Fig. 1. 0.3 THz linear array scanning imaging system and results of performance testing. (a) Schematic illustration of imaging system; (b) photo of imaging system; (c) image of THz focal line; (d) intensity curve extracted from Fig. 1(c) along dashed line; (e) photo of steel resolution test target; (f) THz image of resolution test target

Fig. 2. THz imaging of internal defects in polyethylene samples. (a) Sample with scratch defects; (b) THz image of sample with scratch defects; (c) intensity curve extracted from Fig.2(b) along dashed line; (d) sample with internal hole defects; (e) THz image of sample with internal hole defects; (f) intensity curve extracted from Fig. 2(e) along dashed line

Fig. 3. THz imaging of defects on polyethylene water pipe. (a), (c) Photos of two different defects on surface of polyethylene water pipe; (b), (e) THz images of two defects; (e), (g) photos of metallic washer and blade hidden in water pipe; (f), (h) THz images of washer and blade hidden in water pipe

Fig. 4. THz imaging of scissor and knife hidden in envelopes. (a), (c) Photos of scissor and knife hidden in envelopes; (b), (d) THz images of scissor and knife hidden in envelopes