Over time, the accuracy and speed by which a material can be characterized should improve. Today, the Nicolson-Ross-Weir (NRW) methodology represents a well-established method for extracting complex dielectric properties at microwave frequencies, with the use of a modern vector network analyzer. However, as will be seen, this approach suffers from three fundamental limitations to accuracy. Challenging NRW methods requires a methodical and robust investigation. To this end, using a dielectric-filled metal-pipe rectangular waveguide, five independent approaches are employed to accurately characterize the sample at the Fabry-Pérot resonance frequency (non-frequency dispersive modeling). In addition, manual Graphical and automated Renormalization spectroscopic approaches are introduced for the first time in the waveguide. The results from these various modeling strategies are then compared and contrasted to NRW approaches. As a timely exemplar, 3-D printed acrylonitrile-butadiene-styrene (ABS) samples are characterized and the results are compared with existing data available in the open literature. It is found that the various Fabry-Pérot resonance model results all agree with one another and validate the two new spectroscopic approaches; in doing so, exposing three limitations of the NRW methods. It is also shown that extracted dielectric properties for ABS differ from previously reported results and reasons for this are discussed. From measurement noise resilience analysis, a methodology is presented for determining the upper bound signal-to-noise ratio for the vector network analyzer (not normally associated with such instrumentation). Finally, fused deposition modeling (FDM) 3-D printing can result in a non-homogeneous sample that excites open-box mode resonances. This phenomenon is investigated for the first time analytically and with various modeling strategies.

This paper demonstrates an ultra-light weight microwave rotary vane attenuator (RVA) manufactured using polymer-based 3-D printing. In addition, for the first time, conductive polylactic acid (PLA) is rigorously characterized across both X-and Ku-bands (8 to 18 GHz); while acrylonitrile butadiene-styrene (ABS) has similarly been characterized across Kuband (12 to 18 GHz). Using the results from the conductive PLA characterization process, an electromagnetic model was created for predicting the performance of the RVA. It is shown that, even with its complex internal geometrical features, a mix of both dielectric and conductive PLA building materials, an assembly of multiple parts and a mechanically rotating central section, our experimental proof-of-concept prototype RVA exhibits excellent measured performance across Ku-band. This tunable microwave control device represents a higher-level of functionality for additive manufacturing, when compared to a fixed (i.e., non-movable) 3-D printed structure, opening the way for other groups to routinely 3-D print custom microwave components and subsystems in the not too distant future.

We demonstrate engineering of the low-terahertz range plasmonic spectra of two-dimensional electron systems by modifying their geometry. Specifically, we have modelled, fabricated, and measured two devices for comparison. The first device has a rectangular channel, while the second is trapezoidal, designed to support a richer plasmonic spectrum by causing variation in the device width along the direction of plasmon propagation. We show that while plasmon resonant frequencies and field distributions in the rectangular device can largely be described by a simple onedimensional analytical model, the field distributions modelled in the trapezoidal device shows a more complex pattern with significant variation along the length of the channel, so requiring a two-dimensional treatment. The results illustrate the potential of modifying the channel geometry to obtain different spectra in experiments, with potential applications in the design of novel terahertz-range devices, such as plasmonbased sources and detectors.

Finite difference time-domain (FDTD) technique can be used to model metamaterials by treating them as dispersive material. Drude or Lorentz model can be incorporated into the standard FDTD algorithm for modelling negative permittivity and permeability. FDTD algorithm is readily parallelisable and can take advantage of GPU acceleration to achieve speed-ups of 5x-50x depending on hardware setup. Metamaterial scattering problems are implemented using dispersive FDTD technique on GPU resulting in performance gain of 10x-15x compared to conventional CPU implementation.

While models of terahertz frequency plasmons in 2D electron systems are usually developed by reducing the number of spatial dimensions, fully 3D models may be needed for the design and analysis of realistic structures. Using full-wave electromagnetic simulations, we have analysed the plasmons and magnetoplasmons observed in two recent experiments. Here, we demonstrate agreement between the theoretical and the experimental results, and discuss further device characteristics such as plasmon transmission, reflection, absorption, and field distributions. We then compare the 3D full-wave simulations with a 2D model. Finally, we discuss approaches for increasing signal transmission and reducing reflection, with direct relevance for improving future experiments.