Les microscopes en champ proche micro-ondes sont des outils émergents pour la caractérisation des matériaux. Dans ce travail, une sonde de champ proche a été conçue, décrite et analysée en termes de performance et de résolution. Cette sonde a été associée à deux microscopes en champ proche micro-ondes. Le premier microscope est basé sur de la réflectométrie en intensité et a permis d'évaluer la qualité et la résolution latérale de la sonde. Cette résolution peut atteindre une dimension sub-longueur d'onde ouvrant la voie pour une caractérisation locale des matériaux. La seconde expérience présente la conception d'un banc de caractérisation des matériaux. Ce système met en œuvre un mélangeur I/Q afin d'extraire l'information en intensité et en phase de l'interaction en champ proche. Enfin, la dernière expérience concerne l'injection électromagnétique en champ proche d'un signal hors-bande sur un module de communication. L'ensemble des résultats montrent que l'expérience d'injection en champ proche a le potentiel pour devenir un outil de métrologie important pour l'étude de la susceptibilité. / Microwave near-field microscopes are emerging tools for material characterization. In this work, a near-field probe was designed, described and analyzed in terms of performance and resolution. This probe has been associated with two microscopes in the near microwave field. The first microscope is based on intensity reflectometry and evaluated the quality and lateral resolution of the probe. This resolution can reach a subwavelength dimension, opening the way to local characterization of materials. The second experiment presents the design of a materials characterization bench. This system uses an I/Q mixer to extract information in intensity and phase of near-field interaction. Finally, the last experiment concerns electromagnetic injection in the near field of an out-of-band signal on a communication module. The overall results show that the near-field injection experiment has the potential to become an important metrology tool for susceptibility studies.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Uma parcela significativa da pesquisa cientÃfica hodierna baseia-se na sÃntese, caracterizaÃÃo ou aplicaÃÃo de materiais nanoestruturados. No intuito de possibilitar um maior entendimento das intrigantes propriedades destes materiais, muitas tÃcnicas com resoluÃÃo nanomÃtrica e atà subnanomÃtrica foram criadas nos Ãltimos 50 anos e tÃm passado por um processo de contÃnuo aprimoramento. Apesar do grande desenvolvimento tÃcnico e cientÃfico da instrumentaÃÃo disponÃvel, a caracterizaÃÃo Ãtica com resoluÃÃo nanomÃtrica destes materiais tem se mostrado um desafio para pesquisadores do mundo inteiro. Nesse contexto, as tÃcnicas baseadas em radiaÃÃo de campo prÃximo tÃm despontado como uma boa alternativa para quebra do limite de difraÃÃo, que constitui um limite natural para os instrumentos Ãticos convencionais. AlÃm disso, a microscopia de campo prÃximo em modo de iluminaÃÃo e contato adquire simultaneamente informaÃÃes Ãticas e topogrÃficas do material, o que permite fazer uma distinÃÃo entre as propriedades Ãticas nanomÃtricas reais e as induzidas por topografia. O fenÃmeno de domÃnios cristalogrÃficos tem sido um assunto de interesse da cristalografia desde que ela comeÃou a se desenvolver como ciÃncia. As razÃes Ãbvias para isso sÃo a beleza de formas externas de algumas estruturas de domÃnios, assim como as evidentes e desafiantes relaÃÃes de simetria entre os seus constituintes. Os domÃnios ferroelÃsticos sÃo um dos importantes tipos de domÃnios apresentados por cristais. Tais domÃnios apresentam, algumas vezes, dimensÃes muito reduzidas sem manifestar uma considerÃvel alteraÃÃo na estrutura topogrÃfica da amostra. Por outro lado, o comportamento Ãtico de domÃnios distintos pode ser bem diferente quando sujeitos a uma mesma condiÃÃo de medida. Tais caracterÃsticas tornam esta classe de materiais ideais para um estudo baseado na microscopia de campo prÃximo em modo de iluminaÃÃo e contato. Imagens de domÃnios ferroelÃsticos, utilizando microscopia de campo prÃximo em modo de iluminaÃÃo e contato, foram obtidas com resoluÃÃo nanomÃtrica. Tais imagens, em geral, apresentaram pouquÃssima relaÃÃo com a estrutura topogrÃfica do material, revelando importantes caracterÃsticas Ãticas (ocorrÃncia do efeito de guias de onda nos domÃnios) e estruturais (dimensÃes dos domÃnios ferroelÃsticos, presenÃa de defeitos de deslocamento na rede cristalina). / A significant part of the nowadays scientific research is based on the synthesis, characterization and application of the nanostructured materials. In order to make possible a further understanding of the intriguing properties of these materials, many techniques with nanometric and even subnanometric resolution have been created during the last 50 years and are passing through a process of continuous improvement. In spite of the great scientific and technical development on the available instrumentation, the optical characterization with nanometric resolution of these materials remains a challenge for researchers from all over the world. In this context, techniques based on near field radiation have emerged as a great alternative for the diffraction limit break which is a nature imposed limit for conventional optical instruments. Besides this, contact near field microscopy in illumination mode acquires optical and topographical information of the material simultaneously. This capability permits the distinction between the real and topographic induced nanometric optical features. The domain phenomenon in crystals has been a subject of interest for crystallographers since crystallography started to develop as a scientific branch. The obvious reasons are the beauty of some domain patterns as well as evident and challenging symmetry relations between their constituents. The ferroelastic domains are one of the important kinds of domains presented by crystals. They have, sometimes, very small dimensions without inducing any topographic element on the sample. On the other side the optical behavior of different domains under almost the same measurement condition may be very dissimilar. Such characteristics make then an ideal class of materials for contact near field microscopy in illumination mode based studies. Ferroelastic domains images, using near-field optical microscopy in illumination and contact mode, were obtained with a nanometric resolution. Such images, in general, presented very little relation with the topographical structure of the material, revealing optical and structural features such as occurrence of the waveguide effect in the domains, domainÂs dimensions and presence of dislocations on the crystalline structure.  

Distributed MIMO (DMIMO) communications and specifically the idea of distributed transmit beamforming involves multiple transmitters coordinating among themselves to form a virtual antenna array and steer a beam to one or more receivers. Recent works have successfully demonstrated this concept of beamforming with narrowband, frequency-flat wireless channels. We consider the generalization of this concept to wideband, frequency selective channels and propose two Figures of Merit (FOMs), namely, communication capacity and received power to measure the performance of beamforming. We formulate the precoder design that maximizes the two FOMs as optimization problems and derive general properties of the optimal precoders. The two metrics are equivalent with frequency-flat channels, whereas, they result in vastly different optimal criteria with wideband channels. The capacity maximizing solution also differs from classical water-filling due to the per-transmitter power constraints of the distributed beamforming setting, whereas, the power maximizing solution involves the array nodes concentrating their power in a small, finite set of frequencies resulting in an overall received signal consisting of a small number of sinusoidal tones. We have not been able to derive closed-form solutions for the optimal precoders, but we provide fixed point algorithms that efficiently computes these precoders numerically. We show using simulations that solution to both these maximization problems can yield substantially better performance as compared to simple alternatives such as equal power allocation. The fixed point algorithms also suggest a distributed implementation where each node can compute these precoders on their own iteratively using feedback from a cooperating receiver. We also establish the relationship between various precoders. The idea of maximizing received power suggests a natural application of wireless power transfer(WPT). However, the large-scale propagation losses associated with radiative fields makes antennas unattractive for WPT systems. Motivated by this observation, we also consider the problem of optimizing the efficiency of WPT to a receiver coil from multiple transmitters using near-field coupling. This idea of WPT using near-field coupling is not new; however, the difficulty of constructing tractable and realistic circuit models has limited the ability to accurately predicting and optimizing the performance of these systems. We present a new simple theoretical model and take the more abstract approach of modeling the WPT system as a linear circuit whose input-output relationship is expressed in terms of a small number of unknown parameters. We present a simple derivation of the optimal voltage excitations to be applied at the transmitters to maximize efficiency, and also some general properties of the optimal solution. Obviously, the optimal solution is a function of unknown parameters, and we describe a procedure to estimate these parameters using a set of direct measurements. We also present a series of experimental results, first, with two transmitter coils and a receiver coil in a variety of configurations and then with four transmitter coils and two receiver coils to illustrate our approach and the efficiency increase achieved by using the calculated optimal solution from our model.

The contrast mechanism in Kerr imaging is the apparent angle through which the plane of polarization is rotated upon reflection from a magnetic surface. This can be calculated for a well characterized surface given the polarization state of the incident light. As in traditional optical microscopy, the spatial resolution is limited by diffraction to roughly half the wavelength of the illumination light. The diffraction limit can be circumvented through the use of near-field scanning optical microscopy, in which the illumination source is an evanescent field at the tip of a tapered optical fiber. A novel probe design for near-field optical imaging in reflection mode will be proposed, and experimental work on the development of a near-field Kerr microscope performed up to this point will be presented. The complication in merging these two techniques arises from the complex polarization profile of the evanescent field. This profile can be characterized for a given probe geometry with the use of electromagnetic field modeling software, allowing for subsequent modeling of the polarization profile of the optical response. An algorithm for predicting the optical response to a near-field probe tip from a generalized multilayer thin-film is presented.

Traditional light microscopy suffers from the diffraction limit, which limits the spatial resolution to λ/2. The current trend in optical microscopy is the development of techniques to bypass the diffraction limit. Resolutions below 40 nm will make it possible to probe biological systems by imaging the interactions between single molecules and cell membranes. These resolutions will allow for the development of improved drug delivery mechanisms by increasing our understanding of how chemical communication within a cell occurs. The materials sciences would also benefit from these high resolutions. Nanomaterials can be analyzed with Raman spectroscopy for molecular and atomic bond information, or with fluorescence response to determine bulk optical properties with tens of nanometer resolution. Near-field optical microscopy is one of the current techniques, which allows for imaging at resolutions beyond the diffraction limit. Using a combination of a shear force microscope (SFM) and an inverted optical microscope, spectroscopic resolutions below 20 nm have been demonstrated. One technique, in particular, has been named tip enhanced near-field optical microscopy (TENOM). The key to this technique is the use of solid metal probes, which are illuminated in the far field by the excitation wavelength of interest. These probes are custom-designed using finite difference time domain (FDTD) modeling techniques, then fabricated with the use of a focused ion beam (FIB) microscope. The measure of the quality of probe design is based directly on the field enhancement obtainable. The greater the field enhancement of the probe, the more the ratio of near-field to far-field background contribution will increase. The elimination of the far-field signal by a decrease of illumination power will provide the best signal-to-noise ratio in the near-field images. Furthermore, a design that facilitates the delocalization of the near-field imaging from the far-field will be beneficial. Developed is a novel microscope design that employs two-photon non-linear excitation to allow the imaging of the fluorescence from almost any visible fluorophore at resolutions below 30 nm without changing filters or excitation wavelength. The ability of the microscope to image samples at atmospheric pressure, room temperature, and in solution makes it a very promising tool for the biological and materials science communities. The microscope demonstrates the ability to image topographical, optical, and electronic state information for single-molecule identification. A single computer, simple custom control circuits, field programmable gate array (FPGA) data acquisition, and a simplified custom optical system controls the microscope are thoroughly outlined and documented. This versatility enables the end user to custom-design experiments from confocal far-field single molecule imaging to high resolution scanning probe microscopy imaging. Presented are the current capabilities of the microscope, most importantly, high-resolution near-field images of J-aggregates with PIC dye. Single molecules of Rhodamine 6G dye and quantum dots imaged in the far-field are presented to demonstrate the sensitivity of the microscope. A comparison is made with the use of a mode-locked 50 fs pulsed laser source verses a continuous wave laser source on single molecules and J-aggregates in the near-field and far-field. Integration of an intensified CCD camera with a high-resolution monochromator allows for spectral information about the sample. The system will be disseminated as an open system design.

L'étude des émissions rayonnées d'une source dans tout l'espace, est essentielle pour l'analyse dosimétriques et l’analyse des interférences électromagnétiques. L'importance du dernier augmentent en raison de la nécessité d'avoir une prédiction de la fiabilité des circuits électroniques. De plus, l'utilisation quotidienne des dispositifs et des systèmes émettant des champs électromagnétiques radiofréquences ne cesse d'augmenter. Certains de ces dispositifs fonctionnent à proximité du corps humain, et les opérateurs se trouvent dans la région des champs proches de la source rayonnante, et ils sont exposés à des niveaux de champs électromagnétiques pouvant être élevés. Pour cette raison, l'analyse dosimétrique, qui passe par une cartographie tridimensionnelle (3D) au voisinage de la source rayonnante, doit être effectuée. Pour ce type d'applications, plusieurs scans des champs proches doivent être effectués dans différents plans afin de construire la cartographie de champs 3D. Étant un processus difficile dans les études de compatibilité électromagnétique, la caractérisation en champ proche est traitée par plusieurs algorithmes qui proposent différentes approches pour réaliser le scanning requis au voisinage de la source rayonnante.Dans ce travail, nous introduisons un système de scanning 3D avec des sondes de champ magnétique à trois axes à faible coût. Le fait de disposer de telles sondes permet la mesure simultanée des trois composantes du champ magnétique sur la base d'un seul scan au voisinage du dispositif testé. Les sondes conçues se composent de trois boucles orthogonales combinées ensemble; la première sonde contient trois boucles conventionnelles réunies dans un cube en plastique d'une dimension totale de 10 × 12 × 13 mm3, tandis que la deuxième sonde est une sonde PCB imprimée sur un substrat FR4 de 3,2 mm avec une dimension réduite de 9 × 9 × 3,2 mm3. Les sondes conçues ont été étalonnées avec une cellule TEM et les facteurs d'antenne correspondants ont été extraits. Le système de scanning présenté utilise comme un instrument de mesure un oscilloscope RF- 4 canaux, qui donne la possibilité de mesurer à la fois dans le domaine temporel et dans le domaine fréquentiel.La deuxième partie de cette thèse présente un algorithme de reconstruction basé sur la méthode du spectre d'ondes planes. Afin de réduire le nombre des scans et donc les exigences de temps, l'algorithme présenté nécessite juste un scan en champ proche 2D des composantes de champ, pour reconstruire la distribution du champ magnétique 3D au-dessus du dispositif rayonnant.La troisième partie de la thèse est consacrée à l'analyse dosimétrique des champs électromagnétiques rayonnés à proximité des systèmes RFID et des machines de soudage RF. L'évaluation de l'exposition en champ proche des champs rayonnés des antennes de lecture RFID, fonctionnant à 13,56 MHz et utilisées dans les bibliothèques, a été réalisée. Les mesures du champ magnétique près de l'antenne ont été établies à l'aide des sondes conçues. Les résultats sont ensuite analysés et comparés aux réglementations des normes européennes et des lignes directrices de l'ICNIRP. En outre, l'exposition aux champs électromagnétiques RF des travailleurs à proximité de machines de soudage RF dans un environnement industriel est étudiée. Ces machines, fonctionnant à 27 MHz, émettent de forts rayonnements et l'exposition a eu lieu dans la région de champ proche. La distribution spatiale des champs électromagnétiques dans cette région est étudiée à la fois dans des simulations numériques et des mesures réelles. / The analysis of radiated emissions from a source throughout the space, is very essential for both dosimetric and electromagnetic interference analysis. The concerns about the latter are growing because of the need to have prediction of the system reliability of the electronic circuits. Moreover the everyday use of devices and systems emitting radio frequency electromagnetic fields is continuously increasing. Some of these devices are operating in the vicinity of human body, and operators are in the near-field region of the radiating source, and they are exposed to electromagnetic fields. For this reason, dosimetric analysis, that shows the necessity of having three dimensional (3D) field mapping in the vicinity of the radiating source, should be performed. For this kind of applications, several scans of the near fields should be done within different planes in order to build the 3D field mapping. Being a challenging process in electromagnetic compatibility studies, near field characterization is being treated by several algorithms that propose different approaches to achieve the required scanning on the radiating source.In this work, we introduce a 3D scanning system with a low cost three axis magnetic field probes. Having such probes allow the simultaneous measure of the three components of the magnetic field based on a single planner scan above the device under test. The designed probes consist of three orthogonal loops combined together; the first probe contains three conventional loops joined in a plastic cube with a total dimension of 10×12×13 mm3, whereas the second probe is a PCB probe printed on an FR4 substrate of 3.2 mm with a reduced dimension of 9×9×3.2 mm3. The designed probes were calibrated with a TEM cell and the corresponding antenna factors were extracted. The presented scanning system uses an oscilloscope as a measuring instrument that gives the possibility of both time and frequency domain measurements. The second part of this thesis presents a reconstruction algorithm based on plane wave spectrum method. In order to reduce the number of scans and hence the time requirements, the presented algorithm requires just a 2D near field scan of the field components, to reconstruct the 3D magnetic field distribution above the radiating device.The third part of the thesis is devoted for the dosimetric analysis of the radiated electromagnetic fields near RFID systems and RF-welding machines. The near-field exposure assessment of the radiated fields from RFID reader antennas operating at 13.56 MHz and used in Libraries was performed. The measurements of the magnetic field near the antenna were established using the designed probes. The results are then analyzed and compared to the regulations in European Directives and ICNIRP Guidelines. Moreover, the exposure to RF electromagnetic fields of workers near RF-welding machines in industrial environment is studied. These machines, operating at 27 MHz, emit strong radiation and the exposure takes place in the near-field region. The spatial distribution of the electromagnetic fields in this region is studied in both numerical simulations and measurements.

In recent years, optical near-field has received an ever-increasing attention owing to its ability to localise optical signals beyond the diffraction limit. Optical near-field is a non-propagating field existing in the close vicinity of a matter within a range less than the wavelength of the illumination light and it carries the high spatial frequency information showing the fine details of the matter. An optical near-field can be generated by a near-field optical microscope with a nano-aperture or a metal-coated fibre tip. However, common difficulties associated with this approach, such as a fragile probe, a low throughput and signal-to-noise ratio, and a slow response of gap controlling between the probe and the sample, make it less applicable. Alternatively, optical near-field can be produced by total internal reflection (TIR) occurring at the interface of a prism, which is capable of localising the electromagnetic (EM) field in the close vicinity of the interface. However, in this geometry, no confinement of the field can be achieved in the transverse direction, whereas, in most applications such as optical trapping, micro-fabrication and optical data storage, a transverse confinement of the light field is essential. In order to achieve a transverse confinement of the light field, maintaining the high spatial resolution of the optical near-field, and at the same time eliminating the drawbacks associated with the conventional near-field optical microscope, a novel near-field probe based on a high numerical aperture (NA) TIR objective combined with annular illumination has been developed recently. In this arrangement, an obstruction disk is inserted at the back aperture of the objective to block the light with a convergence angle lower than the critical angle determined by the refractive indices of the two media, resulting in a pure focused evanescent field in the second medium. The evanescent field produced by this method provides a useful tool for studying light-matter interaction at the single molecule level not only because of its high resolution but also due to its inherent merits such as no distance regulation, no heating effect and simple experimental setup. But, the most significant advantage that makes this method unique and superior to the other approaches in terms of producing the optical near-field is that it allows the dynamic control of the focal field by simply modulating the phase or amplitude or even the polarisation state of the incident beam before it enters the objective so that complex illumination beams can be generated, whereas in other fibre probe based approaches this goal is extremely difficult to achieve. To make use of such a novel near-field probe, a thorough theoretical and experimental investigation is required. A complete knowledge of the focused evanescent field is a prerequisite for a wide range of applications including single molecule detection, Raman spectroscopy, near-field non-linear imaging and near-field trapping. Therefore, it is not only necessary but also urgent to exploit the focusing properties of a focused evanescent field under complex field illumination both experimentally and theoretically and this is the major aim of this thesis. The complex fields, which are of particular interest in this thesis, are the radially polarised beam and the Laguerre-Gaussian (LG) beam, because the former owns a more compact circularly symmetric field distribution in the focal region when focused by a high NA objective, while the latter is capable of rotating a trapped particle by transferring the orbital angular momentum. Combining them with the focused evanescent field is potentially able to induce novel functions in the near-field region, which cannot be fulfilled by other near-field approaches. In this thesis, in order to generate these two types of beams, a single liquid crystal spatial light modulator (LCSLM) is employed to produce useful phase modulation to the incident beam. Experimental characterisation of an evanescent focal spot is performed with scanning near-field optical microscopy (SNOM), which is capable of providing the direct mapping of the focused evanescent field not only because of its high spatial resolution and its ability to detect the near-field and far-field signals simultaneously, but also due to the motion of the piezzo-stage enables a three-dimensional characterisation of the evanescent focal spot. In this thesis, a SNOM system with an aluminum coated aperture probe is implemented. The field distributions at both the interface and parallel planes with a small distance away from the interface are obtained. To verify the applicability of SNOM as a characterisation methodology, the field distribution in the focal region of a high NA objective illuminated by a linearly polarised plane wave is measured first. A focus splitting along the direction of incident polarisation is observed threedimensionally near the interface under such a circumstance. It has been demonstrated that the depolarisation effect plays an important role in determining the coupling behaviour of the light into the fibre probe of SNOM. The good match between the experimental results and theoretical predications confirms the validity of SNOM. Theoretical investigation of a tightly focused radially polarised beam is undertaken based on the vectorial-Debye diffraction theory because under the tight focusing of a high NA objective, the vectorial nature of the highly localised field has to be carefully considered in order to represent the field distribution accurately. The calculations on the focusing properties of a radially polarised beam suggest that the longitudinal field component in the focal region plays a dominant role in determining the overall field distribution. Direct measurement of the focused evanescent radially polarised beam in a three-dimensional manner near the interface is performed with SNOM. A highly localised focal spot is achieved in the close vicinity of the coverglass. The measured intensity distributions from SNOM show that correction of the focal spot deformation associated with a linearly polarised beam is achieved by taking advantage of the radially symmetric focal spot of a radially polarised beam. A smaller focal spot is acquired due to the dominant longitudinal polarisation component in the focal region, which possesses a more compact focal intensity distribution than that of the overall field. The experimental results demonstrate a good agreement with the theoretical expectations. The fact that a radially polarised beam is capable of eliminating the focus deformation often presented in the focal region of a high NA objective when a linearly polarised beam is employed can be very useful in many applications, including microfabrication using two-photon photopolymerisation technique. The theoretical study on the two-photon point spread function (PSF) of a radially polarised beam indicates that the focus elongation and splitting associated with a linearly polarised beam are eliminated and the achievable lateral size of the focal spot is approximately a quarter of the illumination wavelength, which is less than half of that under the illumination of a linearly polarised beam. A further reductiont of the lateral size can be expected by using annular radial beam illumination. The investigation on the focusing properties of LG beams has also been one of the major tasks of this thesis. Theoretical investigations of a focused evanescent LG beam suggest that the phase shift induced by the boundary effect when a light beam passes the interface satisfying TIR condition plays a vital role in determining the overall shape of the total field distribution. A severe focal intensity deformation is predicted theoretically in the case of focused evanescent LG beam illumination, which might involve new physical phenomena when applied in the near-field trapping. Such a focal intensity deformation is evidenced experimentally by the direct mapping result obtained from the SNOM probe. A quantitative cross-section comparison with the theoretical predication is conducted, which demonstrates a good agreement. To achieve a controllable optical trap and rotation in the near-field region, complex optical fields such as LG beams carrying orbital angular momentum, have been induced for the manipulation of a polystyrene particle. The influence of the focal intensity deformation on a near-field trapping has been thoroughly investigated. Rotation motion of the particle is examined by mapping the two-dimensional (2D) transverse trapping efficiency of the particle. Theoretical investigation reveals that a significant tangential force component is generated on the particle when it is illuminated by a focused evanescent LG beam. Such findings may prove useful in introducing a rotation mechanism in near-field trapping. The research investigations and methodologies described in this thesis provide a new approach to characterise the near-field focal spot under complex field illumination. It enhances the understanding of the novel near-field probe, thus opening the pathway for numerous near-field applications including optical trapping, two-photon excitation (photopolymerisation) and spectroscopy. The focal field rotation phenomena demonstrated in this thesis may prove particularly beneficial in introducing a rotation mechanism in near-field trapping using a focused evanescent field.

In the last decade, design and application of negative materials have been one of the most interesting subjects in the electromagnetic research. The extraordinary properties of double negative (DNG) and single negative (SNG) materials have been studied extensively over this period. In this thesis, one of the unusual properties of negative materials, the evanescent amplification, is used to improve the sensitivity of the near field probes. The effect of placing DNG and SNG layers between the near field probes and the targets are investigated theoretically. A sensitivity definition is introduced for evanescent probes and it is shown using quantitative measures that the sensitivity can be increased using DNG and SNG materials for a target in vacuum and for a buried target. The electromagnetic loss of the negative materials and the mismatch between the material properties of the host medium and DNG and SNG materials are studied. Using an unmatched DNG layer or SNG layer enhances the sensitivity within an evanescent spectrum range while a lossless and matched DNG layer improves the sensitivity of entire evanescent spectrum. The idea of using negative materials is implemented over conventional near field probes by numerical experiments. Sensitivities of open-ended waveguides and open-ended coaxial lines for a specific application are studied in the presence of negative materials. In the case of precursor pitting detection on airplane bodies, the sensitivity of an open-ended waveguide probe is increased by 35 times for a λ/10 sized cubic crack. It is also shown that the negative material increases the quality of the image generated by the probe. The sensitivity improvement is also verified for an open-ended coaxial line. A 11 times improvement is achieved for a similar detection practice, with a λ/20 sized crack. The effect of coaxial line size and the dielectric material on the sensitivity enhancement are studied. The improvement is studied theoretically and numerically for an electrically small dipole. Theoretical studies show that when a small dipole is placed within a spherical shell made of DNG materials, the antenna parameters of the dipole becomes more sensitive to the position of a target placed outside the negative material shell. The field distribution generated by a small dipole in a multilayered spherical medium is studied for this purpose. Numerical analysis of a small dipole placed next to a planar DNG layer is presented. The DNG layer increases the sensitivity of the dipole due to a λ/30 sized metallic target by 5.5 times. To provide experimental verification, the sensitivity of an electrically small loop is studied. SNG materials with a negative permeability around 1.25 GHz are designed using modified split ring resonators (MSRR). By using the effective parameters of the designed structure, a sensitivity improvement of 10 times is achieved numerically. The improvement is verified using fabricated MSRR structures. The sensitivity of the small loop is enhanced by 9 times for a λ/12.2 sized metallic target. The sensitivity improvements are achieved within the frequency band where the MSRR structures behave as a μ-negative SNG material.

In the last decade, design and application of negative materials have been one of the most interesting subjects in the electromagnetic research. The extraordinary properties of double negative (DNG) and single negative (SNG) materials have been studied extensively over this period. In this thesis, one of the unusual properties of negative materials, the evanescent amplification, is used to improve the sensitivity of the near field probes. The effect of placing DNG and SNG layers between the near field probes and the targets are investigated theoretically. A sensitivity definition is introduced for evanescent probes and it is shown using quantitative measures that the sensitivity can be increased using DNG and SNG materials for a target in vacuum and for a buried target. The electromagnetic loss of the negative materials and the mismatch between the material properties of the host medium and DNG and SNG materials are studied. Using an unmatched DNG layer or SNG layer enhances the sensitivity within an evanescent spectrum range while a lossless and matched DNG layer improves the sensitivity of entire evanescent spectrum. The idea of using negative materials is implemented over conventional near field probes by numerical experiments. Sensitivities of open-ended waveguides and open-ended coaxial lines for a specific application are studied in the presence of negative materials. In the case of precursor pitting detection on airplane bodies, the sensitivity of an open-ended waveguide probe is increased by 35 times for a λ/10 sized cubic crack. It is also shown that the negative material increases the quality of the image generated by the probe. The sensitivity improvement is also verified for an open-ended coaxial line. A 11 times improvement is achieved for a similar detection practice, with a λ/20 sized crack. The effect of coaxial line size and the dielectric material on the sensitivity enhancement are studied. The improvement is studied theoretically and numerically for an electrically small dipole. Theoretical studies show that when a small dipole is placed within a spherical shell made of DNG materials, the antenna parameters of the dipole becomes more sensitive to the position of a target placed outside the negative material shell. The field distribution generated by a small dipole in a multilayered spherical medium is studied for this purpose. Numerical analysis of a small dipole placed next to a planar DNG layer is presented. The DNG layer increases the sensitivity of the dipole due to a λ/30 sized metallic target by 5.5 times. To provide experimental verification, the sensitivity of an electrically small loop is studied. SNG materials with a negative permeability around 1.25 GHz are designed using modified split ring resonators (MSRR). By using the effective parameters of the designed structure, a sensitivity improvement of 10 times is achieved numerically. The improvement is verified using fabricated MSRR structures. The sensitivity of the small loop is enhanced by 9 times for a λ/12.2 sized metallic target. The sensitivity improvements are achieved within the frequency band where the MSRR structures behave as a μ-negative SNG material.

<p>The electromagnetic properties of various plasmonic nanostructures are investigated. These nanostructures, which include random clusters, controlled clusters and particle-film hybrids are applied to surface-enhanced Raman scattering (SERS). A variety of techniques are utilized to fabricate, characterize, and model these SERS-active structures, including nanoparticle functionalization, thin film deposition, extinction spectroscopy, elastic scattering spectroscopy, Raman scattering spectroscopy, single-assembly scattering spectroscopy, transmission electron microscopy, generalized Mie theory, and finite element method. </p><p>Initially, the generalized Mie theory is applied to calculate the near-field of the small random clusters to explain their SERS signal distribution. The nonlinear trend of SERS intensity versus size of clusters is demonstrated in experiments and near-field simulations. </p><p>Subsequently, controlled nanoparticle clusters are fabricated for quantitative SERS. A 50 nm gold nanoparticle and 20nm gold nanoparticles are tethered to form several hot spots between them. The SERS signal from this assembly is compared with SERS signals from single particles and the relative intensities are found to be consistent with intensity ratios predicted by near-field calculation.</p><p>Finally, the nanoparticle/film hybrid structure is studied. The scattering properties and SERS activity are observed from gold nanoparticles on different substrates. The gold nanoparticle on gold film demonstrates high field enhancement. Raman blinking is observed and implies a single molecule signal. Furthermore, the doughnut shape of Raman images indicates that this hybrid structure serves as nano-antenna and modifies the direction of molecular emission. </p><p>In additional to the primary gap dipole utilized for SERS, high order modes supported by the nanoparticle/film hybrid also are investigated. In experiments, the HO mode show less symmetry compared to the gap dipole mode. The simulation indicates that the HO modes observed may be comprised of two gap modes. One is quadrupole-like and the other is dipole-like in terms of near-field profile. The analytical treatment of the coupled dipole is performed to mimic the imaging of the quadrupole radiation.</p> / Dissertation