This dissertation investigates the use of advanced acoustical communication techniques for wireless downhole telemetry systems. Using acoustic waves for downhole telemetry systems is investigated in order to replace the wired communication systems currently being used in oil and gas wells. While the acoustic technology offers great benefits, a clear understanding of its propagation aspects inside the wells is lacking. This dissertation describes a testbed that was designed to study the propagation of acoustic waves over production pipes. The wireless communication system was built using an acoustic transmitter, five connected segments of seven inch production pipes, and an acoustic receiver. The propagation experiments that were conducted on this testbed in order to characterize the channel behavior are explained as well. Moreover, the large scale statistics of the acoustic waves along the pipe string are described. Results of this work indicate that acoustic waves experience a frequency- dependent attenuation and dispersion over the pipe string. In addition, the testbed was modified by encasing one pipe segment in concrete in order to study the effect of concrete on wave propagation. The concrete was found to filter out many of the signal harmonics; accordingly, the acoustic waves experienced extra attenuation and dispersion. Signal processing techniques are also investigated to address the effects of multipaths and attenuation in the acoustic channel; results show great enhancements in signal qualities and the usefulness of these algorithms for downhole communication systems. Furthermore, to explore an alternative to vibrating the body of a cemented pipe string, a testbed was designed to investigate the propagation aspects of sound waves inside the interior of the production pipes. Results indicate that some low-frequency sound waves can travel for thousands of feet inside a cemented pipe string and can still be detected reliably.

Inhomogeneities in the earth (fractures, layering, shape, composition) are responsible for seismic wave scattering and contribute towards amplitude, travel time, frequency and spectral fluctuations observed in seismic records. This thesis presents findings that complement our understanding of seismic scattering and imaging in heterogeneous media. Interest focused on probing the correlation between spatial variations in attributes that characterize the state (physical, chemical) of rocks and seismic waveform data with consideration towards potential implications for seismic survey design to optimize imaging, imaging with converted waves, microseismic monitoring, velocity modeling and imaging of lithological boundaries. The highlights of the research strategy include: • The use of stochastic methods to build realistic earth models that characterize the 1D, 2D and 3D spatial variations in rock properties. These petrophysical earth models are conditioned by experimental (“hard”) data such as geology, wave velocities and density from case study areas like the Bosumtwi impact crater and the base metal deposits in Nash Creek (Canada) and Thompson (Canada). The distributions of the sulfide mineralization at Nash Creek and at Thompson represent two end members of the heterogeneity spectrum. While the sulfide mineralization at Nash Creek is highly disseminated in nature, the sulfide rich zones at Thompson occur as well defined volumes (lens-shaped) having a strong density contrast with respect to the host rocks. • Analysis of modeled forward (transmitted) and backward scattered wave propagation in the heterogeneous earth models. As a result of a study aimed at correlating resonant frequencies to scale length parameters, it is observed that the efficiency of the spectral ratio method is undermined by its sensitivity to the interference between P- and S-waves as well as the impedance contrast. It is also demonstrated that travel time of direct arrivals (transmitted waves) can be used to infer structural heterogeneity and velocity distribution beyond borehole locations. However, the success of imaging with transmitted waves is subject to the influence of geology which must factor in the choice of acquisition geometry. For the first time, multivariate and multidimensional (3D) heterogeneous earth models that are conditioned by hard data from multiple boreholes are constructed. The methodology requires having at least one physical rock property attribute that is sampled along the whole borehole length. This approach helped to characterize the uncertainty in the distribution of rock densities and metal content in a study region of the Nash Creek property. The density data suggests the sulfides are disseminated and this poses challenges for both gravity and seismic imaging methods. Modeling studies suggest seismic methods will not be suited for imaging zones with such disseminated mineralization. On the other hand, when dealing with massive sulfide mineralization that has complex geology (steep dip) like the case in Thompson, the success of the seismic imaging process relies very much on the acquisition geometry as well as the variability of the physical properties of the host rock. Elastic modeling results show that a Vertical Seismic Profiling (VSP) geometry is better suited to capture the down-dip scattered wavefield from the orebody. While surface acquisition geometry with sufficient extended length in the down dip direction can also be used to detect the dipping orebody, its efficiency can however be undermined by background heterogeneity: when the scale length along the direction of dip is comparable to the dimensions of the orebody, the scattered wavefields are strong enough to mask the diffraction hyperbola generated from the ore. Moreover, the study also corroborates that converted waves generated from the scattering processes hold promise as an imaging tool for a dipping orebody as they are least affected by the scattering processes of background heterogeneity.

Inhomogeneities in the earth (fractures, layering, shape, composition) are responsible for seismic wave scattering and contribute towards amplitude, travel time, frequency and spectral fluctuations observed in seismic records. This thesis presents findings that complement our understanding of seismic scattering and imaging in heterogeneous media. Interest focused on probing the correlation between spatial variations in attributes that characterize the state (physical, chemical) of rocks and seismic waveform data with consideration towards potential implications for seismic survey design to optimize imaging, imaging with converted waves, microseismic monitoring, velocity modeling and imaging of lithological boundaries. The highlights of the research strategy include: • The use of stochastic methods to build realistic earth models that characterize the 1D, 2D and 3D spatial variations in rock properties. These petrophysical earth models are conditioned by experimental (“hard”) data such as geology, wave velocities and density from case study areas like the Bosumtwi impact crater and the base metal deposits in Nash Creek (Canada) and Thompson (Canada). The distributions of the sulfide mineralization at Nash Creek and at Thompson represent two end members of the heterogeneity spectrum. While the sulfide mineralization at Nash Creek is highly disseminated in nature, the sulfide rich zones at Thompson occur as well defined volumes (lens-shaped) having a strong density contrast with respect to the host rocks. • Analysis of modeled forward (transmitted) and backward scattered wave propagation in the heterogeneous earth models. As a result of a study aimed at correlating resonant frequencies to scale length parameters, it is observed that the efficiency of the spectral ratio method is undermined by its sensitivity to the interference between P- and S-waves as well as the impedance contrast. It is also demonstrated that travel time of direct arrivals (transmitted waves) can be used to infer structural heterogeneity and velocity distribution beyond borehole locations. However, the success of imaging with transmitted waves is subject to the influence of geology which must factor in the choice of acquisition geometry. For the first time, multivariate and multidimensional (3D) heterogeneous earth models that are conditioned by hard data from multiple boreholes are constructed. The methodology requires having at least one physical rock property attribute that is sampled along the whole borehole length. This approach helped to characterize the uncertainty in the distribution of rock densities and metal content in a study region of the Nash Creek property. The density data suggests the sulfides are disseminated and this poses challenges for both gravity and seismic imaging methods. Modeling studies suggest seismic methods will not be suited for imaging zones with such disseminated mineralization. On the other hand, when dealing with massive sulfide mineralization that has complex geology (steep dip) like the case in Thompson, the success of the seismic imaging process relies very much on the acquisition geometry as well as the variability of the physical properties of the host rock. Elastic modeling results show that a Vertical Seismic Profiling (VSP) geometry is better suited to capture the down-dip scattered wavefield from the orebody. While surface acquisition geometry with sufficient extended length in the down dip direction can also be used to detect the dipping orebody, its efficiency can however be undermined by background heterogeneity: when the scale length along the direction of dip is comparable to the dimensions of the orebody, the scattered wavefields are strong enough to mask the diffraction hyperbola generated from the ore. Moreover, the study also corroborates that converted waves generated from the scattering processes hold promise as an imaging tool for a dipping orebody as they are least affected by the scattering processes of background heterogeneity.

The majority of commercially available ultrasonic transducers used to excite and measure wave propagation in structures can be coupled only to a free surface. While convenient, this method is likely to excite multiple structural modes, making data interpretation difficult. Furthermore, the many modes excited make predicting the structure’s response a computationally intensive task. Here the dynamic radial displacement induced by a transient radial point load is calculated at more than 230,000 points on the outer surface of a virgin steel pipe to simulate a typical experiment. The radial component of the displacement field is calculated by convolving the Green’s functions of the pipe with the transient load. These functions are calculated on personal computers (in a distributed arrangement) by employing modal summation. The mode shapes are obtained from a Semi-Analytical Finite Element formulation used in conjunction with a separation of variables. The results are presented in a four dimensional animation, providing easier interpretations and insight into how to best select observation points for the detection of defects. The accuracy of the calculated displacements is verified experimentally. Agreement is good when magnitude and phase corrections are incorporated from the frequency response curves of the transducers used. / February 2005

Basic diffusion analytical solutions of one-dimensional consolidation are presented for the case of a semi-infinite domain. Typical tractions considered include instantaneous loads of the medium with a free boundary pressure, as well as the case of a permeable membrane located at the forced boundary. <br /><br /> Two-dimensional boundary value problems for a porous half-space, described by the widely recognized Biot's equations of poroelasticity, including inertia effects is discussed. In this poroelastic version of Lamb's problem in the classical theory of linear elastic waves, the surface of a porous half-space is subjected to a prescribed line traction. The following two broadly applicable cases are considered: 1) A steady state harmonic load, 2) An impulsive load (Dirac delta function time dependence). A general analytical solution of the problem in the Fourier -- Laplace space was obtained by the application of the standard Helmholtz potential decomposition, which reduces the problem to a system of wave equations for three unknown potentials, which correspond to three types of motion: P1, slow P2 wave, and the shear wave S. The possibilities of, and procedure for, obtaining analytic solutions in the physical space subsequently are discussed in detail. When viscous dissipation effects are taken into account, a steady-state harmonic line traction solution can be represented in the form of well convergent integrals, while for the case when viscous dissipation is ignored, closed form analytic solutions can be obtained for impulsive forcing with the application of the Cagniard -- de Hoop inversion technique. Numerical studies of the dispersion relation of the Rayleigh, or surface, wave for cases in which the dissipation is not negligible are presented.

The aim of this thesis is to develop and study a method for estimation of the pulse pressure in centrally located arteries. Obtaining the central pulse pressure is desirable for several reasons. For example, the central pulse pressure can be used to assess aortic stiffness, which in turn is an important predictor of cardiovascular mortality. In this thesis a method of estimation based on a one--dimensional wave propagation theory applied to a physiological model of the human systemic arterial tree is studied. For the purpose of validation, recorded pressure signals from twenty four control subjects are used. Various methods for individualization of the tree model are discussed, and a method that utilizes an optimization routine is proposed.

Militära insatser i urban miljö kommer troligen att öka alltmer. Detta kräver soldater till fots eftersom dessa lättare kan förflytta sig via och mellan byggnader. Varje deltagande soldat kommer att behöva egen radioutrustning. Då stadsmiljö är ett relativt outforskat område vad gäller militär radiokommunikation är det viktigt att öka förståelsen för radiovågors utbredning i stadsmiljö. Härtill har institutionen för Informationsöverföring på FOI köpt in programmet Radiowave Propagation Simulator (RPS). RPS används i det här examensarbetet för att genomföra en beräkning för ett statiskt scenario, och till beräkningen infoga påverkan från sändares och mottagares mobilitet. Detta utförs genom att rumsligt extrapolera kanalens impulssvar till att gälla i andra positioner än de ursprungligen var beräknade för. Kanalens impulssvar blir då modifierat så att impulssvarets utbredningsvägar får nya fördröjningstider och dess komplexa signal får ny fas. Metoden, som har tagits fram i det här arbetet, för den rumsliga extrapoleringen har implementerats och utvärderats för ett litet scenario. Det extrapolerade resultatet har sedan jämförts med beräknade resultat från RPS. Analysen visade att metoden ger ett tillförlitligt resultat. Ett annat syfte med examensarbetet har varit att visa hur forskningsresultat (från radiokanalen) kan användas effektivare för att ge högre kvalité på forskningsresultat, både på länk- och på nätnivå.

The main crux of this thesis was to produce a model that was capable of simulating the theoretical performance of different configurations for a spatial measurement system using radio frequency technology. It has been important to study new modalities of spatial measurement since spatial measurement systems are an enabling technology that have allowed for the creation of better medical procedures and techniques, provided valuable data for motion capture in animation and biomechanics, and have improved the quality of manufacturing processes in many industries. However, there has been room for improvement in the functional design and accuracy of spatial measurement systems that will enhance current applications and further develop new applications in medicine, research and industry. <br /><br /> In this thesis, a modelling framework for the investigation of spatial measurement based on radio frequency signals was developed. The simulation framework was designed for the purpose of investigating different position determination algorithms and sensor geomatries. A finite element model using the FEMLAB partial differential equation modelling tool was created for a time-domain model of electromagnetic wave propagation in order to simulate the radio frequency signals travelling from a transmitting source antenna to a set of receiving antenna sensors. Electronic line signals were obtained using a simple receiving infinitesimal dipole model and input into a time difference of arrival localization algorithm. The finite element model results were validated against a set of analytical solutions for the free space case. The accuracy of the localization algorithm was measured against a set of possible applications for a potential radio frequency spatial measurement system design. <br /><br /> It was concluded that the simulation framework was successful should one significant deficiency be corrected in future research endeavours. A phase error was observed in the signals extracted at the receiving antenna locations. This phase error, which can be up to 40°, was attributed to the zeroth order finite elements implemented in the finite element model. This phase error can be corrected in the future if higher order vector elements are introduced into future versions of FEMLAB or via the development of custom finite element analysis software but were not implemented in this thesis due to time constraints. Other improvements were also suggested for future work.

Basic diffusion analytical solutions of one-dimensional consolidation are presented for the case of a semi-infinite domain. Typical tractions considered include instantaneous loads of the medium with a free boundary pressure, as well as the case of a permeable membrane located at the forced boundary. <br /><br /> Two-dimensional boundary value problems for a porous half-space, described by the widely recognized Biot's equations of poroelasticity, including inertia effects is discussed. In this poroelastic version of Lamb's problem in the classical theory of linear elastic waves, the surface of a porous half-space is subjected to a prescribed line traction. The following two broadly applicable cases are considered: 1) A steady state harmonic load, 2) An impulsive load (Dirac delta function time dependence). A general analytical solution of the problem in the Fourier -- Laplace space was obtained by the application of the standard Helmholtz potential decomposition, which reduces the problem to a system of wave equations for three unknown potentials, which correspond to three types of motion: P1, slow P2 wave, and the shear wave S. The possibilities of, and procedure for, obtaining analytic solutions in the physical space subsequently are discussed in detail. When viscous dissipation effects are taken into account, a steady-state harmonic line traction solution can be represented in the form of well convergent integrals, while for the case when viscous dissipation is ignored, closed form analytic solutions can be obtained for impulsive forcing with the application of the Cagniard -- de Hoop inversion technique. Numerical studies of the dispersion relation of the Rayleigh, or surface, wave for cases in which the dissipation is not negligible are presented.

Surface Acoustic Wave (SAW) devices are key components in RF and IF stages of many electronic systems. A Surface Acoustic wave is a mechanical wave, which is excited on the surface of a piezoelectric substrate, when an alternating electric voltage is applied through a comb-like interdigital transducer (electrodes) patterned on it. Most SAW applications to date have been in the sub-2GHz region, but emerging applications require SAW devices at higher frequencies. The traditional models are inadequate to account for pronounced second order effects at the GHz range and also new microfabrication techniques are required to obtain quality devices as the critical dimensions shrink into the nano-scale range at these frequencies. The finite element method (a numerical method of solving differential equations) has the potential to account for these effects and ever increasing sub-micron processing capabilities of LIGA (X-ray lithography) present a promising outlook for high frequency SAW device modeling and fabrication respectively. <p>A finite element model has been developed using commercial software ANSYS for one port SAW resonators and is presented in this thesis. The one port SAW resonators are generally connected in form of ladder networks to form low-loss SAW filters. The spacing between the electrodes and the velocity of the SAW determine the frequency of operation of these devices. A finite element model has been developed for three different types of SAWdevices namely Rayleigh, leaky and longitudinal leaky SAW (LLSAW). The LLSAW has higher velocity as compared to other two types and hence considered in this work as a good prospect for high frequency SAW devices. <p>A full finite element model could not be solved due to high computing requirements and hence some assumptions were made and the results were validated against published results in the literature. The results indicate that even with simplifying assumptions and approximations FE model provides reasonably accurate results, that can be used in device design. Some of the simulations (in LLSAW based devices) in this work were also done with a view towards using LIGA (X-ray lithography) for fabrication of high frequency devices as they have the capability for high aspect ratios.