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Investigation and implementation of Active Willis Metamaterials (AWM) have been done exclusively, in all the available literature, by approaches that do not rely on any solid control theory basis. When coupled with piezoelectric control elements, the available approaches have not included, from the first principles, the exact form of the constitutive relationship of the piezoelectric materials. Furthermore, in all these approaches, stability analysis, robustness, ability to accommodate uncertainty or parameter changes, or consideration of disturbance rejection has not been addressed at all. More importantly, the available formulations have always mixed the flow and effort variables of the AWM, resulting in a form that is totally incompatible for the use in generating, investigating, or even designing any appropriate sensing or control applications of the material. In this paper, the piezoelectric-based AWM is modeled, from the first principles, to develop a constitutive coupling form that enables its use in actuation, sensing, and as an integrated controller that can be analyzed, designed, and optimized using the classical, optimal, and robust control system theories. Lagrange dynamics formulation is used to generate the equations governing the Willis coupling, the piezoelectric coupling, as well as the active robust controller. With this developed controlled-based structure of the AWM, the inherent and powerful capabilities of the AWM that lie in its ability to robustly control the material properties themselves such as the compliance (or stiffness) and specific volume (or density) are demonstrated in great detail via several numerical examples. Controlling these properties enables the AWM to be used in numerous important and imaginative applications such as cloaking, beam shifting, beam focusing, as well as many other applications that are limited only by our imagination. [ABSTRACT FROM AUTHOR]

Transformation elastodynamics can be used to redirect incident waves to mitigate harmful vibrations in the target region. Under the specific Brun–Guenneau–Movchan gauge, the elastic tensor of the transformed domain lacks minor symmetry. Here, we propose a physically realizable seismic cloak composed of lattice-based polar metamaterials capable of exhibiting asymmetric stresses. Both static and dynamic simulations validate the cloaking performance. A metric is calculated to quantify the protective effects, and results demonstrate satisfactory cloaking and aseismic protection across a wide frequency band. [ABSTRACT FROM AUTHOR]

Hiding an isolated object in free space using a transmissive invisibility cloak has become a significant research area, propelled by advancements in metamaterials and transformation optics over the past decade. Despite the availability of various simplified methods for implementing transmissive cloaks, issues such as impedance mismatches and narrow working bandwidths often arise, posing challenges. Achieving a broadband transmissive cloak in free space has proven to be particularly arduous. This study presents a near‐perfect one‐directional broadband transmissive cloak constructed from multilayer metasurfaces of arbitrary shapes, showcasing superior performance across a broadband frequency range. The phase distribution of the metasurfaces and the efficacy of the transmissive cloak are assessed using the generalized Snell's law. An experimental near‐perfect broadband transmissive cloak is successfully demonstrated to operate within the frequency range of 8.5 to 11.2 GHz. This study contributes to reducing the density and mass of cloaks, thereby facilitating the expansion of cloaking capabilities in various directions and across different frequency bands. [ABSTRACT FROM AUTHOR]

Thermal metamaterials are typically achieved by mixing different natural materials to realize effective thermal conductivities (ETCs) that conventional materials do not possess. However, the necessity for multifunctional design of metamaterials, encompassing both thermal and mechanical functionalities, is somewhat overlooked, resulting in the fixation of mechanical properties in thermal metamaterials designed within current research endeavors. Thus far, conventional methods have faced challenges in designing thermal metamaterials with configurable mechanical properties because of intricate inherent relationships among the structural configuration, thermal and mechanical properties in metamaterials. Here, a data‐driven approach is proposed to design a thermal metamaterial capable of seamlessly achieving thermal functionalities and harnessing the advantages of microstructural diversity to configure its mechanical properties. The designed metamaterial possesses thermal cloaking functionality while exhibiting exceptional mechanical properties, such as load‐bearing capacity, shearing strength, and tensile resistance, thereby affording mechanical protection for the thermal metadevice. The proposed approach can generate numerous distinct inverse design candidate topological functional cells (TFCs), designing thermal metamaterials with dramatic improvements in mechanical properties compared to traditional ones, which sets up a novel paradigm for discovering thermal metamaterials with extraordinary mechanical structures. Furthermore, this approach also paves the way for investigating thermal metamaterials with additional physical properties. [ABSTRACT FROM AUTHOR]

Owing to the architected void-filled low-density configurations, metamaterials are prone to defects during the complex manufacturing process, or damages under operational conditions. Recently mechanical cloaking has been proposed to shield the effect of such disorders in terms of homogenized mechanical responses. The major drawback in these studies are that the damage location should be known a priori, and the cloak is designed around that damaged zone before manufacturing. Such postulation does not allow unsupervised damage resilience during the manufacturing and service life of metamaterials by active reconfiguration of the stress field depending on the random and unpredictable evolution of damage. Here, we propose a radically different approach by introducing piezoelectric lattices where the effect of random appearance of any single or multiple disorders and damages with complex shapes, sizes and distributions can be shielded through active multi-physically controlled cloaks by voltage-dependent modulation of the stress fields within the cloaking region. Notably, this can be achieved without breaking periodicity and any additional material in the cloaking region unlike earlier studies concerning mechanical cloaks. The proposed active class of elastic metamaterials will bring a step-change in the on-demand mechanical performance of critically important structural components and unsupervised damage resilience for enhanced durability and sustainability. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

A four level chiral medium is considered to analyze and investigate theoretically the reflection/transmission coefficients of right circularly polarized (RCP) beam and left circularly polarized (LCP) beam as well as their corresponding GH-shifts under the effect of compton scattering. Density matrix formalism is used for calculation of electric and magnetic probe fields coherence. The polarization and magnetization are calculated from probes coherence terms in the chiral medium. The electric and magnetic susceptibilities as well as chiral coefficients are related with polarization and magnetization. The refractive indices of RCP and LCP beams under compton scattering effect is modified from the electric/magnetic susceptibilities, chiral coefficients, mass and charge of electron as well as compton scattering angle. The giant positive and negative birefringent Goos–Hänchen (GH) shifts in reflection and transmission beams are investigated in this manuscript under Compton scattering effect. The RCP and LCP beams obey the normalization condition | R (+ , -) | + | T (+ , -) | = 1 at the interface of a lossy chiral medium of | A (+ , -) | ≃ 0 and a thin sheet of balsa wood under the effect of compton scattering angle, incident angle, probe field detuning, control field Rabi frequency, phases of electric and magnetic fields and phase of superposition states. Significant positive/negative giant GH-shifts in reflection and transmission beams are investigated. The results show potential applications in modification of cloaking devices, image coding, polarizing filters and LCD displays. [ABSTRACT FROM AUTHOR]

Traditional optical transform devices are composed of materials with anisotropic magnetic design, which are difficult to manufacture. Based on the idea of bending waveguide devices, invisibility cloak Device Ⅰ and Ⅱ of isotropic materials are designed. According to the existing conformal coordinate transformation, we have derived the perfect parameters required for the conformal devices. Based on the Maxwell equations and finite edge element method, we give the effects of the designed Device Ⅰ and Ⅱ through perfect parameters. In addition, we use the layered idea to design conformal devices and give relevant numerical results to make their manufacturing possible. [ABSTRACT FROM AUTHOR]

• A multifunctional mechanical model with both amplified illusion and cloaking properties is proposed. • The amplified function can make a small object to produce the same displacement distribution as a large object. • Intelligent control system with the detective and control functions is introduced. • Effectively broaden the effective frequency range of structure in 3300Hz×4400 Hz and 1200Hz×3100 Hz. • The cloaking characteristics of the structure are verified through theoretical, numerical and experimental analysis. Illusion device can make an object to produce a field distribution different from its own, offering potential applications in diverse fields. In this work, we propose a multifunctional metamaterial with intelligent control systems, which exhibits amplified illusion and cloaking characteristics for detecting or hiding objects over different frequency ranges. The amplification function allows a small object to generate the same displacement distribution as a larger object, while the cloaking function renders an object invisible and undetectable. Simulation and experimental results demonstrate the exceptional amplification and cloaking properties of the multifunctional configuration. In contrast to single-function structures like cloaking and focusing, which can only fulfill a specific function, designing a multifunctional structure capable of achieving two or more properties within a single configuration presents a significant challenge. [ABSTRACT FROM AUTHOR]

A four-level atomic medium driven by probe and control fields is used to control and modify linear and nonlinear absorption and gain. The normal and anomalous dispersions as well as group index are also controlled by the strength and parameters of driving fields. The angular momentum l of the redefined Rabi frequencies of the control fields intensify the number of absorption and gain peaks according to 2 l 2 condition. Normal dispersion is observed in the region of gain while anomalous dispersion is noted in the region of absorption. The negative group index is studied in the anomalous dispersive region and the positive group index is associated with the normal dispersion region. The normal/anomalous dispersive region and positive/negative group index region also increased by the angular momentum l of the control fields according to 2 l 2 formula. A positive group index of 1000 is calculated, which reduces the group velocity to 3 × 10 5 m/s . An approximate negative group index of - 1000 is calculated, demonstrating superluminality of the group velocity at - 1 / 3 × 10 5 m/s . The modified results of the current study are useful for speeding up computer chips and time cloak technology. [ABSTRACT FROM AUTHOR]

Static and dynamic metamaterials have been extensively studied for their ability to manipulate different physical fields and directed to broad applications. Because the governing equations of heat transfer consist of nonlinear terms with conservation of mass, momentum and energy, the equations can exhibit elliptical, parabolic, hyperbolic and hybrid configurations under different transfer modes. Such multi-mode transfer characteristics intrinsically make thermal metamaterials distinguish themselves from other metamaterials with unique static and dynamic manipulation mechanisms. Therefore, numerous studies have emerged that use the transformation theory and other methods to control static thermal metamaterials. It leads to the development of thermal cloaks, thermal concentrators, thermal diodes, and so on. Originating from the static style, the manipulation of heat transfer has expanded to dynamic systems in recent years. The introduction of hydrodynamics in metamaterial design leads to numerous novel physics effects, such as dynamic cloaking, zero-drag characteristics, topological heat transfer, nonreciprocal diffusion, and non-Hermitian physics. Moreover, the dynamic thermal metamaterials allow accurate control at both time and space dimensions, leading to exciting applications such as adjustable, reconfigurable, and intelligent thermal meta-devices. However, few studies have systematically analyzed thermal metamaterials from the perspective of static and dynamic manipulation. In this review, we aim at clarifying the connection and distinction of static and dynamic manipulation from the scopes of principle, application, and physical effects. We start with the development of static thermal metamaterials and its application. Subsequently, the development of dynamic thermal metamaterials is presented both in fundamental theory and application. Finally, we summarize the research directions and prospect future research challenges for static and dynamic thermal metamaterials. [ABSTRACT FROM AUTHOR]

Reciprocal scatterers necessarily extinguish the same amount of incoming power when excited from opposite directions. This property implies that it is not possible to realize scatterers that are transparent when excited from one direction but that scatter and absorb light for the opposite excitation, limiting opportunities in the context of asymmetric imaging and nanophotonic circuits. This reciprocity constraint may be overcome with an external bias that breaks time-reversal symmetry, posing however challenges in terms of practical implementations and integration. Here, we explore the use of tailored nonlinearities combined with geometric asymmetries in suitably tailored resonant nanoantennas. We demonstrate that, under suitable design conditions, a nonlinear scatterer can be cloaked for one excitation direction, yet strongly scatters when excited at the same frequency and intensity from the opposite direction. This nonreciprocal scattering phenomenon opens opportunities for nonlinear nanophotonics, asymmetric imaging and visibility, all-optical signal processing and directional sensing. [ABSTRACT FROM AUTHOR]

Transformation optics (TO) provides a powerful tool to manipulate electromagnetic waves, enabling the design of invisibility cloaks, which can render objects invisible. Despite many years of research, however, invisibility cloaks experimentally realized thus far can only operate at a single frequency. The narrow bandwidth significantly restricts the practical applications of invisibility cloaks and other TO devices. Here, a general design strategy is proposed to realize a multiband anisotropic metamaterial characterized by two principal permittivity components, i.e., one infinite and the other spatially gradient. Through a proper transformation and combination of such metamaterials, an omnidirectional invisibility cloak is experimentally implemented, which is impedance‐matched to free space at multiple frequencies. Both far‐field numerical simulations and near‐field experimental mappings confirm that this cloak can successfully suppress scattering from multiple large‐scale objects simultaneously at 5 and 10 GHz. The design strategy and corresponding practical realization bring multiband transformation optical devices one step closer to reality. [ABSTRACT FROM AUTHOR]

When an electromagnetic wave is incident onto an object, the scattering from the object leads to its exposure. An invisibility cloak can bend the electromagnetic wave around the object with phase velocities exceeding the light speed in free space, which seems only possible over a narrow bandwidth, as manifested in the existing approaches, such as transformation optics and scattering cancellation. Here, it is experimentally demonstrated that this bandwidth limitation can be overcome by strategically positioning objects at topological nodes, characterized by minimal electromagnetic field amplitudes and indeterminate phases. This is accomplished using all‐dielectric photonic crystal slabs, which are engineered to exhibit a pair of topological nodes at fixed planes across an extensive bandwidth. This bandwidth expansion is facilitated not by resonance, but by the enforcement of mirror and time‐reversal symmetry. These findings thus introduce a novel topological paradigm for the broadband invisibility devices. [ABSTRACT FROM AUTHOR]

Recently, Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals present tremendous potential in optical applications such as Q-switches and invisible robotic devices because they possess high electro-optic properties and perfect transparency simultaneously. However, due to the difficulties in testing and sample preparation, the nonlinear optical properties of PMN-PT single crystals have not been reported yet, which poses a bottleneck for exploring its nonlinear application. In this work, a large second-order nonlinear coefficient (d31 ∼ 77.9 pm V−1) of single domain PMN-0.39PT single crystal has been revealed, which is times times higher than the maximum nonlinear coefficient of commercial LiNbO3 single crystal (d33 = 25.4 pm V−1). The complete set of nonlinear coefficients of the sample has been determined by second harmonic generation microscopy. This work presents the promising nonlinear optical property in PMN-PT single crystals and opens a door for designing high-performance nonlinear optical devices. [ABSTRACT FROM AUTHOR]

Droplet encapsulations using liquid or solid shells are of significant interest in microreactors, drug delivery, crystallization, and cell growth applications. Despite progress in droplet-related technologies, tuning micron-scale shell thickness over a large range of droplet sizes is still a major challenge. In this work, we report capillary force assisted cloaking using hydrophobic colloidal particles and liquid-infused surfaces. The technique produces uniform solid and liquid shell encapsulations over a broad range (5–200 μm shell thickness for droplet volume spanning over four orders of magnitude). Tunable liquid encapsulation is shown to reduce the evaporation rate of droplets by up to 200 times with a wide tunability in lifetime (1.5 h to 12 days). Further, we propose using the technique for single crystals and cell/spheroid culture platforms. Stimuli-responsive solid shells show hermetic encapsulation with tunable strength and dissolution time. Moreover, scalability, and versatility of the technique is demonstrated for on-chip applications. Encapsulated liquids are important for several microreactor applications, including (bio)chemistry in confined spaces. Here, the authors report on oil-infused particle shells that allow control of shell thickness, stability, and permeability for applications in crystal growth and cell cultivation. [ABSTRACT FROM AUTHOR]

Skin diseases are a thorny and worrying matter, due to the special nature of the diseases and their similarity in the distinctive features of each disease. This makes doctors face difficulty in arriving at the correct diagnosis. There are two ways to determine the type of skin disease: the surgical method, which is a painful and expensive method and requires special preparations, and the second method is a non-invasive imaging the lesion at an acceptable magnification rate that preserves the important features of the disease and applies one of the diagnostic rules. The non-invasive skin scanning method, which makes it possible to detect microscopically small features that are invisible to the unaided eyes is optical imaging of skin disorders. For efficiently recognizing physical structure and Stages of development of skin disease and its response to therapy, non-invasive, and less painful scanning methods, such as confocal laser microscopy (CLM), multi-photon microscopy (MP), Raman microscopy (RM), photo-acoustic microscopy (PAM), optical coherence microscopy (OCT), and dermatoscopy (DMY), have been enhanced and implemented for skin scanning. Optical imaging is a type of skin surface imaging that offers precise visualization of skin features. The DMY is a non-intrusive human body tool for evaluating skin disorders. The device is portable and auto-illumination, which imaging skin structure that is often invisible to the naked eye. DMY produces digital images and records for re-examination for later use. There are 3-types of DMYs, traditional non-polarized light contact DMY (TNPC), polarized light contact DMY (PC), and polarized light contactless DMY (PCS). TNPC-DMY needs to touch the covered skin with an interfacing liquid. PC provides better penetration than TNPC and interfacing liquid is not required. OCT is a light-reflecting imaging system. It produces direct scanning with a resolution of around 10 µm plus a depth into the skin of up to 2*10−3 m, without needing to print or store. It has been utilized frequently in numerous disorders as well as skin scanning. The technology produces efficient visualization of changes in normal skin tissue. OCT results and histological structure show significant agreement in studies of skin tumors, and inflammatory disorders. OCT is available in a variety of designs, including time-variants (TV-OCT), Fourier-domain (FD-OCT), line field confocal (LC-OCT), spectral domain (SD-OCT), and high-resolution (HR-OCT). Therefore, this study, presents an overview of fundamental concept, design, for many various types of each technique, evaluation, and weaknesses according to practical tests and searches. This is very useful for researchers in the field of skin diseases detection, particularly in the field of automated diagnosis by artificial intelligence where the researcher is intimately familiar with the stages of development of diagnostic mechanisms and how traditional methods have contributed development in computer aided diagnosis. The two majors widely used optical imaging methods for skin are dermatoscopy and OCT, which are improving dermatoscopy diagnostic efficacy by five to thirty percent. The outcomes of this research are summarized in the next points, mentioned techniques rely on the kind of lesion being examined and the dermatologist's skill. Low resolution and a lack of optical sectioning capabilities are two drawbacks of optical imaging techniques, which lead to a restricted degree of diagnostic accuracy. [ABSTRACT FROM AUTHOR]

Transformation optics applied to low frequency magnetic systems have been recently implemented to design magnetic field concentrators and cloaks with superior performance. Although this achievement has been amply demonstrated theoretically and experimentally in bulk 3D macrostructures, the performance of these devices at low dimensions remains an open question. In this work, we numerically investigate the non-monotonic evolution of the gain of a magnetic metamaterial field concentrator as the axial dimension is progressively shrunk. In particular, we show that in planar structures, the role played by the diamagnetic components becomes negligible, whereas the paramagnetic elements increase their magnetic field channeling efficiency. This is further demonstrated experimentally by tracking the gain of superconductor-ferromagnet concentrators through the superconducting transition. Interestingly, for thicknesses where the diamagnetic petals play an important role in the concentration gain, they also help to reduce the stray field of the concentrator, thus limiting the perturbation of the external field (invisibility). Our findings establish a roadmap and set clear geometrical limits for designing low dimensional magnetic field concentrators. [ABSTRACT FROM AUTHOR]

Left-handed materials are known to exhibit exotic properties in controlling electromagnetic fields, with direct applications in negative reflection and refraction, conformal optical mapping, and electromagnetic cloaking. While typical left-handed materials are constructed periodic metal-dielectric structures, the same effect can be obtained in composite guest–host systems with no periodicity or structural order. Such systems are typically described by the effective-medium approach, in which the components of the electric permittivity tensor are determined as a function of individual material properties and doping concentration. In this paper, we extend the discussion on the mixing rules to include left-handed composite systems and highlight the exotic properties arising from the effective-medium approach in this framework in terms of effective values and dispersion properties. [ABSTRACT FROM AUTHOR]

Non-visual auditory camouflage plays a major role in the art of underwater deception. In this work, a hybrid active/semi-active omnidirectional cloaking shell structure composed of alternate complementary piezoelectric and smart viscoelastic (PZT/SVE) actuator layers is proposed that can effectively conceal a three dimensional underwater macroscopic object from broadband incident sound waves. The smart hybrid structure incorporates a finite sequence of fully active parallel-connected multimorph PZT constraining layers inter-stacked with semi-active SVE core layers both of which are collaboratively operative in the framework of a Particle Swarm Optimized (PSO) multiple-input multiple-output active damping control (MIMO-ADC) scheme. The elasto-acoustic modeling of the problem is conducted by coupling the spatial state space methodology based on the classical three-dimensional exact piezoelasticity theory with the wave equations for the inner and outer acoustic domains. The acoustic cloaking performance of proposed configuration is evaluated for four distinct classes of highly functional SVE interlayer materials with tunable (field-dependent) rheological properties, namely, magnetorheological elastomer (MRE), shape memory polymer (SMP), electrorheological fluid (ERF), and magnetorheological shear thickening polishing fluid (MRSTPF). Extensive numerical results reveal significant broadband reductions of the far-field backscattering amplitude in the ( f ∞ θ = π , k ex R ex ) as well as the percentage error of external cloaked field (% Err) by incorporating a sufficient number of smart multimorph PZT/SVE material layers. Furthermore, it is concluded that comparable low frequency acoustic cloaking effects is possible without expenditure of any external energy just by employing the entirely inactive MRSTPF-based cloak as an alternative to the semiactive or fully active multimorph PZT/SVE cloaks. The outcome of proposed study can advantageously serve as the first step towards practical development and experimental implementation of future high performance smart acoustic cloaking devices with expanded broadband near-perfect omnidirectional invisibility for three dimensional objects of diverse geometries. [ABSTRACT FROM AUTHOR]

Metamaterials are artificial materials with properties depending mainly on their designed structures instead of their materials. Pentamode metamaterials are one type of metamaterial. They have solid structures with fluid-like properties, which can only withstand compressive stresses, not shear stresses. Two-dimensional pentamode metamaterials are easier to manufacture than three-dimensional models, so they have received wide attention. In this review, the properties, manufacturing, and applications of two-dimensional pentamode metamaterials will be discussed. Their water-like properties are their most important properties, and their velocities and anisotropy can be designed. They can be processed by wire-cut electrical discharge machining, waterjet cutting, and additive manufacturing techniques. They have a broad application prospect in acoustic fields such as acoustic stealth cloaks, acoustic waveguides, flat acoustic focusing lenses, pentamode acoustic meta-surfaces, etc. [ABSTRACT FROM AUTHOR]

Multilayer printed circuit boards (PCBs) can be produced not only in the traditional way but also additively. Both traditional and additive manufacturing can lead to invisible defects in the internal structure of the electronic component, eventually leading to the spontaneous failure of the device. No matter what kind of technology is used for the production of PCBs, when they are used in important structures, quality control is important to ensure the reliability of the component. The nondestructive testing (NDT) of the structure of manufactured electronic components can help ensure the quality of devices. Investigations of possible changes in the structure of the product can help identify the causes of defects. Different types of manufacturing technologies can lead to diverse types of possible defects. Therefore, employing several nondestructive inspection techniques could be preferable for the inspection of electronic components. In this article, we present a comparison of various NDT techniques for the evaluation of the quality of PCBs produced using traditional and additive manufacturing technologies. The methodology for investigating the internal structure of PCBs is based on several of the most reliable and widely used technologies, namely, acoustic microscopy, active thermography, and radiography. All of the technologies investigated have their advantages and disadvantages, so if high-reliability products are to be produced, it would be advantageous to carry out tests using multiple technologies in order to detect the various types of defects and determine their parameters. [ABSTRACT FROM AUTHOR]

Transformation optics (TO) provides an unprecedented technique to control electromagnetic (EM) waves by engineering the constitutive parameters of the surrounding medium through a proper spatial transformation. In general, ideal transformation optical devices require simultaneous electric and magnetic responses along all three dimensions. To ease the practical implementation, previous studies usually made use of reduced parameters or other simplified approaches, which inevitably introduce extra reflection or unwanted phase shift. Up to today, experimental realizations of full-parameter transformation optical devices in free space are still quite limited. Here, a general design strategy is proposed to solve this problem. As a specific example, a full-parameter spatial-compression TO medium with constitutive parameters taking the diagonal form diag(a, a , 1/ a) for the TM wave incidence was designed and realized experimentally. Such spatial-compression TO media were then applied to the implementation of an ideal omnidirectional invisibility cloak capable of concealing a large-scale object over a wide range of illumination angles. Both the simulation and experiment confirm that the cloak allows for nearly unity transmission of EM waves in the forward direction without introducing extra scattering or phase shift. This work constitutes an important stepping stone for future practical implementation of arbitrary full-parameter omnidirectional transformation optical devices. [ABSTRACT FROM AUTHOR]

This paper concerns the analysis of a passive, broadband approximate cloaking scheme for the Helmholtz equation in R d for d = 2 or d = 3. Using ideas from transformation optics, we construct an approximate cloak by "blowing up" a small ball of radius ϵ > 0 to one of radius 1. In the anisotropic cloaking layer resulting from the "blow-up" change of variables, we incorporate a Drude-Lorentz-type model for the index of refraction, and we assume that the cloaked object is a soft (perfectly conducting) obstacle. We first show that (for any fixed ϵ) there are no real transmission eigenvalues associated with the inhomogeneity representing the cloak, which implies that the cloaking devices we have created will not yield perfect cloaking at any frequency, even for a single incident time harmonic wave. Secondly, we establish estimates on the scattered field due to an arbitrary time harmonic incident wave. These estimates show that, as ϵ approaches 0, the L 2 -norm of the scattered field outside the cloak, and its far field pattern, approach 0 uniformly over any bounded band of frequencies. In other words: our scheme leads to broadband approximate cloaking for arbitrary incident time harmonic waves. [ABSTRACT FROM AUTHOR]

The conventional cloak has been studied in vast space while the open cloaking is explored in a few articles and there is a dire need for further investigations in this field. The open cloaks provide a way to exchange information data from the cloaked region to outside and vice versa. In this work, we have investigated the open cloaking phenomenon in acoustic fields at an audible frequency. This study will be helpful in developing a Multiphysics open cloaking platform and cloaked will enable to transfer or prohibition of the exchange of material from one region to another. [ABSTRACT FROM AUTHOR]

The persistent challenge of adhesion in Fused Filament Fabrication (FFF) technology is deeply rooted in the mechanical and chemical properties of utilized materials, necessitating the exploration of potential resolutions. This involves adjustments targeting the interplay of printing parameters, the mechanical fortification of print beds, and the integration of more adhesive materials, resonating across user levels, from enthusiasts to complex industrial configurations. An in-depth investigation is outlined in this paper, detailing the plan for a systematically designed device. Engineered for FFF device installation, the device facilitates the detachment of printed models, while precisely recording the detachment process, capturing the maximum force, and its progression over time. The primary objective is fabricating a comprehensive measurement apparatus, created for adhesion assessment. The device is adaptable across diverse FFF machines and print bed typologies, conforming to pre-defined conditions, with key features including compactness, facile manipulability, and capacity for recurrent measurements. This pursuit involves evaluating adhesion levels in prints made from diverse materials on varying print bed compositions, aiming to establish a comprehensive database. This repository facilitates judicious material and bed type selection, emphasizing maximal compatibility. Emphasis is placed on operating within a thermally stable context, a pivotal prerequisite for consistent and reproducible results. [ABSTRACT FROM AUTHOR]

Urban surveillance of slow‐moving small targets such as drones and birds in low to medium airspace using radar presents significant challenges. Detecting, locating and identifying such low observable targets in strong clutter requires both innovation in radar hardware design and optimisation of processing algorithms. To this end, the University of Birmingham (UoB) has set‐up a testbed of two L‐band staring radars to support performance benchmarking using datasets of target and clutter from realistic urban environment. This testbed is also providing the vehicle to understand how novel radar architectures can enhance radar capabilities. Some of the challenges in installing the radar at the UoB campus are highligted. Detailed benchmarking results are provided from urban monostatic and bistatic field trials that form the basis for performance comparison against future hardware modification. The solution to the challenge of interfacing the radar to the external oscillators is described and stand‐alone bench tests with the candidate oscillators are reported. The testbed provides a valuable capability to undertake detailed analysis of performance of Quantum photonic‐enabled radar and allows for its comparison with conventional oscillator technology for surveillance of low observable targets in the presence of urban clutter. [ABSTRACT FROM AUTHOR]

Liquid detection has been one of the buzzwords that refer to sensing of various liquids, which include water, chemicals, oils, etc. This detection gains more significance with the advent of metamaterials. Metamaterials are proved well suited in antenna designing, cloaking devices, solar cells, and sensors. Many papers reported metamaterial sensors, which can detect liquid chemicals, oils, etc. through shift in resonance frequency. Very few papers reported the applications of metamaterial sensors in water treatment. Water purification is one of the prime essentials for the existence of healthy humankind. It can be used to remove unwanted chemicals, contaminants and gases from water. The process of water purification can be done with various methods such as thermal, adsorption, distillation, desalination, reverse osmosis, etc. The main aim is to produce water required for specific purpose. In this context, role of metamaterials in water purification is of prime significance. Keeping this in view, an attempt is made to review the importance of metamaterial sensors in liquid detection along with water purification and its importance in comparison with earlier techniques already available. [ABSTRACT FROM AUTHOR]

Electronic structure and magneto-elastic characteristics of lanthanide nitrides Ln 3 NIn (Ln = Nd-Tb) are explored by DFT. The structural reported data are reliable with the experimental outcomes and the observed structural characteristics drop from Nd to Tb due to the small atomic radii of Tb compare to Nd. Electrical resistivity and electronic characteristics demonstrate that all the investigated compounds are metallic. The resistivity at 300 K emphasizes that they are effective conductors. These compounds are ideal for situation where large acting load are expected such as implants that bear a disproportionate amount of weight as endoprostheses for hip, knee and as screw, nails and plates, especially when structural materials need to have sufficient bending fatigue strength for skeletal reconstruction. These compounds are antiferromagnetic and their Neel temperatures are 18, 15, 39, 45, 27, and 33 K, respectively. These compounds might be therefore feasible for magnetic cloaking and storage technologies. [ABSTRACT FROM AUTHOR]

In the article "Topological Broadband Invisibility" published in Advanced Optical Materials, Li Zhang, Hongsheng Chen, Yihao Yang, and their colleagues discuss the concept of invisibility cloaks and their limitations. They propose a solution to overcome the narrow bandwidth limitation by positioning objects at topological nodes, which are characterized by minimal electromagnetic field amplitudes and indeterminate phases. The researchers demonstrate this concept using all-dielectric photonic crystal slabs, which have a pair of topological nodes across a wide bandwidth. This research has implications for the development of more effective invisibility cloaks. [Extracted from the article]

Mechanical metamaterials have recently gathered increasing attention for their uncommon mechanical responses enabling unprecedented applications for elastic wave control. Many research efforts are driven towards the conception of always new metamaterials' unit cells that, due to local resonance or Bragg-Scattering phenomena, may produce unorthodox macroscopic responses such as band-gaps, cloaking, focusing, channeling, negative refraction, etc. To model the mechanical response of large samples made up of these base unit cells, so-called homogenization or upscaling techniques come into play trying to establish an equivalent continuum model describing these macroscopic metamaterials' characteristics. A rather common approach is to assume a priori that the target continuum model is a classical linear Cauchy continuum featuring the macroscopic displacement as the only kinematical field. This implies that the parameters of such continuum models (density and/or elasticity tensors) must be considered to be frequency-dependent to capture the complex response of the considered mechanical systems in the frequency domain. These frequency-dependent models can be useful to describe some of the aforementioned macroscopic metamaterials' properties, yet, they suffer some drawbacks such as featuring negative masses and/or elastic coefficients in some frequency ranges which are close to resonance frequencies of the underlying microstructure. This implies that the considered Cauchy continuum is not positive-definite for all the considered frequencies. In this paper, we present a procedure, based on the definition of extra kinematical variables (with respect to displacement alone) and through the use of the inverse Fourier transform in time, to convert a frequency-dependent model into an enriched continuum model of the micromorphic type. All the parameters of the associated enriched model are constant (i.e., frequency-independent) and the model itself remains positive-definite for all the considered frequency ranges. The response of the frequency-dependent model and the associated micromorphic model coincide in the frequency domain, in particular when looking at the dispersion curves. Moreover, the micromorphic (frequency-independent) model results to be well defined both in time- and in the frequency-domain, while the Cauchy (frequency-dependent) model can only exist in the frequency domain This paper aims to build a bridge between the upscaling techniques usually found in the literature and our persuasion that macroscopic continua of the micromorphic type should be used to model metamaterials' response at the macroscopic scale. • Conversion of a frequency-dependent Cauchy model into an enriched continuum model of the micromorphic type. While the first can only be defined in the frequency domain, the latter is well defined both in the frequency and the time domain. • The parameters of the enriched models are constant and frequency-independent. • The frequency-dependent Cauchy continua may exhibit negative material properties (e.g., mass and/or elastic tensor) close to resonance frequencies, while the micromorphic models avoids these issues and remains well-defined and positive definite. • This paper wants to build a bridge between frequency-dependent models and macroscopic (homogenized) models of the micromorphic type for the description of mechanical metamaterials. [ABSTRACT FROM AUTHOR]

In this work we have studied Temporal Cloaking in a 4 level atomic system in the presence of Compton scattering effect. Between the scattered and un-scattered probe light beams multiple time gaps are noted. Furthermore, it is noted that Compton scattering angle has significant influence on the time gap produced in the system. The time gap increased rapidly by increasing the value of φ up to π / 2 and then changes slowly. Temporal time gap up to the order of microseconds is noted which might be useful in information hacking technology. Moreover, the time gap is further modified with pulse width, that could have significant applications in secured communication cloaking devices. • Compton scattering effect greatly influences the time gaps. • Multiple temporal gaps are produced by changing the value of Compton scattering angle. • The time gaps are further modified with pulse width. • The results are helpful in secure communication technology. [ABSTRACT FROM AUTHOR]

• Expressions derived for axial radiation force and energy efficiency factors. • Radiation force can be positive or negative depending on selection of parameters. • Disappearance of extinction power verifies possibility of acoustic invisibility. This work develops a comprehensive analytical formalism to study the boundary-induced effects on a pulsating spherical radiating source near a rigid planar boundary in an inviscid fluid. Using the modal multipole expansion method, the image method and the translational addition theorem for spherical wave functions, exact closed-form expressions are derived for the dimensionless axial acoustic radiation force function as well as the radiation, amplification and extinction energy efficiency factors. The source-boundary distance and the dimensionless size parameter are especially addressed in the numerical simulations for spherical sources with different vibration modes. It is shown that the axial radiation force is positive or negative, depending on the choice of parameters. Moreover, cases when the extinction acoustic power completely vanishes are predicted theoretically for dipole and quadrupole vibrations, which can be used to achieve acoustic invisibility in acoustic cloaking devices and acoustic stealth technologies. Combination of more than one vibration modes is also investigated to better simulate the acoustic manipulation in practical applications. This work can help us understand the underlying mechanism in manipulating the active spherical radiating sources in a bounded field. [ABSTRACT FROM AUTHOR]

• A novel magnetoactive metamaterials with intriguing symmetry-breaking properties is proposed. • The design strategy utilizes the transformative ability of hard-magnetic active elastomers coupled with zero-mode metamaterial characteristics. • The proposed magnetoactive metamaterials enable remotely-tunable elastic cloaking. We propose a magnetic field-induced asymmetric mechanical metamaterial for tunable transformation-based elastic cloaking. The metamaterial is designed by integrating hard-Magnetic Active Elastomers (hMAEs) and combining zero-stress collapse modes to produce a unique asymmetric behavior controlled by an external magnetic field. The relationship bridging the microstructure and the desired cloaking performance is presented. This magneto-metamaterial design is applied to achieve tunable static elastic cloaking. The theoretical predictions, together with the numerical tests under various static loads, demonstrate encouraging cloaking performance. The study also highlights the impact of magneto-mechanical coupling and offers the first remotely-controllable hMAE-based cloaking solution, with promising potential in various applications including stress shielding and stealth technologies. [ABSTRACT FROM AUTHOR]

In recent years, the field of metamaterial cloaks has experienced remarkable progress, propelling it to the forefront of scientific exploration. This comprehensive review seeks to provide a thorough examination of the current research landscape in this domain, specifically emphasizing comparative studies that elucidate the diverse array of approaches employed in the development of metamaterial cloaks. A paramount challenge facing researchers is the attainment of broadband invisibility, signifying the capability to render objects imperceptible across an extensive range of frequencies. To tackle this formidable challenge, scholars have delved into a myriad of methodologies. These include the strategic use of plasmonic materials, the integration of metamaterials with spatially varying structures, and the exploration of non-resonant metamaterials. Each approach brings its unique advantages and limitations to the forefront, underscoring the necessity for a tailored selection based on the intricacies of the intended application. One notable aspect that emerges from comparative analyses is the preponderance of theoretical foundations in the existing body of knowledge. Theoretical frameworks have been instrumental in understanding and predicting the behaviors of metamaterial cloaks. However, it's crucial to acknowledge that experimental-based real prototypes are not as prevalent as their theoretical counterparts. This scarcity underscores the need for increased experimental validations to bridge the gap between theoretical predictions and practical implementations. Despite the current emphasis on theoretical advancements, the development of cloaking metamaterials remains an ever-evolving field. Continuous innovation introduces new approaches and techniques, further enriching our understanding of metamaterial cloak behavior. As this review encapsulates the current state of research, it aspires not only to provide a comprehensive understanding of comparative behaviors but also to catalyze further exploration and experimentation in this captivating arena. The ultimate goal is to inspire a wave of research initiatives that will propel the field of metamaterial cloaks into new frontiers of scientific achievement. [ABSTRACT FROM AUTHOR]

• The thermal cloak in homogeneous isotropic multilayer materials is analyzed. • The influences of the layer's properties in the thermal cloak on the thermal control ability are investigated. • The temperature field of the arbitrary layout composite thermal cloak can be predicted by the deep learning model with almost no time cost. Thermal cloaks can realize thermal manipulation and have been widely applied in the engineering field. Traditional methods, like the finite element method (FEM) and finite difference method, obtain the temperature of the thermal cloak with time-consuming. A deep learning model is proposed to predict the temperature field in homogeneous isotropic multilayer materials. The FEM is applied to solve the thermal cloak and the training data are obtained. The layer's properties, including different layers, thickness, relative thermal conductivities and distribution modes, of the thermal control or manipulative ability for temperature and heat diffusion are also investigated. The deep learning mode is developed by mapping the parameters layout to the temperature field as an image-to-image regression task and the relationship between the layer's properties and the cloaking performances is intelligently established. The temperature field of the arbitrary layout composite can be acquired almost with no time cost. The temperature field with the largest node numbers of medium temperature by the FEM and the deep learning model, is exhibited and compared. Furthermore, we extend the surrogate model to different cases with different boundary conditions, which can still achieve good prediction results. Owing to the high efficiency and complete independence from the mesh densities, the proposed method offers a novel and robust technique for predicting the temperature field and suggestion for the design of the thermal cloak. [ABSTRACT FROM AUTHOR]