The use of ultrasonic arrays for conducting non-destructive evaluation has been drastically increased in recent years. As one of the array imaging, a post-processing beam-forming technique has been proposed that utilizes a complete set of signals of all combinations of transmission and reception elements. This approach is referred to as full matrix capture (FMC) [1]. In FMC, each array element is sequentially used as an emitter and all other array elements are used as receivers. By changing the emitting element, we obtained a set of flaw signals that was used to form the focal beam. The delay-and-sum beam reconstruction based on the post-processing was applied to imaging of internal voids and reinforced steel bars in concrete material. The reconstruction of voids and steels in concrete specimen (400mm x 400mm x 400 mm) was demonstrated using a phased array transducer in the low frequency range. In this study, the array transducer with total 16 elements and center frequency of 50 kHz was developed. The volume fraction of aggregates in concrete was 70 %, and the maximum size of the coarse aggregate was 20 mm. Figure 1 shows the reconstruction result of a slit. For on-site inspection, we introduced a graphics processing unit (GPU) computation to accelerate the post-processing of beam-forming [2]. The flaw detection time was approximately 0.15 s using Geforce GTX880M (NVIDIA)
