Early History Of ISNA

The International Symposia on Nonlinear Acoustics, now referred to as ISNA, have convened regularly since 1968, bringing together scientists and engineers to report and discuss the latest developments in this branch of nonlinear physics. The fact that this series of symposia is still going strong after more than four decades is testimony that nonlinear acoustics has established itself as a distinct, important, and vibrant field of research. In this paper we take a look back at the early years of ISNA to recall how it all began and trace the evolution of the symposia into their current form.Applied Research Laboratorie

Underwater Communication Using Acoustic Parametric Arrays

[EN] This paper presents a study of different types of parametric signals with application to submarine acoustic telecommunications. In all of them, the carrier frequency is 200 kHz, which corresponds to that resonation of the transducer under study, while they differ by the different modulations they present. In this sense, we study modulations with sweeps (4 to 40 kHz), in which represent binary codes (zeros and ones), getting closer to the application in acoustic telecommunications. The different properties of the transmitting signals in terms of communication speed, directivity, efficiency and power needed are discussed as well.We acknowledge the financial support of Plan Estatal de Investigación, ref. FPA2015-65150-C3-2-P (MINECO/FEDER), and of the Generalitat Valenciana, Grant PrometeoII/2014/079.Ardid Ramírez, M.; Campo-Valera, MM.; Tortosa, DD.; Felis-Enguix, I.; Llorens Alvarez, CD.; Martínez Mora, JA. (2018). Underwater Communication Using Acoustic Parametric Arrays. Proceedings. 2(139):1-7. https://doi.org/10.3390/ecsa-4-04907S17213

The development and testing of a parametric SONAR system for use in sediment classification and the detection of buried objects

This thesis describes the work carried out in the development and testing of parametric sonar systems for application in the fields of seabed sediment characterisation and classification, and the detection of seabed embedded objects. Parametric sonar systems offer a number of advantages over conventional sonar systems. This is especially true of the conflicting requirements of both seabed delineation and penetration required for a practical sub-seabed profiling system. Echoes from sub-bottom layers vary in strength dependent on both the boundary acoustic reflectivity and the absorption characteristics of the layer above. Absorption effects are usually frequency dependent, allowing better penetration to lower frequency signals. [Continues.

Studies into the detection of buried objects (particularly optical fibres) in saturated sediment. Part 2: design and commissioning of test tank

This report is the second in a series of five, designed to investigate the detection oftargets buried in saturated sediment, primarily through acoustical or acoustics-relatedmethods. Although steel targets are included for comparison, the major interest is intargets (polyethylene cylinders and optical fibres) which have a poor acousticimpedance mismatch with the host sediment. This particular report details theconstruction of a laboratory-scale test facility. This consisted of three maincomponents. Budget constraints were an over-riding consideration in the design.First, there is the design and production of a tank containing saturated sediment. Itwas the intention that the physical and acoustical properties of the laboratory systemshould be similar to those found in a real seafloor environment. Particularconsideration is given to those features of the test system which might affect theacoustic performance, such as reverberation, the presence of gas bubbles in thesediment, or a suspension of particles above it. Sound speed and attenuation wereidentified as being critical parameters, requiring particular attention. Hence, thesewere investigated separately for each component of the acoustic path.Second, there is the design and production of a transducer system. It was the intentionthat this would be suitable for an investigation into the non-invasive acousticdetection of buried objects. A focused reflector is considered to be the most costeffectiveway of achieving a high acoustic power and narrow beamwidth. Acomparison of different reflector sizes suggested that a larger aperture would result inless spherical aberration, thus producing a more uniform sound field. Diffractioneffects are reduced by specifying a tolerance of much less than an acousticwavelength over the reflector surface. The free-field performance of the transducerswas found to be in agreement with the model prediction. Several parameters havebeen determined in this report that pertain to the acoustical characteristics of the waterand sediment in the laboratory tank in the 10 – 100 kHz frequency range.Third, there is the design and production of an automated control system wasdeveloped to simplify the data acquisition process. This was, primarily, a motordrivenposition control system which allowed the transducers to be accuratelypositioned in the two-dimensional plane above the sediment. Thus, it was possible forthe combined signal generation, data acquisition and position control process to be coordinatedfrom a central computer.This series of reports is written in support of the article “The detection by sonar ofxdifficult targets (including centimetre-scale plastic objects and optical fibres) buriedin saturated sediment” by T G Leighton and R C P Evans, written for a Special Issueof Applied Acoustics which contains articles on the topic of the detection of objectsburied in marine sediment. Further support material can be found athttp://www.isvr.soton.ac.uk/FDAG/uaua/target_in_sand.HTM

Differential Phase Estimation with the SeaMARC II Bathymetric Sidescan Sonar System

A maximum-likelihood estimator is used to extract differential phase measurements from noisy seafloor echoes received at pairs of transducers mounted on either side of the SeaMARC II bathymetricsidescan sonar system. Carrier frequencies for each side are about 1 kHz apart, and echoes from a transmitted pulse 2 ms long are analyzed. For each side, phase difference sequences are derived from the full complex data consisting of base-banded and digitized quadrature components of the received echoes. With less bias and a lower variance, this method is shown to be more efficient than a uniform mean estimator. It also does not exhibit the angular or time ambiguities commonly found in the histogram method used in the SeaMARC II system. A figure for the estimation uncertainty of the phasedifference is presented, and results are obtained for both real and simulated data. Based on this error estimate and an empirical verification derived through coherent ping stacking, a single filter length of 100 ms is chosen for data processing application

Bioinspired low-frequency material characterisation

New-coded signals, transmitted by high-sensitivity broadband transducers in the 40–200 kHz range, allow subwavelength material discrimination and thickness determination of polypropylene, polyvinylchloride, and brass samples. Frequency domain spectra enable simultaneous measurement of material properties including longitudinal sound velocity and the attenuation constant as well as thickness measurements. Laboratory test measurements agree well with model results, with sound velocity prediction errors of less than 1%, and thickness discrimination of at least wavelength/15. The resolution of these measurements has only been matched in the past through methods that utilise higher frequencies. The ability to obtain the same resolution using low frequencies has many advantages, particularly when dealing with highly attenuating materials. This approach differs significantly from past biomimetic approaches where actual or simulated animal signals have been used and consequently has the potential for application in a range of fields where both improved penetration and high resolution are required, such as nondestructive testing and evaluation, geophysics, and medical physics

Ultrasonic transducer design: Feasibility as parametric echosounder in shallow water

In recent decades, acoustic techniques have become the most appropriate tools for biomass estimation in the fishing industry. This is because acoustic waves are the only waves that can be used for remote sensing in the aquatic environment due to their low attenuation compared to electromagnetic waves, which are usually used in long-distance communications in the atmosphere. Ultrasonic echo sounders allow sampling of water columns and cover large areas of ocean by means of sampling campaigns conducted by oceanographic vessels, providing information on fish stocks of commercial interest. Furthermore, as a result of the overexploitation of fishery resources and to cover increasing demand, fish production has been developed as an alternative to capture. Although several species are bred in captivity, in Spain we can highlight three in particular, due to the high economic impact and degree of implantation: Gilt-head bream (Sparus aurata), sea bass (Dicentrarchus labrax) and Bluefin tuna (Thunnus thynnus). There is demand in the aquaculture industry for techniques developed in the field of fishery acoustics to control and estimate biomass. However, various problems related to the geometry of the application and high fish densities in intensive aquaculture have made these techniques difficult to apply directly. The study of biomass and species classification has progressed in parallel with the development of sonar and echo sounder systems used for this type of applications, and particularly with the evolution of ultrasonic transducers. Operation frequency, transmission power, bandwidth and directivity are key factors in the acoustic methods applied to fishing. In addition, other aspects of research are becoming more relevant in this sector, such as the study of nonlinear parametric sound generation. This generation or parametric effect, produced in the medium, has focused so far especially on bathymetry or classification of the oceanic subsoil, by offering much lower operation frequencies with the same directivity as the beam generated at high frequency. Nowadays, their feasibility is studied for application to fisheries or aquaculture, due to the possibility of working at several frequencies with the same transducer, given the same radiation characteristics, which is not possible in the linear regime. This thesis presents the design of an ultrasound transducer for biomass estimation with specific characteristics and demonstrates its capacity to work in a non-linear regime with optimum apertures for use in shallow water or in aquaculture cages. Chapter 2 presents general information on ultrasound waves, the medium through which they are propagated and an introduction to non-linear generation. General concepts in ultrasound generation and design are presented in Chapter 3. Chapter 4 shows the numerical models used to reinforce the experimental results presented during this thesis. Chapter 5 covers the design of the transducer, encompassing all the processes, from characterization of the materials, to assembly, operation and simulation of designed prototypes. To conclude, Chapter 6 presents the behavior of prototypes in a nonlinear regime and their feasibility for estimating biomass of different species in shallow water.Las técnicas acústicas se han convertido en las últimas décadas en las herramientas más apropiadas para la estimación de biomasa en el sector pesquero. Esto es debido a que las ondas acústicas son las únicas que pueden utilizarse para teledetección en el medio acuático, por su baja atenuación, comparadas con las ondas electromagnéticas, que son las usadas habitualmente en comunicaciones a larga distancia en la atmósfera. Las ecosondas ultrasónicas permiten muestrear la columna de agua y cubrir grandes extensiones de océano mediante campañas de muestreo realizadas por buques oceanográficos, ofreciendo información de las poblaciones de peces de interés comercial. Por otro lado, como consecuencia de la sobreexplotación de los recursos pesqueros y para cubrir la demanda creciente para su consumo, se ha desarrollado como alternativa a la captura, la producción piscícola. Aunque hay diversas especies que se crían en cautividad, en España podemos destacar tres en particular, por el alto impacto económico y grado de implantación: Dorada (Sparus aurata), lubina (Dicentrarchus labrax) y atún rojo (Thunnus thynnus). La aplicación de las técnicas desarrolladas en el campo de la acústica de pesquerías para el control y estimación de la biomasa en jaulas flotantes, es una demanda del sector acuicultor. Sin embargo, diferentes problemas relacionados con la geometría de la aplicación y las altas densidades de peces con las que se trabaja en acuicultura intensiva, han dificultado la aplicación directa de las mismas. Los avances en el estudio de la biomasa o en la clasificación de especies han ido en paralelo con el desarrollo de los sistemas sonar y ecosondas usados para este tipo de aplicaciones, y particularmente con la evolución de los transductores ultrasónicos empleados. La frecuencia de trabajo, la potencia de emisión, el ancho de banda, así como la directividad son factores clave en los métodos acústicos aplicados a la pesca. Además, otras vertientes de investigación están adquiriendo mayor relevancia en este sector, como por ejemplo, el estudio de la generación no lineal paramétrica de sonido. Esta generación o efecto paramétrico, producido en el medio, se ha enfocado hasta ahora especialmente en batimetrías o en la clasificación del subsuelo oceánico, por ofrecer frecuencias de trabajo mucho más bajas con la misma directividad que el haz generado a alta frecuencia. Actualmente, se estudia su viabilidad para ser aplicado a pesquerías o a acuicultura, debido a la posibilidad de trabajar a varias frecuencias con un mismo transductor, presentado éstas las mismas características de radiación, lo que no es posible en el régimen lineal. Esta tesis presenta el diseño de un transductor de ultrasonidos para la estimación de biomasa con unas características específicas. Demostrando, además, la capacidad de éste para poder trabajar en régimen no lineal con aperturas adecuadas para su uso en aguas poco profundas o en jaulas de acuicultura. En el capítulo 2 se presenta información general sobre las ondas de ultrasonidos y el medio por donde se propagan, así como una introducción a la generación no-lineal. Conceptos generales sobre la generación de los ultrasonidos y el diseño se presentan en el capítulo 3. En el capítulo 4, se muestran los modelos numéricos utilizados para afianzar los resultados experimentales presentados durante la tesis. El capítulo 5 recoge el diseño del transductor, que englobará todos los procesos, desde la caracterización de los materiales, hasta el montaje, puesta en marcha y simulación de los prototipos creados. Para finalizar el capítulo 6 presenta el comportamiento de los prototipos en régimen no lineal y su viabilidad para estimar biomasa de diferentes especies en aguas poco profundasLes tècniques acústiques s'han convertit en les últimes dècades en les ferramentes més apropiades per a l'estimació de biomassa en el sector pesquer. Això és degut a que les ones acústiques són les úniques que poden utilitzar-se per teledetecció en el medi aquàtic, per la seva baixa atenuació, comparades amb les ones electromagnètiques, que són les usades habitualment en comunicacions a llarga distància en l'atmosfera. Les ecosondes ultrasòniques permeten mostrejar la columna d'aigua i cobrir grans extensions d'oceà mitjançant campanyes de mostreig realitzades per vaixells oceanogràfics, oferint informació de les poblacions de peixos d'interès comercial. Per altre costat, com a conseqüència de la sobreexplotació dels recursos pesquers i per cobrir la demanda creixent per al seu consum, s'ha desenvolupat com a alternativa a la captura, la producció piscícola. Encara que hi ha diverses espècies que es crien en captivitat, a Espanya podem destacar tres en particular, per l'alt impacte econòmic i grau d'implantació: Daurada (Sparus aurata), llobarro (Dicentrarchus labrax) i tonyina vermella (Thunnus thynnus). L'aplicació de les tècniques desenvolupades en el camp de l'acústica de pesqueres pel control i estimació de la biomassa en gàbies flotants, és una demanda del sector aqüicultor. No obstant això, diferents problemes relacionats amb la geometria de l'aplicació i les altes densitats de peixos amb les que es treballa en aqüicultura intensiva, han dificultat l'aplicació directa de les mateixes. Els avanços en l'estudi de la biomassa o en la classificació d'espècies han anat en paral·lel amb el desenvolupament dels sistemes sonar i ecosondes usats per a aquest tipus d'aplicacions, i particularment amb l'evolució dels transductors ultrasònics empleats. La freqüència de treball, la potència d'emissió, l'ample de banda, així com la directivitat són factors clau en els mètodes acústics aplicats a la pesca. A més, altres vessants d'investigació estan adquirint major rellevància en aquest sector, com per exemple, l'estudi de la generació no lineal paramètrica de so. Aquesta generació o efecte paramètric, produït en el medi, s'ha enfocat fins ara especialment en batimetries o en la classificació del subsòl oceànic, per oferir freqüències de treball molt més baixes amb la mateixa directivitat que el feix generat a alta freqüència. Actualment, s'estudia la seva viabilitat per a ser aplicat a pesqueries o a aqüicultura, a causa de la possibilitat de treballar a diverses freqüències amb un mateix transductor, presentat aquestes les mateixes característiques de radiació, el que no és possible en el règim lineal. Esta tesi presenta el disseny d'un transductor d'ultrasons per a l'estimació de biomassa amb unes característiques específiques. Demostrant, a més, la capacitat d'aquest per poder treballar en règim no lineal amb obertures adequades per al seu ús en aigües poc profundes o en gàbies d'aqüicultura. En el capítol 2 es presenta informació general sobre els ultrasons i el mitjà pel qual es propaguen, així com una introducció a la generació no-lineal. Conceptes generals sobre la generació dels ultrasons i el disseny es presenten en el capítol 3. En el capítol 4, es mostren també els models numèrics utilitzats per a refermar els resultats experimentals presentats durant la tesi. El capítol 5 recull el disseny del transductor, que englobarà tots els processos, des de la caracterització dels materials fins al muntatge, posada en marxa i simulació dels prototips creats. Finalment, el capítol 6 presenta el comportament dels prototips en règim no lineal i la seua viabilitat per a estimar biomassa de diferents espècies en aigües poc profundes.Ordoñez Cebrián, P. (2017). Ultrasonic transducer design: Feasibility as parametric echosounder in shallow water [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86192TESI

Underwater communication via particle velocity channels : principles, channel models, and system design

A vector sensor is capable of measuring important non-scalar components of the acoustic field such as the particle velocity, which cannot be obtained by a single scalar pressure sensor. In the past few decades, extensive research has been conducted on the theory and design of vector sensors. On the other hand, underwater acoustic communication systems have been relying on scalar sensors only, which measure the pressure of the acoustic field. By taking advantage of the vector components of the acoustic field, such as the particle velocity, the vector sensor can be used for detecting the transmitted data. In this dissertation, the concept of data detection and equalization in underwater particle velocity channels using acoustic vector sensors was developed. System equations for such a receiver were derived and channel equalization using these sensors was formulated. A multiuser system using vector sensors and space time block codes was also developed, which does not use spreading codes and bandwidth expansion. This is particularly important in bandlimited underwater channels. With regard to channel models for particle velocity channels, characterization of particle velocity channels and their impact on vector sensor communication systems performance were therefore of interest. In multipath channels such as shallow waters, a vector sensor receives the signal through several paths and each path has a different delay (travel time). Motion of the transmitter or receiver in a multipath channel introduces different Doppler shifts as well. Those introduce different levels of correlation in an array of vector sensors. Therefore, in this dissertation, a statistical framework for mathematical characterization of different types of correlations in acoustic vector sensor arrays was developed. Exact and closed-form approximation correlation expressions were derived which related signal correlations to some key channel parameters such as mean angle of arrivals and angle spreads. Using these expressions, the correlations between the pressure and velocity channels of the sensors could be calculated, in terms of element spacing, frequency and time separation. The derived closed-form parametric expressions for the signal correlations can serve as useful tools to estimate some important physical parameters as well. Knowledge of the delay and Doppler spreads in acoustic particle velocity channel is also important for efficient design of underwater vector sensor communication system. In this dissertation, these channel spreads were characterized using the zero crossing rates of channel responses in frequency and time domain. Useful expressions for delay and Doppler spreads were derived in terms of the key channel parameters, mean angle of arrivals and angle spreads. These results are needed for design and performance predication of communication systems in time-varying and frequency-selective underwater particle velocity channels