Electromagnetic spectrum

Materials science

Optoelectronics

Detector

Electromagnetic radiation

Telecommunications

Physics

Far-infrared laser

Terahertz metamaterials

Optics

Quantum mechanics

Terahertz radiation

Terahertz gap

Computer science

Nondestructive testing

Microwave

Laser

Frontiers of Mechanical Engineering

Terahertz (THz) waves, whose frequencies range between microwave and infrared, are part of the electromagnetic spectrum. A gap exists in THz literature because investigating THz waves is difficult due to the weak characteristics of the waves and the lack of suitable THz sources and detectors. Recently, THz nondestructive testing (NDT) technology has become an interesting topic. This review outlines several typical THz devices and systems and engineering applications of THz NDT techniques in composite materials, thermal barrier coatings, car paint films, marine protective coatings, and pharmaceutical tablet coatings. THz imaging has higher resolution but lower penetration than ultrasound imaging. This review presents the significance and advantages provided by the emerging THz NDT technique.

Progress in terahertz nondestructive testing: A review