Ultrasound (the frequency range above 20 KHz) at intensities of 0-3.0 Wcm-2 is used in physical medicine to treat a variety of conditions (joint contractures, fibrosis and scarring and severe pain due to disorders such as frozen shoulder and capsulitis). It is believed to produce a reduction in pain and swelling and increase movement of joints affected by diseases such as arthritis. It is also used to generate hyperthermia for the treatment of neoplastic tumours. The technique involves irradiating tissues with either continuous or pulsed mode ultrasound, using either the field from a single or multielement transducer. Geometrically similar ultrasound transducers even from the same batch can have significantly different efficiencies and the resulting field distributions can also vary. There are several pieces of information required to characterize an ultrasound source. They are frequency, power output, spatial average and spatial peak intensity and details of ultrasonic field distribution. This application of ultrasound requires an experimental method to define the intensity distribution generated by a transducer or array of transducers. A number of different techniques have been used to record intensity distribution. These include sheets of liquid crystal on an absorbing surface, detection of signals using hydrophone probes, thermocouple probes, thermistor probes and the Schlieren technique. The dye/paper method and Starch iodine plate have been developed for the observation of the ultrasonic fields and evaluation of the source pattern.

A new type of ultrasound power meter is described which is robust, portable, easy to operate and therefore suitable for use in the work place by non-specialist personnel. The device should be of particular value in the field of ultrasonic therapy, where a lack of suitable instrumentation has discouraged performance monitoring of ultrasound machines in the past although numerous surveys have found the calibration of such equipment generally to be poor. The mode of operation is based on absorption of the ultrasound beam within a liquid, which expands as the energy becomes degraded to heat. The rate of this thermal expansion is monitored by means of a capacitative liquid level sensor, the output signal being suitably processsed and passed to a microcomputer for analysis. Correction for interchange of heat with the surroundings is carried out automatically by the micro, by recording the 'background drift' in liquid volume for a few seconds prior to insonation and subtracting this from the expansion rate observed during input of ultrasound. Calibration is achieved by measuring the (corrected) expansion rates brought about by known powers supplied from an electrical heating coil. When using the new power meter for measurements of therapeutic ultrasound the performance compares favourably with that of other techniques: the reproducibility is on the order of 5% above about 0.5W, becoming less good below this (reaching about 20% at the minimum measurable power of 25-50mW). Design modifications which may improve performance at low power levels and possibly allow measurement of dignostic ultrasound are suggested.

This work is concerned with the development of an instrument capable of measuring simultaneously both the size and concentration . of suspended fine sands in the presence of silt. A review of the literature of the measurement of suspended solids showed that the most promising approach to develop such an instrument would use ultrasonic methods. A theoretical study of the scattering of ultrasound for suspensions is presented and this shows that an appropriate choice of frequency and scattering geometry will give reduced sensitivity to silt size particles whilst yielding information on the size and concentration of the suspended particles. Laboratory experiments were conducted using a vertical sedimentation test facility and single angle scattering from suspensions of sand and glass balls. The experiments showed that the theory is adequately modelled in practice. A laboratory model of a field instrument, employing analogue and digital signal processing, was then constructed and tests were performed on a range of suspended sediments with different mean size, The ratio of ultrasound scattered through 10° and 170° was found to be concentration independent, being a function of size only. The ultrasound scattered through 10°. suitably processed, was a measure of concentration. A measure of agreement between theoretical predictions and experimental results was obtained and design recommendations for the manufacture of a field instrument are given.

The applications of ultrasonic imaging and signal processing in two-phase flow measurement have been investigated in this thesis. The scattering by single and many scatterers was studied experimentally and numerically. The statistical properties of the scattered waves from many scatterers were examined and the corresponding results are presented. Ultrasonic transmission/reflection mode tomography was introduced. The theories of reflection mode computerised tomography were developed, by which reflectivity functions and scattering amplitude functions can be reconstructed. Image restoration and interpretation methods are presented. Computer simulation of ultrasonic measurements were carried out. A ultrasonic tomographic imaging system was developed, in which fan-shaped sound beam insonification was employed. Static physical models were used to simulate two-phase flows. In order to speed up the data acquisition of a tomographic imaging system, the single receiver mode and multiple receiver mode data acquisition arrangements were studied by experiments. Experiments on imaging small and large objects were carried out. Several signal and image processing methods were examined. A modified histogram equalisation algorithm was developed for processing the resultant ultrasonic images. The experiment results show that the proposed image reconstruction methods are satisfactory. Possible future developments are proposed.

MPH, Faculty of Health Sciences, University of the Witwatersrand, 2006

The purpose of the research was to investigate the effects of aircraft noise on the auditory language processing abilities of English First Language (EFL) primary school learners. Schools located in close proximity to airports are exposed to extremely high levels of chronic, yet intermittent noise. These levels have been shown to cause cognitive, health and hearing problems. However, it is unsure whether this long term exposure to these noise levels may cause auditory language processing problems when hearing is normal, which could result in decreased academic performance. This study utilised a non-experimental, cross sectional and descriptive design, as well as a post-hoc design. Seventy children attending schools that are exposed to high levels of noise were matched according to socio-demographic characteristics to seventy children in quieter schools. All the schools were situated in Durban, South Africa, while the noisy schools were located 1.7 km and 1.9 km from the airport and the quieter schools were 4.6km and 3.5km from the airport. All participants are EFL, have attended the respective schools from grade 1, have hearing within normal limits, are in grade 6 or 7, are 12 years or younger, and have no pre-diagnosed learning, auditory or attention problems. Audiological screening and auditory language processing assessments (subtests of the TAPS, PhAB and the Dollaghan and Campbell task) were undertaken. This study utilised various types of statistical analyses, including descriptive methods, Pearson’s chi-squared tests, Fisher’s tests, three-way ANOVAs, Cramer’s V tests and Cohen’s D tests. The results from the schools that are exposed to noise have scored below average in all the auditory processing subtests. This study aimed to provide evidence that not only can hearing be affected by noise, but so too can the processing of sounds, even when hearing is normal. The results of this study are hoped to serve as a motivation for the provision of speech-language therapy and audiology posts within mainstream legislation with regard to schools due to the large amount of children with auditory language processing difficulties in both noisy and quieter schools, as well as for noise treatment surrounding airports and appropriate to zoning of schools around airports to help and prevent this chronic noise interrupting the development of auditory language processing abilities and thus in turn affecting learning.

Orientador: João Antônio Pereira / Banca: Luiz de Paula do Nascimento / Banca: Newton Sure Soeiro / Resumo: Ruído é, na maioria dos países, o agente nocivo que prevalece na maioria dos ambientes de trabalho. Um trabalhador gasta em média 20% a mais de energia em ambientes com altos níveis de pressão sonora. As estatísticas do INSS comprovam que o ruído tem sido um agente causador de doenças, estresse ocupacional e acidentes de trabalho. A exposição de pessoas a níveis elevados de ruído pode causar comprometimentos orgânicos diversos, sendo também o principal responsável por distúrbios auditivos temporários e permanentes. Assim, é de fundamental importância a caracterização e avaliação do ruído e do seu campo de propagação no ambiente de trabalho. Isso permite a avaliação e, caso necessário, a implementação de ações de controle e mitigação dos seus efeitos. Nesse trabalho foi realizado um estudo das principais técnicas utilizadas para a simulação de ruído em ambientes industriais fechados, visando obter as informações e o conhecimento necessário para a elaboração de modelos de simulação e predição do campo acústico de ambientes industriais, mais especificamente, do piso de geradores de uma Usina Hidrelétrica. O trabalho foi desenvolvido com base na abordagem experimental e teórico e na interação entre elas. Na abordagem experimental foram realizadas diferentes medições para um conjunto de pontos pré-determinados e os dados obtidos foram processados e analisados visando caracterizar o ambiente e identificar as principais fontes de ruído. Os modelos de simulação do ruído foram elaborados com base nas informações e dados da construção predial do ambiente, nas características das fontes identificadas e na disposição espacial dos equipamentos e maquinários auxiliares. O software utilizado para simulação e obtenção dos mapas acústicos do ambiente foi o CadnaSAK que utiliza um método híbrido envolvendo o método fonte imagem virtual e traçado dos raios e tem como base as ... / Abstract: Noise is, in most of the countries, the harmful agent which prevails in most of workplaces. A worker spends, on average, 20% more energy in environments with high sound pressure levels. Statistics from INSS bear out that noise has been a causing agent of diseases, occupational stress and accidents at work. Thus, it is fundamental to know the effects of noise propagation so it is possible to control environment noise levels. The exposure of people to high level noise may cause several organic compromises, and it is further the main responsible for temporary and permanent hearing disorders. Due to it, a study has been done to understand and evaluate the best techniques involved in noise simulation in closed industrial environment, aiming to provide important information to the implementation of a simulation model for the acoustic field of the floor of the generators for the hydroelectric plant at Ilha Solteira. The work has been developed basing on two approaches, experimental and theoretical. On the experimental approach, measurements have been done to an ensemble of predetermined points around each identified source in the environment; the data acquired has been processed and analyzed for further comparison with the values obtained from the simulation model. On the theoretical approach, simulation models for the noise from the floor of the generators at the hydroelectric plant at Ilha Solteira have been done, regarding the actual data from the building construction, as well as identified sources of the environment. The software used was CadnaSAK which uses a hybrid method involving virtual image source method, rays' track and patterning contained in the German standard VDI 3760 to the simulation and achievement of the environment acoustic map. The simulation model has been validated comparing the values acquired through the model with data measured experimentally. The comparison of the values has been done to an ensemble of points ... / Mestre

This thesis describes the problem of finite amplitude acoustic waves in fluids when diffraction effects are also important. To study this problem the example of a circular planar piston transmitter is used. A brief review of the current literature on the finite amplitude field of a circular piston is given. This precedes a set of experimental results which provide support for the current theories. The main concern is with the development of a numerical model which describes the finite amplitude acoustic field within the near-field or fresnel region. The model, although one dimensional, is able to predict the generation of harmonics within the whole of the near-field region. However, only the harmonic amplitudes on the acoustic axis of the piston are taken as an example. Prediction of harmonic growth, harmonic phase and waveform shape is undertaken. It is found that the growth of the harmonics within the near-field is not monotonic, an oscillation in both amplitude and phase is observed with increasing distance. The results give rise to waveform shapes which are asymmetric with respect to their compression and rarefaction phases. Results from the model are compared with experimental measurements. Throughout reference is continually made to the acoustic field within the near-field for the case of infinitesimal waves. This subject is discussed in an appendix, giving a review of the large amount of literature on the subject. Also, a new closed-form expression is developed for the linear field in this region.

This work assesses the potentials of two NDE techniques namely ultrasonic C-scan and acoustic emission for evaluating plasma sprayed coating quality. The coating materials used were aluminium (Metco 54), alumina (Metco 105), molybdenum (Mob3) and self-fusing molybdenum (Mo5O5). It has been established that ultrasonic C-scan imaging can reliably detect thickness variations of the order of 0.05mm in plasma sprayed coatings. Also, by using this technique it is possible to detect the presence of delamination or lack of adhesion between the coating and substrate. Although it was only possible to produce aluminium and alumina coatings with artificially introduced adhesion defects, it has been shown that the presence of such defects in other coatings can also be detected. It has been established that an ultrasonic C-scan technique is not sensitive to the process parameters of plasma spraying. The process parameters investigated were; poor surface preparation, input power and surface cooling. Another major limitation of ultrasonic C-scan technique is the geometrical restrictions where components with high curvatures can not be tested. Acoustic emission activities from plasma sprayed coatings were monitored during four point bend testing. Samples sprayed on poorly prepared surfaces or sprayed without coolant air could be distinguished from control samples using AE characteristics at low strain levels. Also the AE response of the alumina coatings reflected the thickness of the coatings. Thicker coatings produced more AE events. The AE response of the molybdenum (Mo63) and self-fusing molybdenum (Mo5O5) coatings were complex. It was found that they were related to the residual stresses in the coatings. Aluminium coatings showed very little acoustic emission activities.

A number of different aspects of the vibrational anharmonicity of acoustic modes at the long wavelength limit, which relate to mode softening, thermal expansivity, the Gruneisen parameter and structural phase transition has been investigated. Thus the pressure dependences of the second order elastic constants (SOEC) for chalcopyrite CdGeAs2, the rare earth solid solution Sm0. 58Y0. 42S, vacancy compounds Hg5Ga2Te8, Hg3ln2Te6, HgIn2DTe4 and the third order elastic constants (TOEC) of the zincblende structure crystal CuGe2P3, the semimetal bismuth, rare earth monochalcogenide SmS and the hexahalometallate K2SnCl6 have been determined by employing pulse echo overlap and pulse superposition techniques. In tetrahedrally bonded ternary compounds, the bonding effect and influence of defects - sited vacancies - on the acoustic vibrational anharmonicity have been studied. There is a systematical trend between ionicity, shear mode third order elastic constants and phase transition pressures; the shear mode Gruneisen parameters of the vacancy compounds are found to be linearly dependent upon the concentration of the sited vacancies. These results provide a basis for the discussion of the dynamic mechanism of the densification structural phase transition in these materials. A complete set of the TOEC of bismuth has been obtained and is used to estimate the Gruneisen parameter components along the z-axis and in the x-y plane which show a considerable difference in the axial acoustic vibrational anharmonicity in this crystal which has some layer-like character. The anisotropy of the thermal expansivity is ascribed largely to the highly anisotropic nature of the second order elastic compliances. The importance of measurements of the higher order elastic constants in the vicinity of the structural phase transition is that they contain valuable information on the relation between the anharmonic interatomic forces and lattice instability. SmS undergoes an isostructural phase transition at 6.5 Kbar, then goes into an intermediate valence state. The pressure dependences of the ultrasonic wave velocities have been measured up to 6 Kbar. There is a large positive bulk TOEC combination (C111 +6C112 + 2C123)/9 near the transition which is associated with the reduction of the nearest-neighbour repulsive forces and the incipience of lattice instability. A negative C12 been observed in the Measurements on Sm0. 58Y0. 42S which is already in an intermediate valence state. The resultant negative Poisson's ratio is discussed. A phase transition driven by the softening of a rotary optic phonon mode takes place in K2SnCl6 at -11°C (Tc1). The nonlinear elastic properties have been assessed by the determination of nine sets of the TOEC between room temperature and Tc1. These data provide the first actually measured complete TOEC of a crystal in the vicinity of a structural phase transition. The TOEC combination (C111 -C123)/2 increases and (C111 -3C112 + 2C123)/8 decreases with temperature towards Tc1. Results indicate that the TOEC vary substantially with temperature near the transition point and therefore that there exists a strong influence of the optical rotary mode on the acoustic mode (N[110], U[110]) vibrational anharmonicity. Large negative mode Gruneisen parameters have been found in both SmS and K2SnCl6 in the vicinity of the transition.