Microwave Nondestructive Techniques Research Articles

Corrosion detection of reinforced concrete structures based on microwave nondestructive technique

The corrosion of rebars will change the mechanical properties of the reinforced concrete structure, leading to the decline in the structural strength, which seriously threatens the safety and stability of buildings and power equipment foundations. Hence, it is of great significance to detect the internal corrosion of reinforced concrete structures. In this paper, a nondestructive detection method for detecting the corrosion in reinforced concrete structures based on microwave was proposed, and the corrosion state of rebar can be evaluated by the change of microwave information. Compared with other detection methods, microwave nondestructive detection has the advantages of low energy consumption, strong penetration, no contact, and small equipment volume and weight. In order to verify the effectiveness of the method, a microwave nondestructive detection simulation test platform was built and reinforced concrete test models with different corrosion lengths and depths were made. The influences of concrete parameters, the microwave frequency, and the lifting distance of the waveguide were analyzed. The frequency sweeping and moving scanning detection methods of the waveguide were carried out for the test models with different corrosion defects, and the changes of microwave S-parameters under different corrosion defects were obtained. The results show that when the waveguide is placed horizontally by the frequency sweeping detection method, the corrosion length detection effect of rebar is better. When the waveguide is placed vertically by the frequency sweeping detection method, the corrosion depth can be identified and the amplitude of transmission coefficient increases with the increase in the corrosion depth. The corrosion length of rebars can be identified quantitatively by the moving scanning detection method of the waveguide.

Microwave Non-destructive Technique using a Double-ring Resonator for Classification of Transparent Flesh and Yellow gum Mangosteens

One of the most important agricultural commodities exported from Indonesia is mangosteen. Mangosteens are not always fruits without flaws, in any case. To categorize the quality of mangosteen fruits, farmers employ human eyesight. As a result, this data can be unreliable and erroneous after harvesting. Both internal and exterior flaws are possible. Some spots include improper form, a hardening pericarp, yellow gumming, or transparent flesh. Often, the longest part, the translucent skin, might be difficult to see. Treatment for these disorders must be non-invasive and nondestructive. In this essay, a double-ring microstrip resonator modification is suggested and examined. The mangosteen fruits were measured using the resonator and divided into three groups. Ordinary, transparent flesh and yellow gumming are the classifications. 1.4 GHz is the resonator's operating frequency. By detecting the return loss value and the S21 value at a frequency between 100 MHz and 3 GHz, the sensor ascertains the dielectric value of each mangosteen fruit. At frequencies of 1.15 GHz-1.28 GHz and 1.42 GHz-1.52 GHz, and with dielectric constants between 2.98 and 3.28, there is a variation in permittivity values between the categories of regular, clear, and yellow mangosteen.

Regression Predictors for Porosity in Degraded Cladding Based X-Bandmicrowave Non-Destructive Evaluation: A Case Study of Tetra-Boroncarbide

Tetra-Boron Carbide (B4C) are an excellent material for industrial applications in the nuclear, aerospace, and military. It is an excellent neutron absorber for use as a radiation shield. Using B4C as thermal barrier coating reduces the metal surface temperature, shields the substrate metal alloy from excessive heat, and increases system efficiency. In this degraded has been evaluated using non- destructive techniques that are appropriate for the predicament. To track the thermal barrier coating’s integrity over time, a microwave non-destructive technique was used to predict the porosity of the topcoat. Network analyzer (ENA5701C) in X-band (12–18 GHz) was utilized for this investigation. Detection was based on the changes in the electromagnetic properties, such as permittivity . A set of samples contained varied filler ranging of 5, 10, 15, 20 percent particle reinforcement. Most tested samples shows that porosities have maximum permittivity in the range of 15.4 – 16.7 GHz where some resonance occurred when real primitivity represent the capability of B4C to store and dissipate energy. This study suggesting that the proposed methodology could be a valuable aid technique for evaluating degraded on composite material systems in a non-destructive and accurate manner with complex pore morphology

Assessment of Delamination Under Insulation Using Ridge Waveguide

Insulation has been widely used to protect metal substrates in various industries such as turbine blades and oil and gas pipelines. Due to aging and cyclic processes, delamination between the metal component and insulation could grow. Such defects represent a critical problem that may result in catastrophic failure of the asset. Therefore, detecting and evaluating delaminated areas is mandatory for providing urgent maintenance solutions before the failure occurrence. In this paper, microwave non-destructive technique (NDT) is proposed for delamination detection and thickness estimation under dielectric insulation. In microwave NDT, the electromagnetic waves are induced into the dielectric material’s surface using a ridge waveguide. The complex reflection coefficients are acquired using a vector network analyzer for further analysis in the time domain. Next, a time-domain reflectometry (TDR) technique-based inverse discrete Fourier transform is used to evaluate the complex reflection coefficients in terms of delamination’s size and thickness estimation. The delamination evaluation is performed by measuring the maximum peak’s time-step variations instead of the magnitude reduction in conventional TDR techniques in terms of the defect and defect-free reflections. Next, a comparison is made between implementing the proposed technique using a ridge waveguide and a regular rectangular waveguide. The results prove the superiority of using the ridge waveguide for delamination evaluation in terms of sizing and thickness with a minimum error rate of 5% and 7.87%, respectively. These novel results of ridge waveguide due to its small aperture and relatively wide bandwidth. The microwave NDT technique reported here could provide a predictive maintenance tool for many industries to minimize the maintenance effort and cost.

Microwave Non-Destructive Inspection and Prediction of Modulus of Rupture and Modulus of Elasticity of Engineered Cementitious Composites (ECCs) Using Dual-Frequency Correlation.

This research article presents dual-frequency correlation models for predicting the growth of elasticity and flexural strength of engineered cementitious composites (ECCs) using microwave nondestructive inspection technique. Parallel measurements of microwave properties and mechanical properties of ECC specimens were firstly undertaken in the sense of cross-disciplinary experiments. Regression models were developed via means of nonlinear regression to the measured data. The purpose of the study is: (i) to monitor the flexural strength and elasticity growth; and (ii) to predict their mature values under the influence of different initial water contents, via microwave effective conductance at early ages. It has been demonstrated that both the modulus of rupture (MOR) and modulus of elasticity (MOE) can be accurately modeled and correlated by microwave conductance using exponential functions. The moduli developed as a function of conductance whereas the regression coefficient exhibited a linear relation with water-to-binder ratio. These findings have highlighted the effectiveness of the microwave non-destructive technique in inspecting the variation of liquid phase morphology of ECCs. The dual-frequency correlation can be used for structural health monitoring, which is not only for prediction but also provides a means of verification.

Accurate One-Sided Microwave Thickness Evaluation of Lined-Fiberglass Composites

Fiberglass is increasingly used for corrosion-resistant industrial applications. Fiberglass laminate typically consists of a structural layer and a corrosion-resistant layer (commonly referred to as the liner) on the inside of the laminate. Liners are used in all corrosion-resistant fiberglass applications to guard against corrosive chemical attack on the structural layers of the fiberglass. The ability to measure fiberglass thickness from one side of a laminate during equipment operation quickly and easily with high measurement accuracy is extremely important for life assessment and prediction. Microwave nondestructive techniques employing open-ended rectangular waveguides in conjunction with robust and full-wave electromagnetic models have tremendous potential and viability for evaluating complex layered dielectric composite structures for the purpose mentioned here. In this paper, we describe the foundation of this technique, processes involved in optimizing the approach for layered fiberglass evaluation, as well as a number of representative and diverse measurement results demonstrating the efficacy of the technique and the thickness accuracy that can be obtained. In addition, other important issues such as the effect of curvature of the structure and water with different temperatures filling it were also addressed and shown not to adversely affect measurement accuracy associated with liner thickness.

Non-destructive technique for broadband characterization of carbon nanotubes at microwave frequencies

This paper presents a broadband microwave non-destructive technique for characterization of carbon nanotubes (CNTs). Typically, commercially available carbon nanotubes are powder-like samples and, therefore, in this paper, a broadband characterization technique to extract electrical conductivity of powder materials is developed. The technique uses a microstrip line configuration in conjunction with a cavity resonator technique. The electrical conductivity of CNTs is extracted from the measured attenuation in the signal response (|S21|dB) for the microstrip configuration with a signal trace made of copper and a ground plane filled with CNT samples. A resonant cylindrical cavity is also used in the measurement process to help determine a correction factor for the surface roughness of the CNT microstrip ground plane. A novel method to take attenuation due to surface roughness into account to determine conductivity of CNTs is introduced. Experimental and numerical verification of the proposed method is provided. The method developed in this work provides a cost-effective solution where significant amount of time and cost are reduced in the sample preparation process. Measurement results for the electrical conductivity of single-walled CNTs and multi-walled CNTs are presented.

Concrete dielectric properties investigation using microwave nondestructive techniques

The paper deals with dielectric properties of concrete and the effect of frequency, curing time and water to cement (w/c) ratio, concrete compression strength, steel fibre concrete and moisture content on the dielectric properties. The concrete dielectric properties such as transmission coefficients, reflection coefficients, dielectric constants and loss factors; were investigated using microwave nondestructive testing (MNDT) technique. The MNDT system consists of transmit and receive horn lens antennas, a vector network analyzer, mode transitions, and a printer. The horn lens antennas are used for minimizing diffraction effects due to the edges of the sample. Electromagnetic waves at microwave frequency range 7.0–13.0 GHz using free-space microwave method was used for measuring dielectric properties of concrete. Concrete specimens were prepared using different w/c ratios and different compressive strengths. Concrete dielectric properties were measured and correlated with compressive strength and w/c ratio of concrete, curing time. The experimental results indicate that microwave non-destructive technique has correlated well with to determine the compressive strength and w/c ratios of concrete. The results also show the potential to be used to determine the percentage of fiber. This technique is easy to adapt for in situ measurements.

Non-destructive microwave detection of layer thickness in degraded thermal barrier coatings using K- and W-band frequency range

Thermal barrier coatings have been widely used in gas turbine engines in order to protect the substrate metal alloy against high temperature and to enhance turbine efficiency. To monitor thermal barrier coating (TBC) integrity over its lifetime, the detection of top coat (TC) and thermally grown oxide (TGO) thicknesses was carried out using a microwave non-destructive technique. The results showed a good resolution of 1° change in phase for 15 μm TC thickness when a rectangular waveguide operating at relatively high frequency was applied. The phase of the reflection coefficient at the interface of TC and waveguide varies for different TGO and TC thicknesses. Therefore, measuring the phase of the reflection coefficient enables us to accurately calculate these thicknesses. Finally, a theoretical analysis was used to evaluate the reliability of the experimental results.

2420 Development of High-Sensitive Non-Destructive Evaluation Technique of Degraded Thermal Barrier Coatings by Using Microwave

Thermal barrier coatings (TBCs) have been widely used in gas turbine engines in order to protect the substrate metal alloy against high temperature and to enhance turbine efficiency. After service at high temperature, delamination or micro-cracks will initiate in TBC, leading to TBC separation from substrate and ultimately in unexpected gas turbine destruction. TBC failure is primarily attributed to the. growth of TGO and partly to TBC degradation. Currently, there are no reliable nondestructive techniques available to monitor TBC integrity over lifetime of the coating. Thus, to detect TBC and TGO thicknesses, a microwave nondestructive technique that utilizes a rectangular waveguide was developed. The phase of the reflection coefficient at the interface of TBC and waveguide varies for different TGO and TBC thicknesses. Therefore, measuring the phase of the reflection coefficient enables us to accurately calculate TGO and TBC thicknesses. Finally, a theoretical analysis was used to evaluate the reliability of the experimental results.

Microwave and millimeter wave nondestructive testing: A succinct introduction

Microwave nondestructive techniques have a long history dating from the early 1950s, with a strong flurry of activities in the 1960s and 1990s. However, these techniques still are not widely known in the nondestructive testing (NDT) community and often are referred to as “emerging techniques” or “others.” It is only during the last two or three years that some NDT conferences have allocated a whole session or two solely to the topic of microwave NDT. For those involved in the research and development of microwave and millimeter-wave NDT techniques who have long appreciated the advantages of such techniques, this increased visibility is a welcome and encouraging change.

Microwave and Millimeter Wave Nondestructive Testing: A Succinct Introduction

Abstract Microwave nondestructive techniques have a long history dating from the early 1950s, with a strong flurry of activities in the 1960s and 1990s. However, these techniques still are not widely known in the nondestructive testing (NDT) community and often are referred to as “emerging techniques” or “others.” It is only during the last two or three years that some NDT conferences have allocated a whole session or two solely to the topic of microwave NDT. For those involved in the research and development of microwave and millimeter-wave NDT techniques who have long appreciated the advantages of such techniques, this increased visibility is a welcome and encouraging change.

Microwave sensitivity maximization of disbond characterization in conductor backed dielectric composites

A swept frequency microwave nondestructive technique for detection of disbond in a dielectric composite backed by a conducting plate is discussed. The theoretical development is based on an incident plane wave illuminating such a medium, and then formulating the characteristics of the reflected wave. This way the effective reflection coefficient of the medium is found. The phase of this reflection coefficient changes in the presence of a disbonded medium. With the determination of an optimally sensitive frequency range using the theoretical model and the known properties of the composite dielectric material, it is shown that disbonds on the order of a few microns can be accurately detected at relatively low microwave frequencies. Several experimental results are also presented.

Microwave nondestructive detection and evaluation of disbonding and delamination in layered-dielectric slabs

A microwave nondestructive technique for the detection and evaluation of disbonding and delamination in layered-dielectric-slabs backed by a conducting plate is discussed. The theoretical development of the technique is given. An incident wave illuminating such a medium is first considered, and the characteristics of the wave reflected by the metal plate are then formulated. An effective reflection coefficient whose phase characteristics are used in the detection and evaluation of delaminations in the media is determined in this way. The characteristics of this phase as a function of several parameters, such as delamination dielectric constant and thickness, slab dielectric constant, and thickness and the frequency of operation are investigated. The experimental apparatus is described. It was used to perform several experiments to test and verify the theory. Very good agreement was obtained between the theoretical and experimental results. In general, it was concluded that higher frequencies, thicker dielectric plates, and lower values of delamination dielectric constants tend to produce better results for evaluating the nature of a delaminated layer. This technique is simple and easily applicable to environments where these types of layered-slab are used.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>