A programmable logic device includes a delay circuit and a body-bias generator. The network-coding apparatus includes a received signal processing unit receiving at least two signals, and decoding the at least two received signals; and a transmission signal processing unit receiving the at least two decoded signals from the received signal processing unit, merging the at least two decoded signals, and generating a merged transmission signal. The cutting insert has an upper surface, a lower surface, and first and second cutting edge corner parts and, which are provided on the upper surface such that the upper surface has a symmetrical structure with respect to a diagonal direction. The X-ray detector may detect some of the X-rays that return to the downhole tool, as well as some of the X-rays that pass internally through the downhole tool.