Over the years, scientists have been researching on various imaging techniques that can be used to investigate objects that are physically inaccessible in what is known as non-destructive investigation (NDE). Image science deals with the formation (imaging), collection, analysis, duplication, visualization and modification of images. Imaging techniques used in the NDE of materials employ electromagnetic radiation. The electromagnetic spectrum consists of both visible and invisible light, and while the visible part of the spectrum is the colors we can see, there are other types of radiation in the invisible part of the spectrum that can be exploited to allow humans to see beyond what the eyes can see in visible light only (Deng and Liu).
All imaging methods that use electromagnetic radiation in NDE employ Maxwell’s equations and cover a wide range of the electromagnetic spectrum from static DC (direct current) methods such as magnetic particle method to high-frequency methods such as gamma and X-ray methods. The use of electromagnetic radiation in NDE imaging helps detect defects and anomalies in both dielectric and conducting materials by generating either two or three-dimensional image data using electromagnetic principles. For example, X-rays are part of the electromagnetic spectrum, and they are used for medical imaging to show broken bones. However, X-rays are not very useful when investigating other body tissues, and again X-rays can be harmful to certain body areas. In this case, various imaging techniques employing different parts of the electromagnetic spectrum have been developed to allow for the investigation of different body tissues and metabolic functions. For example, magnetic resonance imaging (MRI) techniques are used for brain scans (Royal Society).
In forward imaging techniques, electromagnetic (EM) radiation energy is usually coupled by excitation transducers into the test objects while the receiving sensors on the other end measure the material interaction/energy responses. Depending on the different types/levels of energy, various electromagnetic radiation sensors can be used for a variety of applications such as microwave imaging, eddy current imaging, and terahertz imaging among others. After the EM images have been acquired and stored, the image data is passed through various inversion techniques that involve pattern recognition and object reconstruction among other functions that produce a fully viewable image by the human eye (Deng and Liu). Apart from medical imaging, electromagnetic radiation imaging techniques can be used for geographical imaging, radar, and concealed checking weapon checking at security checkpoints among other applications.
Works Cited:
Deng, Yiming, and Xin Liu. "Electromagnetic Imaging Methods for Non-destructive Evaluation Applications". Sensors 11.12 (2011): 11774-11808. Web. 20 Feb. 2016. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3252010/>.
Royal Society,. "Invigorate - Why Is Medical Imaging Important?". Invigorate.royalsociety.org. N.p., 2010. Web. 20 Feb. 2016. <http://invigorate.royalsociety.org/ks5/its-whats-inside-that-counts/why-is-medical-imaging-important.aspx>.
