Thèses sur le sujet « Underwater and ultrasonic »

This document provides a description about how the problem of the detection of thecenter of a defined geometry object was solved.This named object has been placed in an experimental environment surrounded bywater to be explored using microwaves under the water, to try to find a possibletumor. The receiver antenna is fixed in the tip of the tool of an ABB robot.Due to this working method, it was necessary to locate the center of this object tomake correctly the microwave scanning turning always around the actual center. Thiswork not only consist in give a hypothetic solution to the people who gave us theresponsibility of solve their problem, it is also to actually develop a system whichcarries out the function explained before.For the task of measuring the distance between the tip of the tool where themicrowave antenna is, ultrasonic sensors has been used, as a complement of acomplete system of communication between the sensor and finally the robot handler,using Matlab as the main controller of the whole system.One of these sensors will work out of water, measuring the zone of the object which isout of the water. In the other hand, as the researching side of the thesis, a completeultrasonic sensor will be developed to work under water, and the results obtained willbe shown as the conclusion of our investigation.The document provides a description about how the hardware and software necessaryto implement the system mentioned and some equipment more which were essentialto the final implementation was developed step by step.

The performance of a novel radiator capable of producing ultrasonic waves in air and liquids has been investigated. For commercial transducers when operating in air or liquids, impedance matching is the necessary condition for maximum transfer of energy to the medium (thus no standing waves are involved). 'However, "for this radiator the formation of the mechanical standing waves on it is the key condition for directional radiation of energy into the surrounding environment. Under this condition the radiator exhibits a practical conversion of electrical energy into ultrasound. To further improve the performance of the radiator . the wavelength coincidence condition must be satisfied. This condition implies that the wavelength of the bending vibration developed on the blade to be the same as that in the medium to which it is coupled. Consequently, an end-fire radiation pattern is obtained. The theory of this when applied to water and also for a double blade configuration are presented. The main component of the radiator consists .of a cantilever blade on which a pair of piezoelectric (PZT) ceramic bars are fixed. These the so called excitation gauges, are fixed on both sides of a thin rectangular metal blade near the clamped end. When wavelength coincidence condition is fulfilled, the radiator transmits ultrasonic wave in a highly directional pattern. The direction of propagation of ultrasound is solely steered by frequency of the applied signal. System imperfections such as inter modal coupling when used underwater are considered. An analytical approach is developed to investigate the performance of the radiator for transmission of digital signals in air as well as in water. This method is used to evaluate the efficiency of the device as a suitable means for communication between divers or a diver and an underwater stationary station. Amplitude modulation of speech signals demonstrated the capabilities of a new underwater transmission. system whose narrow beam width is the condition to obtain power gain and performance. The possibility of the same system to be used as a passive sonar is also examined. Finally, simulations of the above system to be implemented in beam-forming in air and in water have been developed.

Capacitive micromachined ultrasonic transducers (CMUT:s) are often used in medical imaging and they show some promise as underwater transducers. This thesis collates the available information about how CMUT:s operate, their strengths and weaknesses and investigates their efficiency as an underwater transducer. The accumulated knowledge was channelled into a simulation of a CMUT as a dampened spring system done in MATLAB and Simulink. The simulation investigated the resonance frequency and bandwidth through simulation and compared the results to experimental results from literature.  CMUT:s have good acoustic matching with water making them sensitive, broadband transducers when used under water. Special care must be taken when choosing the CMUT so that materials and designs can fulfil the task for which it is intended, such as the radius of the membrane, the material of the membrane, the insulating layers in or around the CMUT and the height of the air gap inside. CMUT:s are, for the transmission of sound, less capable than existing lead zirconate-titanate-transducers (PZT-transducers). This problem can be somewhat alleviated through operating the CMUT in collapse-mode but care must be taken so that the CMUT is not damaged during this operation. Simulation results and results from literature show that it is possible to simulate CMUT:s with accuracy. By simulating 10 different CMUT:s, using the geometries and material properties of experimentally tested devices and testing for resonance frequency and bandwidth the results were as follows:The average relative error of resonance frequency was found to be -14 %, if outlier results are excluded and the average relative error of bandwidth proved inaccurate at -54 %

The development of low-frequency SONAR systems, using a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e. when the source and receiver are widely separated, thus allowing multiple viewpoints of a target). Furthermore, time-frequency analysis, in particular Wigner-Ville analysis, takes advantage of the evolution of the time dependent echo spectrum to differentiate a man-made target (e.g. an elastic spherical shell, or cylinder) from a natural one of the similar shape (e.g. a rock). Indeed, key energetic features of man-made objects can aid in identification and classification in the presence of clutter and noise. For example, in a fluid-loaded thin spherical shell, an energetic feature is the mid-frequency enhancement echoes (MFE) that result from antisymmetric Lamb waves propagating around the circumference of the shell, which have been shown to be an acoustic feature useful in this pursuit. This research investigates the enhancement and benefits of bistatic measurements using the Wigner-Ville analysis along with acoustic imaging methods. Additionally, the advantage of joint space-time-frequency coherent processing is investigated for optimal array processing to enhance the detection of non-stationary signals across an array. The proposed methodology is tested using both numerical simulations and experimental data for spherical shells and solid cylinders. This research was conducted as part of the Shallow Water Autonomous Mine Sensing Initiative (SWAMSI) sponsored by ONR.

Le milieu océanique est sujet à de nombreuses sources de fluctuations. Les plus importantes sont les ondes internes, très fréquentes et entrainant des fluctuations de la distribution spatiale du champ de célérité du son. En raison de la longue période de ces phénomènes comparée au temps de propagation des ondes acoustiques pour des applications sonar, le processus peut être considéré figé dans le temps pour chaque réalisation stochastique du milieu. Le développement de bancs d’essais permettant de reproduire les effets de la turbulence atmosphérique a permis des avancées considérables dans le domaine de l’optique adaptative. Nous voyons donc un fort intérêt dans la possibilité de reproduire les effets des ondes internes sur la propagation du son en environnement contrôlé. Un protocole expérimental dans une cuve d’eau est proposé: une onde ultrasonore est transmise à travers une lentille acoustique aléatoirement rugueuse, ce qui produit des distorsions du front d’onde reçu. Les fluctuations des signaux reçus sont contrôlées en modifiant les paramètres statistiques de rugosité de la lentille. Ces paramètres sont reliés à l’analyse dimensionnelle permettant de classifier les configurations étudiées selon des régimes de fluctuations et de prédire les moments statistiques du champ acoustique jusqu’à l’ordre quatre. Une excellente correspondance est observée entre notre protocole expérimental et des résultats théoriques et numériques.La dégradation des performances des techniques de détection classiques appliquées à nos données expérimentales souligne le besoin de techniques correctives. Un état de l’art des techniques existantes dans divers domaines est proposé
The ocean medium is subject to many sources of fluctuations. The most critical ones were found to be internal waves, occurring frequently and inducing fluctuations of the spatial distribution of the sound speed field. Because of the fairly long period of this phenomenon as compared to the propagation time of acoustic waves for sonar applications, the process can be considered frozen in time for each stochastic realization of the medium. The development of testbenches allowing to reproduce the effect of atmospheric turbulence on optic waves propagation under laboratory conditions lead to considerable advancements in the field of adaptive optics. We therefore see a vivid interest in being able to reproduce the effects of internal waves on sound propagation in controlled environments. An experimental protocol in a water tank is proposed: an ultrasonic wave is transmitted through a randomly rough acoustic lens, producing distortions of the received wavefront. The induced signal fluctuations are controlled by tuning the statistical parameters of the roughness of the lens. Especially, they are linked to dimensional parameters allowing to classify the configurations into regimes of fluctuations and to predict the statistical moment of the acoustic pressure up to the fourth order. A remarkable relevance of our experimental scheme is found when compared to theoretical and simulation results. The degradation of classical signal processing techniques when applied to our acquired data highlights the need for corrective detection techniques. A review of the existing techniques in other domains is proposed

Un métaréseau est un assemblage périodique de diffuseurs conçu pour réfléchir ou réfracter une onde vers une direction anormale, non prévue par les lois de Snell-Descartes. Dans ce travail, nous avons conçu, fabriqué et caractérisé expérimentalement de tels métaréseaux pour le contrôle des ondes ultrasonores dans l’eau, en utilisant des tubes et des cylindres en laiton ainsi que des supports plastiques imprimés en 3D. Ces métaréseaux permettent de rediriger un front d'onde incident vers une direction arbitraire souhaitée, avec une efficacité élevée (proche de 100 %), aussi bien en réflexion sur une surface (comme l’interface eau/air) qu'en transmission. L’approche théorique repose sur les principes de la diffraction de Bragg et sur les interactions constructives et destructives des ondes. Les résultats de cette thèse démontrent l'efficacité des métaréseaux à induire des phénomènes acoustiques tels que la rétro-réflexion et la réponse asymétrique, grâce à l’utilisation de structures résonantes et non résonantes, validées par des simulations par éléments finis et des expérimentations. Cette recherche ouvre de nouvelles perspectives pour la manipulation des ondes acoustiques sous-marines, avec des applications potentielles dans les domaines de la détection, de l'absorption et de la réflexion des ondes en milieu marin
A metagrating is a periodic assembly of scatterers designed to reflect or refract a wave toward an anomalous direction, not predicted by Snell's law. In this work, we designed, fabricated, and experimentally characterized such metagratings for the control of ultrasonic waves in water, using brass tubes and cylinders as well as 3D-printed plastic supports. These metagratings enable the redirection of an incident wavefront to an arbitrarily desired direction with high efficiency (close to 100%), both in reflection on a surface (e.g., the water/air interface) and in transmission. The theoretical approach is based on the principles of Bragg diffraction and constructive and destructive wave interactions. The results of this thesis demonstrate the efficiency of metagratings in inducing acoustic phenomena such as retroreflection and asymmetric wave response, achieved through the use of resonant and non-resonant structures, validated by finite element simulations and experiments. This research opens new perspectives for the manipulation of underwater acoustic waves, with potential applications in the fields of wave detection, absorption, and reflection in marine environments

碩士
中華大學
電機工程學系碩士班
99
Nowadays, more and more researchers have been exploring underwater communications systems using the ultrasonic sensors. This type of system has seen much progress recently. Because of the system’s complex environment, it has multi-path propagation, noise interferences that they are made by nature and human, and many disruptions. These issues will affect the underwater communication’s quality and distance. Because of the transmission energy needed, harsh environment, and disturbances due to outside signals, the signal quality is often compromised. In this thesis, a long-distance transceiver design has been completed. This research used the automatic gain control to improve the underwater communication.

碩士
國立臺灣大學
農業機械工程學系研究所
86
It is common to press the transducer against the surface of fruits and vegetab les in the ultrasonic evaluation of produce quality. This method will induce s ome damage on produce if the pressing force is beyond some limit. The objectiv e of this study was to evaluate produce quality non-destructively by employing underwater ultrasonic testing method.Potato samples were selected in the unde rwater ultrasonic test. To find the influencing factors on measuring accuracy, the experimental factors included distance between transducers, height of the water level, and speed of water flow in the water tank. The results showed th at measuring accuracy was mostly affected by the distance between transducers. The attenuation and spectral moment of underwater ultrasonic transmitting wave were studied to correlate with the potato physical properties such as density , porosity, Young's modulus, and moisture content. The influences of porosity, density and Young's modulus on attenuation were found statistically significa nt.Potatoes were penetrated by a tenuous steel bar along the major axis to cre ate different degrees of hollowness. The spectral moment of transmitting ultra sonic wave was found higher in normal potatoes as compared with hollow potatoe s. Thus, the technique of underwater ultrasonic evaluation of potato hollownes s is feasible.Keywords: Potato, Ultrasonic, Underwater, Coefficient of attenua tion, Spectral moment.

碩士
國立臺灣大學
造船及海洋工程學研究所
90
The text mainly confers the design and fabrication of the single circular disc of piezoelectric transducers. Firstly, by integrating of the sound field formula of the circular disc simulates a complete sound field. Then by use of wave equation and boundary equation obtain the impedance matrix of the piezoelectric transducer. The impedance matrix simulates the electric property of the transducer. Then the text explains the design of the structure of the transducer and the best thickness of the matching layer. Mainly, when the main frequency is decided, the purpose is to achieve short waveform, wide band and high sensitivity. Finally, we make two underwater ultrasound transducers according to the theorem of the devise. They are P4 and P5 transducer depending on the piezoelectric material. Then, we compare with the P4, P5 and the original transducer of their acoustics characters. The result will be the reference of the next fabrication.

碩士
國立臺灣海洋大學
電機工程學系
92
This thesis uses beamforming in ultrasonic imaging. Beamforming is a kind of spatial filtering, which strengthen the signal of steering direction and suppress the interference of other directions. Nevertheless, there are a lot of questions have to overcome, such as poor directivity leads to coarse resolution; the noise is unable to reject efficiently due to high side lobe. Hence, in order to design the high performance of ultrasonic array, primary task is research of ultrasonic array, which can influence all kinds of parameters on beam power pattern (BPP). In the situation of lower number of array element and lower circuit complexity, it is essential to raise center frequency or extend interelement spacing for reduction main’s width. Unfortunately, the grating lobe will be occurred when interelement spacing is larger than . Hence, we use the wide-band beamforming technology to suppress grating lobe. Besides, we design architecture of Mill’s cross array to equal 2D array and create tree dimension imaging. We attempt to reach high resolution and high quality ultrasonic imaging with sparse array.

碩士
國立臺灣大學
生物產業機電工程學研究所
89
ABSTRACT The objectives of this study were to develop an automatic system for underwater ultrasonic sorting of potatoes, through the application of LabVIEW, a graphical programming software containing automatic acquisition of ultrasonic signals, calculation of power spectral moments, and building functions for the classifications of potatoes. The output results from running the program was adopted to control the potato sorting mechanism. In the experiment, fresh potato samples were purchased from fruit market . After measuring weight, volume, density, and other characteristics of the potatoes the samples were placed between a pair of underwater ultrasonic probes and then the LabVIEW program was initiated to acquire the received ultrasonic signals and calculate power spectral moments. Potato was artificially cut through the long axis of it by a driller in order to simulate different levels of porosity in potato flesh criterion. The results showed that the bigger the potato's density, the greater the power spectral moments is. The correlation between density and power spectral moments was analyzed and a critical value of power spectral moments was chosen for sorting. The critical value was stored in the program and compared with the measured power spectral moments of each potato. If the measured power spectral moments is greater than the critical value, the potato has small porosity, and vice versa. A sorting mechanism based on this software will achieve the goal of classifying potatoes automatically in underwater ultrasonic system. Keywords:Potato, Ultrasound, Underwater, Automatic sorting, Graphical programming，Spectral moments.

Tese de doutoramento do Programa Doutoral em Engenharia Eletrónica e de Computadores
Underwater wireless communication systems are becoming a priority in terms of research and technological development due to the increasing demand for exploring the oceans’ potential in areas such as pharmaceutical, oil, minerals, environmental and biodiversity. This demand is increasing exponentially with the need for high data rate and near-real-time communications between submerged mobile and static agents. The existing wireless communication technologies using electromagnetic waves or lasers are not very efficient due to the large attenuation in aquatic environment. Ultrasound reveals a lower attenuation, and thus has been used in underwater long-distance communications. But the underwater acoustic medium is one of the less reliable communication channels which represent major challenges for communications. With relatively slow sound speed propagation (~1500 m/s) the delay may represent a problem for communications with real-time applications. A theoretical model of an underwater communication system was also developed. The model allows to emulate the emitter, the hydrophone and the underwater acoustic channel, which includes attenuation, environmental noise, Doppler Effect, multipath and propagation delay. This model supported the study of wireless communications by emulating the transmission of acoustic signals using different types of digital modulations. The acoustic signal attenuation, multipath, ambient noise in several environments theoretical results were compared to those obtained experimentally. Allowing to conclude that the model represents a suitable approximation to the real subaquatic communication channel for the evaluation of digital acoustic communications. An optimization study of ultrasound transducers for underwater communications was addressed, focusing on a piston type emitter operating in the thickness mode (d33). It was discussed how the acoustic impedance, thickness, resonance frequency and structure affect the transducer performance. This work allowed a better understanding of the emitter transducer characteristics allowing reaching the optimum point of operation for specific applications. Focusing on underwater communication, the transducer was optimized by finite element computer simulations. The results were compared with experimental tests and show that four-layer structures increase up to 16 dB in performance when compared to single-layer transducer disks. For high data-rates and real-time applications it was necessary to develop ultrasound transducers able to work at high frequencies and wideband, with suitable responses to digital modulations. It was thus also included a comparison study that shows how the acoustic impedance influences the performance of an ultrasonic emitter when using different digital modulations and operating at frequencies between 100 kHz and 1 MHz and some tens of meters of distance. It is presented a Finite Element Method (FEM) and a MATLAB/Simulink simulation with an experimental validation to evaluate two types of piezoelectric materials: one based in ceramics (high acoustic impedance) with a resonance design and a polymer based (low acoustic impedance) system, designed to optimize the performance when using digital modulations. The transducers performance for Binary Amplitude Shift Keying (BASK), On-Off Keying (OOK), Binary Phase Shift Keying (BPSK) and Binary Frequency Shift Keying (BFSK) modulations with a 1 MHz carrier at 125 kbps baud rate were compared. The transducers materials used were the ceramics PZT-5H and the polymer PVDF. The results show that PVDF transducer has a better performance to digital modulations than PZT-5H transducer, providing the signal full demodulation for all digital modulations tested. On the other hand, the PZT-5H transducer showed a higher output, but fails to perform accurate modulated signals. Finally, the system was validated by the implementation of a full duplex point-to-point communication at 1 Mbps using OOK modulation with a 1 MHz single carrier. The system was successfully tested in a swimming pool at a distance of 6 meters with a 1 Mbps rate, achieving a 3x10-3 Bit Error Rate (BER) using just 1.4 W of power consumption. These results represent an advance in underwater acoustic communications, being the first practical system to achieve data rates up to 1 Mbps.
O desenvolvimento de sistemas de comunicação subaquáticos sem fios está a tornar-se uma prioridade na comunidade científica no sentido de aumentar o desenvolvimento tecnológico. Este facto deve-se à crescente necessidade de exploração do potencial dos oceanos em áreas científicas diversas como farmacêutica, petrolífera, mineral, ambiental e até do próprio estudo da biodiversidade. Essa necessidade aumenta exponencialmente com a necessidade de comunicações de alto débito e em tempo real entre agentes submersos móveis e estáticos. As tecnologias de comunicações sem fios existentes, nomeadamente as que utilizam ondas eletromagnéticas ou lasers não são muito eficientes, devido, em grande parte, à atenuação no ambiente subaquático. Os ultrassons revelam uma menor atenuação tendo sido, por isso, utilizados em comunicações subaquáticas em longas distâncias. Contudo o canal acústico subaquático definisse como um dos mais difíceis, devido em parte as suas características únicas, o que apresenta ser um enorme desafio. Como a velocidade de propagação do som é relativamente lenta (~1500 m/s), o atraso pode representar um problema para as aplicações em tempo real. Foi desenvolvido um modelo teórico do sistema de comunicações subaquáticos que permite emular o emissor, o hidrofone e o canal acústico subaquático. No canal acústico subaquático foi simulado o efeito da atenuação, ruído ambiente, efeito de Doppler, multipath e atraso de propagação. Este modelo é indicado para o estudo das comunicações subaquáticas, emulando a transmissão de sinais acústicos utilizando diferentes tipos de modulações digitais. Neste estudo foram testados, a atenuação do sinal acústico, multipath, ruído em diversos ambientes e os resultados teóricos foram comparados com os obtidos experimentalmente. Permitindo concluir que o modelo representa uma aproximação adequada do canal de comunicação, permitindo a avaliação das comunicações digitais acústicas. Inclui ainda um estudo de otimização de transdutores de ultrassons para comunicações subaquáticos, tendo como base o emissor do tipo pistão, operando ao longo da espessura (d33). Foi analisada ainda a forma como a impedância, espessura, frequência de ressonância acústica e estrutura afetam o desempenho do transdutor. Este trabalho permitiu uma melhor compreensão das características do transdutor emissor que permitem atingir o ponto ótimo de operação para aplicações específicas. Tendo como base a comunicação subaquática, o transdutor foi otimizado usando os resultados de simulações pelo Método dos Elementos Finitos. Os resultados foram comparados com os testes experimentais, onde se mostra que as estruturas de quatro camadas podem aumentar até 16dB no desempenho quando comparados com discos de transdutor de única camada. Para aplicações em tempo real e de elevado debito, foi necessário desenvolver transdutores de ultrassons capazes de operar em banda larga a altas frequências, com resposta adequada às modulações digitais. Foi, portanto, incluído também um estudo comparativo que mostra como a impedância acústica influencia o desempenho do emissor de ultrassons quando se utilizam modulações digitais a operar com frequências entre 100 kHz e 1 MHz abrangendo distâncias de algumas dezenas de metros. São apresentadas simulações por Método de Elementos Finitos (MEF) e MATLAB/Simulink com validação experimental de modo a avaliar dois tipos de materiais piezoelétricos: um com base cerâmica PZT-5H (alta impedância acústica) com um design de ressonância e outro de base de polimérica PVDF (baixa impedância acústica), otimizado para modulações digitais. O desempenho dos transdutores foi comparado para as modulações: Binary Amplitude Shift Keying (BASK), On-Off Keying (OOK), Binary Phase Shift Keying (BPSK) e Binary Frequency Shift Keying (BFSK) com uma portadora de 1 MHz a 125 kbps. Os resultados mostram que o transdutor de PVDF tem um melhor desempenho do que transdutor PZT-5H, proporcionando a desmodulação completa do sinal para todas as modulações digitais testadas. Por outro lado, o transdutor de PZT-5H mostrou uma potência acústica mais elevada, embora não consiga produzir sinais modulados precisos. Finalmente, o sistema foi validado através da implementação de uma comunicação ponto-aponto bidirecional de 1 Mbps utilizando uma modulação OOK com uma portadora de 1 MHz. O sistema foi testado com sucesso numa piscina a uma distância de 6 metros com uma taxa de 1 Mbps, com um BER (Bit Error Rate) de 3x10-3, utilizando apenas 1,4 W de consumo de potência. Estes resultados representam um avanço nas comunicações acústicas subaquáticas, sendo o primeiro sistema prático de atingir velocidades até 1 Mbps.

碩士
國立臺灣大學
農業機械工程學系研究所
87
It is common to press the transducer against the surface of fruits and vegetables in the ultrasonic evaluation of produce quality. This testing method might induce some damage if the pressing force is beyond the limit. The objectives of this study was to evaluate produce quality non-destructively by employing underwater ultrasonic testing method and discuss the feasibility of developing a underwater ultrasonic detection machine for potato. Potato samples were selected in this study. The treatments for studying influencing factors on ultrasonic measuring accuracy were water level, distance between transducers and speed of the conveyor belt. Relationships between the characters of underwater transmitting ultrasonic waves (attenuation and spectral moment) and the timing of measurement were also investigated. The results showed that the underwater ultrasonic transmitting waves were affected by timing of measurement. Potatoes were penetrated by a steel bar along the major axis to create different degrees of hollowness. The spectral moment of transmitting ultrasonic wave was found smaller in hollow potato than in normal potato. It is feasible to develop a underwater ultrasonic detection machine for potato.

To maximise effectiveness, towed underwater sonar bodies generally require perturbations from the steady state motion to be minimised. The instantaneous position of the towed body is influenced by the unsteady, wave-induced motion of the surface vessel, transmitted via the tow cable. This can render the trajectory of the underwater body beyond acceptable limits for sonar operations. In an effort to decouple this motion, a two-part tow configuration has been employed. This thesis describes a three-dimensional dynamic computer model developed to investigate two-part tows by modelling the individual cables separately and coupling them dynamically. This approach also enables the modelling of series and parallel multiple tow configurations. The cable system, modelled using a three degree-of freedom finite difference approach, is then coupled to the six degree-of-freedom underwater towed bodies at the appropriate locations of the cable system. The modelling of the cable as a continuous medium and the derivation of the stress wave speeds are also presented, followed by the validity and.effects of representing it as a discretised model. The solution to the dynamic equations describing the motion of the discretised tow configuration is carried out using an implicit multi-step numerical technique, subject to specific boundary conditions. This allows the values to be improved through an iterative procedure, until sufficient convergence is achieved. An introduction into the use of such numerical techniques in engineering and an analysis of the numerical procedure used in the solution are also presented. The requirements for accuracy and numerical stability of the integration technique are investigated and a guide to the time interval for the time stepping algorithm is deduced. The computer model is successfully validated using experimental results from scaled model tests in a circulating water channel. These results together with those obtained from full scale sonar trials utilising small coastal craft are used to further investigate the behaviour of the two-part tow configuration to varying parameters. The experimental results and the computer model enables the user to identify the optimum tow configuration for the prevailing conditions. The thesis also presents a detailed review of the various methods available to investigate underwater cables and vehicles, together with prediction methods for their hydrodynamic coefficients. The latter coefficients for the scaled models used in the project are obtained via experimental procedures. Although a number of investigations have been carried out dealing with aspects of underwater towing operations, the strength of this investigation lies in that it combines these aspects, i. e. mathematical modelling, computer simulation, prediction of the hydrodynamic coefficients, scaled model experiments, full scale trials, and the analysis of the numerical technique, into one study.

碩士
國立臺灣海洋大學
電機工程學系
96
The purpose of this thesis is to research and improve the ultrasonic phased array imaging system. In the aspect of scanning system, we use the piezoelectric ceramic with 600 KHz resonance frequency in this system and manufacture a one-dimension transmitting array and a receiving element. By using the beam-controlled technology to trigger the array, we are able to perform the scanning over the target objects. We also apply the independence loop method and the spacing matching method to increase the signals strength of the transmitting array. In the aspect of imaging system, we use the ultrasonic phased array in application of distance measurement is based on TOF (time-of-flight) method. Moreover, with the scanning function that is collocated in front-end circuits; the relative location information of the target objects are collected. Then, after the processing of the LabVIEW graph-controlled programs, 2 Dimensional images of the target objects could be acquired. In order to widen the extent of the system applications, we put the array system together with PTU (pan and tilt unit) and adopt the 9-grid scanning method to enlarge the scope of the output image; separate tests have been physically performed in the lab water tank and undersea environments.

碩士
國立臺灣海洋大學
電機工程學系
94
This thesis is mainly about the ultrasonic array system and we uses beam forming technology to make ultrasonic array achieve the scanning purpose and joins Labview graphical program to accomplish the related applications of measuring distance and imaging. We use the transmitting and receiving piezoelectric ceramic with 600 kHz resonance frequency in this system and manufacture a one-dimension transmitting transducer which has 19 elements and a receiving transducer which has a single element. Moreover, we take a phased pulsing system to vary delay time and to produce phase-shifted signals as a mechanism for controlling transmitting angles. The system is able to scan from -15 to 15 degrees and takes receiving transducer to transform sound pressure into voltage. Finally, it uses an A/D convert card and Labview graphical program to store up the signals and to make analysis. Moreover, we use ultrasonic arrays in applications of distance measurement and imaging are based on TOF (time of fight) method. The transmission distance of ultrasonic waves is acquired when we multiply the time interval that is between the time of transmitting the signals at the transmitter terminal and the time of receiving the signals at the receiver terminal by the speed of sound. Based on the relative positions of the transmitter and receiver and the signals that we receive, we can find out the distance we want to measure. After, we take the distance information and the signals, also utilizing Labview graphical program, the system forms a two-dimension matrix of relative positions, and acquires a 2D image. The system is practically applied to underwater salvage tasks and provides object distances and reference images. Cooperating with CCD image information, it can locate and recognize the objects. This system can help robotic arms implement underwater salvage tasks.

碩士
國立臺灣海洋大學
電機工程學系
106
This paper uses semiconductor process technology to fabricate ultrasonic sensing components for underwater environments. It mainly uses the electro-mechanical conversion characteristics of piezoelectric material lead zirconate titanate Pb(〖Zr〗_0.52 〖Ti〗_0.48) O_3to transmit and receive ultrasonic waves under the water surface. The main structure of the self-made component includes a lower electrode, a buffer layer, a piezoelectric layer, an upper electrode, and a waterproof layer, and the intensity of the transmitted signal is changed by adjusting the surface area of the piezoelectric layer of the element and improve the receiving intensity of sound waves by changing the number of component arrays, adjusting the film thickness of the piezoelectric layer, and improving the component yield. The ultrasonic emission component produced in this paper consists of 1 by 64 single elements. An array of elements in the component is connected in parallel to analyze the surface area of the piezoelectric layer of the transmitting element. Comparing the total surface area of the piezoelectric layer of the emitting end element is 64 mm^2and 48 mm^2. The ultrasonic receiving component compares the array number to include 2880 (48*60) elements and 3360 (48*70) elements to form a parallel array. After the ultrasonic wave receiving component is completed, the underwater component is measured in water, received signal intensity measurement, sound field measurement, component sensitivity measurement, etc. The electrical measurement part includes the measurement of the resonance and anti-resonance frequency, the dielectric constant quantity measurement, the measurement of the isoelectric circuit, the electromechanical coupling coefficient measurement and the hysteresis curve measurement, etc. In this paper, the thickness of the lead zirconate titanate film and the number of component arrays of the ultrasonic receiving component are changed to analyze the characteristics of the ultrasonic receiving array. As the thickness of the piezoelectric layer PZT film of the receiving end element increases to 2000 nm, a higher dielectric value and component sensitivity can be obtained, and the intensity of the transmitted and received signals is emitted by the self-made emitting element and received by the self-made sensing element. The strongest signal strength of 1.2V can be received in the 10MHz band. According to the analysis of the number of component arrays, the resonant frequency of the array number 2880 is 64.97 MHz. When the number of arrays is increased to 3360, the resonant frequency of the measuring component is 48.636MHz. As the number of arrays increases, the resonance and anti-resonance frequencies of the components decrease, but the effect of changing the number of component arrays on the dielectric value is not significant.

碩士
國立臺灣海洋大學
電機工程學系
93
This paper forms on ultrasonic arrays fabrication and charcterization and use the ultrasonic array method principle design and manufacture the ultrasonic head, can use the ultrasonic array to get a beam steering. Simultaneously we design a transmission and receive arrays can effective control directive beam by step motor. This paper also according to the ultrasonic receiver principle to conversion the echo signal to the computer and application to image. This paper according to the beam forming principle to design the ultrasonic arrays, and test some parameter example d33 and resonance frequency, this experiment are already to formulate this element size and standard, the we use the water-repellent process on the transducer according to the matching layer, and test the influence at resonance frequency, bandwidth and impedance, the result prove that add matching layer can improve bandwidth, simultaneously this experiment is already Success get beam forming exist, beside we have building a underwater ultrasonic image experiment structure, use step motor to turn transmission angular, effective change the transmission angular and we use ultrasonic receiver array get the echo signal. As to the simulation, we also simulation the ultrasonic image and design the Optimum ultrasonic array, beside we also test the directive sound field, echo signal and image process. And according to the underwater ultrasonic image experiment structure Use PXI data receive card, to get the echo wave into the computer and make the initial image process.

碩士
國立臺灣海洋大學
電機工程學系
95
This paper is mainly about ultrasonic electronic scan transmitting to the target object from underwater, after picking the echo signal data, improve signal to noise ratio by imaging utilizing graphic control program and using wave filtration and superposition signals. This ultrasonic image system transmits and receives signal by using piezoelectricity ceramics to make ultrasonic array while piezoelectricity ceramics is often used to make ultrasonic transducer. However, in this paper piezoelectricity ceramics elements are used to make 19-element and 64-element one-dimensional transmitting array and receiving array, and the frequency of the signal transmit by this system is 600KHz. Moreover, the signal emitter used can carry out electronic beam by controlling the transmitting delay time of array elements. Ultrasonic imaging scan underwater images mainly by means of TOF (time-of-flight). At the same time of picking signals, we get the distance of ultrasonic transmission by the time taken from transmitting end shot to the receiving end getting signals multiplied by velocity of sound. The distance to the target object can be measured according to the related positions of the transmitting end to the receiving end, and the ultrasonic signals and distance data obtained can image utilizing Labview graphic control program. Even more clear images can be obtained by locking the target object. Besides, the imaging scope can be enlarged by 9-frames scan collocating PTU (pan and tilt unit)

碩士
國立臺灣海洋大學
電機工程學系
105
In this paper, the ultrasonic sensor is fabricated by semiconductor process technology, and the lead zirconate titanate Pb(Zr0.52Ti0.48)O3 was used as the acoustic wave sensing layer. The focus of the research is to install the self-made ultrasonic sensor and 64 array ultrasonic transmitter in the Remotely Operated Vehicle (ROV) for underwater image acquisition, and the ultrasonic sensing device changes the sensing frequency by the structural adjustment of the piezoelectric layer and the upper and lower electrode layers, enhance the sonic wave receive intensity and image resolution. In this paper, the ultrasonic sensing device is made up of 48 × 70 single device in parallel, after ultrasonic sensor device is prepared, underwater measurements and electrical measurements will be performed. The underwater measurements included sonic wave receiving intensity measurement, device sensing sensitivity measurement, device sonic field measurement and the measurement of device installed in the Remotely Operated Vehicle for underwater image acquisition. The electrical measurements included resonant frequency and anti-resonant frequency measurement, electromechanical coupling coefficient measurement, equivalent circuit measurement, dielectric constant measurement and hysteresis curve measurement. In this paper, the ultrasonic sensing device at the frequency of 600kHz, the device sensing sensitivity is about -212.17dBreV/μPa. The ultrasonic sensing device at the frequency of 7MHz has the highest device sensing sensitivity, which is about -170.86dBreV/μPa. In the measurement of device installed in the Remotely Operated Vehicle for underwater image acquisition, underwater object distance of 20 cm image is better.