The air coupled ultrasonic testing technology (hereinafter referred to as air coupling) was proposed as early as the 1960s. However, due to the attenuation of ultrasonic waves by air, the large impedance difference at the gas-solid interface causing a large amount of reflection of ultrasonic waves, and the low conversion efficiency of ultrasonic skin transducers, its research and application development have been slow. With the continuous development of air coupling theory, materials science, and digital signal processing technology, air coupled ultrasonic testing technology has made new breakthroughs in the 21st century.

The biggest difference between air coupled ultrasound and conventional ultrasound detection methods is the use of air as the coupling medium, replacing the original liquid or solid coupling agent. Therefore, the development of air coupled ultrasound detection technology faces certain technical difficulties.