Research on the propagation efficiency of ultrasonic guided waves in the rail

Ultrasonic guided waves (UGW) technique has the advantages of low detection frequency, long detection distance, strong anti-electromagnetic interference ability, and large coverage. Hence it has potential advantages in real-time detection of breakages in the rail. Based on the research background of UGW-based broken rail detection, this paper focuses on the characteristics optimization of piezoelectric ultrasonic transducers (PUTs) to improve the propagation efficiency of UGW in the rail. Due to the influence of energy attenuation, multimodal, dispersion, and on-site noise when the UGW propagates in the rail, the amplitude of the received UGW signal is low and the signal-to-noise ratio is poor. Therefore, this thesis mainly systematically studies the characteristics optimization of PUTs from the aspects of impedance matching, driving circuit optimization, and excitation signal optimization. The main work is as follows: 1. To deeply study of the electromechanical characteristics of longitudinal vibration sandwich piezoelectric ultrasonic transducer (referred to as PUTs), the PSpice equivalent circuit models of a piezoelectric ultrasonic transducer and the PSpice equivalent circuit model of a pitch-catch setup are established based on one-dimensional wave and transmission line theory. The PSpice model of the PUT and the PSpice model of the pitch-catch setup are analyzed from the time and frequency domains, respectively, and the accuracy of the built PSpice models is verified through some experiments. It is shown that the PSpice model of a PUT established above is highly scalable and can be combined with amplifiers, driving circuits, diodes. 2. With the aim of solving the problem of impedance mismatch between the piezoelectric ultrasonic transducer and the driving circuit and the rail surface, the effect of the impedance matching on the electromechanical properties of the piezoelectric ultrasonic transducer was studied from the electrical and acoustic ends, respectively. From the electrical side, the effects of different electrical impedance matching networks on the electromechanical characteristics of PUTs are studied in both time and frequency domains. It is shown that in the two LC impedance matching networks, the matching network formed by the series inductance and parallel capacitance is better. From the acoustic side, an experimental method is used to study the effect of acoustic impedance matching on the transient characteristics of PUTs. It is concluded that when the epoxy resin is doped with 10% tungsten powder and the coating thickness is 8 mm, the acoustic impedance matching effect is better. 3. To overcome the problems of the existing driving circuits that the excitation voltage is not high enough, the extra high voltage DC voltage is required and the impedance matching is not considered, this thesis proposed a high voltage pulse driving circuit based on the full-bridge topology. The driving circuit takes into account the suppression of overshoot and oscillation when the power MOSFET is turned off, and at the same time conducts the impedance matching and tailing absorption of the excitation signal for PUTs. The suppression of overshoot and oscillation adopts the RC snubber circuit, and the tailing absorption is accomplished by a bleeder resistor and a bidirectional thyristor. The correctness and effectiveness of the proposed high-voltage pulse driving circuit are verified through experiments. It was also found that the combined use of electrical impedance matching and absorption circuits can effectively improve the energy conversion efficiency of PUTs. 4. To obtain the optimal performance of PUTs, the excitation signal of PUTs is optimized in terms of excitation signal frequency and excitation coding. First of all, to solve the problem of PUTs with having a resonance frequency shift after loading, this thesis proposes an optimal excitation frequency tracking method based on a digital band-pass tracking filtering. Then its correctness and stability are verified through some field experiments. Secondly, to improve the signal-to-noise ratio of the UGW signal, it is proposed to apply the Barker code excitation method to the broken rail detection, and use the pulse compression technique at the receiving end to realize the rapid recognition of the signal characteristics. Finally, for the case where the pulse-compressed signal produces undesirable peak sidelobes due to the effects of bandwidth, multipath, and noise, an adaptive peak detection algorithm based on the Hilbert transform combined with a digital bandpass tracking filter and a triangle filter. The accuracy and effectiveness of the above-mentioned Barker code excitation method and the adaptive peak detection algorithm are verified through experiments. The study in this thesis presents a feasible solution for improving the propagation efficiency of UGW in the rails and at the same time provides theoretical guidance for the large-scale application of the real-time broken rail detection system based on UGW

Investigation into the use of zero angle ultrasonic probe array for defect detection and location

The steel industry like any other manufacturing process is under constant pressure to deliver higher quality defect free material at lower cost to customers. This push for zero defects has led to improved manufacturing processes and the need for more reliable, faster defect testing methods. Ultrasound fundamentally provides a mechanical stress, produced by tensile, compressive, shearing or flexural forces, which are of such low intensity that no material damage occurs. The remit of the project was to investigate and develop the latent potential within the Present automated ultrasonic immersion system using an array of normal angle probes, used for billet inspection. The work presented in this thesis describes the research undertaken to develop a system using, 10mm diameter, standard zero angled 5MHz ultrasonic transducers. The transducers were used at linear separation distances of between 22.5mm and 45mm set in a typical 8-probe array orientation. The developed technique is potentially transferable to other ultrasonic multi-probe array applications and demonstrates that time of flight diffraction can be realised using normal probes, and termed Normal Probe Diffraction, (NPD). The technique located defects, using the intersection of ellipses, with an error of <0.5% of the signal transit distance and, with the application of a correlation filter, improved the Signal to Noise Ratio (SNR) from—20dB to 17.0dB

High bit-rate digital communication through metal channels

The need to transmit digital information across metallic barriers arises frequently in industrial control applications. In some applications, the barrier can be penetrated with wiring, while in others this may not be possible. For example, metal bulkheads, pressure vessels, or pipelines may require a level of mechanical integrity that prohibits mechanical penetration. This study investigates the use of ultrasonic signaling for data transmission across metallic barriers, discusses the associated challenges, and analyzes several alternative communication system implementations.Several recent e orts have been made to develop through-metal ultrasonic communication systems, with approaches ranging widely in bitrate, complexity, and power requirements. The transceiver designs presented here are intended to cover a range of target applications. In systems having low data rate requirements, simple transceivers with low hardware/software complexity can be used. At high data rates, however, severe echoing in the ultrasonic channel leads to intersymbol interference. Reliable high speed communication therefore requires the use of channel equalizers, and results in a transceiver with higher hardware/software complexity.In this thesis, issues related to the design of reliable through-metal ultrasonic communication systems are discussed. These include (1) the development of mathematical models used to characterize the channel, (2) application of equalization techniques needed to achieve high-speed communication, and (3) analysis of hardware/software complexity for alternative transceiver designs.Several groups have developed through-metal ultrasonic communication systems in the recent past, though none has produced a mathematical model that accurately describes the phenomena found within the channel. The channel model developed in this thesis can be used at several stages of the transceiver design process, from transducer selection through channel equalizer design and ultimately system performance simulation.Using this channel model, we go on to develop and test several ultrasonic throughmetal transceiver designs. Ultrasonic through-metal communication systems are finding use in a wide variety of applications. Some require high throughput, while others require low power consumption. The motivation for developing several designs { ranging from low complexity, low power to high complexity, high throughput { is so that the best design can be matched to each application.After these transceiver designs are developed, we present an analysis of their computational requirements so that the most appropriate transceiver can be chosen for a given application.Ph.D., Electrical Engineering -- Drexel University, 201

Acoustic and Elastic Waves: Recent Trends in Science and Engineering

The present Special Issue intends to explore new directions in the field of acoustics and ultrasonics. The interest includes, but is not limited to, the use of acoustic technology for condition monitoring of materials and structures. Topics of interest (among others): • Acoustic emission in materials and structures (without material limitation) • Innovative cases of ultrasonic inspection • Wave dispersion and waveguides • Monitoring of innovative materials • Seismic waves • Vibrations, damping and noise control • Combination of mechanical wave techniques with other types for structural health monitoring purposes. Experimental and numerical studies are welcome

Technology 2003: Conference Proceedings from the Fourth National Technology Transfer Conference and Exposition, Volume 1

Proceedings from symposia of the Technology 2003 Conference and Exposition, December 7-9, I993, Anaheim, CA. Volume 1 features the Plenary Session and the Plenary Workshop, plus papers presented in Advanced Manufacturing, Biotechnology/Medical Technology, Environmental Technology, Materials Science, and Power and Energy

Study of an attitude reference system utilizing an electrically suspended gyro final report, 1 aug. 1964 - 31 mar. 1965

Miniature electrically suspended gyroscope for spacecraft attitude reference syste

Modelling, Simulation and Data Analysis in Acoustical Problems

Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years