Application of Pulse Compression Technology in Electromagnetic Ultrasonic Thickness Measurement

Electromagnetic ultrasonic thickness measurement has the advantages of no couplant and no contact. But the signals are so weak that they are easily submerged in the noise. So, the pulse compression technology is applied to raise the signal to noise ratio and lift-off distance effectively. The barker sequences are set as transmitting pulse in the measurement system, the received signals are processed with pulse compression in the experiments. By comparing the performances of barker code with single pulse requiring high levels average filtering, the signal to noise ratio is highly improved. The 5 × 13 combined barker sequence performs best among the different combined barker sequences. Its signal to noise ratio reaches 20.11 dB and the maximum lift-off is up to 3.0 mm due to the increasement of the total transmission power.