arXiv subjects

Cheng-Wei Qiu

Publications and source records attributed to Cheng-Wei Qiu.

At least 109 records · Page 6Linked to original sources

arXiv2015

Invisible sensor: Simultaneous sensing and camouflaging in multiphysical fields

To manipulate various types of physical signals in one single device has long captivated the attention of scientists and engineers. This however is very challenging, if not impossible, even for emerging metamaterials. Up to date, many artificial materials have been proposed, theoretically and (or) experimentally, for manipulating various waves/signals on a one-function-one-device basis. In this work, for the very first time, we employ undecorated natural materials to experimentally demonstrate a simultaneous camouflage for thermal current and electric dc current on the same device. It demonstrates how ingenuity can overcome the limitations of natural material systems without the need for complex decoration to impart inhomogeneous and (or) anisotropic properties, which was previously considered impossible to accomplish except by using metamaterials.

physics.optics↗

arXiv2015

A unified theory correcting Einstein-Laub electrodynamics solves dilemmas in the photon momenta and electromagnetic stress tensors

To unify and clarify the persistently debated electromagnetic stress tensors (ST) and photon momenta, we establish a theory inspired by the Einstein-Laub formalism inside an arbitrary macroscopic object immersed in any complex medium. Our generalized Einstein-Laub force and ST yield the total force experienced by any generic macroscopic object due to the internal field interacting with its atoms, charges and molecules. Appropriate scenarios are established for the conservation of a newly proposed momentum that we call non-mechanical generalized Einstein-Laub momentum, along with the kinetic and canonical momenta of photons. Our theory remains valid even in a generally heterogeneous or bounded embedding background medium without resorting to hidden momenta, and unambiguously identifies the existence domain, or validity domain, of the STs and photon momenta proposed to date. This existence domain is the region either outside a macroscopic scatterer with only exterior fields, or at its interior with only inside fields. The appropriate identification of such existence domain constitutes the basis of our unified theory. Finally, a thought experiment is proposed, which shows that the appropriate force and the photon momentum in the embedding medium can also be properly identified if the background is comparatively larger than the embedded scatterer. It also explains the fully different roles of the Abraham and Minkowski photon momenta in the embedding medium. Most importantly, our unified theory reveals that a unique formulation of the momentum conservation law is unfeasible, though a generalized expression of the ST and momentum density is achievable in terms of new concepts that we introduce, namely, the effective polarization and effective magnetization.

physics.optics↗

arXiv2014

Manipulating Steady Heat Conduction by Sensu-shaped Thermal Metamaterials

The ability to design the control of heat flow has innumerable benefits in the design of electronic systems such as thermoelectric energy harvesters, solid-state lighting, and thermal imagers, where the thermal design plays a key role in performance and device reliability. However, to realize one advanced control function of thermal flux, one needs to design one sophisticated, multilayered and inhomogeneous thermal structure with different composition/shape at different regions of one device. In this work, we employ one identical sensu-unit with facile natural composition to experimentally realize a new class of thermal metamaterials for controlling thermal conduction (e.g., thermal concentrator, focusing/resolving, uniform heating), only resorting to positioning and locating the same unit element of sensu-shape structure. The thermal metamaterial unit and the proper arrangement of multiple identical units are capable of transferring, redistributing and managing thermal energy in a versatile fashion. It is also shown that our sensu-shape unit elements can be used in manipulating dc currents without any change in the layout for the thermal counterpart. The proposed scheme can also be applied to control dc electric currents and dc magnetic fields that governed by Laplace equation. These could markedly enhance the capabilities in thermal sensing, thermal imaging, thermal-energy storage, thermal packaging, thermal therapy, and more domains beyond.

physics.optics↗

arXiv2014

Subwavelength focusing of azimuthally polarized beams with vortical phase in dielectrics by using an ultra-thin lens

We demonstrate that a planar and ultrathin binary lens can focus an azimuthally polarized beam with vortical phase (APV) to a subwavelength spot of transverse polarization. The results elaborates that, in the multi-layer medium, this focused spot, which is beyond the Rayleigh diffraction limitation, can be well maintained for several wavelengths after travelling through the dielectric interfaces, which is not attainable by using other vector beams (i.e., radially, linearly and circularly polarized beams) as the illuminating light. This compact optical system can be valuable in data writing and defect identification of wafer or silicon chips, owing to the enhanced polarized focusing through interfaces. It also enables to be highly integrated with traditional microscopy for the far-field super-resolution imaging, surface scanning and detection, and subwavelength focusing, owing to the enhanced focusing performance (reduced width and extended length) as well as the planarized configuration of the ultrathin lens.

physics.optics↗

arXiv2014

Manipulating dc currents with bilayer bulk natural materials

The principle of transformation optics has been applied to various wave phenomena (e.g., optics, electromagnetics, acoustics and thermodynamics). Recently, metamaterial devices manipulating dc currents have received increasing attention which usually adopted the analogue of transformation optics using complicated resistor networks to mimic the inhomogeneous and anisotropic conductivities. We propose a distinct and general principle of manipulating dc currents by directly solving electric conduction equations, which only needs to utilize two layers of bulk natural materials. We experimentally demonstrate dc bilayer cloak and fan-shaped concentrator, derived from the generalized account for cloaking sensor. The proposed schemes have been validated as exact devices and this opens a facile way towards complete spatial control of dc currents. The proposed schemes may have vast potentials in various applications not only in dc, but also in other fields of manipulating magnetic field, thermal heat, elastic mechanics, and matter waves.

cond-mat.mtrl-sci↗

arXiv2014

Robust acoustic cloaking with density-near-zero materials

Using the phenomenon of extraordinary sound transmission (EST) through artificially constructed density-near-zero (DNZ) materials, we propose an alternative approach to realize a very robust acoustic cloaking, which includes one absorber and one projector connected by an energy channel. The elementary unit cell is made of one single-piece homogeneous copper, but it well maintains both the original planar wavefront and the nearly perfect one-dimensional transmission, in the presence of any inserted objects. Furthermore, the overall cloaked space can be increased, designed, and distributed by arbitrarily assembling additional DNZ cells without any upper limit in the total cloaking volume. We demonstrate acoustic cloaking by different combinations of DNZ cells in free space as well as in acoustic waveguides, which enables any objects inside the cells imperceptible along undistorted sound paths.

physics.class-ph↗

arXiv2013

Experimental demonstration of light capsule embracing super-sized darkness inside via anti-resolution

We theoretically and experimentally demonstrate the focusing of macroscopic 3D darkness surrounded by all light in free space. The object staying in the darkness is similar to staying in an empty light capsule because light just bypasses it by resorting to destructive interference. Its functionality of controlling the direction of energy flux of light macroscopically is fascinating, similar in some sense to the transformation-based cloaking effect. Binary-optical system exhibiting anti-resolution (AR) is designed and fabricated, by which electromagnetic energy flux avoids and bends smoothly around a nearly perfect darkness region. AR remains an unexplored topic hitherto, in contrast to the super-resolution for realizing high spatial resolution. This novel scheme replies on smearing out the PSF and thus poses less stringent limitations upon the object's size and position since the created dark (zero-field) area reach 8 orders of magnitude larger than the square of wavelength in size. It functions very well at arbitrarily polarized beams in three dimensions, which is also frequency-scalable in the whole electromagnetic spectrum.

physics.optics↗

arXiv2013

Bilayer Isotropic Thermal Cloak

Invisibility has attracted intensive research in various communities, e.g., optics, electromagnetics, acoustics, thermodynamics, etc. However, the most of them have only been experimentally achieved by virtue of simplified approaches due to their inhomogeneous and extreme parameters imposed by transformation-optic method, and usually require challenging realization with metamaterials. In this paper, we demonstrate an advanced bilayer thermal cloak with naturally available materials first time. This scheme, directly from thermal conduction equation, has been validated as an exact cloak rather than a reduced one, and we experimentally confirmed its perfect performance (heat-front maintenance and heat protection) in an actual setup. The proposed scheme may open a new avenue to control the diffusive heat flow in ways inconceivable with phonons.

cond-mat.mtrl-sci↗

arXiv2013

Achieving Giant Magneto-optic Effects with Optical Tamm States in Graphene-based Photonics

We manipulate optical Tamm states in graphene-based photonics to achieve and steer large magneto-optical effects. Here we report the presence of a giant Faraday rotation via a single graphene layer of atomic thickness while keeping a high transmission. The Faraday rotation is enhanced across the interface between two photonic crystals due to the presence of an interface mode, which presents a strong electromagnetic field confinement at the location of the graphene sheet. Our proposed scheme opens a promising avenue to realize high performance graphene magneto-optical devices that can be extended to other two-dimensional structures.

physics.optics↗

arXiv2013

Creation of Tunable Homogeneous Thermal Cloak with Constant Conductivity

Invisible cloak has long captivated the popular conjecture and attracted intensive research in various communities of wave dynamics, e.g., optics, electromagnetics, acoustics, etc. However, their inhomogeneous and extreme parameters imposed by transformation-optic method will usually require challenging realization with metamaterials, resulting in narrow bandwidth, loss, polarization-dependence, etc. On the contrary, we demonstrate that tunable thermodynamic cloak can be achieved with homogeneous and finite conductivity only employing naturally available materials. The controlled localization of thermal distribution inside the coating layer has been presented, and it shows that an incomplete cloak can function perfectly. Practical realization of such homogeneous thermal cloak has been suggested by using two naturally occurring conductive materials, which provides an unprecedentedly plausible way to flexibly realize flexible thermal cloak and manipulate thermal flow.

cond-mat.mtrl-sci↗

arXiv2013

Creation of Ghost Illusions Using Metamaterials in Wave Dynamics

The creation of wave-dynamic illusion functionality is of great interests to various scientific communities, which can potentially transform an actual perception into the pre-controlled perception, thus empowering unprecedented applications in the advanced-material science, camouflage, cloaking, optical and/or microwave cognition, and defense security, etc. By using the space transformation theory and engineering capability of metamaterials, we propose and realize a functional ghost illusion device, which is capable of creating wave-dynamic virtual ghost images off the original object's position under the illumination of electromagnetic waves. The scattering signature of the object is thus ghosted and perceived as multiple ghost targets with different geometries and compositions. The ghost-illusion material, being inhomogeneous and anisotropic, was realized by thousands of varying unit cells working at non-resonance. The experimental demonstration of the ghost illusion validates our theory of scattering metamorphosis and opens a novel avenue to the wave-dynamic illusion, cognitive deception, manipulate strange light or matter behaviors, and design novel optical and microwave devices.

physics.optics↗

arXiv2013

Acoustic Wavefront Manipulation: Impedance Inhomogeneity and Extraordinary Reflection

Optical wavefront can be manipulated by interfering elementary beams with phase inhomogeneity. Therefore a surface allowing huge, abrupt and position-variant phase change would enable all possibilities of wavefront engineering. However, one may not have the luxury of efficient abrupt-phase-changing materials in acoustics. This motivates us to establish a counterpart mechanism for acoustics, in order to empower the wide spectrum of novel acoustic applications. Remarkably, the proposed impedance-governed generalized Snell's law (IGSL) of reflection is distinguished from that in optics. Via the manipulation of inhomogeneous acoustic impedance, extraordinary reflection can be tailored for unprecedented wavefront manipulation while ordinary reflection can be surprisingly switched on or off. Our results may power the acoustic-wave manipulation and engineering. We demonstrate novel acoustic applications by planar surfaces designed with IGSL.

physics.optics↗

arXiv2012

Anisotropy-induced Fano resonance

An optical Fano resonance, which is caused by birefringence control rather than frequency selection, is discovered. Such birefringence-induced Fano resonance comes with fast-switching radiation. The resonance condition $\varepsilon_t< 1/\varepsilon_r$ is revealed and a tiny perturbation in birefringence is found to result in a giant switch in the principal light pole induced near surface plasmon resonance. The loss and size effects upon the Fano resonance have been studied Fano resonance is still pronounced, even if the loss and size of the object increase. The evolutions of the radiation patterns and energy singularities illustrate clearly the sensitive dependence of Fano resonance upon the birefringence.

physics.optics↗

arXiv2011

Broadband phase-preserved optical elevator

Phase-preserved optical elevator is an optical device to lift up an entire plane virtually without distortion in light path or phase. Using transformation optics, we have predicted and observed the realization of such a broadband phase-preserved optical elevator, made of a natural homogeneous birefringent crystal without resorting to absorptive and narrowband metamaterials involving time-consuming nano-fabrication. In our demonstration, the optical elevator is designed to lift a sheet upwards, and the phase is verified to be preserved always. The camouflage capability is also demonstrated in the presence of adjacent objects of the same scale at will. The elevating device functions in different surrounding media over the wavelength range of 400-700 nm. Our work opens up prospects for studies of light trapping, solar energy, illusion optics, communication, and imaging.

physics.optics↗

arXiv2011

Birefringence induced polarization-independent and nearly all-angle transparency through a metallic film

We propose an birefringence route to perfect electromagnetic (EM) wave tunneling through a metallic film which relies on homogeneous birefringent coatings with moderate and positive parameters only. EM transparency is achieved in such an birefringent-metal-birefringent (BMB) structure for both polarizations and over nearly all incident angles. The stringent restrictions in conventional dielectric-metal-dielectric media, i.e., dielectrics with extremely negative permittivity, high magnetic field and polarization dependence (only for TE waves), are not required in our method. The criterion for perfect transmission is obtained by analyzing the effective medium theory and EM fields of such a birefringent structure. The solutions hold for lossless and lossy cases in a quite large frequency range.

physics.optics↗

arXiv2011

Can a single gradientless light beam drag particles?

Usually a light beam pushes a particle when the photons act upon it. This is due to that the electric-dipole particle in the paraxial beam is considered. We investigate the scattering forces in non-paraxial gradientless beams and find that the forces can drag certain particles towards the beam source. The major criterion to be carried out to get the attractive force is the strong non-paraxiality of the light beam. The cone angle denoting the non-paraxiality has been investigated to unveil its importance on achieving dragging force. We hope the attractive forces will be very useful in nanoparticle manipulation.

physics.optics↗

arXiv2011

Analytical spectral-domain scattering theory of a general gyrotropic sphere

We propose an analytical scattering theory in spectral domain to model the electromagnetic (EM) fields of a gyrotropic sphere in terms of the eigen-functions and their associated spectral eigenvalues/coefficients in a recursive integral form. Applying the continuous boundary conditions of electromagnetic fields on the surface between the free space and gyrotropic sphere, the spectral coefficients of transmitted fields inside the gyrotropic sphere and the scattered fields in the isotropic host medium can be obtained exactly by expanding spherical vector wave eigenfunctions. Numerical results are provided for some representative cases, which are compared to the results from adaptive integral method (AIM). Good agreement demonstrates the validity of the proposed analytical scattering theory for gyrotropic spheres in spectral domain using Fourier transform.

cond-mat.mtrl-sci↗

arXiv2009

Electromagnetic interaction of arbitrary radial-dependent anisotropic spheres and improved invisibility for nonlinear-transformation-based cloaks

An analytical method of electromagnetic wave interactions with a general radially anisotropic cloak is established. It is able to deal with arbitrary parameters ($ε_r(r)$, $μ_r(r)$, $ε_t(r)$ and $μ_t(r)$) of a radially anisotropic inhomogeneous shell. The general cloaking condition is proposed from the wave relations for the first time. We derive the parameters of a novel class of spherical nonlinear cloaks and examine its invisibility performance by the proposed method at various nonlinear situations. Spherical metamaterial cloaks with improved invisibility performance is achieved with optimal nonlinearity in transformation and core-shell ratio.

physics.optics↗