Metamaterials: Characteristics, Process, and Applications

This page covers metamaterial characteristics or features, the metamaterials process, and metamaterials applications such as antennas, sensors, absorbers, etc.

Introduction

Materials possessing properties not found in nature, such as a negative index of refraction (n), are known as metamaterials.

The term is a combination of “meta” and “material,” where “meta” is a Greek word that refers to something beyond or advanced.

These are man-made materials. In other words, they are composite materials with material properties not commonly found in ordinary materials. Metamaterials can be characterized based on Maxwell’s equations.

The following figure depicts the classification of materials based on ε (permittivity) and μ (permeability). Metamaterials are categorized into two main types:

• Resonant metamaterials (e.g., left-handed metamaterials, refractive index less than one)
• Nonresonant metamaterials (e.g., anisotropic metamaterials, hyperbolic metamaterials)

As shown, there are four quadrants:

• First Quadrant: ε > 0, μ > 0 - These are right-handed materials, commonly found. They support forward-propagating waves.
• Second and Fourth Quadrants: ε < 0, μ > 0 - These describe electric plasmas, which support evanescent waves.
• Third Quadrant: ε < 0, μ < 0 - This quadrant represents metamaterials. They are also known as left-handed or double-negative materials.

Metamaterials Process of Realization

The following should be considered in the process of metamaterial realization:

• Finding a material with a negative “n” is very difficult in nature. It can be generated or manufactured by forming an array of metal split rings and rods (i.e., short parallel wires).
• Split-ring resonators produce a permeability μ that is negative, while rods produce a permittivity ε that is also negative.
• The metallic rings and rods dimensions must be smaller compared to one wavelength but larger compared to an atomic dimension to achieve a negative index of refraction.
• It is possible to obtain imaging beyond the diffraction limit of λ/2 as set by Abbe. Sub-wavelength imaging is very difficult to obtain in regular materials. This is because evanescent waves decay exponentially with distance, making them effectively non-existent at the image plane.

Metamaterials Applications

Following are the applications of metamaterials:

• Antennas: Metamaterials can be used in the design of antennas. It helps in cell phone antenna design with five times smaller size with wider bandwidth (700MHz-2.7GHz).
• Absorbers: Metamaterials can act as absorbers.
• Superlenses: Metamaterials can be used to create superlenses.
• Cloaks: Metamaterials can be used for cloaking applications.
• Sensors: Metamaterials can be used as sensors.
• Phase Compensators: Metamaterials can act as phase compensators.