Educational open source kit for the evaluation of acoustic leaky wave antennas with metamaterials.

There is a growing interest in the field of acoustic metamaterials. These materials use periodic structures to exhibit properties not usually found in nature, such as negative mass or negative compressibility. The physics supporting these devices might seem counterintuitive at first, necessitating additional educational resources in this area. A leaky wave antenna (LWA) is a good example of a practical device that can be implemented as a standard material and a metamaterial. As the latter, the device extends its operational range, linking concepts related to both versions. This work presents an experimental open source kit designed for teaching the basic notions, including a computational routine for testing its analytical performance. The kit shown in this work has interchangeable units to experiment with several configurations (slit, axisymmetric, periodic hole, and membrane based metamaterial) and parameters of the antenna's design. The kit provides an opportunity to get hands-on experience on the real-life performance of LWAs, thanks to the use of low-cost materials, minimal equipment, and the practical nature of the antenna.

Resonant gratings with an etch-stop layer and a fabrication-error tolerant design.

Sub-wavelength gratings (SWG) have shown much promise for applications such as lightweight high bandwidth reflectors, polarising filters and focusing lenses. Unfortunately, grating performance may be rapidly degraded through variability in grating dimensions. We demonstrate, in particular, how an error in depth of etch can be detrimental to the performance of zero contrast grating reflectors. We mitigate the impact of this fabrication error through the introduction of an etch stop layer and in so doing we experimentally realise a high bandwidth reflector based on this modified structure. Another common fabrication error is variation in the duty-cycle of fabricated gratings. This duty-cycle variation can weaken grating performance, however we demonstrate that grating designs that exhibit tolerance to duty-cycle fluctuation can be identified through simulation. Finally, we discuss the impact of lateral etching and the resulting sidewall concavity. We present our approach for numerically predicting the spectral response from such a grating and also for convenience we outline an approach for quickly approximating grating performance. Good agreement is observed between these numerical predictions and measurements made on a HCG with concave sidewalls.

Realization of high-contrast gratings operating at 10 µm.

We present a new material pairing that can be used to realize high-contrast gratings at wavelengths of 10 µm and greater. Using only optical lithography, the material pair solves the absorption issue limiting the popular Si/SiO2 pairing from operation above 6 µm. We describe the obstacles that exist with the currently used grating materials for this wavelength range and outline why our chosen materials overcome this obstacle. We numerically demonstrate that gratings utilizing these materials are capable of wideband high reflectivity. We experimentally show that the spectral response of gratings that are fabricated using such a process show good agreement with theoretically predicted performance.

Magneto-optical circulator designed for operation in a uniform external magnetic field.

We propose an approach for the design of resonant cavities employed in magnetophotonic crystal (MPC) circulators and isolators. Starting from the analysis of a model circularly symmetric cavity, we show how to obtain a significant splitting of the eigenfrequencies of the two counterrotating cavity modes without introducing subdomains magnetized in opposite directions. Using the multiple-scattering method extended to handle uniaxial gyrotropic materials, we demonstrate numerically an MPC circulator working in a uniform external magnetic field.