Epsilon-Near-Zero Metamaterials

This Element introduces the exotic wave phenomena arising from the extremely small optical refractive index, and sheds light on the underlying mechanisms, with a primary focus on the basic concepts and fundamental wave physics. The authors reveal the exciting applications of ENZ metamaterials, which have profound impacts over a wide range of fields of science and technology. The sections are organized as follows: in Section 2, the authors demonstrate the extraordinary wave properties in ENZ metamaterials, analyzing the unique wave dynamics and the resulting effects. Section 3 is dedicated to introducing various realization methods of the ENZ metamaterials with periodic and non-periodic styles. The applications of ENZ metamaterials are discussed in Sections 4 and 5, from the perspectives of microwave engineering, optics, and quantum physics. The authors close in Section 6 by presenting an outlook on the development of ENZ metamaterials and discussing the key challenges addressed in future works.

Exploiting space-time duality in the synthesis of impedance transformers via temporal metamaterials

Multisection quarter-wave impedance transformers are widely applied in microwave engineering and optics to attain impedance-matching networks and antireflection coatings. These structures are mostly designed in the spatial domain (time harmonic) by using geometries of different materials. Here, we exploit such concepts in the time domain by using time-varying metamaterials. We derive a formal analogy between the spectral responses of these structures and their temporal analogs, i.e., time-varying stepped refractive-index profiles. We show that such space-time duality grants access to the vast arsenal of synthesis approaches available in microwave engineering and optics. This allows, for instance, the synthesis of temporal impedance transformers for broadband impedance matching with maximally flat or equi-ripple responses, which extend and generalize the recently proposed quarter-wave design as an antireflection temporal coating. Our results, validated via full-wave numerical simulations, provide new insights and deeper understanding of the wave dynamics in time-varying media, and may find important applications in space-time metastructures for broadband frequency conversion and analog signal processing.

Measurement of the Dielectric Constant and Loss Tangent of Polyester / Walnut Shells by the Cavity Perturbation Method at the Microwave X-band Frequencies

In this paper, the cavity perturbation method was used to measure the dielectric properties of materials that are important for understanding the response to microwave waves, in terms of the ability of these materials to store energy and dissipate it as heat, respectively. Compounds (polyester / walnut shells) were prepared, and for different weight concentrations of walnut shells (WS) additive, the proportions ranged between (0% - 25%). The used cavity is rectangular in shape with a theoretically resonance frequency of around (9.9978 GHz) and exiting the dominant mode (TE101). The study shows the highest values of each dielectric constant with a weight concentration (25%) of the walnut shells, and the loss tangent without any material change to the sample. These compounds have been found to be useful in applications of electromagnetic materials such as microwave engineering and protection from biological influences when exposed to the field of microwaves, which is why it is very important to test their dielectric properties.

Alternative derivations for the fields inside a waveguide

Generally, the longitudinal magnetic field of the transverse electric (TE) wave inside a waveguide is obtained by solving the corresponding Helmholtz wave equation, which further leads to the derivation of the remaining fields. In this paper, we provide an alternative way to obtain this longitudinal magnetic field by making use of one of the Maxwell’s equations instead of directly relying on the Helmholtz wave equation. The longitudinal electric field of the transverse magnetic (TM) wave inside a waveguide can also be derived in a similar fashion. These derivations, which are different from those found in the introductory textbooks on microwave engineering, make the study of waveguides more interesting.

Metamaterials and their applications: An overview

Metamaterials are man-made substances with unique spatial alternations in their constituent components. They are widely used in modifying elastic, acoustic, or electromagnetic properties of materials. Metamaterials induce low/high-frequency band gaps to control wave propagations with different wavelengths and are also frequently applied in microwave engineering, waveguides, dispersion compensation, smart antennas, and lenses. For instance, permittivity and permeability of the metamaterials can take positive or negative values. Due to smaller single-cell dimensions than their wavelength, the selective frequency of surface-based metamaterials is used for waveguiding. The need for adjustable bandgaps can also lead to a plethora of research into metamaterials’ tunability for structures that operate at different speeds. In this article, recent studies in the field of metamaterials and their applications are reviewed. The piezoelectric metamaterials and the electromagnetic metamaterials are introduced that is followed by a review of new types of chiral metamaterials. Additionally, absorber, nonlinear, terahertz, tunable, photonic, selective surface-based frequency in acoustic metamaterials are comparedand some remarks on tuning bandgaps methods in locally resonant metamaterials are provided.

The Design of Virtual Laboratories in Microwave Engineering Education

The transformation of physical laboratory to virtual laboratory is necessary for distance learning, especially during the pandemic. The educators face challenges when designing and developing virtual laboratories. Therefore, this chapter aimed to present the implementation of virtual laboratories in microwave engineering education, which can be a reference for the educators. The first section introduces microwave, microwave engineering course, and laboratory experiments in the course. The following section reviews and presents the technological tools for the design and development of virtual laboratories. Furthermore, three examples of virtual experiments are discussed based on their design, pedagogical approach, virtual tools, and laboratory manual. The last part discusses the benefits, challenges, and future direction of virtual laboratories in microwave engineering education.