Permeability Of Metamaterials Research Articles

A metamaterial‐incorporated wireless power transmission system for efficiency enhancement

SummaryIn this paper, an efficient wireless power transmission (WPT) system that incorporates a new negative permeability metamaterial is presented. The operating principle of the metamaterial with negative permeability is first analyzed. To improve transmission efficiency of the WPT system at the operating frequency of 13.56 MHz, a new metamaterial with three open rings is designed. By respectively placing a single metamaterial slab and double metamaterial slabs at different positions between transmitting coil and receiving coil, the performance of the proposed WPT system is evaluated by simulation work. The corresponding magnetic field distribution is also analyzed. Besides, comparison is made with the conventional WPT system without metamaterial. It is found that transmission efficiency of the proposed WPT system is obviously improved when incorporating the metamaterial since the designed metamaterial effectively focuses magnetic field towards the receiving coil. Comparing with the conventional system, the results also show that the proposed WPT system is more robust to lateral and angular misalignment of the receiving coil. With the designed metamaterial, it is found that the proposed system with double metamaterial slabs performs better than that with a single metamaterial slab.

Applications of negative permeability metamaterials for electromagnetic resonance type wireless power transfer systems

With the development of electric drive systems such as unmanned aerial vehicles and electric vehicles, the charging problem of power supply devices has become increasingly prominent. However, the traditional charging method requires physical circuits, which makes it impossible to achieve freedom of the position in actual use. The wireless power transmission technology, which mainly relies on electromagnetic wave to complete energy transmission, is expected to get rid of the restriction of physical space location and solve the problem of charging location, which has great potential in medical treatment, rescue, detection and other fields. However, the low transmission efficiency and short transmission distance caused by electromagnetic field leakage are the two main problems faced by radio energy transmission systems. In general, with the increase of transmission distance, the transmission efficiency will drop sharply. Fortunately, inserting a negative permeability metamaterial with extraordinary electromagnetic characteristics into the transmitting and receiving coils will greatly alleviate this attenuation trend and can also shield electromagnetic radiation to a certain extent. In this paper, some experiments of negative permeability metamaterials used in electromagnetic resonance type wireless power transfer systems are summarized for reference.

Electromagnetic metamaterials—from effective media to field programmable systems

Electromagnetic metamaterials are periodic or nonperiodic artificial structures comprising basic elements in subwavelength scales. They can be used to control electromagnetic waves by designing the basic elements and their spatial arrangements. Metamaterial has been a research hotspot in physical and information sciences. In this review, I present the history and main progresses achieved in metamaterial studies conducted in the State Key Laboratory of Millimeter Waves at Southeast University, which were performed in three stages. In the first stage, we improved the developments in effective-medium metamaterials. In particular, we proposed a general theory to accurately describe the effective permittivity and permeability of metamaterials. Based on the general theory, we designed and realized a three-dimensional (3D) wideband ground-plane invisibility cloak, free-space electrostatic invisibility cloak, electromagnetic black hole, electromagnetic illusions, and radially anisotropic zero-index metamaterial for omni-directional radiations and nearly perfect power combinations of source arrays. Moreover, we undertook significant efforts in engineering applications of microwave metamaterials, such as broadband and low-loss 3D transformation-optic lens for wide-angle scanning, 3D planar gradient-index lens for high-gain radiations, and random metasurfaces to reduce radar cross sections. In the second stage, we opened up a new direction of plasmonic metamaterials from the viewpoint of microwave transmission lines. We proposed an ultrathin, narrow, and flexible corrugated metallic strip to guide spoof surface plasmon polaritons (SPPs) with small bending and radiation losses, based on which we designed and realized a series of passive SPP devices (such as power divider, coupler, filter, and resonator), active SPP devices (such as amplifier and duplexer) and SPP antennas in the microwave bands. We demonstrated a significant feature of the ultrathin SPP transmission line in overcoming challenges of signal integrity existing in the traditional integrated devices and circuits. We built up a full-SPP wireless communication system with unique properties to remotely transmit two movies in two deep-subwavelength-distance channels exhibiting excellent performance. In the third stage, we established a new area of metamaterial-information metamaterial. We proposed to describe the metamaterial using digital coding from the information science viewpoint, which directly resulted in a new kind of metamaterial-digital coding metamaterial. We theoretically and experimentally illustrated that the digital coding metamaterials comprising digital units can be controlled using different coding sequences to achieve different functions. When the digital state of the coding unit was controlled using a field programmable gate array (FPGA), we realized a field programmable metamaterial that can manipulate electromagnetic waves in real time and generate numerous different functions using a single piece of hardware. The digital coding metamaterial provides a platform to establish a digital space on the physical space and enriches the methodology and theory of metamaterials. We proposed measuring the information capacity of metamaterials using Shannon entropy and presented the convolution and addition theorems on metamaterial platforms, which can be used to simultaneously control the physical properties and digital information. Based on information metamaterials, we established new-architecture microwave imaging systems, wireless communication systems, and other intelligent information systems.

A Dual-Band Negative Permeability and Near-Zero Permeability Metamaterials for Wireless Power Transfer System

A contactless energy charging platform is an emerging technology that can improve the conveniences of electronic charging devices. This article presents a novel asymmetric wireless power transfer (WPT) system by integrating with two kinds of dual-band metamaterials, which is suitable for recharging the portable electronic devices. The design key of the metamaterial is to achieve the dual-band negative permeability (DB-MNG) and near-zero permeability (DB-MNZ) for enhancing efficiency and reducing leakage magnetic field of the WPT system, simultaneously. Especially, the corresponding simulation and experimentation are carried out to verify the validity of the DB-MNG metamaterial for increasing the efficiency at 13.56 and 27.12 MHz. Moreover, considering the charging environment of portable devices, various misalignments between the device and DB-MNG metamaterial are discussed to maintain continuous power availability. Meanwhile, the dual-band shielding performance of DB-MNZ metamaterial is proved at 13.56 and 27.12 MHz. As a result, the DB-MNZ metamaterial shield performs better than ferrite sheet and its performance is similar to that of aluminum sheet.

Tunneling modes induced by interface states in 1D photonic crystals with single negative materials

We investigate the electromagnetic wave propagating in one dimensional photonic crystals with alternating layers of negative permittivity materials and negative permeability metamaterials. The band structure and transmission spectra are obtained. In the negative effective permittivity and negative effective permeability regime, we find new interface modes propagating along the interfaces between the two different media with even and odd parities, respectively. For the oblique incident case, the new propagation modes result in the emergence of a transmission band within the zero-ϕeff gap of these photonic crystals. By adjusting the plasma density or the thickness of the plasma layer, the zero-ϕeff gap as well as the transmission band of the interface modes can be tuned, which can facilitate the design of tunable filters at the microwave frequency range.

Effective parameters of a metamaterial composed of dielectric coated conducting cylindrical rods

AbstractIn the first part, the scattering characteristics of an isolated dielectric coated conducting rod have been investigated. The types of considered coatings for the scattering analysis are realistic materials including barium strontium titanate, magnetodielectric, gallium arsenide, and silicon carbide. It is found that the gallium arsenide coating can be used to significantly reduce the scattering from a thin perfectly electric conducting cylindrical rod at specific observation angles. In the second part, the effective permittivity and permeability of metamaterials composed of two dimensional periodic arrangements of these dielectric coated conducting cylindrical rods have been studied. An increase in the double negative (DNG) bandwidth of a metamaterial composed of barium strontium titanate coated conducting rods has been observed in contrast to the corresponding bandwidth of a metamaterial composed of only barium strontium titanate material rods. Also an additional plasmonic epsilon negative (ENG) bandwidth has been found in case of a metamaterial composed of barium strontium titanate coated conducting rods. It is further studied that the widest ENG, mu negative, and DNG bandwidths exist for a metamaterial composed of gallium arsenide rods.

Investigation of Negative and Near-Zero Permeability Metamaterials for Increased Efficiency and Reduced Electromagnetic Field Leakage in a Wireless Power Transfer System

In order to meet both safety and efficiency requirements of wireless power transfer (WPT) systems, reducing electromagnetic field (EMF) leakage and improving efficiency are critical factors in the implementation of systems. Recently, metamaterials have exhibited the ability to control the electromagnetic wave propagation. In this paper, the WPT system integrating with near-field mu-near-zero (NF-MNZ) and mu-negative permeability (MNG) metamaterials is proposed to control EMF leakage below a certain level and improve transfer efficiency. The NF-MNZ and the MNG metamaterials are placed on both sides and in the middle of the WPT system, respectively. In addition, the property of the NF-MNZ metamaterial slab and its working principle on the WPT system are analyzed. The shielding performance of the NF-MNZ metamaterial are evaluated via numerical simulation and experimental investigation. Finally, the efficiency and the magnetic field strength of the WPT system with two different types of metamaterials have been investigated by the experimental measurements. At the transfer distance of 40 cm, the experimental results show that the efficiency of the WPT system is increased by 12.06% and the magnetic field strength is reduced by 62.09%.

Study of efficiency improvement for wireless power transfer based on negative permeability metamaterials

In order to enhance the transmission efficiency of wireless power transfer (WPT), a negative permeability metamaterials (NPM) with a structure of honeycomb composed by units of hexagon-shaped spirals copper is proposed in this paper. The unit parameters of the NPM are optimized, to make sure the negative permeability at 6.78 MHz. The S -parameters of the designed NPM are measured by a network analyzer and the permeability is extracted. It shows that the honeycomb NPM have a negative permeability at 6.2–6.7 MHz. A two-coil WPT is setup and the transmission efficiency of WPT embedded with NPM at the different position and with different structure are investigated. The measured results show that the 2-slab honeycomb NPM have a good performance compared with the 1-slab NPM, and the efficiency can be increased up to 12.5% at a distance of 30 cm.

Structural Evolution Design and Optimization for the Metamaterials with Broadband Frequency-Independent Negative Permeability

Broadband frequency-independent operations are strongly desired in metamaterial applications. In this work, we unveil the roles of each element acting in the metamaterial unit with a structural evolution design methodology. Starting with “split ring resonator” (SRR) prototype structures, we focus on the variations of elements on the magnetic response and successfully realize the structures of “clock-like” and “wire pairs” with double and broadband frequency-independent negative permeability (0.725 to 0.9 THz, μ = − 0.75). Our results suggested that multi-resonance modes induced by elements integration could extend working bands. By well parameters tuning, the phase mismatch during multi-modes interactions could be utilized to modify the working bands with frequency-independent features as well. Our investigations are beneficial to the design of functional negative permeability metamaterials with broadband operations.

The effect of the dielectric layer thickness on the negative permeability in metamaterials

In this work, we investigate the influences of the dielectric layer on the magnetic resonance of the cut-wire pair structure (CWP). The interaction between the cut-wires is modeled through a LC circuit, based on which, the magnetic resonant frequency is calculated. Furthermore, the dependence of the resonant bandwidth on the structure parameters is also determined. By tuning the dielectric layer thickness, we obtained a noticeable broadening of the negative permeability regime of 17%, which represents the enhancement of the magnetic resonance. A good agreement between the theory, simulation, and practical experiment has been demonstrated. We believe that our results should be consequential with regard to the determination of the mechanism behind the wave-matter interaction in the GHz frequency regime.

Investigation of negative permeability metamaterials for wireless power transfer

In order to enhance the transmission efficiency of wireless power transfer (WPT), a negative permeability metamaterials (NPM) with a structure of honeycomb composed by units of hexagon-shaped spirals copper is proposed in this paper. The unit parameters of the NPM are optimized, to make sure the negative permeability at the special frequency. The S-parameters of the designed NPM are measured by a network analyzer and the permeability is extracted, it shows the honeycomb NPM has a negative permeability at 6.43 MHz. A two-coil WPT is setup and the transmission efficiency of WPT embedded with NPM at the different position and with different structure are investigated. The measured results show that the 2-slab honeycomb NPM have a good perform compared with the 1-slab NPM, and the efficiency can be increased up to 51%. The results show that honeycomb NPM embedded in the WPT help to improve the transmission efficiency remarkable.

Scattering from metamaterial coated nihility sphere

BackgroundTo show the Back-Scattering efficiencies of nihility sphere become non-zero, scattering from metamaterial coated nihility sphere has been carried out in the presented work.MethodsThe field phasors are expanded in terms of spherical wave vector function along with assumed scattering coefficients. Boundaries conditions are applied at each interface, i.e., free space- metamaterial coating and metamaterial coating-nihility sphere core.ResultsScattering coefficients are obtained by using boundary conditions at each interface. The scattering efficiencies are obtained in graphical form by varying both permittivity and permeability of metamaterial using MATHEMATICA software. Under some special conditions obtained results are compared with already published literature to show the correctness of present formulations.ConclusionIt is observed that Back-Scattering efficiencies of nihility sphere becomes non-zero when we introduce a metamaterial coating layer on it. It is also noticed that the scattering efficiencies are dependent on coating thickness as well as permittivity and permeability of metamaterials.

Spectral Dependence of the Refractive Index of Magneto-Optical Metamaterials

A new approach is proposed for determining the optical properties of metamaterials with a complex unit cell geometry. It is based on the concept of an effective dielectric constant eeff (ω) and magnetic permeability μeff (ω) as a sum of Lorentzian functions, each of which is responsible for a certain dipole or multipole resonance of the structure. It is found that for "fishnet" metamaterials the spectral dependences eeff (ω) and magnetic permeability μeff (ω) are determined by a small number of resonances. This approach is used to calculate the effective dielectric constant and magnetic permeability of metamaterials with ordered and disordered unit cells. The spectra obtained by this analytical model are in good agreement with numerical simulations.

Impedance matching control method for an underwater magnetic resonance-based wireless power transfer system with metamaterials

In this paper, a new method of improving the efficiency of the underwater magnetic resonance-based wireless power transfer (MRWPT) system is proposed. A kind of the negative permeability (MNG) metamaterials with low megahertz frequency is designed, which can be adjusted to work well in the system. The S-parameters, resonant frequency, and permeability of metamaterials are worked out for analysis. A new impedance matching control method was also proposed for reducing the reflection loss in a way to help the sea water MRWPT system to achieve the maximum efficiency. This method is also able to reduce the unnecessary power loss caused by power fluctuation. The measured results show that the performance of the proposed metamaterials and the proposed control method are perfect in improving its efficiency in sea water.

An electromagnetic parameters extraction method for metamaterials based on phase unwrapping technique

A new method of extracting effective permittivity and permeability of metamaterials has been developed in this paper. Scattering parameters are used to represent effective wave impedance and refractive index of the metamaterials. Considering analytical continuation of effective refractive index of the metamaterials in the upper half of a complex angular frequency plane, a phase unwrapping technique has been implemented to solve branch ambiguity of the refractive index caused by complex inverse cosine function. An empirical formula to estimate the starting frequency in the phase unwrapping technique has been developed to improve the efficiency of the parameter retrieval procedure. Numerical results including five slabs of rods and split-ring resonators (SRRs) and a structure composed of two SRRs and four capacitively loaded strips are given to demonstrate good accuracy, high efficiency, and noise insensitivity of the proposed retrieval method.

Experiments on multiple-receiver magnetic resonance-based wireless power transfer in low megahertz with metamaterials

In this paper, an efficient magnetic resonance-based wireless power transfer (MRWPT) system with metamaterials is proposed. The negative permeability (MNG) metamaterials for this system with low-megahertz frequency is designed, which can be adjusted to work well at a variable receiving angle ranging from 0° to 45° along z-direction. The S-parameters, resonant frequency and permeability of metamaterials are computed for analysis. The transmission efficiency of the multiple-receiver MRWPT system in free space is compared to that in the presence of metamaterials placed in front of transmission and receive coils. The measured results show that the performance of the proposed metamaterials is perfect in improving the efficiency with incident electromagnetic waves from various directions.

Role of anomalous self-steepening in controlling self-accelerating Airy pulses in nonlinear metamaterials

The additional dispersive magnetic permeability in metamaterials (MMs) described by the Drude model is able to generate the anomalous self-steepening (SS) effect which can be positive, negative even zero. This provides more great flexibility for us to control ultrashort pulse propagation, when compared with the corresponding case in naturally positive-index materials (PIMs). In this paper, we theoretically investigate the self-accelerating control of Airy pulse through such anomalous SS effect in MMs with a cubic nonlinearity. The emphasis is given to the counterintuitive dynamical behavior different from those in PIMs. It is shown that positive SS in MMs acts to promote the self-acceleration of such pulse and the corresponding spectral features exhibits a broad redshifted behaviors, as it does in PIMs; while the negative SS gives rise to the appearance of the opposite situation. That is to say, the self-acceleration of Airy pulse will be delayed through broadening the spectrum toward blue side. Meanwhile, the effect of the specific truncation coefficient imposed on Airy pulses in MMs also be discussed under the roles of positive and negative SS, respectively. Our findings show that the SS effect in MMs can provide a more powerful tool in controlling the self-accelerating of Airy pulse when compared with the corresponding case in PIMs.

Enhanced generation of a second-harmonic wave in a composite of metamaterial and microwave plasma with various permittivities.

The generation of a second-harmonic wave, which is one typical nonlinear feature, is enhanced in a composite of plasma and metamaterial. When we generate plasma by an injection of microwaves, whose frequencies are fundamental, we observe intensified second-harmonic waves in the cases of negative-refractive-index states in which both metamaterial permeability and plasma permittivity are negative for the fundamental waves. We performed the measurements at multiple levels of microwave input power up to 300 W to regulate permittivity in the negative polarity for the fundamental wave and in the transient region, including the positive-zero-negative values, for the second-harmonic wave. We clarified that the observed enhancement results from high electron density in negative-permittivity plasma, the propagating fundamental frequency wave not being attenuated in the negative-refractive-index state, and partial phase matching between the fundamental and second-harmonic waves.

Nonlinear TE-Polarized Surface Plasmons at the Interface between Graphene and Metamaterials

Nonlinear TE-polarized surface plasmons localized at the interface between graphene and metamaterials are investigated analytically. The normalized momentum of graphene surface plasmons at the interface between graphene and metamaterials composed of arrays of wires and split-ring resonators (SRR) embedded into a nonlinear dielectric exhibits bistable behavior with the magnetic field intensity. The effect is explained by the hysteresis-type dependence of the nonlinear permeability of metamaterials on the field intensity.

Improving Power Transfer Efficiency of a Short-Range Telemetry System Using Compact Metamaterials

Wireless power transfer using resonant inductive coupling has been employed in a number of applications, including wireless charging of electronic devices and powering of implanted biomedical devices. In these applications, power is transferred over short distances, which are much smaller (~ λ/100) than the wavelength of operation. In such systems, the power transfer efficiency of the link is inversely related to the range of operation. The power transfer efficiency is principally a function of the Q's of the individual coils and the coupling between them. In this paper, we demonstrate improvements in power transfer efficiencies using negative permeability metamaterials by increasing the mutual coupling between coils. A metamaterial slab is designed for operation at 27 MHz and is compact in size. The power transfer efficiency of the telemetry system in free space is compared to that in the presence of the metamaterial placed near one of the coils. The efficiency of the system increased in the presence of the metamaterial even as the free-space separation was held constant. This shows that compact negative permeability metamaterials can be used to increase power transfer efficiency of short-range telemetry systems used in various applications.