ultrasound

Additive manufacturing of metal alloys yields great potential for the aerospace industry (and others) as it allows the generation of geometrically complex structures with high specific strength, low density and high corrosion resistance. For example, General Electric has demonstrated the possibility of printing titanium fuel injectors for their LEAP engine, EADS has printed a nacelle hinge bracket for the Airbus A320, Boeing incorporated more than 300 printed parts in their 777X airplane … For such critical applications, the structural quality of printed parts is of utmost importance.

Non-destructive testing (NDT) refers to techniques that are used in the life-cycle of a structural component to investigate their quality, functionality and 'health' without destroying the object, nor affecting its properties. The continuous development of more advanced materials, like fiber reinforced plastics, requires new and more sophisticated NDT techniques. One such an innovative NDT technique is the Ultrasonic Polar Scan (UPS) which has recently been developed, both experimentally and numerically, in our research group.

Dear Sir，

As we know, periodic signals are best analysed in the frequency domain while stochastic signals are usually more profitably analysed in the time domain. The analysis in the frequency domain usually concern only one signal while in the time domain often involves the comparison of several different signals.

1) what are the general methods for transforming the frequency domain into time domain, and which should be superior?