Different procedures are presented for the retrieval of effective constitutive parameters of metamaterial structures realized by multilayer lossless periodic structures. These structures are modeled as Floquet-wave based multiport networks connected by pieces of transmission lines. A generalized Bloch method is then adopted to find the dominant modes of the volumetric homogenized metamaterial. Starting from the results of this analysis, the constitutive tensors of an equivalent homogeneous material are defined. Different levels of equivalence are defined, denoted as “external equivalence,” “dispersion equivalence,” “single-mode equivalence,” and “double-mode equivalence.” The corresponding homogenization processes are characterized by an increasing level of completeness (in the description of the metamaterial behavior) and of sophistication (concerning the processing of the full-wave analysis outcomes). The defined homogenization procedure accounts for dispersion in time (frequency) and space (wavenumber), as well as for anisotropy.

We present a comprehensive analysis of the imaging characteristics of a scanning microwave microscopy (SMM) system operated in the transmission mode. In particular, we use rigorous three-dimensional finite-element simulations to investigate the effect of varying the permittivity and depth of sub-surface constituents of samples, on the scattering parameters of probes made of a metallic nano-tip attached to a cantilever. Our results prove that one can achieve enhanced imaging sensitivity in the transmission mode SMM (TM-SMM) configuration, from twofold to as much as 5× increase, as compared to that attainable in the widely used reflection mode SMM operation. In addition, we demonstrate that the phase of the S₂₁-parameter is much more sensitive to changes of the system parameters as compared to its magnitude, the scattering parameters being affected the most by variations in the conductivity of the substrate. Our analysis is validated by a good qualitative agreement between our modeling results and experimental data. These results suggest that TM-SMM systems can be used as highly efficient imaging tools with new functionalities, findings which could have important implications to the development of improved experimental imaging techniques.

U-shaped microwave resonators implemented by RF MEMS switches can be considered the result of a novel design approach for obtaining small-footprint tunable resonators, owing to the bent shape of the resonator and the microsystem solution for changing the frequency of resonance. In this paper, we discuss the design approach for potential configurations of U-shaped structures combined with ohmic RF MEMS switches. Owing to their prospective application in RADAR and satellite systems, the devices were assessed for K-Band operation, specifically for 15 GHz, 20 GHz, and 26 GHz. The ON-OFF states determined by an electrostatic actuation of metal beams composing the RF MEMS ohmic switches allow for selecting different path lengths corresponding to different frequencies. In this contribution, initial configurations were designed and manufactured as a proof-of-concept. The advantages and critical aspects of the designs are discussed in detail.

In this work, we present the analytical modeling and preliminary experimental results for the choice of the optimal frequencies when performing amplitude and phase measurements with a scanning microwave microscope. In particular, the analysis is related to the reflection mode operation of the instrument, i.e., the acquisition of the complex reflection coefficient data, usually referred as S₁₁. The studied configuration is composed of an atomic force microscope with a microwave matched nanometric cantilever probe tip, connected by a λ/2 coaxial cable resonator to a vector network analyzer. The set-up is provided by Keysight Technologies. As a peculiar result, the optimal frequencies, where the maximum sensitivity is achieved, are different for the amplitude and for the phase signals. The analysis is focused on measurements of dielectric samples, like semiconductor devices, textile pieces, and biological specimens.

In this paper, we present in detail the design, both electromagnetic and mechanical, the fabrication, and the test of the first prototype of a Scanning Microwave Microscope (SMM) suitable for a two-port transmission measurement, recording, and processing the high frequency transmission scattering parameter S₂₁ passing through the investigated sample. The S₂₁ toolbox is composed by a microwave emitter, placed below the sample, which excites an electromagnetic wave passing through the sample under test, and is collected by the cantilever used as the detector, electrically matched for high frequency measurements. This prototype enhances the actual capability of the instrument for a sub-surface imaging at the nanoscale. Moreover, it allows the study of the electromagnetic properties of the material under test obtained through the measurement of the reflection (S₁₁) and transmission (S₂₁) parameters at the same time. The SMM operates between 1 GHz and 20 GHz, current limit for the microwave matching of the cantilever, and the high frequency signal is recorded by means of a two-port Vector Network Analyzer, using both contact and no-contact modes of operation, the latter, especially minded for a fully nondestructive and topography-free characterization. This tool is an upgrade of the already established setup for the reflection mode S₁₁ measurement. Actually, the proposed setup is able to give richer information in terms of scattering parameters, including amplitude and phase measurements, by means of the two-port arrangement.