Near-field acoustical holography (NAH) has been used extensively for acoustical imaging of infinitesimal-amplitude (or small-amplitude) sources. However, recent interests are in the application of NAH to image finite-amplitude (or high-amplitude) sources such as jets and rockets. Since NAH is based on linear equations and finite-amplitude sources imply nonlinear effects, which cause shock formation and consequently an altered spectral shape, a feasibility study is carried out to determine the effect of nonlinear propagation on NAH. Jet and rocket sources typically have a distinct spectral shape resembling a ‘haystack’ and center frequencies varying from 30 to 300 Hz. To test the effect of nonlinear propagation on jet or rocket noise, several waveforms with varying spectral shapes and center frequencies were created and numerically propagated in one dimension using a nonlinear propagation algorithm. Bispectral methods were used to determine the amount and effect of nonlinearity, showing that higher center frequencies lead to more nonlinearities for a given amplitude. Also, higher-order statistical analysis of the time derivative of the waveforms was used to determine information about the relative amount of waveform steepening and shock coalescence occurring. NAH was then used to reconstruct the original waveform magnitude and the errors were determined. It was found that the ‘haystack’ spectral shape can be preserved by the nonlinear effects leading to low amplitude-reconstruction errors, whereas a narrow-band spectral shape will become altered and reconstruct very poorly. However, if nonlinear effects become strong due to higher center frequencies, longer propagation distances or higher amplitudes, even the ‘haystack’ shape will become altered enough to cause poor reconstruction. Two-dimensional propagation studies were also performed from two point sources, showing differences between linear and nonlinear propagation.

Using a near-field array of acoustic resonators, it is possible to modify a focused pressure field and enforce a spatial frequency corresponding to the resonator array spacing. This higher spatial frequency makes it possible to focus and image with a resolution that is better than if the focusing were in free space. This near-field effect is caused by the phase shifting properties of resonators and, specifically, the delayed phase found in waves with a temporal frequency lower than that of the resonators in the array. Using time reversal, arrays of resonators are explored and the subwavelength focusing is used to describe the ability to image subwavelength features. A one-dimensional equivalent circuit model accurately predicts this interaction of the wave field with an array of resonators and is able to model the aggregate effect of the phononic crystal of resonators while describing the fine spatial details of individual resonators. This model is validated by a series of COMSOL full-wave simulations of the same system. The phase delay caused by a single resonator is explored in a simple experiment as well as in the equivalent circuit model. A series of experiments is conducted with a two-dimensional array of resonators and complex images are produced which indicate the ability to focus complex sources with better resolution.

Infrared antennas are employed in sensing applications requiring specific spectral, polarization, and directional properties. Because of their inherently small dimensions, there is significant interaction, both thermal and electromagnetic, between the antenna, the antenna-coupled sensor, and the low-frequency readout structures necessary for signal extraction at the baseband modulation frequency. Validation of design models against measurements requires separation of these effects so that the response of the antenna-coupled sensor alone can be measured in a calibrated manner. Such validations will allow confident extension of design techniques to more complex infrared-antenna configurations. Two general techniques are explored to accomplish this goal. The extraneous signal contributions can be measured separately with calibration structures closely co-located near the devices to be characterized. This approach is demonstrated in two specific embodiments, for removal of cross-polarization effects arising from lead lines in an antenna-coupled infrared dipole, and for removal of distributed thermal effects in an infrared phased-array antenna. The second calibration technique uses scanning near-field microscopy to experimentally determine the spatial dependence of the electric-field distributions on the signal-extraction structures, and to include these measured fields in the computational electromagnetic model of the overall device. This approach is demonstrated for infrared dipole antennas which are connected to coplanar strip lines. Specific situations with open-circuit and short-circuit impedances at the termination of the lines are investigated.

No description available.

This dissertation evaluates the design of several defense schemes for wireless medical devices to address security issues. These schemes are designed to enable efficient and effective access control of wireless medical devices in both non-emergency and emergency situations. In recent years, the range of available wireless medical devices has increased and includes cardiac pacemakers, insulin pump, defibrillators, cochlear implants, neurostimulators, and various drug delivery systems. Unfortunately, most existing wireless medical devices lack sufficient security mechanisms to protect patients from malicious attacks. Thus, with the rise in use of medical implants, security becomes a critical issue as attacks on wireless medical devices may harm patients. Security on wireless medical devices is a relatively new field, which has not been thoroughly researched yet. The authors of a lot of articles have proposed token based, certification based and proximity based schemes to address the issue. However, most of the current solutions have many limitations and cannot be widely applied. Therefore, better solutions are needed. In order to address this issue, we design a novel and multiple-layer access control framework for wireless medical devices. In a low layer level, we utilize bi-channel technology and multi-factor authentication to defend against various attacks at wireless medical devices. Our system utilizes near field communication (NFC) to do device pairing and uses the medical device's wireless radio to perform remote programming. This approach defends against most attacks because our NFC pairing scheme guarantees that the successful communication range between the programmer and wireless medical devices is less than 6cm. When the patient is in a crowded area such as on public transportation, a different person's mobile devices and the patient's medical devices may be located less than 6cm apart; we use the patient's cell phone to detect such an environment. To avoid attacks in crowded areas, we design a scheme to detect such a situation using the patient's cell phone. User involvement is used on non-implantable medical devices (IMDs) and a patient access pattern based access control (PAPAC) scheme is used on IMDs. We also design a response time based scheme to defend against fake patient attacks. Our analyses and experiments show that the protection schemes are efficient and effective. In a high layer level, we design patient infusion pattern based access control (PIPAC) scheme for wireless medical devices. Specifically, insulin pumps are most widely applied wireless medical devices. The pump parameters and doses can be adjusted by anyone with an easily obtained USB device. The hacker can deliver a lethal dose without knowing the device's serial number in advance. To address this issue, we propose a PIPAC for wireless insulin pumps. This scheme employs a supervised learning approach to learn normal patient infusion patterns in terms of the dosage amount, rate, and time of infusion, which are automatically recorded in insulin pump logs. The generated regression models are used to dynamically configure a safe infusion range for abnormal infusion identification. Our proposed algorithms are evaluated with real insulin pump logs used by several patients for up to 6 months. The experimental results demonstrate that our scheme can reliably detect a single overdose attack with a success rate up to 98\% and defend against a chronic overdose attack with a very high success rate. For IMDs in non-emergency case, the PAPAC scheme we design utilizes the patient's IMD access pattern to address resource depletion (RD) attacks. It is a novel support vector machine (SVM) based scheme. This SVM based scheme is very effective at defending against RD attacks. Our experimental results show that the average detection rate is above 90\%. For IMDs in emergency cases, we design a novel biometrics based two-level secure access control scheme that utilizes a patient's biometrics to prevent unauthorized access to the IMD. The scheme consists of two levels: level-one employs a patient's some basic biometrics and is lightweight; level-two uses a patient's customized iris data to achieve effective authentication. The experimental results show that our IMD access control scheme is very effective and has small overhead in terms of battery, CPU and memory. Thus, it is suitable for IMDs. Both the false acceptance rate (FAR) and false rejection rate (FRR) are close to zero with a suitable threshold. Protecting wireless medical devices is a very challenging task due to their extremely limited resource constraints. It is necessary to balance the overhead of security schemes and security requirements. In this dissertation, we will first discuss security vulnerabilities in wireless medical device systems. Then we will present our framework using smart phones and other technologies, such as near field communication based access control. Further, we will describe the detailed design of this framework. Finally, extensive experiments show that our schemes can achieve good performance with small overhead. / Computer and Information Science

Yes / Near field imaging using microwaves in medical applications is of great current interest for its capability and accuracy in identifying features of interest, in comparison with other known screening tools. This paper documents microwave imaging experiments on breast cancer detection, using active antenna tuning to obtain matching over a wide bandwidth. A simple phantom consisting of a plastic container with a low dielectric material emulating fatty tissue and a high dielectric constant object emulating a tumor is scanned between 4 to 8 GHz with a UWB microstrip antenna. Measurements indicate that this prototype microwave sensor is a good candidate for such imaging applications. / Yorkshire Innovation Fund, Research Development Project (RDP)

State-of-the-art silicon-based power supplies have reached a point of maturity in performance. Efficiency, power density, and cost are major trade-offs involved in further improvements. Most products are custom designed with significant non-recurrent engineering and manufacturing processes that are labor intensive. In particular, conventional magnetic components, including transformers and inductors, have largely remained the same for the past five decades. Those large and bulky magnetic components are major roadblocks toward an automated manufacturing process. In addition, there is no specific approach to reduce electromagnetic interference (EMI) in conventional practices. In certain cases, EMI filter design even requires a trial-and-error process. With recent advances in wide-bandgap (WBG) power semiconductor devices, namely, SiC and GaN, we have witnessed significant improvements in efficiency and power density, compared to their silicon counterparts. In a power factor correction (PFC) rectifier/inverter, the totem-pole configuration with critical conduction mode (CRM) operation to realize zero-voltage switching (ZVS) is deemed most desirable for a switching frequency 10 times higher than current practice. With a significantly higher operating frequency, the integration of inductors with embedded windings in the printed circuit board (PCB) is feasible. However, a PCB winding-based inductor has a fundamental limitation in terms of its power handling capability. The winding loss is proportional to the magnetomotive force (MMF), which is Ni. That is to say, with the number of layers (turns) and currents increased, winding loss is increased nonlinearly. Furthermore, for a large-size planar inductor, flux distribution is usually non-uniform, resulting in dramatically increased hysteresis loss and eddy loss. Thus, current designs are challenged by the capability to increase their power range. To address those issues, a modular building block approach is proposed in this dissertation. A planar PCB inductor is formed by an array of pillars that are integrated into one magnetic core, where each pillar handles roughly 750 W of power. The winding loss is reduced by limiting the number of turns for each pillar. The core loss is minimized with a proposed planar magnetic structure where rather uniformly distributed fluxes were observed in the plates. The proposed approach has a similar loss to a conventional litz wire-based design but features a higher power density and can be easily assembled in automation. A 3 kW high frequency PFC converter with 99% efficiency is demonstrated as an example. Furthermore, PCB-based designs up to 6 kW are provided. Another challenge in a WBG-based PFC/inverter is the high common-mode (CM) noises associated with the high dv/dt of the WBG devices. Symmetry and cancellation techniques are often employed to suppress CM noises in switching power converters. Meanwhile, shielding technique has been demonstrated to effectively suppress CM noises in an isolated converter with PCB-based transformer design. However, for non-isolated converters, such as PFC circuits, none of the techniques mentioned above are deemed applicable or justifiable. Recently, the balance technique has been demonstrated to effectively suppress CM noises up to a point where the parasitic ringing between the inductor and its winding capacitor is observed. This dissertation presents an improved balance technique in a PCB-based coupled inductor design that compensates for the detrimental effect of the interwinding capacitors. A CM noise model is established to simplify the convoluted couplings into a decoupled representation so as to illustrate the necessary conditions for realizing a balanced network. In the given 1 kW PFC example, CM noise suppression is effective in the frequency range of interest up to 30 MHz. The parasitic oscillation of inductors, known to be detrimental for CM noise reduction, is circumvented with the improved magnetic structure. By applying the balance technique to a PFC converter and the shielding technique to an LLC DC/DC converter, significant noise reductions were realized. This provides the opportunity to use a simple one-stage EMI filter to achieve the required EMI noise attenuation for a server power supply. This dissertation further offers an in-depth study on reducing the unwanted near-field couplings between the CM/DM inductors and DM filter capacitors, as well as unwanted self-parasitics such as the ESL of the DM capacitors. An exhaustive finite element analysis (FEA) and near field measurements are conducted to better understand the effect of frequency on the polarization of the near field due to the displacement current. The knowledge gained in this study enables one to minimize unwanted mutual coupling effects by means of physical placement of these filter components. Thus, for the first time, a single-stage EMI filter is demonstrated to meet the EMI standard in an off-line 1 kW, 12 V server power supply. With the academic contributions in this dissertation, a PCB winding-based inductor can be successfully applied to a high-frequency PFC/inverter to achieve high efficiency, high power density, automation in manufacturing, lower EMI, and lower cost. Suffice it to say, the proposed approach enables a paradigm shift in the designing and manufacturing of a PFC/inverter for the next generation of power supplies. / Doctor of Philosophy / State-of-the-art silicon device-based switching power supplies have reached a point of maturity in performance. Efficiency, power density, and cost are major trade-offs involved in performance improvements. Most products are custom designed, requiring significant non-recurrent engineering and labor-intensive manufacturing processes. In particular, conventional magnetic components, including transformers and inductors, have largely remained the same for the past five decades. Those large and bulky magnetic components are major roadblocks toward an automated manufacturing process. In addition, there is no specific approach to reduce electromagnetic interference (EMI) in conventional practices. In consequence, a large multi-stage EMI filter is usually adopted between the power converter and the grid to reduce the EMI noise. It generally occupies 1/4-1/3 of the total converter volume. In certain cases, EMI filter design even requires a trial-and-error process. Suffice it to say, EMI is still regarded as both science and art. With recent advances in wide-bandgap (WBG) power semiconductor devices, namely, SiC and GaN, we have witnessed significant improvements in efficiency and power density, compared to their silicon counterparts. With GaN devices, the switching frequency of a PFC converter is able to be increased by 10 times compared to the state-of-the-art design without compromising efficiency. With a significantly higher operating frequency, the integration of inductors with embedded windings in the printed circuit board (PCB) is feasible. However, the state-of-the-art PCB winding-based inductor has a fundamental limitation in power range. Its winding loss and core loss increase dramatically in high powers. To address this issue, a modular building block approach is proposed in this dissertation. A planar PCB inductor is formed by an array of pillars that are integrated into one magnetic core, where each pillar handles roughly 750 W of power. The winding loss is reduced by limiting the number of turns for each pillar. The core loss is minimized with a proposed planar magnetic structure where rather uniformly distributed fluxes have been observed in the magnetic core plates. A 3 kW high-frequency PFC converter with a 99% peak efficiency is demonstrated as an example. Furthermore, PCB-based designs up to 6 kW are provided. Another challenge in a WBG-based PFC/inverter is the high common-mode (CM) noises caused by the high switching speed of the WBG devices. Symmetry and cancellation techniques are often employed to suppress CM noises in switching power converters. Meanwhile, shielding technique has been demonstrated to effectively suppress CM noises in an isolated converter with PCB-based transformer. However, for non-isolated converters, such as PFC circuits, none of the techniques mentioned above are deemed applicable or justifiable. Recently, the balance technique has been demonstrated to effectively suppress CM noises up to several MHz. However, the CM noise reduction is not effective beyond that. This dissertation presents an improved balance technique in a PCB-based coupled inductor to circumvent the limits. In the given 1 kW PFC example, CM noise suppression is effective in the frequency range of interest up to 30 MHz. By applying the balance technique to a PFC converter and the shielding technique to an LLC DC/DC converter, significant noise reductions were realized. This provides the opportunity to use a simple one-stage EMI filter to achieve the required EMI noise attenuation for a server power supply. It features a smaller volume compared to a conventional multi-stage filter. To further enhance the filter's performance at high frequencies, an exhaustive finite element analysis and near field measurements are conducted to better understand the effect of frequency on the polarization of the near field due to the displacement current. The knowledge gained in this study enables one to minimize unwanted mutual coupling effects through physical placement of these filter components. Several approaches for improving the filter performance at high frequency are conducted. With these approaches applied, a single-stage filter is demonstrated in an off-line 1 kW, 12 V server power supply. Thus, for the first time, a single-stage EMI filter can be contemplated to meet the EMI standard in server power supplies. With the academic contributions in this dissertation, a PCB-winding based inductor can be successfully applied to a high-frequency PFC/inverter to achieve high efficiency, high power density, automation in manufacturing, lower EMI, and lower cost. Suffice it to say, the proposed approach in this work enables a paradigm shift in the designing and manufacturing of a PFC/inverter for the next generation of power supplies.

El proceso de atomización desde una vena o lámina líquida hasta multitud de gotas dispersas en un medio gaseoso ha sido un fenómeno de interés desde hace varias décadas, especialmente en el campo de los motores de combustión interna alternativos. Multitud de estudios experimentales han sido publicados al respecto, pues una buena mezcla de aire-combustible asegura una evaporación y combustión mucho más eficientes, aumentando la potencia del motor y reduciendo la cantidad de contaminantes emitidos. Con el auge de las técnicas computacionales, muchos modelos han sido desarrollados para estudiar este proceso de atomización y mezcla. Uno de los últimos modelos que han aparecido es el llamado ELSA (Eulerian-Lagrangian Spray Atomization), que utiliza un modelo Euleriano para la parte densa del chorro y cambia a un modelo Lagrangiano cuando la concentración de líquido es suficientemente pequeña, aprovechando de esta manera las ventajas de ambos. En el presente trabajo se ha desarrollado un modelo puramente Euleriano para estudiar la influencia de la geometría interna de la tobera de inyección en el proceso de atomización y mezcla. Se ha estudiado únicamente el proceso de inyección diésel. Este modelo permite resolver en un único dominio el flujo interno y el externo, evitando así las comunes simplificaciones y limitaciones de la interpolación entre ambos dominios resueltos por separado. Los resultados actuales son prometedores, el modelo predice con un error aceptable la penetración del chorro, el flujo másico y de cantidad de movimiento, los perfiles de velocidad y concentración, así como otros parámetros característicos del chorro. / Martí Gómez-Aldaraví, P. (2014). DEVELOPMENT OF A COMPUTATIONAL MODEL FOR A SIMULTANEOUS SIMULATION OF INTERNAL FLOW AND SPRAY BREAK-UP OF THE DIESEL INJECTION PROCESS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43719 / Premios Extraordinarios de tesis doctorales

This thesis explores how the diffraction pattern in the near-field region of a chromium feature edge on a photomask gets altered for three scenarios: First, an analytical study using the Fresnel diffraction integral is performed that investigates what happens when the thin-mask approximation is omitted and the chromium layer is given a thickness. Another analytical study is performed where the edges of a test feature are altered to simulate deviations in the linewidth or a translation of the whole feature, image subtraction is then used to create a difference pattern by subtracting a reference diffraction pattern from the diffraction pattern created by the altered test feature. Lastly, a numerical study using Fourier optics is performed to investigate the effect that introducing four common defects: extrusions, intrusions, dark spots, and pinholes, around the edge will have on the diffraction pattern by subtracting the diffraction pattern from a reference half-plane and again analyzing the resulting difference pattern. Introducing a thickness to the chromium layer alters the diffraction pattern by creating a small crease around the area of the edge in reflective mode, resulting in something similar to a double edge. The high optical density of chromium nullified any effect the thickness had when viewing the system through transmission mode. A linear relation between a change in linewidth or translation of a feature and the peak intensity of the difference pattern is observed that might be used for edge detection. The defect diameter of an extrusion or intrusion seems to correlate in a quadratic way with the peak fringe intensity of the subtracted difference pattern along the x-axis as the defect is fully visible. For a dark spot or pinhole defect being translated away from a chromium edge, the central fringe along the y-axis of the difference pattern follows a sinusoidal curve as it translates further away from the edge. The amplitude of this curve is related to the defect size.

The structure of a material, whether at the atomic scale or patterned at the nanoscale, is the basis of many of its physical properties—color, emission wavelength, optical nonlinearity, electrical conductivity, thermal conductivity, brittleness, and more. Therefore, one of the most important developments in photonics, electronics, and magnetics is the ability to manipulate the nanostructure of materials as a way to augment their natural qualities and adapt them to greater applications. The cleanroom debuted in the mid-20th century, alongside and followed by an assortment of precision nanofabrication instruments performing photolithography, electron-beam lithography, ion implantation, femtosecond laser machining, etc. While these techniques have demonstrated breakthroughs such as fabricating ever-smaller transistors keeping pace with the famous Moore’s Law, they require cleanroom facilities, multi-step processing, or leave behind debris or residue. Such impurities have an outsize effect on a burgeoning class of materials with desirable optical and electronic properties—two-dimensional (2D) layered van der Waals materials—as their dimensions approach the single-atom limit, leading a desire for additional approaches to material nanostructuring. In this thesis, we describe a novel approach to generating atomically sharp linear nanostructures in hexagonal boron nitride (hBN) via resonant optical phonon pumping with a pulsed mid-infrared laser and detail its development from discovery to a useful technique that complements established approaches to nanopatterning. The femtosecond laser is tuned to the material’s infrared-active transverse optical TO (E1u) phonon, located at ? = 7.3 ?? or 1367 cm-1, and its polarization aligned parallel to the crystal zigzag axis, in the direction of the phonon’s characteristic atomic motion. The optical field coherently drives and amplifies the intrinsic ionic motion toward bond breakage, resulting in a gentle tearing of the hBN flake along the crystal axis at the material damage threshold. All processing is performed in situ at room temperature under ambient conditions, free from cryogenics and vacuum setups, unlike in the conventional nanofabrication methods confined to the cleanroom. This phenomenon is termed “unzipping” to depict the rapid formation and emanation of a crack tens of nanometers wide from a point within the laser-excited area. The generation of these fea- tures is ascribed to the large atomic displacements and localized bond strain produced by strongly driving the crystal at an intrinsic resonance, which is absent under non-resonant irradiation and is greatly sensitive to the relative angle between the crystal orientation and the linear laser polarization. We perform detailed characterization of the unzipped features and their host hBN flakes us- ing atomic force microscopy (AFM) topographic imaging, scanning electron microscopy (SEM), atomic-scale lateral force microscopy (LFM), nanoindentation in the plastic deformation regime, and near-field optical probing (scattering-type scanning near-field optical microscopy, s-SNOM) to reveal their atomically sharp, six-fold symmetric, orientation-selective, defect-seeded nature. Then, we fabricated several nanostructures—gratings, Fabry-Perot resonators, and cleaved and shaped flakes—to demonstrate the technique in useful nanophotonics applications. The preliminary Fabry-Perot resonator, examined in the near-field with nanoscale Fourier-transform infrared spectroscopy (nano-FTIR), exhibited performance that is competitive with similar structures fabricated by cleanroom etching. Our initial approach achieved a quality factor of ? ≈ 70, already on par with ? = 50 to 100 achieved by conventional nanofabrication methods. The cleanliness, sharpness, and directionality of nanostructures fabricated in situ via unzipping, along with the ability to deterministically seed the location of its constituent line defects using nanoindentation, enable vast future applications in patterning hBN and other polar crystals that possess optically-addressable, high-energy optical phonon modes in the mid-infrared.