Przemyslaw Lopato

Terahertz detection and identification of defects in layered polymer composites and composite coatings

Modern industry makes more and more extensive use of various composite materials. In this paper, for the purposes of various composite materials evaluation, the terahertz imaging method is presented. Basalt fibre-reinforced composites and polymeric anticorrosion coatings are considered. Basalt fibre composites are the innovative materials that are being increasingly used in modern industry. The paper also briefly introduces a specific type of complex coating of steel applied in the industry (e.g. oil or chemical). Two methods of defects detection in the mentioned structures are presented. The first method is based on a system identification, whereas the second one is on the estimation of time-domain signal parameters. Finally, the results achieved during terahertz inspection of coatings are compared with those obtained using active thermography.

Full wave numerical modelling of terahertz systems for nondestructive evaluation of dielectric structures

Purpose – The purpose of this paper is to describe the full‐wave modelling of pulsed terahertz systems utilized in non‐destructive testing.Design/methodology/approach – At the outset, some basic information on the terahertz NDT are outlined and then, general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness.Findings – It is possible to model in a relatively simple way a terahertz system for nondestructive evaluation of dielectric materials. In contrast to other published work, the entire measuring setup is modelled, including photoconductive antenna with hemispherical lens, focusing lens and evaluated material with exemplary defect.Originality/value – This paper gives a description of the terahertz non‐destructive testing system with comparison of simulated and measured results.

Automatic defect recognition for pulsed terahertz inspection of basalt fiber reinforced composites

Purpose – The purpose of this paper is to present a system for automatic recognition of defects detected in non-conductive polymer composites using pulsed terahertz imaging. Design/methodology/approach – On the beginning, non-destructive evaluation of composites using electromagnetic waves in terahertz frequency is shortly introduced. Next automatic defects recognition (ADR) algorithm is proposed, focussing on new features calculation. Dimensionality of features space is reduced by using principal component analysis. Finally, results of basalt fiber reinforced composite materials inspection and identification using artificial neural networks is presented and discussed. Findings – It is possible to develop ADR system for non-destructive evaluation of dielectric materials using pulsed terahertz technique. New set of features in time and frequency domains is proposed and verified. Originality/value – ADR in non-destructive testing is utilized in case of digital radiography and ultrasonic testing. Terahertz inspection with pulsed excitation is reported as a source of many useful information about the internal structure of the dielectric material. Up to now ADR based on terahertz non-destructive evaluation systems was not utilized.

Terahertz examination of fatigue loaded composite materials

Abstract. The aim of this study was to investigate the possibility of using electromagnetic radiation in the terahertz frequency range for testing of polymer composites. Glass, natural and basalt fiber reinforced polyester composites as well as sandwich structures after fatigue tests were evaluated. We examined detection abilities of detects and inhomogeneities occurred during bending process at various amounts of load cycles. Extraction and monitoring of proposed parameter enables accurate evaluation of composite structures condition.

Numerical modelling of terahertz systems for nondestructive evaluation of dielectric materials

In this paper we deal with full-wave modelling of pulsed terahertz systems utilized in non-destructive testing. At the outset, some basic information on the terahertz NDT and next general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness.

COMPARATIVE ANALYSIS OF SELECTED EDDY CURRENT TRANSDUCERS FOR TITANIUM ALLOY EVALUATION

Titanium alloy based details due to their mechanical properties continue to be in extensive use in various structures (mainly aerospace, automotive and petro‐chemical industrial applications). In this paper comparative study of various types of eddy current NDT transducers for testing titanium elements was done. Probes of absolute, differential and array configurations were constructed and analyzed. Two and three dimensional numerical analysis (FEM) were done in order to find the best type and configuration of the proposed transducers.

A Circular Microstrip Antenna Sensor for Direction Sensitive Strain Evaluation

In this paper, a circular microstrip antenna for stress evaluation is studied. This kind of microstrip sensor can be utilized in structural health monitoring systems. Reflection coefficient S11 is measured to determine deformation/strain value. The proposed sensor is adhesively connected to the studied sample. Applied strain causes a change in patch geometry and influences current distribution both in patch and ground plane. Changing the current flow in patch influences the value of resonant frequency. In this paper, two different resonant frequencies were analysed because in each case, different current distributions in patch were obtained. The sensor was designed for operating frequency of 2.5 GHz (at fundamental mode), which results in a diameter less than 55 mm. Obtained sensitivity was up to 1 MHz/100 MPa, resolution depends on utilized vector network analyser. Moreover, the directional characteristics for both resonant frequencies were defined, studied using numerical model and verified by measurements. Thus far, microstrip antennas have been used in deformation measurement only if the direction of external force was well known. Obtained directional characteristics of the sensor allow the determination of direction and value of stress by one sensor. This method of measurement can be an alternative to the rosette strain gauge.

Terahertz computed tomography with pulsed excitation and multi-parametric reconstruction

In this paper a terahertz computed tomography (THz CT) system with pulsed excitation is presented. In case of this method for each position/pixel, the time signal is recorded (in contrast to x-ray tomography, where just a single value is obtained). Based on acquired waveform many features can be calculated. For this reason multi-parametric reconstruction algorithm is proposed: tomographic reconstruction based on inverse Radon transform is performed for each parameter and then fusion of results is made using artificial neural network. Performance of the system and proposed algorithm was experimentally verified using foamed polystyrene phantoms.

Detection and classification of weld defects in industrial radiography with use of advanced AI methods

The paper presents and shortly discusses the AI algorithms created for automated detection and classification of weld defects on the basis of radiography images. The three approaches are described: with use of fuzzy logic, with use of artificial neural networks and that basing on rough sets theory. The data evaluating the accuracies of obtained classifiers as well as chosen examples are attached.

Energy and Entropy Based Signal Processing for Terahertz Inspection of Homogeneous and Composite Materials Adhesive Joints

Modern industry makes extensive use of various composite materials In this paper terahertz imaging method is proposed for evaluation of various composite materials adhesive joints. The results of inspection (A-scans and C-scans) as well as 2-D distributions of proposed parameters are presented for method validation.