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

Аналітичне дослідження впливу конструкції ультразвукового пакетного п’єзокерамічного перетворювача на амплітуду коливань

В роботі розглянуті питання, пов’язані з розрахунком геометричних розмірів пакетних перетворювачів на основі п’єзокераміки. Отримані співвідношення для розрахунку геометричних розмірів пакету в залежності від робочої частоти, матеріалу накладок та товщини пакету п’єзокераміки. Отримано аналітичний вираз для розрахунку амплітуди коливальної швидкості на робочій поверхні перетворювача в режимі холостого ходу. Проведено порівняльний аналіз розрахунків резонансної частоти для отриманих аналітичних виразів та результатів, отриманих розрахунками методом кінцевих елементів. Показано, що розбіжність результатів не перевищує 10%. В результаті аналітичного дослідження показано, що асиметричний перетворювач дає більшу амплітуду коливань у порівнянні з симетричним незалежно від матеріалу накладок. Збільшення амплітуди коливальної швидкості можна досягти збільшенням товщини пакету або виконанням робочої накладки з матеріалу, що має менший хвильовий опір.The issues related to the calculation of the sandwich converters geometric dimensions based on piezoceramics are presented in this paper. The equations for the package geometric dimensions are obtained depending on the operating frequency, the material of the pads and the thickness of the piezoceramic package. An analytical expression is obtained to calculate the oscillatory velocity amplitude on the working surface of the transducer in the idle mode. The comparative analysis of the calculated resonance frequency by analytical expressions and the calculated value by finite element method is carried out. It is shown that the discrepancy does not exceed ten percent. As a result of the analytical study, it is shown that the asymmetric transducer gives a greater amplitude of oscillations compared to the symmetric one, independent of the lining material. Increasing the amplitude of the oscillatory velocity can be achieved by increasing the thickness of the packet or by performing a working lining of a material having a lower wave resistance.В работе рассмотрены вопросы, связанные с расчетом геометрических размеров пакетных преобразователей на основе пьезокерамики. Получены соотношения для расчета геометрических размеров пакета в зависимости от рабочей частоты, материала накладок и толщины пакета пьезокерамики. Получено аналитическое выражение для расчета Рис. 14. Залежність нормованої до 1В амплітуди коливальної швидкості на частоті 22кГц при різних матеріалах робочої накладки та пакету з 4-х кілець п’єзокераміки APC-841 з розмірами кільця 50206 мм 81 ISSN 2521-1943. Mechanics and Advanced Technologies #3 (87), 2019 амплитуды колебательной скорости на рабочей поверхности преобразователя в режиме холостого хода. Проведен сравнительный анализ расчетов резонансной частоты для полученных аналитических выражений с расчетами методом конечных элементов. Показано, что расхождение результатов не превышает 10 %. В результате аналитического исследования показано, что асимметричный преобразователь дает большую амплитуду колебаний по сравнению с симметричным, в независимости от материала накладок. Увеличения амплитуды колебательной скорости можно достичь увеличением толщины пакета или выполнением рабочей накладки из материала, имеющего меньший волновое сопротивление. Ключевые слова: ультразвуковой преобразователь; пьезокерамика; пакетный пьезопреобразователь; резонансная частота; амплитуда колебаний

УЛЬТРАЗВУКОВОЙ ПРЕОБРАЗОВАТЕЛЬ С РАДИАЛЬНО РАСПОЛОЖЕННЫМИ ПЬЕЗОКЕРАМИЧЕСКИМИ ПАКЕТАМИ

В настоящей статье описывается конструкция ультразвукового ппьезоэлектрического преобразователя увеличенной акустической мощности. Повышение мощности достигается за счет суммирования акустической мощности нескольких преобразователей Ланжевена, установленных на единой излучающей накладке. Проведенные исследования позволили установить, что основной недостаток этого пьезопреобразователя заключается в разрушении пьезокерамических колец в следствии высокой неравномерности распределения амплитуд колебаний в местах их установки. Теоретические и экспериментальные исследования позволили провести оптимизацию и устранить выявленный недостаток пьезоэлектрического преобразователя.  При этом в качестве критерия оптимизации был выбран максимум равномерности распределения амплитуд колебаний в области присоединения пьезокерамических колец. В результате проведенных исследований разработана оптимизированная конструкция высокочастотных преобразователей. Определено, что установка 9-11 радиально расположенных пьезокерамических пакетов обеспечивает минимальную неравномерность колебаний в области присоединения пьезоколец при этом преобразователь рассчитанный на 30 кГц обеспечивает акустическую мощность не менее 1450 Вт с КПД 78%

Ultrasound power measurement system design using PVDF sensor and FPGA technology

Ultrasound machine is widely used in industrial and medical institutions. With the purpose of avoiding the unwanted power exposed on human, ultrasound power meter is employed to measure output power of ultrasound machine for diagnostic, therapeutic and non-destructive testing purposes. The existing ultrasound power meter, however, is high-cost, low-resolution and only for specific machine. Radiation balance method consists of calculation and calibration complexity while the calorimetric produces inaccurate result compared to the standard. On the other hand, application of piezoelectric sensor in hydrophone-based measurement requires advancement on processing device and technique. This work deals with the development of ultrasound power measurement system on Field Programmable Gate Array (FPGA) platform. Polyvinylidene Fluoride (PVDF) was employed to sense medical ultrasonic signal. PVDF film’s behavior and its electro-acoustic model were observed. Signal conditioner circuit was then described. Next, a robust low-cost casing for PVDF sensor was built, followed by the proposal of the use of digital-system ultrasound processing algorithm. The simulated sensor provided 2.5 MHz to 8.5 MHz response with output amplitude of around 4 Vpp. Ultrasound analog circuits, after filtering and amplifying, provided frequency range from 1 MHz until 10 MHz with -5 V to +5 V voltage head-rooms to offer a wideband medical ultrasonic acceptance. Frequency from 500 kHz to 10 MHz with temperature span from 10 oC to 50 oC and power range from 1 mW/cm2 up to 10 W/cm2 (with resolution 0.05 mW/cm2) had been expected by using the established hardware. The test result shows that the platform is able to process 10 us ultrasound data with 20 ns time-domain resolution and 0.4884 mVpp magnitude resolutions. This waveform was then displayed in the personal computer’s (PCs) graphical user interface (GUI) and the calculation result was displayed on liquid crystal display (LCD) via microcontroller. The whole system represents a novel design of low-cost ultrasound power measurement system with high-precision capability for medical application. This may improve the existing power meters which have intensity resolution limitation (at best combination, of all products, utilize: 0.25 MHz - 10 MHz frequency coverage; 10 oC to 30 oC working temperature; 0 W/cm2 - 30 W/cm2 power range; 20 mW/cm2 resolution), neither having mechanism to handle the temperature disturbance nor possibility for further data analysis

Vibration control in cricket bats using piezoelectric-based smart materials

The vibrations of a Cricket bat are traditionally passively damped by the inherent damping properties of wood and flat rubber panels located in the handle of the bat. This sort of passive damping is effective for the high frequency vibrations only and is not effective for the low frequency vibrations. Recently, the use of Smart materials for vibration control has become an alternative to the traditional vibration control techniques which are usually heavy and bulky, especially at low frequencies. In contrast, the vibration controls with Smart materials can target any particular frequency of vibration. This has advantages such as it results in smaller size, lighter weight, portability, and flexibility in the structure. This makes it particularly suitable for traditional techniques which cannot be applied due to weight and size restrictions. This research is about the study of vibration control with Smart materials with the ultimate goal to reduce the vibration of the Cricket bat upon contact with a Cricket ball. The study focused on the passive piezoelectric vibration shunt control technique. The scope of the study is to understand the nature of piezoelectric materials for converting mechanical energy to electrical energy and vice versa. Physical properties of piezoelectric materials for vibration sensing, actuation and dissipation were evaluated. An analytical study of the resistor-inductor (R-L) passive piezoelectric vibration shunt control of a cantilever beam was undertaken. The modal and strain analyses were performed by varying the material properties and geometric configurations of the piezoelectric transducer in relation to the structure in order to maximize the mechanical strain produced in the piezoelectric transducer. Numerical modelling of structures was performed and field-coupled with the passive piezoelectric vibration shunt control circuitry. The Finite Element Analysis (FEA) was used in order for the analysis, optimal design and for determining the location of piezoelectric transducers. Experiments with the passive piezoelectric vibration shunt control of beam and Cricket bats were carried out to verify the analytical results and numerical simulations. The study demonstrated that the effectiveness of the passive piezoelectric vibration shunt control is largely influenced by the material properties of the structures to be controlled. Based on the results from simple beam evaluations, vibration reduction of up to 42% was obtained with the designed Smart Cricket bat. Finally, for the control circuit to automatically track the frequency shift of structures required in real applications, an adaptive filter protocol was developed for estimating multiple frequency components inherent in noisy systems. This has immediate application prospects in Cricket bats

Development of techniques for detection and dissolution enhancement of mineral deposits in petroleum pipelines using ultrasound.

Scale formation in petroleum pipelines causes progressive flow reductions, leading to large production losses and operating costs. The composition and thickness of the scale deposits vary widely, but with present technology they cannot be accurately quantified or monitored. Remedial treatments such as chemical de-scaling etc. are therefore largely based on guesswork, which can lead to expensive chemical wastage and production shutdowns. This project is intended to address some of the above problems using ultrasonic techniques. Work presented in this thesis branches out into two main areas of interest, namely: (a) developments concerning location of deposits from both top-side and down-hole locations; and (b) developments relating to enhancement of scale removal, using ultrasound. With regard to top-side scale detection, the major challenge in this work was to develop a technique by which acoustic signatures are synthetically generated, which can be used with the techniques previously developed for pipeline inspection. This required the determination of a suitable type of transducer and the study of its radiation characteristics in developing comprehensive mathematical models for artificially generating reference echoes. The model allowed the first three multiple echoes (in steel objects) to be computed for given test parameters. Close agreement of the synthesised echoes with practical measurements was demonstrated with good repeatability. An essential requirement for the detection of deposits in down-hole is the accurate alignment of the test probes with respect to the pipe-wall. In this regard, a novel technique for remote alignment of the transducers was successfully formulated. It is based on identifying symmetrical properties of the signals received from the test probe itself when scanned around the correct angular position with respect to the target. However, through extensive practical measurements, it was found that an important requirement for applying this technique is to know in advance whether a particular combination of probe, target diameter and separation distance would give satisfactory angular resolution. Extensive practical examination of these factors showed that no general conclusion can easily be drawn with respect to this requirement. Therefore a mathematical model was successfully developed, which would predict the suitability of given probe/target parameters. It has been reported in previous studies that ultrasonic irradiation could greatly enhance the chemical dissolution of localised deposits during de-scaling operations. In this regard, a major challenge was to improve the efficiency of power transducers radiating into confined spaces at elevated temperatures. That required the study of radiation characteristics of ultrasonic power transducers and compensation techniques to regain loss of efficiency at elevated temperatures. Alternative types of transducers - based on flexural-horn designs - were also investigated and their relative merits presented. Significant findings related to the performance variations of ultrasonic transducers and transmission cables at elevated temperatures have been made. After examining the transducer efficiency drop with temperature, a closed-loop compensation strategy was proposed for maintaining optimal performance. The matching requirements of the cables transmitting power from top-side to down-hole power transducers were also investigated as part of optimisation of ultrasonic power output. From this study it was found that, within the temperature range of interest, the cable in itself does not require changes to the matching requirements as the environmental temperature fluctuates. However, it was noted that the transducer impedance changes rapidly with temperature and therefore a unified compensation strategy incorporating both cable and transducer impedances was proposed as a better solution. Overall, the main objectives of the project concerning pipeline scale detection were well achieved, namely: (a) modelling of a suitable type of ultrasonic transducer to synthesise the reference multiple echoes to aid top-side scale detection; and (b) development of a remote sensing technique for ultrasonic probe alignment in downhole pipes. With regard to dissolution enhancement, techniques for enhancing power output of ultrasonic transducers to aid dissolution enhancement of scale deposits have been determined. Further work includes the improvements to software algorithms developed and hardware integration to achieve the expected performance of the techniques presented

Integrated sensors for process monitoring and health monitoring in microsystems

This thesis presents the development of integrated sensors for health monitoring in Microsystems, which is an emerging method for early diagnostics of status or “health” of electronic systems and devices under operation based on embedded tests. Thin film meander temperature sensors have been designed with a minimum footprint of 240 m × 250 m. A microsensor array has been used successfully for accurate temperature monitoring of laser assisted polymer bonding for MEMS packaging. Using a frame-shaped beam, the temperature at centre of bottom substrate was obtained to be ~50 ºC lower than that obtained using a top-hat beam. This is highly beneficial for packaging of temperature sensitive MEMS devices. Polymer based surface acoustic wave humidity sensors were designed and successfully fabricated on 128° cut lithium niobate substrates. Based on reflection signals, a sensitivity of 0.26 dB/RH% was achieved between 8.6 %RH and 90.6 %RH. Fabricated piezoresistive pressure sensors have also been hybrid integrated and electrically contacted using a wire bonding method. Integrated sensors based on both LiNbO3 and ZnO/Si substrates are proposed. Integrated sensors were successfully fabricated on a LiNbO3 substrate with a footprint of 13 mm × 12 mm, having multi monitoring functions for simultaneous temperature, measurement of humidity and pressure in the health monitoring applications

Sensorless Position Control of Piezoelectric Ultrasonic Motors:a Mechatronic Design Approach

This dissertation considers mechatronic systems driven by piezoelectric ultrasonic motors (PUM). The focus is set on optimal system design and sensorless position control. Mechatronic industry faces the challenge to deliver ever more efficient and reliable products while being confronted to increasingly short time to market demands and economic constraints driven by competition. Although optimal design strategies are applied to master this challenge, they do not entirely respond to the given circumstances, as often only local criteria are optimised. In order to obtain a globally optimal solution, the many subfunctions of a mechatronic system and their models must be interrelated and evaluated concurrently from the very beginning of the design process. In this context PUM have been used increasingly during the last decade for various positioning applications in the field of mechatronic systems, laboratory equipment, and consumer electronics where their performances are superior to conventional electromechanical drive systems based on DC or BLDC motors. The position of the mobile component must be controlled. In some cases open-loop control is a solution, but more often than not sensors are used as feedback device in closed-loop control. Sensors are expensive, large in size and add fragile hardware to the device that compromises its reliability. Thus, not only the superior performance is not fully exploited but also the economical feasibility of the PUM drive system is jeopardised. Replacing sensors by advanced control techniques is an approach to these problems that is well established in the field of BLDC motors. Those sensorless control strategies are not directly transferrable, because of the fundamentally different working principles of PUM. Hence, the research of sensorless closed-loop position control techniques applicable to PUM and their validation with digitally controlled functional models is the very topic of this thesis. We propose a dedicated design methodology to this statement of the problem. A core model of the mechatronic system is conceived as general and simple as possible. It then develops for the different interrelated views reflecting the mechanical, electromechanical, drive electronic, sensorial and digital control functions of the global system. Each one becoming more specific and detailed in this process, the different views still enable mutual constraint adjustments and the dynamic integration of results from the other views during the design process. Starting with the stator of the PUM, a view describes the mechanical displacement. An electric equivalent model is written such that power input from the drive electronics is related to the mechanical energy transmitted to the mechanics. The resulting differential equations are solved by the finite element method (FEM). Position feedback configurations in the mobile part of the PUM are modelled analytically in order to be implemented in digital control and their electrical implications are updated to the stator model. In this way, sensors do not necessarily materialise physically any more, but are distributed among the mechanical configuration, the drive electronics and the digital controller. With respect to the sensor data, the controller is not simply receiving finalised data on the measured system parameter, but rather implements the sensor itself in software. Finally, the position detection performance obtained with the aforementioned design methodology was evaluated with the example of mechatronic locking devices actuated by custom-made as well as OEM motors. Functional models of motors, electronics and digital controllers were used to identify the limits of the proposed methods, and suggestions for further research were deduced. These results contribute to the development of robust sensorless position controllers for PUM