Ultrasonic non-destructive testing using pulse compression

In the testing of highly absorbent materials, it is necessary to use high transmitted power to obtain echoes with an acceptable signal-to-noise ratio from deep defects. However, the maximum peak power which can be used is limited by the construction problems of the probes and the physical properties...

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Main Author: Fuei K. Lam
Format: Default Thesis
Published: 1975
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Online Access:https://hdl.handle.net/2134/7932
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spelling rr-article-95420751975-01-01T00:00:00Z Ultrasonic non-destructive testing using pulse compression Fuei K. Lam (7203704) Mechanical engineering not elsewhere classified untagged Mechanical Engineering not elsewhere classified In the testing of highly absorbent materials, it is necessary to use high transmitted power to obtain echoes with an acceptable signal-to-noise ratio from deep defects. However, the maximum peak power which can be used is limited by the construction problems of the probes and the physical properties of the crystal materials. Using longer pulses to transmit more energy could improve the detection, but would reduce the resolution of the system. Pulse compression techniques which overcome the conflict between resolution and pulse duration, provide a possible solution to the above problem. The method involves the transmission of a long coded pulse and the processing of the received echo to obtain a relatively narrow pulse, thus preserving resolution. After a study of the principles of pulse compression, various practical schemes were investigated, and the linear frequency-modulated pulse compression systems were found to be most economical to implement. Upon being received, the pulse may be compressed by means of a dispersive ultrasonic delay line, and simple Gaussian shape filter may be employed to reduce the resulting sidelobes. Theoretical studies on the dispersive modes of propagation of elastic waves in narrow metallic strips were then made, and demonstrated the feasibility of using a metallic strip as the dispersive delay device, provided that equalisers are introduced to compensate for the inherent time delay non-linearities in the strip. Design problems associated with the piezoelectric bar transducers for use with the line were also investigated. Based on the above studies, a pulse compression testing system consisting of a transmitting unit, a pair of wide-band transmitting and receiving transducers and a receiving unit, has been constructed. The transmitting unit comprises a linear frequency-modulated oscillator and timing circuits; the receiving unit incorporates equalisers, a weighting filter and an aluminium strip delay line. The operating system achieves a time bandwidth product of 80 and a sidelobe level of -25 dB. Practical tests were carried out and test results are reported. Finally, the power and limitations of the testing system are discussed. 1975-01-01T00:00:00Z Text Thesis 2134/7932 https://figshare.com/articles/thesis/Ultrasonic_non-destructive_testing_using_pulse_compression/9542075 CC BY-NC-ND 4.0
institution Loughborough University
collection Figshare
topic Mechanical engineering not elsewhere classified
untagged
Mechanical Engineering not elsewhere classified
spellingShingle Mechanical engineering not elsewhere classified
untagged
Mechanical Engineering not elsewhere classified
Fuei K. Lam
Ultrasonic non-destructive testing using pulse compression
description In the testing of highly absorbent materials, it is necessary to use high transmitted power to obtain echoes with an acceptable signal-to-noise ratio from deep defects. However, the maximum peak power which can be used is limited by the construction problems of the probes and the physical properties of the crystal materials. Using longer pulses to transmit more energy could improve the detection, but would reduce the resolution of the system. Pulse compression techniques which overcome the conflict between resolution and pulse duration, provide a possible solution to the above problem. The method involves the transmission of a long coded pulse and the processing of the received echo to obtain a relatively narrow pulse, thus preserving resolution. After a study of the principles of pulse compression, various practical schemes were investigated, and the linear frequency-modulated pulse compression systems were found to be most economical to implement. Upon being received, the pulse may be compressed by means of a dispersive ultrasonic delay line, and simple Gaussian shape filter may be employed to reduce the resulting sidelobes. Theoretical studies on the dispersive modes of propagation of elastic waves in narrow metallic strips were then made, and demonstrated the feasibility of using a metallic strip as the dispersive delay device, provided that equalisers are introduced to compensate for the inherent time delay non-linearities in the strip. Design problems associated with the piezoelectric bar transducers for use with the line were also investigated. Based on the above studies, a pulse compression testing system consisting of a transmitting unit, a pair of wide-band transmitting and receiving transducers and a receiving unit, has been constructed. The transmitting unit comprises a linear frequency-modulated oscillator and timing circuits; the receiving unit incorporates equalisers, a weighting filter and an aluminium strip delay line. The operating system achieves a time bandwidth product of 80 and a sidelobe level of -25 dB. Practical tests were carried out and test results are reported. Finally, the power and limitations of the testing system are discussed.
format Default
Thesis
author Fuei K. Lam
author_facet Fuei K. Lam
author_sort Fuei K. Lam (7203704)
title Ultrasonic non-destructive testing using pulse compression
title_short Ultrasonic non-destructive testing using pulse compression
title_full Ultrasonic non-destructive testing using pulse compression
title_fullStr Ultrasonic non-destructive testing using pulse compression
title_full_unstemmed Ultrasonic non-destructive testing using pulse compression
title_sort ultrasonic non-destructive testing using pulse compression
publishDate 1975
url https://hdl.handle.net/2134/7932
_version_ 1797196929850933248