Browsing by Subject "Electromagnetics"
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Item An adaptive measurement protocol for fine-grained electromagnetic side-channel analysis of cryptographic modules(2019-09-12) Iyer, Vishnuvardhan Venkatramani; Yilmaz, Ali E.An adaptive measurement protocol is presented to increase effectiveness of fine-grained electromagnetic side-channel analysis (EM SCA) attacks that attempt to extract the information that is unintentionally leaked from physical implementations of cryptographic modules. Because measured fields vary with probe parameters as well as the data being encrypted, identifying the optimal configurations requires searching among a large number of possible configurations. The proposed protocol is a multi-step acquisition that corresponds to a greedy search in a 4-D configuration space consisting of probe’s on-chip coordinates, orientation, and number of signals acquired. This 4-D space can be extended to a 6-D space by repeating the protocol for different probe sizes and heights. This approach is presented as an alternative to current fine-grained EM SCA techniques that perform exhaustive full-chip scans to isolate information leaking locations. To demonstrate the feasibility of the approach, the protocol is tested by performing EM SCA attacks for different configurations and identifying the best attack configuration for two realizations of the advanced encryption standard (AES), subject to the precision of the measurement equipment. It is found that the protocol requires ~20× to ~25× less acquisition time compared to an exhaustive search for the optimal attack configuration.Item Engineering exotic linear and nonlinear electromagnetic responses using spatial and spatiotemporal modulation(2019-05) Tymchenko, Mykhailo; Alù, Andrea; Belkin, Mikhail; Bank, Seth R.; Wasserman, Daniel; Khanikaev, Alexander B.Periodicity and modulation lie at the heart of modern electromagnetic, acoustic and mechanical engineering, dramatically altering the way in which waves interact with periodically structured media. The main idea driving the intense research into periodic systems is the fact that periodicity breaks the dependence on natural properties of constituent media and instead allows one to blend the responses of various materials and leverage their geometric shapes to obtain collective responses on demand. In the realm of electromagnetics, over the past two decades there has been an explosive surge of interest to artificially engineered time-invariant periodic structures thanks to numerous fascinating linear and nonlinear effects they enable. In this dissertation, I will present some transformative developments in the area of efficient nonlinear generation and wave mixing in thin 2D periodic structures based on multi-quantum-wells, as well as show the possibility to engineer to the great extent the dispersion topology of surface waves propagating along ideally thin conducting sheets with 1D spatial periodicity such as graphene ribbons. In parallel with the progress in obtaining desired responses in time-invariant periodic structures, significant progress is being made in applying temporal and synchronous spatial and temporal modulation to engage new degrees of freedom and extend the spectrum of achievable electromagnetic phenomena even further. In this dissertation, I will also show that spatiotemporal modulation applied to electronic networks holds a key to obtain ultrawideband and extremely compact delays far beyond those achievable in time-invariant systems. Spatiotemporal modulation also allows for all kinds of nonreciprocal devices to be seamlessly integrated in an electronic chip by overcoming the size and magnetic material incompatibility constraints. This fact holds a truly groundbreaking potential for future electronic devices and wireless systems by enabling their simultaneous transmit-and-receive operation. Finally, I will show that spatiotemporal modulation enables a direct translation of some of the most advanced and intricate concepts of condensed matter physics – topological insulators – to the realm of classical electronic circuits. Compared to standalone nonreciprocal devices, topologically-nontrivial electronic circuits provide an even larger toolbox to obtain various nonreciprocal functionalities by enforcing a wideband unidirectional transmission robust to defects and imperfectionsItem Envelope-tracking integral equation methods for band-pass transient scattering analysis(2015-09-28) Kaur, Guneet; Yilmaz, Ali E.; Ling, Hao; Alu, Andrea; Demkowicz, Leszek; Schulz, KarlThis dissertation presents envelope-tracking (ET) integral equation methods to efficiently analyze band-pass scattering problems. Unlike the traditional time-domain marching-on-in-time (TD-MOT) schemes, ET-MOT schemes solve for space-time samples of not the current density but its complex envelope. The time step size used in ET-MOT schemes is inversely proportional to the bandwidth of the fields of interest and not their maximum frequency content; thus, ET-MOT schemes can use (much) larger time step sizes for band-pass analysis: the smaller the bandwidth of the fields compared to their maximum frequency content, the larger the time step size in ET-MOT solutions compared to those in the TD-MOT solutions. Despite the reduction in the number of time steps, ET-MOT schemes suffer from high computational costs that also affect time- and frequency-domain integral equation methods. This dissertation presents an FFT-based algorithm, the ET adaptive integral method (ET-AIM), to reduce the computational complexity of ET-MOT schemes. ET-AIM is both theoretically and empirically compared to its time-domain and frequency-domain counterparts, TD-AIM and FD-AIM, respectively. Because the performance of the envelope-tracking methods is a complex function of the bandwidth of interest and because each method has different accuracy-efficiency tradeoff, only limited deductions can be made from theoretical comparison of the methods. Thus, in addition to theoretical comparisons, an empirical approach for comparing the different methods is presented: To perform a fair, meaningful, and generalizable comparison, benchmark problems are identified, an appropriate error norm is defined, and the key parameters of the methods are optimized subject to a constraint on the error norm. Computational costs are measured and compared for all three methods for solving progressively larger benchmark scattering problems for varying frequency bandwidths. This dissertation also proposes an out-of-core algorithm to ameliorate the high memory requirement of FFT-accelerated time-marching methods. The proposed algorithm exchanges the core memory requirement with external storage space requirement without significantly increasing the simulation time. The performance of the proposed methods is demonstrated by solving surface- and volume-integral equations pertinent to scattering problems that involve good conductors and inhomogeneous volumes with complex dielectric properties. For example, numerical results obtained using ET-AIM are presented for analysis of scattering of radar pulses from a PEC missile, a generic aircraft, etc. and antenna radiation near anatomically realistic human body model.Item Finite element modeling of electromagnetic radiation and induced heat transfer in the human body(2013-08) Kim, Kyungjoo; Demkowicz, Leszek; Eijkhout, Victor; Van de Geijn, Robert A.This dissertation develops adaptive hp-Finite Element (FE) technology and a parallel sparse direct solver enabling the accurate modeling of the absorption of Electro-Magnetic (EM) energy in the human head. With a large and growing number of cell phone users, the adverse health effects of EM fields have raised public concerns. Most research that attempts to explain the relationship between exposure to EM fields and its harmful effects on the human body identifies temperature changes due to the EM energy as the dominant source of possible harm. The research presented here focuses on determining the temperature distribution within the human body exposed to EM fields with an emphasis on the human head. Major challenges in accurately determining the temperature changes lie in the dependence of EM material properties on the temperature. This leads to a formulation that couples the BioHeat Transfer (BHT) and Maxwell equations. The mathematical model is formed by the time-harmonic Maxwell equations weakly coupled with the transient BHT equation. This choice of equations reflects the relevant time scales. With a mobile device operating at a single frequency, EM fields arrive at a steady-state in the micro-second range. The heat sources induced by EM fields produce a transient temperature field converging to a steady-state distribution on a time scale ranging from seconds to minutes; this necessitates the transient formulation. Since the EM material properties depend upon the temperature, the equations are fully coupled; however, the coupling is realized weakly due to the different time scales for Maxwell and BHT equations. The BHT equation is discretized in time with a time step reflecting the thermal scales. After multiple time steps, the temperature field is used to determine the EM material properties and the time-harmonic Maxwell equations are solved. The resulting heat sources are recalculated and the process continued. Due to the weak coupling of the problems, the corresponding numerical models are established separately. The BHT equation is discretized with H¹ conforming elements, and Maxwell equations are discretized with H(curl) conforming elements. The complexity of the human head geometry naturally leads to the use of tetrahedral elements, which are commonly employed by unstructured mesh generators. The EM domain, including the head and a radiating source, is terminated by a Perfectly Matched Layer (PML), which is discretized with prismatic elements. The use of high order elements of different shapes and discretization types has motivated the development of a general 3D hp-FE code. In this work, we present new generic data structures and algorithms to perform adaptive local refinements on a hybrid mesh composed of different shaped elements. A variety of isotropic and anisotropic refinements that preserve conformity of discretization are designed. The refinement algorithms support one- irregular meshes with the constrained approximation technique. The algorithms are experimentally proven to be deadlock free. A second contribution of this dissertation lies with a new parallel sparse direct solver that targets linear systems arising from hp-FE methods. The new solver interfaces to the hierarchy of a locally refined mesh to build an elimination ordering for the factorization that reflects the h-refinements. By following mesh refinements, not only the computation of element matrices but also their factorization is restricted to new elements and their ancestors. The solver is parallelized by exploiting two-level task parallelism: tasks are first generated from a parallel post-order tree traversal on the assembly tree; next, those tasks are further refined by using algorithms-by-blocks to gain fine-grained parallelism. The resulting fine-grained tasks are asynchronously executed after their dependencies are analyzed. This approach effectively reduces scheduling overhead and increases flexibility to handle irregular tasks. The solver outperforms the conventional general sparse direct solver for a class of problems formulated by high order FEs. Finally, numerical results for a 3D coupled BHT with Maxwell equations are presented. The solutions of this Maxwell code have been verified using the analytic Mie series solutions. Starting with simple spherical geometry, parametric studies are conducted on realistic head models for a typical frequency band (900 MHz) of mobile phones.Item Investigation of high-frequency propagation channels through pipes and ducts for building interior reconnaissance(2012-05) Whitelonis, Nicholas John, 1984-; Ling, Hao; Neikirk, Dean; Wilson, Preston; Powers, Edward; Alu, AndreaRecently, there is strong interest in the through-wall sensing capabilities of radar for use in law enforcement, search and rescue, and urban military operations. Due to the high attenuation of walls, through-wall radar typically operates in the low GHz frequency region, where resolution is limited. It is worthwhile to explore other means of propagating radar waves into and back out of a building’s interior for sensing applications. One possibility is through duct-like structures that are commonly found in a building, such as metal pipes used for plumbing or air conditioning ducts. The objective of this dissertation is to investigate techniques to acquire radar images of targets through a pipe. First, using the pipe as an electromagnetic propagation channel is studied. A modal approach previously developed for computing the radar cross-section of a circular duct is modified to compute the transmission through a pipe. This modal approach for transmission is validated against measured data. It is also shown that a pipe is a high-pass propagation channel. The modal analysis is then extended to two-way, through-pipe propagation for backscattering analysis. The backscattering from a target is observed through a pipe in simulation and measurement. Next, methods to form two-dimensional radar images from backscattering data collected through a pipe are explored. Four different methods previously developed for free-space imaging are applied to the problem of imaging through a pipe: beamforming, matched filter processing, MUSIC, and compressed sensing. In all four methods it is necessary to take into account the propagation through the pipe in order to properly generate a focused radar image. Each method is demonstrated using simulation and validated against measurement data. The beamforming and matched filter methods are found to suffer from poor cross-range resolution. To improve resolution, the MUSIC algorithm is applied and shown to give superior resolution at the expense of more complicated data collection. The final method, compressed sensing, is shown to achieve good cross-range resolution with simpler data collection. A comparison of the tradeoffs between the four methods is summarized and discussed. Two additional extensions are studied. First, a method for computing the transmission through an arbitrary pipe network using the generalized scattering matrix approach is proposed and implemented. Second, a new method for computing joint time-frequency distributions based on compressed sensing is applied to analyze the backscattering phenomenology from a pipe.Item An investigation on transmitter and receiver diversity for wireless power transfer(2011-05) Jun, Bong Wan; Ling, Hao; Alu, AndreaThis thesis investigates near-field wireless power transfer using multiple transmitters or multiple receivers. First, transmitter diversity is investigated in terms of the power transfer efficiency (PTE). It is found that an improvement in the PTE can be achieved by increasing the number of transmitters. Furthermore, a region of constant PTE can be created with the proper arrangement of transmitters. Next, receiver diversity is investigated in detail. An improvement in the PTE can be also achieved by increasing the number of receivers. However, it is shown that when two or more receivers are closely located, the PTE is reduced due to mutual coupling between receivers. This is termed a ‘sink’ phenomenon, and it is investigated through measurement and simulation. Finally, to account for more general situations of multiple transmitters and multiple receivers, Monte-Carlo simulation is applied. The cumulative distribution function (CDF) is used to interpret the results of the Monte-Carlo simulation. The transmitter and receiver diversity gain can be found based on the CDF. Moreover, the sink phenomenon can be observed by analyzing the CDF curve. Several strategies for positioning receivers are introduced to reduce the sink phenomenon. The results of the Monte-Carlo simulation also show that a saturation in the transmitter or receiver gain is reached when the number of transmitters or receivers is increased. Therefore, increasing the number of transmitters or receivers beyond a certain number does not help increase the PTE.Item Modeling and simulation of electromagnetically-interacting low-temperature plasma discharges for actively controlled metamaterials(2020-06-22) Pederson, Dylan Michael; Raja, Laxminarayan L.; Bisetti, Fabrizio; Goldstein, David; Hallock, Gary; Varghese, PhilipIn this work, we present a framework for computational modeling of microwave-induced nonthermal plasma discharges interacting with dielectric and conducting structures, with applications to actively-controlled metamaterials and photonic crystals. The discharge model is based on a low-temperature quasi-neutral description of the plasma with lumped chemistry for ionization, attachment and recombination. The first part of this work details the development of a local time-stepping strategy for the finite-difference time- domain method on an adaptive mesh. The algorithm is implemented on a quad/octree mesh in order to demonstrate its computational efficiency for plasma-metamaterial problems. In the second part of this work we study how dense low-temperature plasmas are generated by metamaterial and photonic crystal systems, as well as how they modify the system behavior. We show that the existence of a plasma in the vicinity of a metamaterial can be used to shift the characteristic resonance frequency of the system and reduce over- all system transmission due to absorption in the plasma. We demonstrate that in some instances, the presence of a plasma permits a surface plasmon polariton propagating mode with a corresponding low-frequency pass band. The final part of this work focuses on the development of an extended fluid model which accounts for nonlinear electron dynamics in the presence of strong electromagnetic fields. The influences of nonlinear electron dynamics on the plasma response are found to be dominated by the electron inertial effects and wave-induced magnetization. These effects are shown to lead to efficient harmonic generation in plasmas with spatial extent smaller than the wave skin depth and plasma frequency exceeding the wave frequency. Furthermore, magnetized electron gyration effects are shown to lead to an electromagnetic Hall drift, modified electron mean energy, and modified transport coefficients for cross-field diffusion and mobility.Item New frontiers in microwave metamaterials : magnetic-free non-reciprocal devices based on angular-momentum-biasing and negative-index metawaveguides(2015-08) Estep, Nicholas Aaron; Alù, Andrea; Gharpurey, Ranjit; Ling, Hao; Shvets, Gennady; Wang, ZhengIn this work, metamaterial concepts are applied to improve the design and realization of microwave components of a new generation. Conventional radiation sources, despite the mature and efficient development over the past century, maintain fundamental limitations. Slow-wave structures, such as backward-wave oscillators and traveling-wave tubes, function on the order of several operational wavelengths, leading to bulky architectures. Cherenkov radiation-based detectors are constrained to forward propagation, where the detection or diagnostic scheme may be damaged by energetic particles. Metamaterial concepts, specifically negative-index structures, provide new opportunities for these applications. In this context, we developed a detailed design of a negative-index metamaterial conducive to microwave generation. We experimentally validated a negative-index waveguide based on patterned plates of complementary split ring resonators. The design is conducive to interaction between particles and waves; it maintains a scalable negative-index band along with a longitudinal electric field component for particle interaction. The sub-wavelength resonant nature of the metamaterial allows for a compact design. In a different field of research, there is also significant need to squeeze the dimensions of microwave components. We have developed magnet-less, non-reciprocal, microwave circulators based on angular-momentum-biasing, which allow the realization of non-reciprocal devices that do not require magnets, and therefore lead to cheaper, lighter and significantly smaller devices. Angular-momentum-biasing, theoretically proposed recently in our research group, effectively mimics the collective alignment of electron spins seen in a ferromagnetic medium under a magnetic bias. Through spatiotemporal modulation, one can generate electrical rotation, leading to strong nonreciprocal response without magnetism. We have experimentally proven the theory on lumped element circulators and proposed transmission-line variations, providing over 50 dB of isolation in a range of frequency bands. This method provides efficient, easily tunable, fully integrable, compact devices that may revolutionize the future of integrated components. We have developed rigorous design principles that not only provide guidance for designs based on desired performance metrics, but also proves the passive nature of the concept. Furthermore, we have crafted mechanisms to enhance the bandwidth performance and improve linearity.Item Nonlinear, passive and active inclusions to tailor the wave interaction in metamaterials and metasurfaces(2013-08) Chen, Pai-Yen; Alú, AndreaMetamaterials have experienced a rapid growth of interest over the past few years and new capabilities are being explored to broaden the range of their unique electromagnetic properties for functional devices, including tunable, switchable, and nonlinear properties. In the future, there is the prospect of opening even more exciting applications with metamaterials, not yet imagined and thought not to be possible with currently available techniques. In my dissertation, I discuss several solutions for passive and active metamaterials and metasurfaces, with a particular focus on their potential applications, enabling a new class of metamaterials in the spectral range from radio frequencies (RF) and microwaves, terahertz (THz) to visible light. First, I demonstrate that by loading plasmonic nanoantennas with nonlinear nanoparticles, the nonlinear optical processes, such as multiple wave mixing, high harmonic generation, phase conjugation and optical bistability may be realized at the nanoscale, thanks to the strongly enhanced optical near fields accompanied with the plasmonic resonance. I present here the design, practical realization, and homogenization theory of nonlinear optical metamaterials and metasurfaces formed by optical nanoantenna arrays loaded with nonlinearities. As an extreme case of light manipulation at the "atomic" scale, I also study the collective oscillation of massless Dirac fermions inside grapheme monolayers, in which surface plasmon polaritons are controlled by electrostatic gating. I present how a graphene monolayer may serve as a building block and design paradigm for adaptable, switchable and frequency-configurable THz metamaterials and nanodevices, realizing various functionalities for cloaking, sensing, absorbing, switching, modulating, phasing, filtering, impedance transformation, photomixing and frequency synthesis in the THz spectrum. Last I present various metamaterial designs applied to invisibility cloaks based on the scattering cancellation mechanism enabled by plasmonic materials and passive/active metamaterials and metasurfaces. This cloaking technology may be used for camouflaging, enhancing the sensitivity and signal-to-noise ratio in RF wireless communication and sensor networks. In addition, electrically-small antennas based on the phase compensation effect offered by metamaterials with low or negative material properties are presented, with tailorable modal frequencies, bandwidth, and radiation properties.Item Nonreciprocal and non-Hermitian metamaterials(2021-05-05) Duggan, Robert Stanley; Alù, Andrea; Bank, Seth R; Wasserman, Daniel M; Li, Xiaoqin; Porter, EmilyThe modern field of electromagnetic metamaterials focuses on engineering materials at the subwavelength scale for enhanced control over wave phenomena. This includes spatial structuring, but also applying suitable shaping of material properties in the time dimension. In this work, we extend the idea of spatiotemporal modulation of materials, and show how effectively modulating the permittivity tensor in time and space can be utilized for extreme nonreciprocal responses that do not require special materials or strong magnetic bias. This is possible with nonlinear optical materials or optomechanical structures, and shows behavior analogous to the canonical Faraday effect arising in a ferrite with a magnetic bias. This scheme can be utilized for a wide range of nonreciprocal devices, including Faraday rotators, isolators, circulators, and topological insulators. Non-Hermitian metamaterials is also a growing subfield of this area of science and technology, as material loss and gain result in a number of interesting spectral properties. In this work, we discuss how we can utilize the idea of embedded eigenstates, which have vanishing radiation lifetimes, to sculpt the profile of thermal emission, with a goal of narrow bandwidth and directive emitters. We will then show what fundamental limits arise in structures that seek broad bandwidth superluminal behavior based on amplification, which break the requirements imposed by passivity, but are still constrained by causality. Finally, we will provide an analysis of a proposed class of sensors based on spectral singularities in non-Hermitian structures known as exceptional points, with Monte-Carlo simulations backed up by rigorous sensing theory, attempting to make a fair comparison across a wide range of sensors.Item Study on the feasibility of using electromagnetic methods for fracture diagnostics(2012-08) Saliés, Natália Gastão; Sharma, Mukul M.; Ling, HaoThis thesis explores two ways of developing a fracture diagnostics tool capable of estimating hydraulic fracture propped length and orientation. Both approaches make use of an electrically conductive proppant. The fabrication of an electrically conductive proppant is believed to be possible and an option currently on the market is calcined petroleum coke. The first approach for tool development was based on principles of antenna resonance whereas the second approach was based on low frequency magnetic induction. The former approach had limited success due to the lack of resonant features at the stipulated operating conditions. Low frequency induction is a more promising approach as electromagnetic fields showed measurable changes that were dependent on fracture length in simulations. The operation of a logging tool was simulated and the data showed differences in the magnetic field magnitude ranging from 2% to 107% between fracture sizes of 20m, 50m, 80m, and 100m. Continuing research of the topic should focus not only on simulating more diverse fracture scenarios but also on developing an inversion scheme necessary for interpreting field data.