arXiv subjects

Ming Wah Ng

Publications and source records attributed to Ming Wah Ng.

3 recordsLinked to original sources

arXiv2016

Multi-Octave Metamaterial Reflective Half-Wave Plate for Millimetre and Sub-Millimetre wave Applications

The quasi-optical modulation of linear polarization at millimeter and sub-millimeter wavelengths can be achieved by using rotating half wave plates (HWPs) in front of polarization sensitive detectors. Large operational bandwidths are required when the same device is meant to work simultaneously across different frequency bands. Previous realizations of half wave plates, ranging from birefringent multi-plate to mesh-based devices, have achieved bandwidths of the order of 100%. Here we present the design and the experimental characterization of a reflective HWP able to work across bandwidths of the order of 150%. The working principle of the novel device is completely different from any previous realization and it is based on the different phase-shift experienced by two orthogonal polarizations respectively reflecting off an electric conductor and off an artificial magnetic conductor.

astro-ph.IM↗

arXiv2014

W-Band Pancharatnam Half Wave Plate Based on Negative Refractive Index Metamaterials

Electromagnetic metamaterials, made from arrangements of subwavelength sized structures, can be used to manipulate radiation. Designing metamaterials that have a positive refractive index along one axis and a negative refractive index along the orthogonal axis can result in birefringences, $Δn>1$. The effect can be used to create wave plates with subwavelength thicknesses. Previous attempts at making wave plates in this way have resulted in very narrow usable bandwidths. In this paper, we use the Pancharatnam method to increase the usable bandwidth. A combination of Finite Element Method and Transmission Line models were used to optimise the final design. Experimental results are compared to the modelled data.

physics.ins-det↗

arXiv2014

Dog Bone Triplet Metamaterial Wave Plate

Metamaterials are artificially made sub-wavelength structures arranged in periodic arrays. They can be designed to interact with electromagnetic radiation in many different and interesting ways such as allowing radiation to experience a negative refractive index (NRI). We have used this technique to design and build a quasi-optical Half Wave Plate (HWP) that exhibits a large birefringence by virtue of having a positive refractive index in one axis and a NRI in the other. Previous implementations of such NRI-HWP have been narrow band ($\sim$1-3%) due to the inherent reliance on needing a resonance to create the NRI region. We manufacture a W-band prototype of a novel HWP that uses the Pancharatnam method to extend the bandwidth (up to more than twice) of a usual NRI-HWP. Our simulated and experimentally obtained results despite their differences show that a broadening of a flat region of the phase difference is possible even with the initially steep gradient for a single plate.

astro-ph.IM↗