The article reviews some of the basic principle of FMC/TFM data acquisition and imaging processes and compares them to standard phased array techniques. An introduction to the most important American Society for Mechanical Engineers (ASME) Boiler and Pressure Vessel Code is also provided.
In theory, the advanced ultrasonic testing technique Full Matrix Capture / Total Focusing Method (FMC/TFM) should offer improved inspection performance compared to Phased Array Ultrasonic Testing (PAUT) in terms of flaw detection, resolution, classification and some cases sensitivity. The pure data volume acquired by FMC provides the TMF imaging algorithm with significantly more data, or A-scans, from which accurate 2-D reconstruction of the region of interest. The FMC/TFM concept was considered for non-destructive testing about 2 decades ago  and compared to standard linear, focused, and steered PAUT. The linear 0 degree scan shown in Figure 1 pulses all the elements in the aperture at the same time and then sums up the received waveforms from each aperture to create a single A-scan. The process is repeated N – (a + 1) times where N is the size of the array, a is the aperture size and assuming step size of 1. This scan is referred to as B-scan, E-scan, and liner 0-degree scan. The pulsing sequence and resulting B-scan are shown in Figure 1 for an automated 2-D scan with the B-scan in the top right corner using an Olympus X3 PAUT platform.
Figure 1: Example pulsing sequence and resulting PAUT image for 0-degree B-scan.
The focusing point of a fixed aperture linear scan is static and set by the aperture length and testing frequency. Linear scan, 0-degree or at specific angles, are achieved by treating the individual elements of the aperture as separate emitters and applying time delays to the excitation signal sent to each emitter. Each element serves as a unique receiver to which an identical time delay is applied. The received time-delayed waveform for each element within the aperture are summed to create the aperture’s A-scan. The pulsing sequency and resulting focused B-scan are shown in Figure 2 for an automated 2-D scan with the B-scan on the right side of the display using an Olympus X3 PAUT platform.