THESIS
2020
1 online resource (xvi, 87, 7, 7, 5, 7 pages) : illustrations (some color)
Abstract
Hybrid resonances were discovered in acoustics a few years ago. In this thesis, I demonstrate through full waveform simulations the realization of microwave hybrid
resonance by using a simple H-fractal metallic metasurface, with unit cell’s
lateral dimension much subwavelength in size. With an extremely thin back cavity,
the resonances of the copper slits structure at different frequencies can be
hybridized to generate a new mode near the anti-resonance frequency. The oscillator
strength and dissipation of the hybrid resonance can be easily tuned, with
total absorption occurring when the surface impedance matches that of vacuum.
Similar to the acoustic case, the local fields are found to be much larger than the
incident wave amplitude while the surface averaged fields are comparable to...[
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Hybrid resonances were discovered in acoustics a few years ago. In this thesis, I demonstrate through full waveform simulations the realization of microwave hybrid
resonance by using a simple H-fractal metallic metasurface, with unit cell’s
lateral dimension much subwavelength in size. With an extremely thin back cavity,
the resonances of the copper slits structure at different frequencies can be
hybridized to generate a new mode near the anti-resonance frequency. The oscillator
strength and dissipation of the hybrid resonance can be easily tuned, with
total absorption occurring when the surface impedance matches that of vacuum.
Similar to the acoustic case, the local fields are found to be much larger than the
incident wave amplitude while the surface averaged fields are comparable to the
incident fields. The total thickness of the surface is less than the peak absorption
wavelength by two orders of magnitude. In addition, I indicate the existence of
anomalous hybrid resonance, which differs from normal hybrid resonance for its
particular behavior in terms of the inverse of surface impedance under impedance
matching condition.
I present another possible application of hybrid resonance in artificial complementary
boundary conditions, i.e., perfect magnetic conductor (PMC) boundary
condition in electromagnetics and acoustic soft boundary (ASB). Two strategies
are given and verified by simulations for realizing nearly perfect artificial PMC
in microwave, creating a high impedance metasurface with fractal metallic slits
near its resonance frequency and fractal metallic wires near the anti-resonance
frequency. Meanwhile, three types of membrane-based acoustic metamaterials
are proposed to achieve ASB, with their thicknesses as well as lateral dimensions
being one order of magnitude smaller than the relevant ASB occurring
wavelengths. The most interesting thing is that by changing the thickness of
the back cavity only, a perfect electric conductor (PEC) boundary condition can
be changed into an impedance matching condition or even a PMC boundary
condition with exact same metasurface. The boundary condition transitions by
changing the thickness of cavity are also achievable in acoustics.
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