Various modulated hybrid pulse compression for advanced ultrasound technology and its non-destructive testing application

Abstract

Ultrasound is a sound wave with a frequency greater than 20 kHz. It obeys the propagation laws of reflection, refraction, diffraction, and scattering. Because of its excellent physical properties, ultrasound has been used in a variety of fields, including industry and medicine. There are many techniques that use ultrasound as detection methods in the field of non-destructive testing (NDT) and medical treatment. In a typical ultrasound system, a sine wave or pulse signal with a fit window is considered as the transmitted signal. This results in low accuracy in some special situations, such as testing high attenuation material. The signal-to-noise ratio (SNR) is an important parameter for evaluating the performance of an echo signal or imaging. However, under high attenuation materials or noisy conditions, SNR will significantly decrease. Under these conditions, valid information in the received signal will be obscured by noise. This situation can cause errors in the detection system. In an ultrasound system, increasing the SNR of the echo signal can reduce detection errors and improve accuracy. First, in ultrasound systems, a noise reduction method based on pulse compression has been investigated and applied. Convolution and modulation were used in the proposed method to generate new hybrid emission signals. The hybrid codes can only be distinguished by a special matched filter that is related to the emission signals. The echo signals processed by a special matched filter have a high main lobe and a very low side lobe, implying that the side lobe level and SNR will increase. When compared to traditional denoising methods, the proposed method can significantly improve SNR while only requiring a change in the transmission code without requiring any hardware changes. Second, in a low voltage ultrasonic testing (UT) system, a hybrid phase modulated code excitation method based on the Barker and Golay code pairs was proposed and implemented. In a UT system, the lower the pulsing voltage, the lower the SNR of the signal. Attempting to reduce the pulsing voltage will result in noisy and unusable results. The proposed hybrid method can increase main lobe power in low average power transmitted and received signals. The proposed method has been theoretically examined and then tested in simulation studies. The experimental results showed that the main lobe level of the code produced by convolution of Barker code and Golay code pairs is around 30 dB higher than the simple pulse, and the main lobe of the combined code is around 15 dB higher than the traditional Barker code, with the sidelobe being the same as the Baker code that constitutes this combined code. As a result, the combined code’s peak sidelobe level (PSL) is approximately 5 dB lower than the traditional Barker code. Because of this, UT devices can be used in real-world applications, even in low-voltage situations. Third, the torsional wave mode T(0,1) hybrid phase modulated code excitation method has been proposed and applied in a long range guided wave testing (GWT) system. The proposed hybrid method combines the Barker and Golay code pair and is modulated by a fitted sine wave. This method combines the benefits of these two coding methods and increases code length flexibility. The SNR and PSL of the processed signal are used to assess the method’s performance. The proposed method has been tested in GWT using both finite element method (FEM) simulation and real-world testing. The results of pipeline laboratory testing revealed that the best increasing SNR of BCG is around 33.5 dB when compared to a simple pulse at 40 kHz, and the peak sidelobe level is around -24 dB. The proposed method, as well as other traditional methods, were used for pipeline defect detection testing. The results of the tests showed that the hybrid coded excitation method can detect notches that are difficult to detect with other methods and effectively improve the SNR. The applied method’s increasing SNR is around 6 dB, which agrees with the simulation and laboratory testing results. In UGW testing, the proposed coded excitation method was highly regarded. Finally, the non-linear frequency modulated (NLFM) hybrid pulse compression method has been proposed and implemented in an ultrasound imaging (UI) system. The proposed code combines the Barker and Golay codes and is modulated using a non-linear frequency method based on the Zak transform. Theoretical research on signal generation and decoding has been presented, as well as cyst phantom simulation. The simulation analysis shows that the novel code method can improve the contrast ratio by 15.96 dB and the SNR by 36.64 dB when compared to a simple pulse signal. Overall, this study demonstrated that the proposed novel method can be effectively used in ultrasound detection methods to improve performance.