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Diffusion metamaterials [1] [2] are a subset of the metamaterial family, which primarily comprises thermal metamaterials, particle diffusion metamaterials, and plasma diffusion metamaterials. Currently, thermal metamaterials play a pivotal role within the realm of diffusion metamaterials. The applications of diffusion metamaterials span various fields, including heat management, chemical sensing, and plasma control, offering capabilities that surpass those of traditional materials and devices.
In 1968, Veselago introduced the concept of negative refractive index. [3] Subsequently, John Pendry recognized the potential of using artificial microstructures to achieve unconventional electromagnetic properties. He conducted pioneering research involving metal wire arrays [4] and split ring structures. [5] His groundbreaking contributions [4] [5] ignited a surge of interest in the field of electromagnetic or optical metamaterials. Researchers began to focus on manipulating transverse waves through metamaterials, a concept governed by Maxwell's equations, which serve as wave equations.
In 2000, Ping Sheng unveiled the phenomenon of local resonance in sonic materials, [6] which possess longitudinal wave properties. This discovery expanded the horizons of metamaterial research to encompass other wave systems. This extension included control equations such as the acoustic wave equation and elastic wave equation.
In 2008, Ji-Ping Huang extended the application of metamaterials to thermal diffusion systems. [7] His initial research focused on steady-state heat conduction equations. Using transformation theory, he introduced the concept of thermal cloaking. [7] In 2013, the application of metamaterials was further extended to particle diffusion systems, with the first proposal of particle diffusion cloaking under low diffusivity conditions. [8] Subsequently, in 2022, metamaterials were applied to plasma diffusion systems, [9] where transformation theory was used to design functional devices capable of showcasing several novel phenomena, including cloaking.
Contemporary researchers can categorize the realm of metamaterials into three primary branches, [1] each defined by its governing equations: electromagnetic and optical wave metamaterials which involve Maxwell's equations for transverse waves; other wave metamaterials which involve various wave equations for longitudinal and transverse waves; and diffusion metamaterials which involve the diffusion processes described by diffusion equations. [1] [10] In diffusion metamaterials, which are designed to control a variety of diffusion behaviors, the key measurement is the diffusion length. This metric varies over time yet remains unaffected by frequency changes. On the other hand, wave metamaterials, engineered to alter different modes of wave travel, rely on the wavelength of incoming waves as their critical dimension. This value is constant over time but shifts with frequency. Essentially, the fundamental metric for diffusion metamaterials is distinctly different from that of wave metamaterials, revealing a relationship of complementarity between them.
It denotes a theoretical methodology that links spatial geometric structural parameters with physical properties such as thermal conductivity. This is achieved through the application of coordinate transformations between two separate spatial domains. [7] Its roots can be traced back to the realm of transformation optics, originally conceived for wave systems. [11]
Diffusion metamaterials can be crafted by explicitly solving the relevant diffusion equations while considering suitable boundary conditions, such as thermal conduction equations. [12] [13]
Prominent examples of effective medium theories include the Maxwell-Garnett theory [14] [15] and the Bruggeman theory. [16]
This method is proposed based on the cancellation of relevant physical quantities, such as temperature disturbances. [12] [13]
This method relies on various types of phase transitions and can be employed to craft diffusion metamaterials featuring novel properties, such as a zero-energy-consumption thermostat [17] and thermal meta-terrace. [18]
It encompasses finite element simulations, [19] machine learning, [20] topology optimization, [21] particle swarm optimization, [22] and similar techniques. [23]
In accordance with the definition, metamaterials must possess a characteristic length. For example, electromagnetic or optical metamaterials employ incident wavelengths as their characteristic lengths, and their structural elements are (significantly) smaller in size compared to these characteristic lengths. This design principle enables us to gain insights into the unique properties of these artificially engineered materials through the lens of effective medium theory. [1]
Similarly, diffusion metamaterials possess analogous characteristic length scales. [1] Taking thermal metamaterials as an example, the characteristic length for conductive thermal metamaterials is the thermal diffusion length. [24] Convective thermal metamaterials are characterized by the migration length of the fluid, while radiative thermal metamaterials hinge on the wavelength of thermal radiation.
Diffusion metamaterials have found multiple practical applications. In the field of thermal metamaterials, the thermal cloak structure has been utilized for providing infrared thermal protection in underground shelters. [25] Designs of thermal metamaterials have been used in managing heat in electronic devices, [26] and films with radiative cooling have been used in commercial applications. [27]
In mathematics and physics, a soliton is a nonlinear, self-reinforcing, localized wave packet that is strongly stable, in that it preserves its shape while propagating freely, at constant velocity, and recovers it even after collisions with other such localized wave packets. Its remarkable stability can be traced to a balanced cancellation of nonlinear and dispersive effects in the medium. Solitons were subsequently found to provide stable solutions of a wide class of weakly nonlinear dispersive partial differential equations describing physical systems.
A metamaterial is a type of material engineered to have a property that is rarely observed in naturally occurring materials. They are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. These materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, size, orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.
Negative refraction is the electromagnetic phenomenon where light rays become refracted at an interface that is opposite to their more commonly observed positive refractive properties. Negative refraction can be obtained by using a metamaterial which has been designed to achieve a negative value for (electric) permittivity (ε) and (magnetic) permeability (μ); in such cases the material can be assigned a negative refractive index. Such materials are sometimes called "double negative" materials.
Sir John Brian Pendry, is an English theoretical physicist known for his research into refractive indices and creation of the first practical "Invisibility Cloak". He is a professor of theoretical solid state physics at Imperial College London where he was head of the department of physics (1998–2001) and principal of the faculty of physical sciences (2001–2002). He is an honorary fellow of Downing College, Cambridge, and an IEEE fellow. He received the Kavli Prize in Nanoscience "for transformative contributions to the field of nano-optics that have broken long-held beliefs about the limitations of the resolution limits of optical microscopy and imaging.", together with Stefan Hell, and Thomas Ebbesen, in 2014.
The soliton hypothesis in neuroscience is a model that claims to explain how action potentials are initiated and conducted along axons based on a thermodynamic theory of nerve pulse propagation. It proposes that the signals travel along the cell's membrane in the form of certain kinds of solitary sound pulses that can be modeled as solitons. The model is proposed as an alternative to the Hodgkin–Huxley model in which action potentials: voltage-gated ion channels in the membrane open and allow sodium ions to enter the cell. The resulting decrease in membrane potential opens nearby voltage-gated sodium channels, thus propagating the action potential. The transmembrane potential is restored by delayed opening of potassium channels. Soliton hypothesis proponents assert that energy is mainly conserved during propagation except dissipation losses; Measured temperature changes are completely inconsistent with the Hodgkin-Huxley model.
The Hartman effect describes how the delay time for a quantum tunneling particle is independent of the thickness of the opaque barrier. It is named after Thomas Hartman, who discovered it in 1962.
The Fermi–Ulam model (FUM) is a dynamical system that was introduced by Polish mathematician Stanislaw Ulam in 1961.
Relativistic heat conduction refers to the modelling of heat conduction in a way compatible with special relativity. In special relativity, the usual heat equation for non-relativistic heat conduction must be modified, as it leads to faster-than-light signal propagation. Relativistic heat conduction, therefore, encompasses a set of models for heat propagation in continuous media that are consistent with relativistic causality, namely the principle that an effect must be within the light-cone associated to its cause. Any reasonable relativistic model for heat conduction must also be stable, in the sense that differences in temperature propagate both slower than light and are damped over time.
An acoustic metamaterial, sonic crystal, or phononic crystal is a material designed to control, direct, and manipulate sound waves or phonons in gases, liquids, and solids. Sound wave control is accomplished through manipulating parameters such as the bulk modulus β, density ρ, and chirality. They can be engineered to either transmit, or trap and amplify sound waves at certain frequencies. In the latter case, the material is an acoustic resonator.
A photonic metamaterial (PM), also known as an optical metamaterial, is a type of electromagnetic metamaterial, that interacts with light, covering terahertz (THz), infrared (IR) or visible wavelengths. The materials employ a periodic, cellular structure.
A seismic metamaterial, is a metamaterial that is designed to counteract the adverse effects of seismic waves on artificial structures, which exist on or near the surface of the Earth. Current designs of seismic metamaterials utilize configurations of boreholes, trees or proposed underground resonators to act as a large scale material. Experiments have observed both reflections and bandgap attenuation from artificially induced seismic waves. These are the first experiments to verify that seismic metamaterials can be measured for frequencies below 100 Hz, where damage from Rayleigh waves is the most harmful to artificial structures.
The term chiral describes an object, especially a molecule, which has or produces a non-superposable mirror image of itself. In chemistry, such a molecule is called an enantiomer or is said to exhibit chirality or enantiomerism. The term "chiral" comes from the Greek word for the human hand, which itself exhibits such non-superimposeability of the left hand precisely over the right. Due to the opposition of the fingers and thumbs, no matter how the two hands are oriented, it is impossible for both hands to exactly coincide. Helices, chiral characteristics (properties), chiral media, order, and symmetry all relate to the concept of left- and right-handedness.
A metamaterial absorber is a type of metamaterial intended to efficiently absorb electromagnetic radiation such as light. Furthermore, metamaterials are an advance in materials science. Hence, those metamaterials that are designed to be absorbers offer benefits over conventional absorbers such as further miniaturization, wider adaptability, and increased effectiveness. Intended applications for the metamaterial absorber include emitters, photodetectors, sensors, spatial light modulators, infrared camouflage, wireless communication, and use in solar photovoltaics and thermophotovoltaics.
Theories of cloaking discusses various theories based on science and research, for producing an electromagnetic cloaking device. Theories presented employ transformation optics, event cloaking, dipolar scattering cancellation, tunneling light transmittance, sensors and active sources, and acoustic cloaking.
Mechanical metamaterials are rationally designed artificial materials/structures of precision geometrical arrangements leading to unusual physical and mechanical properties. These unprecedented properties are often derived from their unique internal structures rather than the materials from which they are made. Inspiration for mechanical metamaterials design often comes from biological materials, from molecular and crystalline unit cell structures as well as the artistic fields of origami and kirigami. While early mechanical metamaterials had regular repeats of simple unit cell structures, increasingly complex units and architectures are now being explored. Mechanical metamaterials can be seen as a counterpart to the rather well-known family of optical metamaterials and electromagnetic metamaterials. Mechanical properties, including elasticity, viscoelasticity, and thermoelasticity, are central to the design of mechanical metamaterials. They are often also referred to as elastic metamaterials or elastodynamic metamaterials. Their mechanical properties can be designed to have values that cannot be found in nature, such as negative stiffness, negative Poisson’s ratio, negative compressibility, and vanishing shear modulus.
Dyakonov surface waves (DSWs) are surface electromagnetic waves that travel along the interface in between an isotropic and an uniaxial-birefringent medium. They were theoretically predicted in 1988 by the Russian physicist Mikhail Dyakonov. Unlike other types of acoustic and electromagnetic surface waves, the DSW's existence is due to the difference in symmetry of materials forming the interface. He considered the interface between an isotropic transmitting medium and an anisotropic uniaxial crystal, and showed that under certain conditions waves localized at the interface should exist. Later, similar waves were predicted to exist at the interface between two identical uniaxial crystals with different orientations. The previously known electromagnetic surface waves, surface plasmons and surface plasmon polaritons, exist under the condition that the permittivity of one of the materials forming the interface is negative, while the other one is positive. In contrast, the DSW can propagate when both materials are transparent; hence they are virtually lossless, which is their most fascinating property.
Suresh Kumar Bhatia is an Indian-born chemical engineer and professor emeritus at the School of Chemical Engineering, University of Queensland. He is known for his studies on porous media and catalytic and non-catalytic solid fluid reactions. He was awarded an ARC Australian Professorial Fellowship (2010–15) and is an elected fellow of the Indian Academy of Sciences (1993), and the Australian Academy of Technological Sciences and Engineering (2010). In 1993, the Council of Scientific and Industrial Research, the Indian government's peak agency for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, for his contributions to the engineering sciences.
Quantum Trajectory Theory (QTT) is a formulation of quantum mechanics used for simulating open quantum systems, quantum dissipation and single quantum systems. It was developed by Howard Carmichael in the early 1990s around the same time as the similar formulation, known as the quantum jump method or Monte Carlo wave function (MCWF) method, developed by Dalibard, Castin and Mølmer. Other contemporaneous works on wave-function-based Monte Carlo approaches to open quantum systems include those of Dum, Zoller and Ritsch, and Hegerfeldt and Wilser.
Anatoliy Hlibovych Zahorodniy is a Ukrainian theoretical physicist and an organizer of science; an academician of NANU, Vice President (2011-2020) and President of the National Academy of Sciences of Ukraine. Director of Nikolay Bogolyubov Institute of Theoretical Physics of the NAS of Ukraine. Doctor of Physical and Mathematical Sciences (1990), Professor (1998), Laureate of the State Prize of Ukraine in Science and Technology (2005), Honored Worker of Science and Technology of Ukraine (2012). He has been a Member of the National Security and Defense Council of Ukraine.
Ji-Ping Huang is a Chinese theoretical physicist known for his invention of the concept of diffusion metamaterials.
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