A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Investigation of nanophotonic structures for imaging and sensing(2017) ZHANG, ZHIJIAN; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to image micro/nano scale objectives with miniaturized optical components has always been of great interest due to its great potential in applications such as microscopy, nanofabrication, and biomedical monitoring. However, in traditional practice using dielectric lenses, the focal size is inevitably limited by the Abbe’s diffraction limit (0.51fλ/ρ). Here, λ is the wavelength in vacuum, and f and ρ are the focal length and the radius of the lens, respectively. Moreover, the performance of conventional spherical lenses deteriorates as their sizes approach the wavelength. On the other hand, owing to the recent advances in micro/nano fabrication techniques, miniature sensors have received much attention, which are highly desirable in many sensing applications for physical, chemical, and biomedical parameter measurements. However, the performance of miniature sensors usually suffers from the similar difficulty as miniaturized imaging systems. Recently nanophotonic structures have been explored for the development of miniaturizing imaging and sensing systems due to their capability of confining and manipulating light at a subwavelength scale. In this dissertation work, several different mechanisms that nanophotonic structures can be used to help enhance the performance of imaging and sensing in miniaturized systems are investigated. First, plasmonic lens utilizing the nanophotonic structure to achieve the subwavelength focusing ability is studied. Three different regions in the plasmonic lens design are defined. Furthermore, a plasmonic lens in the Fresnel’s region is designed and k.ed to achieve a sub-diffraction limit focus. Second, radially polarized light generated by the TEM mode in the annular aperture in metal is investigated, which can further enhance the focusing ability. Third, in terms of sensing, an ultra-thin plasmonic interferometer constructed with a nano-hole array is fabricated on a fiber facet. By using this structure, the multi-parameter sensing capability of this interferometer is demonstrated; high sensitivity refractive index and temperature sensing are achieved. Finally, a novel sensor design based on the cladding modes and buffer modes generated by the planar grating on the fiber facet is proposed. Experimental studies of this sensor demonstrate its superior temperature sensitivity and the potential of multi-parameter sensing.Item Electromagnetic Interference Reduction using Electromagnetic Bandgap Structures in Packages, Enclosures, Cavities, and Antennas(2007-11-26) Mohajer Iravani, Baharak; Ramahi, Omar M.; Granatstein, Victor L.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electromagnetic interference (EMI) is a source of noise problems in electronic devices. The EMI is attributed to coupling between sources of radiation and components placed in the same media such as package or chassis. This coupling can be either through conducting currents or through radiation. The radiation of electromagnetic (EM) fields is supported by surface currents. Thus, minimizing these surface currents is considered a major and critical step to suppress EMI. In this work, we present novel strategies to confine surface currents in different applications including packages, enclosures, cavities, and antennas. The efficiency of present methods of EM noise suppression is limited due to different drawbacks. For example, the traditional use of lossy materials and absorbers suffers from considerable disadvantages including mechanical and thermal reliability leading to limited life time, cost, volume, and weight. In this work, we consider the use of Electromagnetic Band Gap (EBG) structures. These structures are suitable for suppressing surface currents within a frequency band denoted as the bandgap. Their design is straight forward, they are inexpensive to implement, and they do not suffer from the limitations of the previous methods. A new method of EM noise suppression in enclosures and cavity-backed antennas using mushroom-type EBG structures is introduced. The effectiveness of the EBG as an EMI suppresser is demonstrated using numerical simulations and experimental measurements. To allow integration of EBGs in printed circuit boards and packages, novel miniaturized simple planar EBG structures based on use of high-k dielectric material (r > 100) are proposed. The design consists of meander lines and patches. The inductive meander lines serve to provide current continuity bridges between the capacitive patches. The high-k dielectric material increases the effective capacitive load substantially in comparison to commonly used material with much lower dielectric constant. Meander lines can increase the effective inductive load which pushes down the lower edge of bandgap, thus resulting in a wider bandgap. Simulation results are included to show that the proposed EBG structures provide very wide bandgap (~10GHz) covering the multiple harmonics of of currently available microprocessors and its harmonics. To speed up the design procedure, a model based on combination of lumped elements and transmission lines is proposed. The derived model predicts accurately the starting edge of bandgap. This result is verified with full-wave analysis. Finally, another novel compact wide band mushroom-type EBG structure using magneto-dielectric materials is designed. Numerical simulations show that the proposed EBG structure provides in-phase reflection bandgap which is several times greater than the one obtained from a conventional EBG operating at the same frequency while its cell size is smaller. This type of EBG structure can be used efficiently as a ground plane for low-profile wideband antennas.