探触子の受信指向性と空中超音波における虚像の解析

摘要

空中超音波探傷で試験体を画像化したとき虚像が発生することがある。虚像は試験体内の多重反射に より広がった信号を凹面の受信探触子で受信し、受信信号振幅が変動したことが原因である。受信探触子の信号は 受信各面の信号が合成されることにより指向性や焦点位置が発生しているように見える。凹面受信探触子の受信信 号をシミュレーシヨンで調べ、焦点位置の信号が強調される状況は複数の散乱信号が発生する時であることを述べ た。平面信号が受信される時は凹面の開口角が大きいと受信点ごとの時間差が発生して受信強度が低下し、受信波 形の波長も長くなったことを確認した。受信時は受信時間差が少ない小さな受信面にすることで虚像を低減できた。%A virtual image may be generated when the specimen is imaged with aerial ultrasonic flaw detection. The virtual image is due to the received signal amplitudes fluctuating by receiving the signal spread by multiple reflection in the specimen with the concave receiving probe. As the signal of the receiving probe is combined with the signals of the receiving surfaces, it seems that directivity and focal position are generated. It is stated that the received signal of the concave receiving probe is examined by simulation and the situation where the signal of the focal position is emphasized is the time when plural scattering signals are generated. When a plane signal is received, it is confirmed that when the concave aperture angle is large, a time difference occurs between reception points, the reception intensity decreases, and the wavelength of the reception waveform also increases. When receiving, virtual images can be reduced by making small reception surface with less reception time difference.