OCENA NAPRĘŻEŃ W KONSTRUKCJACH STALOWYCH ZA POMOCĄ METOD ELEKTROMAGNETYCZNYCH WYKORZYSTUJĄCYCH CZUJNIKI MIKROPASKOWE I UMOŻLIWIAJĄCE MONITOROWANIE PROCESU MAGNETYZACJI AC

In this paper the results of utilization of  electromagnetic methods operating in low and high frequency range for evaluation of stress state  and plastic deformation in steel elements are presented. In low frequency range Barkhausen noise and magnetic hysteresis loop method for evaluation of stress level and growth of plastic deformation changes were utilized.  The methods allow to monitor parameters related to magnetization process under AC filed. Additionally in this paper the possibility of utilization of high frequency method for estimation of deformation extent (i.e. elongation) caused by stress will be presented. In this experiment the frequency response (the reflection coefficient S11) is measured. The strong relation of antennas resonant frequency to patch dimensions is utilized in order to obtain information about deformation of the sample.W artykule zostały przedstawione wyniki jakie uzyskano za pomocą metod elektromagnetycznych, zarówno niskoczęstotliwościowych, jak i wysokoczęstotliwościowych do oceny zmian stanu naprężeń oraz deformacji plastycznych w elementach stalowych. W zakresie niskich częstotliwości do oceny stopnia naprężenia oraz zmian plastycznych wykorzystano metodę obserwacji szumu Barkhausena oraz magnetycznej pętli histerezy. Metody te umożliwiają monitowanie parametrów związanych z procesem magnesowania stali polem zmiennym. Dodatkowo w pracy przedstawiono możliwość wykorzystania metody wysokoczęstotliwościowej do oszacowania odkształcenia (w tym przypadku wydłużenia) spowodowanego naprężeniem. W tym celu zaprojektowano i wykonano przetwornik mikropaskowy. W badaniu mierzono odpowiedź częstotliwościową (współczynnik odbicia S11). Silna zależność częstotliwości rezonansowej  przetwornika mikropaskowego  od  wymiarów promiennika została wykorzystana do określenia deformacji próbki

Terahertz inspection of dielectric and composite materials using Synthetic Aperture Focusing Technique

Nondestructive evaluation using terahertz frequency electromagnetic waves is becoming more and more popular. Similar operating principle allows the use of inverse algorithms derived from the ultrasonic technique (UT). In this paper algorithm and results of synthetic aperture focusing technique (SAFT) applied to pulsed terahertz inspection of dielectric and composite objects are presented. The results of both measurements and FDTD simulations are processed by implemented SAFT algorithm

Double-Sided Terahertz Imaging of Multilayered Glass Fiber-Reinforced Polymer

Polymer matrix composites (PMC) play important roles in modern industry. Increasing the number of such structures in aerospace, construction, and automotive applications enforces continuous monitoring of their condition. Nondestructive inspection of layered composite materials is much more complicated process than evaluation of homogenous, (mostly metallic) structures. Several nondestructive methods are utilized in this case (ultrasonics, shearography, tap testing, acoustic emission, digital radiography, infrared imaging) but none of them gives full description of evaluated structures. Thus, further development of NDT techniques should be studied. A pulsed terahertz method seems to be a good candidate for layered PMC inspection. It is based on picosecond electromagnetic pulses interacting with the evaluated structure. Differences of dielectric parameters enables detection of a particular layer in a layered material. In the case of multilayered structures, only layers close to surface can be detected. The response of deeper ones is averaged because of multiple reflections. In this paper a novel inspection procedure with a data processing algorithm is introduced. It is based on a double-sided measurement, acquired signal deconvolution, and data combining. In order to verify the application of the algorithm stress-subjected glass fiber-reinforced polymer (GFRP) was evaluated. The obtained results enabled detection and detailed analysis of delaminations introduced by stress treatment and proved the applicability of the proposed algorithm

Pulsed excitation terahertz tomography – multiparametric approach

This article deals with pulsed excitation terahertz computed tomography (THz CT). Opposite to x-ray CT, where just a single value (pixel) is obtained, in case of pulsed THz CT the time signal is acquired for each position. Recorded waveform can be parametrized - many features carrying various information about examined structure can be calculated. Based on this, multiparametric reconstruction algorithm was proposed: inverse Radon transform based reconstruction is applied for each parameter and then fusion of results is utilized. Performance of the proposed imaging scheme was experimentally verified using dielectric phantoms

Application of a Single Cell Electric-SRR Metamaterial for Strain Evaluation

Strain is a crucial assessment parameter in structural health monitoring systems. Microstrip sensors have been one of the new types of sensors used to measure this parameter in recent years. So far, the strain directionality of these sensors and the methods of miniaturization have been studied. This article proposes the use of a single cell metamaterial as a resonator of the microstrip sensor excited through the microstrip line. The proposed solution allowed for significant miniaturization of the microstrip sensor, with just a slight decrease in sensitivity. The proposed sensor can be used to measure local deformation values and in places with a small access area. The presented sensor was validated using numerical and experimental methods. In addition, it was compared with a reference (rectangular geometry) microstrip sensor

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

Microstrip Patch Strain Sensor Miniaturization Using Sierpinski Curve Fractal Geometry

In this paper miniaturization of a microstrip patch strain sensor (MPSS) using fractal geometry was proposed and analyzed. For this purpose, the transducer of Sierpinski curve geometry was utilized and compared with the most commonly utilized rectangular resonator-based one. Both sensors were designed for the same resonant frequency value (2.725 GHz). This fact allows analysis of the influence of the patch (resonator) shape and size on the resonant frequency shift. This is very important as the sensors with the same resonator shape but designed on various operating frequencies have various resonant frequency shifts. Simulation and experimental analysis for all sensors were carried out. A good convergence between results of simulation and measurements was achieved. The obtained results proved the possibility of microstrip strain sensor dimensions reduction using Sierpinski curve fractal geometry. Additionally, an influence of microstrip line deformation for proposed sensors was studied

Detection and Identification of Defects in 3D-Printed Dielectric Structures via Thermographic Inspection and Deep Neural Networks

In this paper, we propose a new method based on active infrared thermography (IRT) applied to assess the state of 3D-printed structures. The technique utilized here—active IRT—assumes the use of an external energy source to heat the tested material and to create a temperature difference between undamaged and defective areas, and this temperature difference is possible to observe with a thermal imaging camera. In the case of materials with a low value of thermal conductivity, such as the acrylonitrile butadiene styrene (ABS) plastic printout tested in the presented work, the obtained temperature differences are hardly measurable. Hence, the proposed novel IRT method is complemented by a dedicated algorithm for signal analysis and a multi-label classifier based on a deep convolutional neural network (DCNN). For the initial testing of the presented methodology, a 3D printout made in the shape of a cuboid was prepared. One type of defect was tested—surface breaking holes of various depths and diameters that were produced artificially by inclusion in the printout. As a result of examining the sample via the IRT method, a sequence of thermograms was obtained, which enabled the examination of the temporal representation of temperature variation over the examined region of the material. First, the obtained signals were analysed using a new algorithm to enhance the contrast between the background and the defect areas in the 3D print. In the second step, the DCNN was utilised to identify the chosen defect parameters. The experimental results show the high effectiveness of the proposed hybrid signal analysis method to visualise the inner structure of the sample and to determine the defect and size, including the depth and diameter