Implantable medical devices (IMDs) are medically necessary devices embedded in a human body that monitor chronic disorders or automatically deliver therapies, such as insulin pumps or pacemakers. Typically, they are small form-factor devices with limited battery and processing power. Most IMDs have wireless capabilities that allow them to share data with an offboard programming device, such as a smartphone application, that has more storage and processing power than the IMD itself. Additionally, the programming device can send commands back to the IMD to change its settings according to the treatment plan. As such, wirelessly sharing information between an IMD and offboard device can help medical providers monitor the patient's health remotely while giving the patient more insight into their condition, more autonomy, and fewer in-person appointments. However, serious security concerns have arisen as researchers have demonstrated it is possible to hack these devices to obtain sensitive information or potentially harm the patient. This is particularly easy to do as most IMDs transmit their data in the clear to avoid allocating their limited resources to encrypting their packets. As these concerns and the percentage of the American population with IMDs grows, there is another fear that bad actors could exploit the link between the programming device and IMD. Theoretically, a hacker could launch a man in the middle attack to send the IMD unauthorized commands, reprogramming it to act as a radio, sniffing signals of interest in the environment. As such, the hacker could use the IMD as a software defined radio (SDR) that captures sensitive or even classified information without the patient's knowledge. If this were to happen, it is possible an unwitting person with an IMD who has access to classified or sensitive information could be used to exfiltrate data that, in the wrong hands, could be used for corporate espionage or to the detriment of national security. While governing bodies agree that cybersecurity risks are present in IMD systems, there are no requirements for IMD manufacturers to create their devices with security measures that mitigate these risks. Researchers have proposed physical, technical, and administrative security measures for IMDs, but other existing wireless security techniques may apply to the healthcare space and need to be explored. Beamforming is an array signal processing technique that relies on individual elements of antenna arrays adjusting their phase and amplitude to create an overall effect of directing RF energy in a particular direction. Similarly, cooperative beamforming uses several physically separate "friendly" beamforming-capable devices to collectively send artificial noise to eavesdroppers while ensuring the signal is successfully received by the intended receiver. Although there are several cooperative jamming algorithms, they share the underlying principles of minimizing SINR at potential eavesdroppers while maximizing the SINR at the intended receiver. Researchers exploring cooperative jamming have largely used models to estimate its impact on channel secrecy. While RF propagation and communication system modeling provides valuable insight into system performance, many theoretical and empirical models are limited by the extent to which the operational environment matches that of the model itself. Ray tracing, alternatively, is more widely applicable as it accounts for a 3D environment and the objects a signal interacts with in that space. A ray is defined as an individual RF signal that travels in a straight line through a uniform medium; obeys the laws of reflection, refraction, and diffraction; and carries energy. As the ray interacts with objects in the environment, its energy will decrease by some amount that depends on the materials and geometry of the object. While research has predominantly focused on applications like cellular communications, the same principles of minimizing SINR at potential eavesdroppers while maximizing the SINR at the intended receiver can be applied to IMDs. As IMD use cases assume the programmer is nearby, the friendly nodes will not need to act as relays and can instead focus all their power on jamming. The number of cooperative jammers will be low to simulate the number of devices an individual might have in a workspace or office setting, like a personal phone, smart watch, or laptop, and realistic power constraints will be observed. Further, ray tracing software will provide additional visual insights into how various building materials like drywall, concrete, brick, and glass impact cooperative jamming. Through these simulations, the trade-off between secrecy rate and physical separation and layout of friendly nodes can be determined, which in turn may inform how companies or individuals can protect their proprietary and personal information. / Master of Science / Implantable medical devices (IMDs) are medically necessary devices embedded in a human body that monitor chronic disorders or automatically deliver therapies, such as insulin pumps or pacemakers. The data on IMDs need to be processed and their settings might need to be adjusted, but IMDs themselves usually cannot support direct user input, such as through screens or buttons, as they are inaccessible without surgery or generally too small to have space for displays. Further, they lack processing power and battery life due to their small form-factors, so relatively little data remains onboard. Instead, it is more convenient for the IMDs to wirelessly send their data to a more powerful external device like a smartphone. Since smartphones have more battery and processing resources available, and are easily recharged, they can store more data, monitor trends in the patient's health records, and upload the data to a server which the doctors can access. Additionally, these devices can send commands back to the IMD to change its settings according to the treatment plan. As such, wirelessly sharing information between an IMD and offboard programming device can help medical providers monitor the patient's health remotely while giving the patient more insight into their condition, more autonomy, and fewer in-person appointments. However, serious security concerns have arisen as researchers have demonstrated it is possible to hack these devices to obtain sensitive information or potentially harm the patient. As these concerns and the percentage of the American population with IMDs grows, there is another fear that bad actors could exploit the link between the programming device and IMD. Theoretically, a hacker could send the IMD unauthorized commands that change the IMD's behavior so that they are reprogrammed to act as radios listening for signals in the environment in order to steal sensitive or even classified information. While governing bodies agree that cybersecurity risks are present in IMD systems, there are no requirements for IMD manufacturers to create their devices with security measures that mitigate these risks. Researchers have proposed physical, technical, and administrative security measures for IMDs, but other existing wireless security techniques may apply to the healthcare space and need to be explored. Cooperative jamming is an existing defensive wireless technique that reduces the likelihood of an eavesdropper gaining access to unauthorized information. A known set of "friendly" transmitters each transmit noise to eavesdroppers while ensuring the signal is successfully received by the intended receiver. Researchers exploring cooperative jamming have largely used models to estimate its impact on channel secrecy. While RF propagation and communication system modeling provides valuable insight into system performance, many theoretical and empirical models are limited by the extent to which the operational environment matches that of the model itself. Ray tracing, alternatively, is more widely applicable as it accounts for a 3D environment and the objects a signal interacts with in that space. A ray is defined as an individual RF signal that travels in a straight line through a uniform medium; obeys the laws of reflection, refraction, and diffraction; and carries energy. As the ray interacts with objects in the environment, its energy will decrease by some amount that depends on the materials and geometry of the object. Thus, using ray tracing to model cooperative jamming will provide new insights into the degree to which cooperative jamming could be used to protect an IMD from eavesdroppers, and how companies or individuals can protect their proprietary and personal information.

Advances in hardware acceleration has resulted in development of a variety of hardware accelerated ray tracing libraries. The purpose of this bachelor thesis is to investigate if a simple ray tracer, based on a hardware accelerated ray tracing library, can achieve acceptable frame rates in rendering simple 3D game-related environments. Games are often associated with fast rasterization-based rendering techniques, but rasterization is limited where instead ray tracing holds many advantages. Background research was done to gain knowledge about related work, state-of-the-art in ray tracing and available hardware accelerated libraries. By using a method similar to Kanban and Scrum [36], the implementation was split up into different tasks, prioritizing the tasks of implementing basic functionalities of a ray tracer. A simple ray tracer was implemented based on the chosen library Embree, a framework developed at Intel Corporation. Results show that the scenes rendered in lower resolutions (800 x 600) are good candidates for having a stable frame rate of 30 FPS, which is not enough in order to render a real game. The standard of games today require high resolution (full HD 1920 x 1080) and complex scenes. Earlier studies show that Embree has potential of higher performance and looking back the performance of real-time ray tracing has improved, but is still limited to low resolutions and simple lighting and shading models. / Framsteg inom hårdvaruacceleration har resulterat i att en rad olika hårdvaruaccelererade bibliotek för strålföljning utvecklats. Syftet med denna kandidat-uppsats är att undersöka om en enkel strålföljare, baserad på ett hårdvaruaccelererat bibliotek för strålföljning, kan uppnå acceptabla bildfrekvenser vid rendering av enkla spel-relaterade miljöer i 3D. Datorspel förknippas ofta med snabba renderingstekniker. Rasteriseringsalgoritmen är dock begränsad där istället strålföljning har många fördelar. En litteraturstudie gjordes för att få kunskap om relaterade arbeten, state-of-the-art i strålföljning och tillgängliga hårdvaruaccelererade bibliotek. Genom att använda en metod som kan liknas vid Kanban och Scrum [36], blev implementationen uppdelad i olika uppgifter (eng. tasks), där implementationen av grundläggande funktioner av en strålföljare hade högsta prioritet. En enkel strålföljare implementerades med det valda biblioteket Embree, ett ramverk som utvecklas hos Intel Corporation. Resultaten visar att scenerna som renderas med lägre upplösningar (800 x 600) är goda kandidater för att uppnå en stabil bildfrekvens med 30 bilder per sekund (eng. frames per second), vilket inte är tillräckligt för att rendera ett riktigt spel. Standarden hos spel idag kräver hög upplösning (full HD 1920 x 1080) och komplexa scener. Tidigare studier visar att Embree har potential för högre prestanda och tidigare resultat visar att prestandan av interaktiv strålföljning har förbättrats, men att den fortfarande är begränsad till låga upplösningar och enklare belysningsmodeller.

Zugl.: Erlangen-Nürnberg, University, Diss., 2009.

The main focus of this research was to gain an understanding as to how waves propagate through structures. Lamb's Problem was studied on an isometric half plane, where numerical results were obtained. The calculated wavefronts for this problem were in agreement to the numerical results. When a distributed pressure is applied on an isometric half plane, after a long period of time, the wavefronts look as if a point force was applied on the half plane. Waves propagating through an orthotropic material were obtained numerically; it was found that Huygens' Principle cannot be used to calculate the wavefronts. The impact of spherical and cylindrical projectiles on glass plates was studied next. The waves introduced into the material were calculated using Finite Element Analysis, and compared to calculated wavefronts using Snell's Law, where they were found to be in agreement with one another. The effects of circular and square discontinuities were also studied, where a creeping wave that is produced after a wave propagates past a circular hole is explained. A sandwich beam was also modeled using FEA, where the wavefronts were obtained, and were found to be in agreement with calculated wavefronts. The displacement of the bottom layer of the sandwich beam was obtained numerically; it was found that the bending of the beam occurs at the same time as whether the middle layer is present or not.

High speed ray tracing for a headlamp lens and advanced algorithms for ray analysis are investigated. First, the basics of ray tracing, Algorithm to search intersection points between a ray and surfaces and refraction are reviewed, including intersection search for a ray with aspheric surfaces. A spherical surface, a plane surface, and a point cloud are reviewed as objects. Snell’s law is introduced from Fermat’s principle in 2D. Then, it extended to three dimensional spaces. Second, photometry is reviewed for the post processing of ray tracing, due to the convolution effect of its area. To accelerate ray tracing, the Nvidia GPU and CUDA platform of general purpose computing is evaluated in this study. Its architecture and memory architecture is unique. In addition, Mathematica is used in this study for file IO and graphic output with unique CUDA interface. Then, the each ray tracing method is validated using a spherical lens, aspherical lens, and a headlamp lens. From the comparison, the double precision floating Nagata triangular patch method is best in accuracy. Acceleration of ray tracing using CUDA was successful having 2 times implement in 362 million rays traced, compared to commercially available ray trace packages under the same computing resources.

The goal of this thesis is to evaluate the usability of hardware accelerated ray tracing in near-future rendering engines. Specifically, DirectX Ray Tracing API and Nvidia Turing architecture are being examined. Design and implementation of a hybrid rendering engine with support for hardware accelerated ray tracing is included and used in implementation of frequently used graphical effects -- hard and soft shadows, reflections, and Ambient Occlusion. The assessment is made in terms of difficulty of integration into a rendering engine, performance of the resulting system and suitability of implementation of chosen graphical effects. Performance parameters -- including number of rays cast per second, time to build acceleration structures and computation time on the GPU -- are tested and discussed.

Black hole visualization is a problem of raytracing over curved spacetimes. This paper discusses the physics of light in curved spacetimes, the geometry of black holes, and the appearance of objects as viewed through a relativistic camera (the Penrose-Terrell effect). It then discusses computational issues of how to generate images of black holes with a computer. A method of determining the most efficient series of steps to calculate the value of a mathematical expression is described and used to improve the speed of the program. The details of raytracing over curved spaces not covered by a single chart are described. A method of generating images of several black holes in the same spacetime is discussed. Finally, a series of images generated by these methods is given and interpreted. / text

Inversion for refraction statics is a key part of three-dimensional (3D) reflection seismic processing. The present thesis has two primary goals directed toward improvement of refraction statics inversion. First, I attempt to improve the quality of the travel-time data right at the beginning of the processing sequence and before any inversion. Any error in the travel times or geometry caused during acquisition or processing would propagate into the resulting model and may harm the resulting image. To implement rigorous, model-independent data quality control, I view the first-arrival travel times as surfaces in 3D, which allows utilization of the travel-time reciprocity condition to check for errors in geometry and in first-arrival picking.<p> The second goal of this study is in development of a new inversion approach for refraction statics specifically for 3D seismic datasets. The first-break travel-times are decomposed by using a ô-p parameterization, which allows an automatic derivation of a high-quality initial subsurface model. This model is further improved by using accurate, multi-layer ray-tracing and inversion techniques to obtain accurate refraction statics. An iterative inversion scheme based on the Simultaneous Iterative Reconstruction Technique is utilized, and its performance is measured and discussed. To assess the quality of the inverse and establish the optimal grid sizes, I use several types of resolution tests. Finally, the surface consistent statics is calculated and applied to a real dataset from southern Saskatchewan. A comparison of the resulting statics model with statics calculated by using standard industry software is made, and the statics correction is incorporated in seismic processing.<p> An overall result of this study is in demonstration that the fully 3D, ô-p based travel-time inversion method works, is applicable to large seismic datasets, and results in detailed shallow subsurface models and reliable statics solutions. Several recommendations for extending and improving the proposed approaches are also made.

Inversion for refraction statics is a key part of three-dimensional (3D) reflection seismic processing. The present thesis has two primary goals directed toward improvement of refraction statics inversion. First, I attempt to improve the quality of the travel-time data right at the beginning of the processing sequence and before any inversion. Any error in the travel times or geometry caused during acquisition or processing would propagate into the resulting model and may harm the resulting image. To implement rigorous, model-independent data quality control, I view the first-arrival travel times as surfaces in 3D, which allows utilization of the travel-time reciprocity condition to check for errors in geometry and in first-arrival picking.<p> The second goal of this study is in development of a new inversion approach for refraction statics specifically for 3D seismic datasets. The first-break travel-times are decomposed by using a ô-p parameterization, which allows an automatic derivation of a high-quality initial subsurface model. This model is further improved by using accurate, multi-layer ray-tracing and inversion techniques to obtain accurate refraction statics. An iterative inversion scheme based on the Simultaneous Iterative Reconstruction Technique is utilized, and its performance is measured and discussed. To assess the quality of the inverse and establish the optimal grid sizes, I use several types of resolution tests. Finally, the surface consistent statics is calculated and applied to a real dataset from southern Saskatchewan. A comparison of the resulting statics model with statics calculated by using standard industry software is made, and the statics correction is incorporated in seismic processing.<p> An overall result of this study is in demonstration that the fully 3D, ô-p based travel-time inversion method works, is applicable to large seismic datasets, and results in detailed shallow subsurface models and reliable statics solutions. Several recommendations for extending and improving the proposed approaches are also made.

Zugl.: Aachen, Techn. Hochsch., Diss., 2009