abstract: Near-field thermal radiation occurs when the distance between two surfaces at different temperatures is less than the characteristic wavelength of thermal radiation. While theoretical studies predict that the near-field radiative heat transfer could exceed Planck’s blackbody limit in the far-field by orders of magnitudes depending on the materials and gap distance, experimental measurement of super-Planckian near-field radiative heat flux is extremely challenging in particular at sub-100-nm vacuum gaps and few has been demonstrated. The objective of this thesis is to develop a novel thermal metrology based on AFM bi-material cantilever and experimentally measure near-field thermal radiation. The experiment setup is completed and validated by measuring the near-field radiative heat transfer between a silica microsphere and a silica substrate and comparing with theoretical calculations. The bi-material AFM cantilever made of SiNi and Au bends with temperature changes, whose deflection is monitored by the position-sensitive diode. After careful calibration, the bi-material cantilever works as a thermal sensor, from which the near-field radiative conductance and tip temperature can be deduced when the silica substrate approaches the silica sphere attached to the cantilever by a piezo stage with a resolution of 1 nm from a few micrometers away till physical contact. The developed novel near-field thermal metrology will be used to measure the near-field radiative heat transfer between the silica microsphere and planar SiC surface as well as nanostructured SiC metasurface. This research aims to enhance the fundamental understandings of radiative heat transfer in the near-field which could lead to advances in microelectronics, optical data storage and thermal systems for energy conversion and thermal management. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

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A near-eld generalization of Friis transmission equation has previously been proposed in the literature. Using this generalization, it is possible to calculatethe mutual coupling between two antennas as a weighted integral over the antenna far-fields. In this thesis, a change of variables is used to remove the singularity in the integrand and a normalization of the antenna far-field is suggested to take mismatch and thermal losses into account. The resulting non-singular integral has been implemented in a computer program that can be used to calculate the mutual coupling between two arbitrarily polarized antennas given the antenna far-fields and the geometrical separation between the antennas. The program has several advantages compared to previous programs based on the near-field generalization of Friis transmission equation. Firstly, this program can calculate the mutual coupling between two arbitrarily polarized and oriented antennas whereas previous programs could only be used for linearly polarized and polarization-matched antennas. Secondly, the advantage of the non-singular form is the improved numerical stability. The mutual coupling calculated using this program is demonstrated to agree well with results from full three-dimensional simulations of antennas located in each others near-fields using commercial software. Finally, we investigate for the first time if this integral relation can be used to calculate approximate values of the mutual coupling between antennas on an electrically large vehicle. / En närfältsgeneralisering av Friis transmissionsekvation har tidigare foreslagits i litteraturen. Med denna generalisering kan den ömsesidiga kopplingen mellan två antenner beraknas som en viktad integral over antennernas fjärrfältsamplituder. I denna rapport används ett variabelbyte för att ta bort singulariteten i integranden och en normering av fjärrfaltsamplituden föreslås for att ta hänsyn till antennernas förluster. Den resulterande icke-singulära integralen har implementerats i ett datorprogram som kan användas for att beräkna kopplingenmellan två godtyckligt polariserade antenner givet antennernas fjärrfältsamplituder och geometriska separation. Programmet har flera fördelar jämfört med tidigare program som baserats på närfältsgeneraliseringen av Friis transmissionsekvation. För det första kan detta program anvandas för att beräkna kopplingen mellan två godtyckligt polariserade och orienterade antenner då tidigare program har varit skrivna for linjarpolariserade och polarisationsmatchade antenner. Dessutom uppnås en högre numerisk stabilitet eftersom den ickesingulära formen av integralen används. Det demonstreras i flera exempel att kopplingen som beräknats med detta program för antenner som befinner sig i varandras närfält stämmer väl överens med resultat som beräknats med kommersiell mjukvara. Avslutningsvis undersöks om denna närfältsgeneralisering kan användas for att approximativt beräkna kopplingen mellan två antenner på en elektriskt stor farkost.

In the last two decades, two major earthquakes have occurred in Japan: the 1995 Kobe earthquake and the 2011 Great East Japan earthquake. In the 2011 Great East Japan earthquake, many bridge structures were destroyed by the tsunamis, but it is interesting to study the ground motion induced damage and also how this earthquake differed from the one in 1995. In this thesis, the seismic response of a bridge designed according to the current Japanese Design Specifications was evaluated when it is subjected to near-field ground motions recorded during the 1995 Kobe earthquake and far-field ground motions recorded during the 2011 Great East Japan earthquake. For this purpose, a series of nonlinear dynamic response analysis was conducted and the seismic performance of the bridge was verified in terms of its displacement and ductility demand. It was found from the dynamic response analysis that the seismic response of the target bridge when subjected to the ground motions from the 2011 Great East Japan earthquake was smaller than during the 1995 Kobe earthquake. Although the ground motions from the 2011 Great East Japan earthquake were very strong, they were not as strong as the ground motions from the 1995 Kobe earthquake. The results obtained in this thesis clarify the validity of the Type I and Type II design ground motions. The target bridge used in this thesis was designed according to the post-1990 design specifications and showed limited nonlinear response when subjected to the different ground motions which shows how efficient the enhancement of the seismic performance of bridges has been since the 1990’s.

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Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in the acoustic far field of the ANC system. The experimental results are compared to the theoretical pressure null locations in order to determine the efficacy of the point source model. The results closely matched the point source model with a loudspeaker as the primary source, and the sound power reduction was greatly reduced when error sensors were placed in non-ideal locations. A weakness of the current near-field modeling process is that a point monopole source is used to characterize the acoustic noise from an axial cooling fan, which may have multipole characteristics. A more complete characterization of fan noise may be obtained using a procedure based on the work of Martin and Roure [J. Sound Vib. 201 (5), 577--593 (1997)]. Pressure values are obtained over a hemisphere in the far field of a primary source and the contributions from point source distributions up to the second order, centered at the primary source, may be calculated using a multipole expansion. The source information is then used in the aforementioned theoretical near-field calculation of pressure. The error sensors are positioned using the complete fan characterization. The global far-field attenuation for the multipole expansion model of fan noise is compared to that of previous experiments. Results show that the multipole expansion model yields a more accurate representation the near field, but is not successful in achieving greater sound power reductions in the far field.

Wireless sensor network (WSN) nodes communicate securely using pre-installed cryptographic keys. Although key pre-installation makes nodes less expensive, the technical process of installing keys prevents average users from deploying and controlling their own WSNs. Wireless pairing enables users to set up WSNs without pre-installing keys, but current pairing techniques introduce numerous concerns regarding security, hardware expense, and usability. This thesis introduces dynamic Near Field Communication (NFC) pairing, a new pairing technique designed for WSNs. This pairing overcomes the limitations of both key pre-installation and current pairing techniques. Dynamic NFC pairing is as secure as using pre-installed keys, requires only inexpensive NFC hardware, and is easy to use since the user simply holds nodes close together to add them to a network. A sample application shows the power of dynamic NFC pairing. The user adds sensors and actuators to a WSN by holding each node close to a central node or network coordinator. Data readings stream instantly from each sensor to a web page where the user may view data as well as click buttons to cause events to occur on the actuators. This happens quickly and securely without exposing the user to the complexity of cryptographic keys.

Next generation photonics-based technologies will ultimately rely on novel materials and devices. For this purpose, phenomena at subwavelength scales are being studied to advance both fundamental knowledge and experimental capabilities. In this dissertation, concepts specific to near-field optics and experimental capabilities specific to near-field microscopy are used to investigate various aspects of the statistical properties of random electromagnetic fields in the vicinity of optically inhomogeneous media which emit or scatter radiation. The properties of such fields are being characterized within the frame of the coherence theory. While successful in describing the far-field properties of optical fields, the fundamental results of the conventional coherence theory disregard the contribution of short-range evanescent waves. Nonetheless, the specific features of random fields at subwavelength distances from interfaces of real media are influenced by the presence of evanescent waves because, in this case, both propagating and nonpropagating components contribute to the detectable properties of the radiation. In our studies, we have fully accounted for both contributions and, as a result, different surface and subsurface characteristics of inhomogeneous media could be explored. We investigated different properties of random optical near-fields which exhibit either Gaussian or non-Gaussian statistics. We have demonstrated that characteristics of optical radiation such as first- and second-order statistics of intensity and the spectral density in the vicinity of random media are all determined by both evanescent waves contribution and the statistical properties of the physical interface. For instance, we quantified the subtle differences which exist between the near- and far-field spectra of radiation and we brought the first experimental evidence that, contrary to the predictions of the conventional coherence theory, the values of coherence length in the near field depend on the distance from the interface and, moreover, they can be smaller than the wavelength of light. The results included in this dissertation demonstrate that the statistical properties of the electromagnetic fields which exist in the close proximity of inhomogeneous media can be used to extract structural information. They also suggest the possibility to adjust the coherence properties of the emitted radiation by modifying the statistical properties of the interfaces. Understanding the random interference phenomena in the near-field could also lead to new possibilities for surface and subsurface diagnostics of inhomogeneous media. In addition, controlling the statistical properties of radiation at subwavelength scales should be of paramount importance in the design of miniaturized optical sources, detectors and sensors.

The focus of this dissertation is the study of measuring light not by energy transfer as is done with a standard photodetector such as a photographic film or charged coupled device, but rather by the forces which the light exerts on matter. In this manner we are able to replace or complement standard photodetector-based light detection techniques. One key attribute of force detection is that it permits the measurement of light over a very large range of frequencies including those which are difficult to access with standard photodetectors, such as the far IR and THz. The dissertation addresses the specific phenomena associated with optically induced force (OIF) detection in the near-field where light can be detected with high spatial resolution close to material interfaces. This is accomplished using a scanning probe microscope (SPM), which has the advantage of already having a sensitive force detector integrated into the system. The two microscopies we focus on here are atomic force microscopy (AFM) and nearfield scanning optical microscopy (NSOM). By detecting surface-induced forces or force gradients applied to a very small size probe (~ 20 nm diameter), AFM measures the force acting on the probe as a function of the tip-sample separation or extracts topography information. Typical NSOM utilizes either a small aperture (~ 50 150  nm diameter) to collect and/or radiate light in a small volume or a small scatterer (~ 20 nm diameter) in order to scatter light in a very small volume. This light is then measured with an avalanche photodiode or a photomultiplier tube. These two modalities may be combined in order to simultaneously map the local intensity distribution and topography of a sample of interest. A critical assumption made when performing iv such a measurement is that the distance regulation, which is based on surface induced forces, and the intensity distribution are independent. In other words, it is assumed that the presence of optical fields does not influence the AFM operation. However, it is well known that light exerts forces on the matter with which it interacts. This light-induced force may affect the atomic force microscope tip-sample distance regulation mechanism or, by modifying the tip, it may also indirectly influence the distance between the probe and the surface. This dissertation will present evidence that the effect of optically induced forces is strong enough to be observed when performing typical NSOM measurements. This effect is first studied on common experimental situations to show where and how these forces manifest themselves. Afterward, several new measurement approaches are demonstrated, which take advantage of this additional information to either complement or replace standard NSOM detection. For example, the force acting on the probe can be detected while simultaneously extracting the tip-sample separation, a measurement characteristic which is typically difficult to obtain. Moreover, the standard field collection with an aperture NSOM and the measurement of optically induced forces can be operated simultaneously. Thus, complementary information about the field intensity and its gradient can be, for the first time, collected with a single probe. Finally, a new scanning probe modality, multi-frequency NSOM (MF-NSOM), will be demonstrated. In this approach, the tuning fork is driven electrically at one frequency to perform a standard tip-sample distance regulation to follow the sample topography and optically driven at another frequency to measure the optically induced force. This novel technique provides a viable alternative to standard NSOM scanning and should be of particular interest in the long wavelength regime, e.g. far IR and THz.

PM2.5 variability within the neighborhood scale has not been thoroughly studied for wood burning communities. High variability in near-field PM2.5 concentration may lead to harmful public exposure since monitoring does not occur on that scale. This study measures near-field PM2.5 variability by measuring black carbon (BC), a component of PM2.5, in a 1 km2 area located in Cambria, California. BC and meteorological data (when meteorological instruments were available) were measured over thirteen 12-hour intensive operation periods (IOPs) occurring over the winters of 2009 and 2010. Near-field BC variability was measured to understand the type of exposures found in communities where many homes are burning wood simultaneously within a small area. In addition, relationships between meteorological, geographical, and burning source characteristics and BC were observed as tools for understanding BC concentration. The computer air dispersion modeling programs, ISC-PRIME and ISCST3, were also evaluated for applicability to the near field. BC concentrations were measured using 1- to 2-minute resolution aethalometers and 12 hour resolution Personal Environmental Monitors (PEMs). On average, over all IOPs and sites, aethalometer and PEM BC averages were very similar, ranging between 200 and 250 ng/m3, or 4 and 5 µg/m3 for PM2.5, and standard deviations were often high. Averaging all BC measurements, aethalometer BC standard deviation values were 360 percent of the average BC concentration and PEM BC standard deviations were 120 percent the average BC concentration. The average standard deviation detected during each IOP was 190 percent of the average BC concentration for aethalometers and 79 percent of the average BC concentration for PEMs. The average standard deviation detected at each site was 220 percent of the average BC concentration for aethalometers and 76 percent of the average BC concentration for PEMs. The larger standard deviations measured by higher resolution aethalometers demonstrated that low resolution instruments, such as PEMs, are unable to detect high concentrations that may occur. In addition to examining BC variability, multiple linear regression analyses were conducted to determine the impact of meteorological variables and geographic and burning source characteristics on BC concentration and a weighted BC deviation function (BC standard deviation divided by average BC concentration). Time impacts, humidity, and wind speed, accounted for about 50 percent of variability in aethalometer average BC and BC deviation. However, because all model assumptions were not satisfied, improvements are needed. Regression models based on PEM BC found wind speed and direction to account for about 80 percent of average PEM BC variability and number of burning sources to account for about 30 percent of PEM BC deviation. Although PEM BC models accounted for a high percentage of BC variability, few data points were available for the PEM analyses and more IOPs are needed to determine their accuracy. When evaluating correlations between geographic and burning source characteristics and PEM BC concentrations, specific IOP and PEM sampling location explained almost 70 percent of variability in BC concentration, though model residuals suggested model bias. IOP likely explained variation in burning patterns and meteorology over each night while sampling location was likely a proxy for housing density, tree coverage, and/or elevation. Because all regression model assumptions could not be satisfied, the predictors were also observed graphically. Plotting BC concentration versus the number of burning sources suggested that number of burning sources may affect BC concentration in areas of low tree coverage and high housing density and in the case that the level of surrounding vegetation and structures are minimal. More data points will be needed to determine whether or not these relationships are significant. ISC-PRIME and ISCST3 modeling overall tended to under predict BC concentrations with average modeled-to-measured ratios averaging 0.25 and 0.15, for ISC-PRIME and ISCST3, respectively. Correction factors of 9.75 and 18.2 for ISC-PRIME and ISCST3, respectively, were determined to bring modeled BC concentrations closer to unity, but the range of ratios was still high. Both programs were unable to consistently capture BC variability in the area and more investigation will be needed to improve models. The results of the study indicate high BC variability exists on the near-field scale, but that the variability is not clearly explained by existing regression and air dispersion models. To prevent public exposure to harmful concentrations, more investigation will be needed to determine factors that largely influence pollutant variability on the neighborhood scale.