Effect of temperature on the performance of a giant magnetostrictive ultrasonic transducer

The effect of temperature on the performance of a giant magnetostrictive ultrasonic transducer (GMUT) was investigated by measuring variations in the resonance frequency and mechanical quality factor of the GMUT at different temperatures. The equivalent circuit model of the GMUT was presented and the total electrical impedance equation was obtained. Curves of the impedance circle were obtained at different temperatures to determine the resonance frequency and mechanical quality factor. To verify the impedance-based results and obtain precise values of the resonance frequency and effective frequency bandwidth, the amplitude-frequency response within the same temperature range was examined experimentally. These results were consistent with those of the impedance analysis, which demonstrates the validity of the equivalent circuit model. Moreover, the resonance frequency and effective bandwidth of the GMUT were found to decrease with increasing temperature, which means that the vibration amplitude is more sensitive to variation in the resonance frequency at high temperature owing, for example, to static or dynamic system loading, changes in the material properties, or drive-signal variability. Accordingly, the temperature in the GMUT should be precisely controlled to improve the stability of vibration

Investigation of methods for data communication and power delivery through metals

PhD ThesisThe retrieval of data from a sensor, enclosed by a metallic structure, such as a naval vessel, pipeline or nuclear flask is often very challenging. To maintain structural integrity it is not desirable to penetrate the wall of the structure, preventing any hard-wired solution. Furthermore, the conductive nature of the structure prevents the use of radio communications. Applications involving sealed containers also have a requirement for power delivery, as the periodic changing of batteries is not possible. Ultrasound has previously been identified as an attractive approach but there are two key challenges: efficient/reliable ultrasonic transduction and a method of overcoming the inherent multipath distortion resulting from boundary reflections. Previous studies have utilised piezoelectric contact transducers, however, they are impractical due to their reliance on coupling, i.e. the bond between the transducer and the metal surface, which leads to concerns over long term reliability. A non-contact transducer overcomes this key drawback, thus highlighting the electromagnetic acoustic transducer (EMAT) as a favourable alternative. This thesis presents the design and testing of an EMAT with appropriate characteristics for through-metal data communications. A low cost, low power data transmission scheme is presented for overcoming acoustic multipath based on pulse position modulation (PPM). Due to the necessary guard time, the data rate is limited to 50kbps. A second solution is presented employing continuous wave, Quadrature phase shift keying (QPSK) modulation, allowing data rates in excess of 1Mbps to be achieved. Equalisation is required to avoid intersymbol interference (ISI) and a decision feedback equaliser (DFE) is shown to be adept at mitigating this effect. The relatively low efficiency of an EMAT makes it unsuitable for power delivery, consequently, an alternative non-contact approach, utilising inductive coupling, is explored. Power transfer efficiency of ≈ 4% is shown to be achievable through 20mm thick stainless steel.ICS department of BAE Systems Submarine Solutions, EPSR

A high-tolerance matching method against load fluctuation for ultrasonic transducers

Fluctuation of acoustic load significantly weakens the performance of ultrasonic system. To address this problem in a simple way, we consider the main input and output variables related to the ultrasonic transducer's performance and propose a detailed mathematical model based on the simplest LC matching network containing only one capacitor and one inductor. In this model, a new resonance frequency f0 brought by matching components was found and defined. The optimum analysis method is used to solve the model, and a high-tolerance matching method against load fluctuation is obtained. Analysis indicates that when activated at the mechanical resonance frequency, the impedance and apparent power of the PT matched by the proposed method are constant no matter how the load changes, and thereby can significantly increase the stability and robustness of ultrasonic systems. For its simple structure and high performance, the proposed matching method can be widely applied in most ultrasonic systems. The tolerance of the proposed method against other environmental factors and high-order LC matching networks were also discussed. In addition, the feasibility and advantage of the proposed matching method are also verified by experiments

A novel fast resonance frequency tracking method based on the admittance circle for ultrasonic transducers

For ultrasonic systems, the resonance frequency tracking (RFT) is the most critical step. The rapid development in advanced material processing and microelectronics package has increased the demand of high speed RFT. Therefore, this paper proposes a fast RFT (FRFT) method according to the characteristics of piezoelectric transducers' (PT) admittance circle. In the proposed method, the PT is driven at two different frequencies, and the PT's admittance is collected and calibrated. Then, the PT's mechanical resonance frequency is derived using the admittance information after calibration. The proposed method is not affected by the parallel capacitor and the matching circuit. Additionally, the optimal initial values of the involved parameters are determined in order to improve the accuracy of the proposed method. Furthermore, an improved method based on multiple tracking is also provided. Simulations and experiments demonstrate that using the proposed FRFT method, the ultrasonic system can track the resonance frequency in a short time with high accuracy

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

MODELING METHODOLOGY OF PULSE-ECHO ULTRASOUND SYSTEM FOR MEDICAL IMAGING DIAGNOSTICS

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 김수환.A flexible clinical ultrasound system must operate with different transducers, which have characteristic impulse responses and widely varying impedances. The impulse response determines the shape of the high-voltage pulse that is transmitted and the specifications of the front-end electronics that receive the echoand the impedance determines the specification of the matching network through which the transducer is connected. System-level optimization of these subsystems requires accurate modeling of pulse-echo (two-way) response, which in turn demands a unified simulation of the ultrasonics and electronics. This thesis proposed modeling methodology of pulse-echo ultrasound system for medical imaging diagnostics and the development of pulse-echo ultrasound system simulator in the Matlab/Simulink environment by using the modeling methodology. This simulator is realized by combining Matlab/Simulink models of the high-voltage transmitter, the transmission interface, the acoustic subsystem which includes wave propagation and reflection, the receiving interface, and the front-end receiver. To demonstrate the effectiveness of our simulator, the models are experimentally validated by comparing the simulation results with the measured data from commercial ultrasound system. Proposed pulse-echo ultrasound simulator, which is developed by our modeling methodology, could be used to quickly provide system-level feedback for an optimized tuning of electronic design parameters.CHAPTER 1 INTRODUCTION 1 1.1 ULTRASOUND IMAGING 1 1.2 HISTORY OF ULTRASOUND IMAGING 5 1.3 CHALLENGE AND APPROACH 8 1.4 THESIS ORGANIZATION 11 CHAPTER 2 FUNDAMENTALS OF ULTRASOUND SYSTEMS 12 2.1 BASIC ULTRASOUND PHYSICS 12 2.1.1 SOUND WAVES 12 2.1.2 REFLECTION 15 2.1.3 SCATTERING 18 2.1.4 REFRACTION 19 2.1.5 DIFFRACTION 21 2.1.6 ABSORPTION 22 2.1.7 ATTENUATION 24 2.2 ULTRASOUND SYSTEM OVERVIEW 26 2.3 PIEZOELECTRIC TRANSDUCER 29 2.4 HIGH-VOLTAGE TRANSMITTER 32 2.5 FRONT-END RECEIVER 33 CHAPTER3 MODELING OF ULTRASOUND TRANSDUCER 35 3.1 THEORETICAL MODELS 35 3.1.1 LEACH MODEL 35 3.1.2 ACOUSTICAL ATTENUATION 38 3.1.3 PROPAGATING MEDIUM 42 3.1.4 DIFFRACTION EFFECTS 44 3.1.5 PARASITIC COMPONENTS 45 3.2 BUTTERWORTH VAN-DYKE MODEL 47 3.3 ANALYTICAL MODEL 52 CHAPTER 4 DEVELOPMENT OF MATLAB/SIMULINK PULSE-ECHO ULTRASOUND SYSTEM SIMULATOR 56 4.1 MODELING STRATEGY FOR PULSE-ECHO ULTRASOUND SYSTEM 56 4.2 HIGH-VOLTAGE TRANSMITTER MODEL 60 4.3 ACOUSTIC SUBSYSTEM AND INTERFACING ELECTRONICS MODELS 62 4.4 FRONT-END RECEIVER MODEL 67 4.4.1 T/R SWITCH AND ACTIVE TERMINATION 67 4.4.2 HARMONIC DISTORTION 70 4.4.3 AMPLIFIER AND FILTER 72 4.4.4 SAMPLING CLOCK JITTER 74 4.4.5 ANALOG-TO-DIGITAL CONVERTER 76 CHAPTER 5 EXPERIMENTS VERSUS SIMULATION 78 5.1 VALIDATION OF SUBSYSTEMS 78 5.1.1 ACOUSTIC SUBSYSTEM AND INTERFACING ELECTRONICS 78 5.1.2 FRONT-END RECEIVER 83 5.2 VALIDATION OF COMPLETE SYSTEM 87 5.2.1 EXPERIMENTAL SETUP 87 5.2.2 COMPARISON SIMULATION AND MEASUREMENTS 91 5.3 DISCUSSION 95 CHAPTER6 CONCLUSIONS 97 BIBLIOGRAPHY 99 ABSTRACT IN KOREAN 105Docto

A Three – tier bio-implantable sensor monitoring and communications platform

One major hindrance to the advent of novel bio-implantable sensor technologies is the need for a reliable power source and data communications platform capable of continuously, remotely, and wirelessly monitoring deeply implantable biomedical devices. This research proposes the feasibility and potential of combining well established, ‘human-friendly' inductive and ultrasonic technologies to produce a proof-of-concept, generic, multi-tier power transfer and data communication platform suitable for low-power, periodically-activated implantable analogue bio-sensors. In the inductive sub-system presented, 5 W of power is transferred across a 10 mm gap between a single pair of 39 mm (primary) and 33 mm (secondary) circular printed spiral coils (PSCs). These are printed using an 8000 dpi resolution photoplotter and fabricated on PCB by wet-etching, to the maximum permissible density. Our ultrasonic sub-system, consisting of a single pair of Pz21 (transmitter) and Pz26 (receiver) piezoelectric PZT ceramic discs driven by low-frequency, radial/planar excitation (-31 mode), without acoustic matching layers, is also reported here for the first time. The discs are characterised by propagation tank test and directly driven by the inductively coupled power to deliver 29 μW to a receiver (implant) employing a low voltage start-up IC positioned 70 mm deep within a homogeneous liquid phantom. No batteries are used. The deep implant is thus intermittently powered every 800 ms to charge a capacitor which enables its microcontroller, operating with a 500 kHz clock, to transmit a single nibble (4 bits) of digitized sensed data over a period of ~18 ms from deep within the phantom, to the outside world. A power transfer efficiency of 83% using our prototype CMOS logic-gate IC driver is reported for the inductively coupled part of the system. Overall prototype system power consumption is 2.3 W with a total power transfer efficiency of 1% achieved across the tiers

Acoustic power distribution techniques for wireless sensor networks

Recent advancements in wireless power transfer technologies can solve several residual problems concerning the maintenance of wireless sensor networks. Among these, air-based acoustic systems are still less exploited, with considerable potential for powering sensor nodes. This thesis aims to understand the significant parameters for acoustic power transfer in air, comprehend the losses, and quantify the limitations in terms of distance, alignment, frequency, and power transfer efficiency. This research outlines the basic concepts and equations overlooking sound wave propagation, system losses, and safety regulations to understand the prospects and limitations of acoustic power transfer. First, a theoretical model was established to define the diffraction and attenuation losses in the system. Different off-the-shelf transducers were experimentally investigated, showing that the FUS-40E transducer is most appropriate for this work. Subsequently, different load-matching techniques are analysed to identify the optimum method to deliver power. The analytical results were experimentally validated, and complex impedance matching increased the bandwidth from 1.5 to 4 and the power transfer efficiency from 0.02% to 0.43%. Subsequently, a detailed 3D profiling of the acoustic system in the far-field region was provided, analysing the receiver sensitivity to disturbances in separation distance, receiver orientation and alignment. The measured effects of misalignment between the transducers are provided as a design graph, correlating the output power as a function of separation distance, offset, loading methods and operating frequency. Finally, a two-stage wireless power network is designed, where energy packets are inductively delivered to a cluster of nodes by a recharge vehicle and later acoustically distributed to devices within the cluster. A novel dynamic recharge scheduling algorithm that combines weighted genetic clustering with nearest neighbour search is developed to jointly minimise vehicle travel distance and power transfer losses. The efficacy and performance of the algorithm are evaluated in simulation using experimentally derived traces that presented 90% throughput for large, dense networks.Open Acces

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