Wyniki wyszukiwania - Biblioteka Nauki

1

Dolphin-Inspired Target Detection for Sonar and Radar

100%

Leighton T. , White P.

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tom Vol. 39, No. 3

319--332

EN

Gas bubbles in the ocean are produced by breaking waves, rainfall, methane seeps, exsolution, and a range of biological processes including decomposition, photosynthesis, respiration and digestion. However one biological process that produces particularly dense clouds of large bubbles, is bubble netting. This is practiced by several species of cetacean. Given their propensity to use acoustics, and the powerful acoustical attenuation and scattering that bubbles can cause, the relationship between sound and bubble nets is intriguing. It has been postulated that humpback whales produce ‘walls of sound’ at audio frequencies in their bubble nets, trapping prey. Dolphins, on the other hand, use high frequency acoustics for echolocation. This begs the question of whether, in producing bubble nets, they are generating echolocation clutter that potentially helps prey avoid detection (as their bubble nets would do with man-made sonar), or whether they have developed sonar techniques to detect prey within such bubble nets and distinguish it from clutter. Possible sonar schemes that could detect targets in bubble clouds are proposed, and shown to work both in the laboratory and at sea. Following this, similar radar schemes are proposed for the detection of buried explosives and catastrophe victims, and successful laboratory tests are undertaken.

2

Sounds in space: the potential uses for acoustics in the exploration of other worlds

100%

Leighton T. , Petculescu A.

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2008

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tom Vol. 11

225-239

EN

This paper examines the past and future uses for acoustics in space research. Whilst on the larger scales in some topic areas, acoustical models have proved to be useful in extraterrestrial research, in other areas there has been not so much use made of acoustical techniques. One particular area where greater use might be made of acoustical sensors is in the deployment of acoustical sensors on probes sent out to other moons and planets. This is surprising given that acoustical sensors deliver benefits that are particularly useful for planetary probes, in terms of weight, bandwidth, ruggedness and cost. Whilst geoacoustical data could be obtained from many bodies, those which contain a dense atmosphere or an ocean offer intriguing additional possibilities. Examples from Mars, Venus, Titan, Enceladus and Europa will be discussed.

3

Towards field measurement of populations of methane gas bubbles in marine sediment: an inversion method required for interpreting two-frequency insonification data from sediment containing gas bubbles

80%

Leighton T. , Mantouka A. , White P. , Klusek Z.

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2008

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tom Vol. 11

203-224

EN

This paper describes a key stage in the process for developing a new device for the measurement of gas bubbles in sediment. The device is designed to measure gas bubble populations within the top 2 m of marine sediments, and has been deployed at inter-tidal sites along the South coast of England. Acoustic techniques are particularly attractive for such purposes because they can be minimally invasive. However they suffer from the limitation that their results can be ambiguous. Therefore it is good practice to deploy more than one acoustic technique at time. The new device does just this, but it is designed with the practical economy that the task is accomplished with the minimum number of transducers. One of the measurement techniques relies on insonifying the sediment with two frequencies. This paper outlines how the bubble size distribution is inferred through inversion of the signals detected when two frequencies are projected into the sediment. The high attenuation of the sediment makes this interpretation far more difficult that it would be in water. This paper outlines these difficulties and describes how they can be overcome.

4

An assessment of cleaning mechanisms driven by power ultrasound using electrochemistry and highspeed imaging techniques

80%

Offin D. , Vian C. , Birkin P. , Leighton T.

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2008

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tom Vol. 11

299-312

EN

The cleaning of a surface is monitored in real time using a number of physical measurements. In particular an electrochemically inactive material is removed from an electrode while the electrode is able to detect a redox system in the bulk liquid. The removal of the material from the surface is monitored as an increased Faradaic current at the electrode surface. This signal is used to assess the ability of the cleaning method employed, in this case the application of power ultrasound to the system, as a function of the position of the electrode with respect to the sound source. It is shown that, depending on the conditions employed, surface cleaning is driven by different mechanisms. In order to validate these findings highspeed imaging of the system was undertaken and the results correlated with the electrochemical data. In addition a number of novel electrodes were also employed to assess the cleaning efficiency as a function of the electrode geometry employed. Implications for surface cleaning in the presence of power ultrasound are suggested.

5

Experimental evidence for enhanced target detection by sonar in bubbly water

80%

Leighton T. , Finfer D. , White P.

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2008

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tom Vol. 11

181-203

EN

A sonar system has been developed which allows one to discriminate targets from scattered energy from bubbles. The underlying theory and experimental testing of this system are presented. The effectiveness of this sonar system is demonstrated through experimentation within a large fresh water tank in which bubble clouds are generated. Some of the practical requirements associated with such an experiment are detailed.

6

The development of a passive acoustic device for monitoring the effectiveness of shockwave lithotripsy in real time

41%

Leighton T. , Fedele F. , Coleman A. , McCarthy C. , Jamaluddin A. , Turangan C. , Ball G. , Ryves S. , Hurrell A. , Stefano de A. , White P.

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2008

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tom Vol. 11

159-180

EN

This paper reports how laboratory experiments and hydrocode simulations (of cavitation and shock wave propagation) have been used to generate a clinical device which can deliver real benefit to patients with kidney stones. Currently X-ray or ultrasound B-scan imaging are used to locate the stone and to check that it remains targeted at the focus of the lithotripter during treatment. Neither imaging method is particularly effective in allowing the efficacy of treatment to be judged during the treatment session. In this study, laboratory experiment and Computational Fluid Dynamics simulations of the complex interactions between the shock wave, the stone, and the human tissue, have been used to develop a new clinical device. This device, which has been tested in clinical trials, exploits the passive acoustic emissions generated by these interactions, to identify whether the stone remains in the focus, and to what extent the treatment has been successful.