Metamaterials are amongst the advanced materials made up initially with metal structures. However, there is a huge ongoing work on dielectric metasurfaces and metamaterials with the aim of replacing metal structures with dielectric ones in order to reduce the electromagnetic losses.
1. Introduction to Metamaterials
Metamaterials are amongst the advanced materials made up initially with metal structures. However, there is a huge ongoing work on dielectric metasurfaces and metamaterials with the aim of replacing metal structures with dielectric ones in order to reduce the electromagnetic losses.
Metamaterials’ physical properties rely mostly on their structures. In 1968, Veselago
[1] explored materials of negative permittivity and permeability. Such characteristics though are not present in naturally found materials and can only be generated in metamaterials. During the electromagnetic wave transmission such as wave propagation, the effects generated by metamaterials can be clearly observed. Evolution of the topic of metamaterials with time is presented in
Figure 1. From an applications point of view, metamaterials could be used in devices such as antennas
[2], photonic filters
[3], integrated network sensors
[4] or new superlayers for the microwave and terahertz fields
[5]. The deep understanding of metamaterials offers fullness of novel options ranging from laboratories concepts to practical engineering applications.
Figure 1. Schematic depicting the evolution of the field of metamaterials over the years, from 1968 to nowadays.
The term “metamaterial” comes from the Greek words “meta” and “material”, while “meta” refers to something that is beyond usual, rearranged, changed or innovative. It is an engineered material intended to attain unique properties and capabilities which are absent in natural materials. The term metamaterial is introduced by Walser in 1999
[6]. Metamaterial cannot be obtained from any continuous and homogenous medium, that is why the metamaterials are always of a composite nature. Usually, metamaterials are constructed from discrete resonant micro- and nanometer-scale objects which mimic the electromagnetic reaction of atoms and molecules of natural substances to make them interact with light and other forms of energy in specific controllable ways.
2. Evolution of Metamaterials
In 2019, Vicari et al.
[7] modeled the growth of metamaterial-containing devices across eight different applications (displayed in
Figure 2). The model looked at potential addressable markets based on various parameters including the cost, maturity and performance. It is based on inputs from a wide range of primary and secondary research. Vicari and his team explicitly seized the markets for metamaterial components in communications, sensing and acoustic applications. Many other applications are likely to appear and were grouped together into an “other” category. Market forecast for metamaterials is put at $10.7 billion by 2030. Through 2025, communications uses are by far the leading growth driver; however, by 2030, sensing uses grow to be the largest segment, reaching $5.5 billion compared to $4.4 billion in communications.
Figure 2. Metamaterials market forecast: metamaterial devices are poised to grow to $10.7 billion by 2030 in 5G networks, autonomous vehicles and connected vehicles. Adapted from Ref.
[7].
The origin of metamaterials could be linked to various examples of the pyramid brick wall, Parthenon columns and medieval ruby glass, as shown in
Figure 3. Other “historical” examples of metamaterials are, for instance, the work on the rotation of the polarization plane through artificial twisted structures performed in 1898, and the artificial dielectric structures for microwave antenna lenses achieved in 1945. The modern (formally named) metamaterial was noticeable when Pendry et al.
[8] anticipated that arrays of conducting wire can function with a negative value of effective permittivity at a relatively low frequency (<200 THz), whereas the split ring resonators (SRRs) can be utilized to facilitate a strong magnetic resonance which resulted in an effective permeability negative value. In 2000, by linking both structures and overlapping the negative frequency bands, a metamaterial carrying a negative refraction index was presented for the first time, where the directions of the wave vector and the energy flux, also known as backwards waves, were opposite in a negative index medium. These experiments have proven the predictions of Veselago’s 1968 negative index materials
[1], such as negative refraction, Doppler’s reversed effect and Cherenkov’s reversed radiation
[9].
Figure 3. Examples of some “historical” original metamaterials, adapted from Ref.
[10].