Editorial Feature

An Overview of Microwave Nondestructive Testing

This article presents a thorough analysis of microwave nondestructive testing, its advantages, and the various techniques used to undertake it. This testing method is suitable for analyzing materials in a way that does not damage the sample in instances where visual inspection is not thorough enough.

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What is Nondestructive Testing?

Nondestructive analysis is used for testing the soundness of a material for surface or internal flaws or biomechanical parameters without causing deterioration or suitability for function. There are numerous methods to detect defects in parts and systems based on their deployment stage.

Nondestructive Evaluation (NDE) or Nondestructive Testing (NDT) is the identification and characterization of faults or defects on the inside or outside of elements without damaging or otherwise altering the composition.

NDT processes enable and provide a cost-effective means of evaluating a specimen for independent study and examination, or they may be used to verify the molecular composition in a production-quality management process.

In many cases, the procedure to find a deficit requires the use of more than one NDT method. It might require several methods as well as exploratory, intrusive procedures. The efficacy of the assessment is dependent on a better understanding of the origins, advantages, and limits of each NDT technique.

What is Microwave Nondestructive Testing?

Microwave nondestructive testing (MNDT) of substances is an essential discipline that includes the creation of sensors/probes, procedures, and calibration techniques for detecting flaws, fractures, faults, vacancies, heterogeneity, moisture levels, and other problems using microwaves.

Microwave inspection can be done in two ways: a reflection phase or a transmission phase. The microwave information is passed through the element in the sample in reflection mode. The microstructural reflection of the substance is gathered and evaluated in terms of amplitude and/or aspect characteristics.

Transmission mode, on the other hand, employs a probe to send the radio wave from one side of the specimen and another sensor to receive the data from the other half. Reflection coefficients, propagation correlation coefficient, dielectric properties, loss coefficients, and complicated porosity and permeability as a function of the frequency (microwaves) and temperatures are the characteristics determined by MNDT procedures. By using appropriate modeling and validation, these observed characteristics may be connected to material properties of relevance.

Preference for Microwave NDT over Conventional Methods

Microwave Nondestructive Testing (MNDT) approaches have benefits over other NDT techniques (such as radiographic testing, ultrasonic testing, electromagnetic testing, and eddy current testing) in terms of cost reduction, better penetration in organic or inorganic substances, high resolution, and the microwave sensor's capacitive characteristic (antenna).

Further Reading: Non-Destructive Testing of Computer Components

Due to the non-contact characteristic of free-space measurement techniques, it is possible to make accurate, reliable, and repeatable MNDT readings on composites under high or low ambient temperature and complicated electrostatic environmental factors (e. g., DC biassing fields, ionizing radiation, etc.) with appropriate adjustment. This inspection method is increasingly being utilized for quality management and assessing the state of concrete constructions. Recently, the MNDT approach has been employed to quantify the slope-of-grain of timber for grading purposes.

Testing Methods

A major microwave nondestructive examination technique is the Chipless Radio-Frequency Identification (RFID) Sensor System. It is being researched for use in structural health monitoring (SHM) technologies. A sensing label is used for metal constructions that are being investigated. The sensor reader communicates with the sensing tags by sending a bandwidth pulse through the transmitters.

Guided Microwave Testing (GMT) is another approach utilized to explore the pipeline's expanded lengths. The electromagnetic wave will be emitted by the transmitters through sensing wire test equipment during GMT. The microwave signal will strike the liquid's interface and be reradiated to the sensor, then to the transmitter’s enclosure.

The microwave transmission line sensor is one of the transmission lines used in microwave NDT. The materials that have been inspected will serve as superconductors for the microwave circuitry. The substance permeability will alter if and only if the components include flaws.

The replies of the impulses will be returned in order to identify the position and extent of the flaws. Another technique is microwave open-ended wavefront imaging. In microwave open-ended waveguide scanning, two types of sensors are used: open-ended coaxial sensors and open-ended rectangular broadband sensors.

The most common are open-ended coaxial sensors. However, with a maximum operating frequency of 50 GHz, numerous coaxial sensors of varying diameters may be chosen. Ground-penetrating radar (GPR) is a non-destructive testing (NDT) subsurface imaging technology approach in which an incident electromagnetic wave transmits through the substance under inquiry.

Couple spiral inductors (CSI) are another type of specialized probe that is widely used in microwave non-destructive testing. These are made up of two spiral coupled inductors formed by essential and auxiliary circuits. The measuring of the transmitted power from the second winding to the primary coil is the concept used in this sensor.

Limitations of the Technique

Microwave nondestructive testing has a few drawbacks along with its various advantages. The morphology of an element can occasionally alter the sensitivity of examination. External electric and magnetic fields can significantly affect the accuracy of the results.

In addition, the extensive setup and additional sensors might raise the overall cost of the operation. Furthermore, microwave technologies have several limitations in material inspection, including lower resolution quality images, fuzzy fault morphology, and complex data analysis.

Despite these limitations, it is one of the most researched techniques, especially in the civil engineering, structural engineering, and sensing fields.

In short, microwave NDT inspections are paving the way for novel evaluation methods where visual testing is not enough, but much more research is required to overcome their shortcomings.

References and Further Reading 

Ghodgaonkar, D. K. & Ali, N. A., 2022. Microwave Nondestructive Testing of Composite Materials using Free-Space Microwave Measurement Techniques. [Online]
Available at: https://www.ndt.net/article/wcndt00/papers/idn251/idn251.htm

Sobkiewicz, P., Bieńkowski, P. & Błażejewsk, W., 2021. Microwave defectoscopy – detection of composite delamination. Journal of Physics: Conference Series, Volume 1782. 012034. Avalable at: https://iopscience.iop.org/article/10.1088/1742-6596/1782/1/012034

Wahab, A. et al., 2019. Review on microwave nondestructive testing techniques and its applications in concrete technology. Construction and Building Materials, Volume 209, pp. 135-146. http://eprints.utm.my/id/eprint/87980/

Wang, X. et al., 2022. Microwave detection with various sensitive materials for humidity sensing. Sensors and Actuators B: Chemical, Volume 351. 130935. Available at: https://www.sciencedirect.com/science/article/pii/S0925400521015033?via%3Dihub

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Ibtisam Abbasi

Written by

Ibtisam Abbasi

Ibtisam graduated from the Institute of Space Technology, Islamabad with a B.S. in Aerospace Engineering. During his academic career, he has worked on several research projects and has successfully managed several co-curricular events such as the International World Space Week and the International Conference on Aerospace Engineering. Having won an English prose competition during his undergraduate degree, Ibtisam has always been keenly interested in research, writing, and editing. Soon after his graduation, he joined AzoNetwork as a freelancer to sharpen his skills. Ibtisam loves to travel, especially visiting the countryside. He has always been a sports fan and loves to watch tennis, soccer, and cricket. Born in Pakistan, Ibtisam one day hopes to travel all over the world.


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