Parameter Design of Linear Frequency Modulated Excitation Waveform for Ultrasonic Nondestructive Testing of Metallic Materials

An improved time reversal mirror based on standard linear frequency modulation waveform

“…First, according to the actual detecting demand, the waveform of the expected detecting signal is designed in advance. Then, according to the response function of the selected detecting system, the exciting signal corresponding to the detecting signal designed in advance is solved by means of adaptive filtering (26) www.nature.com/scientificreports/ deconvolution method. Finally, the exciting signal obtained is input to the detecting system by the arbitrary signal generator to get the desired detecting signal.…”

“…In a ultrasonic detecting system, due to the limitation of the transducer’s bandwidth, the detecting echo signal obtained by LFM exciting signal is always distorted, which results in serious reduction of the matched filtering effect. What’s more, distortions of the detecting signal becomes more serious with the increasing of the bandwidth of the exciting signal 26 , 32 . Testing and recording the transmitted and received signals of the determined detecting system under the impulse excitation, and then the exciting signal corresponding to the desired detecting signal can be obtained by adaptive filtering deconvolution method, which can eliminate the influence of transport channel response 32 .…”

“…In recent years, TRM technology has showed great research significances and application values in the fields of defect detection of composite materials, medical diagnosis and treatment, underwater target recognition and so on [18][19][20][21][22][23][24][25] . However, The conventional exciting signal widely used in the TRM is a narrow pulse signal with a high bandwidth, which can obtain the high axial resolution and detect micro-size defects 8,14,26 . While the SNR and detecting range are required to be higher, the pulse width needs to be increase, which inevitably affect the axial resolution of the detecting signal.…”

“…Inspired by radar signal processing technology, encoded signals based on pulse compression technology has broken the limitation of the time bandwidth product 27,28 . As the controllable and special signal with a large time bandwidth product, the linear frequency modulation (LFM) signal is initially used in the field of radar system, and then gradually spreads to ultrasonic applications 26,[28][29][30][31] . The application of the LFM excitation improves the SNR and detecting depth of ultrasonic detection and overcomes some defects of conventional excitations 26 .…”

“…As the controllable and special signal with a large time bandwidth product, the linear frequency modulation (LFM) signal is initially used in the field of radar system, and then gradually spreads to ultrasonic applications 26,[28][29][30][31] . The application of the LFM excitation improves the SNR and detecting depth of ultrasonic detection and overcomes some defects of conventional excitations 26 . In a ultrasonic detecting system, due to the limitation of the transducer's bandwidth, the detecting echo signal obtained by LFM exciting signal is always distorted, which results in serious reduction of the matched filtering effect.…”