Pulse compression technique applied to ultrasonic nondestructive testing of concrete

The pulse compression technique is successfully and widely used in many fields for improving the signal to noise ratio (SNR); which is especially useful when the environment is noisy and the SNR is poor. Since high frequency ultrasound is strongly attenuated in concrete, only low frequency ultrasound can be used in ultrasonic nondestructive testing (NDT) of concrete. In this study the pulse compression technique is proposed for the ultrasonic NDT of concrete. Using this technique, the amount of ultrasonic energy of all frequencies introduced into the concrete and detected by the receiver can be increased. After decoding the received signals, the resolution of the ultrasonic image of concrete can be enhanced since the ultrasonic energy is increased and the frequency band of the signal is broadened. The experimental results show that there must be an appropriate offset between the source and the receiver to keep off the strong surface waves and backward scattering echoes which contaminate the echoes reflected from deep flaws. The results obtained from the present technique are better than those from the traditional method (pulse-echo method).