Non-contact ultrasonic guided wave inspection of rails: field test results and updates

Abstract

The University of California at San Diego (UCSD), under a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, is developing a system for high-speed and non-contact rail defect detection. A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection, paired with a real-time statistical analysis algorithm, has been realized. This system requires a specialized filtering approach based on electrical impedance matching due to the inherently poor signal-to-noise ratio of air-coupled ultrasonic measurements in rail steel. Various aspects of the prototype have been designed with the aid of numerical analyses. In particular, simulations of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach (LISA) algorithm. The system's operating parameters were selected based on Receiver Operating Characteristic (ROC) curves, which provide a quantitative manner to evaluate different detection performances based on the trade-off between detection rate and false positive rate. Results from the first field test of the non-contact air-coupled defect detection prototype conducted at the Transportation Technology Center (TTC) in Pueblo, Colorado, in October 2014 are presented and discussed in this paper. The results indicate that the prototype is able to detect internal cracks with high reliability.

Guided wave–based rail flaw detection technologies: state-of-the-art review

“…Another prototype developed by the UCSD group consisting of a cylindrically focused air-coupled piezoelectric transmitter was used to substitute for the laser, as shown in Figure 21. 13,172–174 The new challenge with this method is the low SNR since most of the energy excited by the air-coupled transmitter is reflected back in air due to the large acoustic impedance mismatch between air and rail. 66,174 To alleviate reflected signals, a specially focused transmitter has been used in combination with highly resonant impedance matching networks (L-matching networks) in reception.…”

“…13,172–174 The new challenge with this method is the low SNR since most of the energy excited by the air-coupled transmitter is reflected back in air due to the large acoustic impedance mismatch between air and rail. 66,174 To alleviate reflected signals, a specially focused transmitter has been used in combination with highly resonant impedance matching networks (L-matching networks) in reception. The electrical impedance matching network essentially creates resonant conditions at the frequency of interest at the receivers’ side to amplify the signal.…”

“…The electrical impedance matching network essentially creates resonant conditions at the frequency of interest at the receivers’ side to amplify the signal. 66,174…”

“…The results of these tests, evaluated in terms of probability of detection versus probability of false alarms (receiver operating characteristic curves), indicated a good detection performance at speeds of 1.6 and 8 km/h, and much poorer performance at speeds of 16 and 24 km/h. 66,174…”

“…Theoretical analysis of this approach has been done early by Ryue et al 13,93,166–175 Recently, UCSD proposed a new scheme of non-contact receivers, without using active transmitters, as shown in Figure 22. 176–178 This high-speed ultrasonic rail inspection system was developed based on passively reconstructing the rail’s transfer function from the excitations naturally caused by the rolling wheels of a moving train.…”