers capable of generating wide band ultrasonic surface waves on metallic samples. A lab-based laser-EMAT system has been developed to observe the ultrasonic surface wave propagation and interaction with surface breaking defects on the sample rail head surface. A wide band EMAT generating surface waves with a frequency content between approximately 50 and 500 kHz is used to propagate ultrasonic waves on the surface of a rail head down the length of the sample. A stabilised Michelson interferometer is used to measure the out-of-plane displacement of the surface wave. A complete picture of the ultrasonic surface wave on the sample surface over time is reconstructed using this technique, with exceptionally high spatial and temporal resolution. Despite the curvature of the rail head, the ultrasonic surface wave propagating down the rail is found to have similar properties to Rayleigh waves by direct comparison to those observed on flat samples using the same technique.

Acoustic emission from wire ropes during proof load and fatigue testing

Abstract: The paper describes an experimental investigation into the enhancement of proof and fatigue testing procedures for wire ropes by incorporating data from acoustic transducer signals. During proof load tests on a selection of damaged wire ropes, it is shown that acoustic emission increases significantly after the damage is inflicted, even though ropes continue to pass the proof test. The relationship between acoustic emission signal characteristics and wire breaks is investigated and it is found that the most effective acoustic signal discriminators are energy and amplitude. Finally, the pattern of acoustic emission signals during a fatigue test is studied and a suggestion is made for a filtering technique to improve the recognition of imminent failure.

Eddy current nondestructive testing with giant magneto-impedance sensor

Abstract: Technologies based on magnetic sensors with high sensitivity such as magneto-resistance (AMR, GMR), fluxgate or squid sensors have demonstrated their capability to improve the performances of the classical eddy current (EC) probes. In this paper, a new kind of magnetic sensor based on giant magneto-impedance (GMI) effect has been evaluated. This sensor combines good sensitivity performances at low frequencies and small size. The design of a probe using this new technology has been optimized with fast semi-analytical models. The performances of this GMI based probe have then been successfully evaluated on a 304 L stainless steel mock up for the detection of embedded flaws.

High-frequency eddy current conductivity spectroscopy for residual stress profiling in surface-treated nickel-base superalloys

Abstract: Recent research results indicated that eddy current conductivity measurements can be exploited for nondestructive evaluation of subsurface residual stresses in surface-treated nickel-base superalloy components. Most of the previous experimental studies were conducted on highly peened (Almen 10-16A) specimens that exhibited harmful cold work in excess of 30% plastic strain. Such high level of cold work causes thermo-mechanical relaxation at relatively modest operational temperatures; therefore the obtained results were not directly relevant to engine manufacturers and end users. The main reason for choosing peening intensities in excess of recommended normal levels was that in low-conductivity engine alloys the eddy current penetration depth could not be forced below 0.2 mm without expanding the measurements above 10 MHz which is beyond the operational range of most commercial eddy current instruments. In this paper we report the development of a new high-frequency eddy current conductivity measuring system that offers an extended inspection frequency range up to 50 MHz with a single spiral coil. In addition to its extended frequency range, the new system offers better reproducibility, accuracy, and measurement speed than the previously used conventional system.

Microelectronic package characterisation using scanning acoustic microscopy

Abstract: In a highly competitive market, reliable techniques for manufacturing quality control of electronic devices are demanded. Characterisation of modern microelectronic package integrity becomes more difficult due to the continued miniaturisation of electronic device and the complexity of advanced micro-assembling technologies such as chip-scale packages and 3D IC stacks. In this paper, sparse representations of acoustic signals are sought to improve the scanning acoustic microscopy (SAM), a common non-destructive tool for failure analysis of microelectronic packages. Sparse representation of an ultrasonic signal is obtained by decomposing it in an overcomplete dictionary. Detection and location of ultrasonic echoes are then performed on the basis of the resulting redundant representation. The method offers a solution to the deconvolution problem for restoration of the ultrasonic reflectivity function. It can restore closely space overlapping echoes beyond the resolution of the conventional SAM system. It also produces high resolution and accurate estimates for ultrasonic echo parameters, i.e., time-of-flight, amplitude, centre frequency, and bandwidth. These merits of the proposed method are explored in various potential applications for microelectronic package characterisation.

Impact wave and damage detections using a strain-free fiber Bragg grating ultrasonic receiver

Abstract: A strain-free mobile fiber Bragg grating (FBG) ultrasonic receiver is applied for the impact-related experiments of carbon fiber reinforced plastic laminates. The strain-free FBG sensor detects an impact-induced acousto-ultrasonic wave and its responses are compared with those of a piezoelectric sensor. Ultrasonic mode wavelength-related averaging effect in FBG ultrasonic sensors is also reported. The mobile FBG sensor can be useful for the acoustic characterization and the sensor placement optimization being required before construction of a built-in FBG network. Finally, the mobility of the strain-free FBG sensor head is extended to ultrasonic scanning application. Based on its high scanning spatial resolution, impact damage sizing is conducted more precisely.

A defect shape reconstruction algorithm for pulsed thermography

Abstract: An algorithm for the defect shape reconstruction from pulsed thermography data was developed. The aim was to reconstruct the defect shape in a test sample with known thermal properties. The algorithm consists of a defect shape correction unit and a simulation unit. The defect shape correction unit is designed to extract the defect shape roughly and refine it sequentially while the simulation unit models the heat conduction process in the inspected sample. The developed iterative algorithm is able to reconstruct 2D as well as 3D defect shapes. The algorithm was tested using experimental data obtained on a plate-shaped steel sample with a wall thickness profile. Robust defect shape reconstruction results were demonstrated.

Numerical modeling of general cracks from the viewpoint of eddy current simulations

Abstract: This study discusses numerical modeling of fatigue and stress corrosion cracking in eddy current simulations. Ten fatigue crack specimens and another 10 stress corrosion crack specimens are prepared for this purpose. The specimens are made of type 316 stainless steel and measure 10 mm in thickness for a general evaluation of the model. Eddy current inspections of the specimens are performed using a differential type plus point probe; the specimens then undergo destructive tests to confirm the true profiles of the cracks. Subsequent numerical simulations are conducted to evaluate the equivalent conductivity and width of the cracks. The simulations demonstrate that a fatigue crack can be modeled as a non-conductive region, and it is not necessary to know exactly how wide the opening of a fatigue crack is. They also revealed, in contrast, that stress corrosion cracking needs to be modeled as a conductive region with a certain width.

Optical inspection for quantification of decay on stone surfaces

Abstract: This paper examines a novel approach of corrosion damage analysis based on image processing for quantitative and qualitative evaluation of degradation effects on stone surfaces. This methodology can be applied in situ in association with a variety of non-destructive monitoring schemes, and on images acquired from several imaging modalities, capturing from micro- to macro-scale characteristics. Our analysis methodology was evaluated on three non-destructive monitoring techniques of cleaned and not cleaned stone surfaces, namely on digital camera, reflectography and fiber optic microscope images. Further to validating the potential of the various imaging modalities, the paper also assesses the corrosion rate and the efficiency of the recruited cleaning methods. The derived results are in accordance with chemical analyses revealing the deterioration patterns of the studied surfaces.

Numerical evaluation of the ill-posedness of eddy current problems to size real cracks

Abstract: This study evaluates whether or not eddy current testing is applicable to the sizing of cracks that appear in a general structure. Two 10 mm thick specimens with artificial stress corrosion cracking are prepared, eddy current testing is performed to gather eddy current signals that result from cracking, and numerical inversions are performed to evaluate the maximum depths of the cracking. The inversions estimate the depths of the cracks are 0.8 and 1.6 mm. Although the simulated signals agree well with the measured ones, destructive tests reveal that the true depths are 1.27 and 2.58 mm. Another numerical simulation is conducted to discuss the ill-posedness of the inverse problem of sizing crack depths from eddy current signals. The simulation simply models a crack as a rectangular region with a constant length and uniform conductivity inside and calculates the eddy current signals of 1024 cracks having variety of depths, widths, and conductivities. Analyzing the results of the simulation reveal that information contained in conventional single-frequency eddy current tests is not sufficient to size conductive cracks in a general sense.

Lift-off effect in high-frequency eddy current conductivity spectroscopy

Abstract: Precision eddy current measurements have been shown to be capable of characterizing the near-surface residual stress and cold work profiles in surface-treated components. To capture the peak compressive residual stress in moderately shot-peened (Almen 4–8 A) nickel-base superalloys, the eddy current inspection frequency has to be as high as 50–80 MHz. Unfortunately, spurious self- and stray-capacitance effects render the complex eddy current coil impedance variation with lift-off, the so-called lift-off curve, highly nonlinear, which makes it difficult to achieve accurate eddy current conductivity measurements beyond 25 MHz in the presence of even the slightest lift-off uncertainties. As opposed to the well-known inductive lift-off effect that decreases with increasing probe size, the capacitive lift-off effect increases with probe size. Both effects increase with frequency with the inductive effect being initially stronger, but then taken over at high frequencies by the faster growing capacitive effect. Since the two effects produce opposite curvature in the lift-off curve, in the frequency range where they are approximately equal to the lift-off curve becomes essentially linear and fairly accurate, conductivity measurements can be conducted even in the presence of lift-off variations.

Analytical modelling in low-frequency electromagnetic measurements of steel casing properties

Abstract: Published studies on low-frequency (10 Hz–100 kHz) electromagnetic measurements of oil-well steel casing properties are mainly experimental and focus on certain regions of the space and frequency distributions of an exciter magnetic field inside a casing. We present an analytical model, based on the work of Dodd and Deeds, and employ it to analyse the whole space–frequency characteristic. We show that the model predictions and sensitivity analysis are consistent with the known effects of coil separation and excitation frequency on the measurements. The modelled responses to pulsed excitation are in good quantitative agreement with the experiments. The model can be applied in optimal design of the measurement systems and model-based measurement of the casing properties.

Fourier-transformed eddy current technique to visualize cross-sections of conductive materials

Abstract: A pulsed eddy current NDE system is useful for detecting deep flaws in conductive materials. We have developed a pulsed eddy current NDE system using a magneto-resistive sensor. The induction coil generates a pulsed magnetic field which has a frequency component between 0 and 3 kHz, and a maximum amplitude of about 4 μ T . Aluminum plates with flaws at depths of 1 and 2 mm were measured, and the intrinsic frequency responses of the plates were obtained using a proposed Fourier transformation method. Cross-sectional images of the samples could then be directly constructed from the intrinsic responses. We also demonstrated estimation of quantitative values for the depths of flaws. The estimated depth was well defined for a sample with a flaw at a depth of 2 mm. The estimated value was slightly different for a sample with a flaw at a depth of 1 mm due to lack of frequency components above 3 kHz. These results indicate that the proposed system is a very promising tool for NDE tomography.

Application of the ultrasonic characterization methods for highly attenuating plastic materials

Abstract: In this paper, prediction of the back surface reflection, which is based on attenuation and phase velocity dispersion estimation method, in highly attenuating plastic (polyvinylidene fluoride—PVDF) has been described. Estimation of the attenuation law is based on the inverse transfer function of the object approximation in the frequency domain. The oscillating character of the inverse transfer function of the highly attenuating plastic material gives rise to an ill-posed problem for approximation. It has been solved in two ways: application of the Tikhonov regularization process and iterative adjustment of the approximation parameters. The estimated attenuation coefficient α 0 and power n have been used for calculation of phase velocity dispersion using the Kramers–Kronig relations and having attenuation coefficient measured at single-frequency value. The reconstructed waveforms of the ultrasonic back surface reflections using the estimated attenuation and phase velocity dispersion curves have been presented and compared with the experimental one.

A non-destructive technique for the elastic characterization of thin isotropic plates

Abstract: The paper presents a non-destructive technique for determining the dynamic elastic properties of isotropic thin square plates. It is based on the measurement of at least two of the first four resonant frequencies of the samples and allows to determine the elastic constants directly using polynomial interpolating functions. These functions are derived from suitable data obtained by means of finite element analyses. The procedure is tested on metallic and ceramic specimens. Samples are excited to vibrate by drivers with continuously variable frequency output or by impact. The effect of the different sources of error on the calculation of elastic properties is also discussed.

An adaptive method for channel equalization in MFL inspection

Abstract: Influenced by the lift-off value between the pipeline and coil sensors, the various properties of electronic component and the different location of coil sensor, the output signal's amplitude and phase of each channel are different despite the same flaw in magnetic flux leakage (MFL) inspection. The channel-to-channel mismatch may severely degrade the performance of testing equipment and disturb the evaluation of the level of flaw unless some form of compensation is employed. In this paper an adaptive method for channel equalization in MFL inspection is presented by using the finite impulse response filter. Both theoretical analysis and experimental results have shown the effectiveness of the proposed method.

Rotating polar-coordinate ART applied in industrial CT image reconstruction

Abstract: With incomplete or noisy projections, algebraic reconstruction technique (ART) algorithms can get better image qualities than convolution back-projection (CBP) algorithm. But, it's too slow to meet the practical industrial requirements. Rotating polar-coordinate technique was introduced into ART in this paper, forming Polar-ART (PART) algorithm. PART is 2.7 times as fast as ART with nearly the same quantitative accuracy and it does not need as much memory as ART, which is proved by experiments on 60 Co container CT inspection system. A drawback of PART is the loss of resolution in reconstructed images.

Damage diagnostics on a welded zone of a steel truss member using an active sensing network system

Abstract: In this paper, a sensor network system based on an active sensing scheme is introduced to identify cracks, which may occur at a welded zone of a steel truss member. The active sensing network system offers special potential for real world applications, as it is light, cheap, and useful as a built-in system. Four pairs of pitch–catch Lamb wave signals are utilized from the active sensing network system. In order to extract damage-sensitive features from the dispersive Lamb waves, a robust wavelet transform is applied to the original response signals. Peak values in the wavelet coefficients corresponding to the A 0 Lamb mode are only considered for application to the damage index. The root-mean-square change of the peak values due to damage is proposed as a damage index. In addition, a least-squares curve-fitting algorithm is applied to the damage indices in order to obtain a practical damage indicator with a threshold value that presents the damage tolerance. Finally, damage localization is carried out by investigating the change rates of the damage index according to each damage step. The applicability of the proposed methods has been demonstrated by an experimental study.

A novel method for FDTD numerical GPR imaging of arbitrary shapes based on Fourier transform

Abstract: Ground penetrating radar (GPR) systems are very powerful tools with a wide range of advantages in non-destructive testing. Target detection is one of the serious results of GPR application. The landmine detection in the soil and reinforcement bars and holes in the concrete is some of the GPR object detection examples. In this research, the targets are modeled in different cases, an air hole or a conductive material. A cracked surface is also modeled for both conductive and dielectric media. For modeling, the three-dimensional (3D) finite difference time-domain (FDTD) method is applied. Perfectly matched layer (PML) absorbing boundary condition is used for simulating the physical absorbers and free space. The results were shown in time domain. The difference between results helps to distinguish the target depth and electrical properties. For better specification of the target shape, a transform in frequency domain is used. This transform contains a Fourier transform in a selected frequency. The results show a sudden change in the frequency response over the hole or target scanning. By this idea, the shape of any arbitrary hole or crack can be extracted.