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.

Manipulating dc currents with bilayer bulk natural materials

The concentration of electromagnetic waves is of utmost importance in many engineering applications such as energy harvesting devices. According to the transformation optics methodology, a feasible approach for obtaining arbitrary shape concentrators is proposed. Contrary to the previous works, the obtained materials are homogeneous and independent of the concentrator shape. That is, regardless of the input geometry, always one constant material, which is optic-null medium (ONM), is used, and the performance of the device will not alter. This competency will ease the design process and circumvent the sophisticated calculations of the necessitating materials. To demonstrate such a capability, several numerical full-wave simulations were performed for different shapes of concentrators. Furthermore, with the aid of effective medium theory (EMT), the ONM was realized using split-ring resonator-meander line metamaterial blocks. Then, as a proof of concept, an arbitrary shape concentrator was designed according to EMT and by exploiting the retrieved parameters of the realized metamaterials. It was observed that the realization results exhibit strong agreement with the theoretical investigations and corroborate the generality and effectiveness of the proposed designing method.The concentration of electromagnetic waves is of utmost importance in many engineering applications such as energy harvesting devices. According to the transformation optics methodology, a feasible approach for obtaining arbitrary shape concentrators is proposed. Contrary to the previous works, the obtained materials are homogeneous and independent of the concentrator shape. That is, regardless of the input geometry, always one constant material, which is optic-null medium (ONM), is used, and the performance of the device will not alter. This competency will ease the design process and circumvent the sophisticated calculations of the necessitating materials. To demonstrate such a capability, several numerical full-wave simulations were performed for different shapes of concentrators. Furthermore, with the aid of effective medium theory (EMT), the ONM was realized using split-ring resonator-meander line metamaterial blocks. Then, as a proof of concept, an arbitrary shape concentrator was designed according...

Geometry free materials enabled by transformation optics for enhancing the intensity of electromagnetic waves in an arbitrary domain

Recently, thermal manipulation has gained the attention of the scientific community due to its several applications. In this paper, based on a transformation-thermodynamics methodology, a special type of material, called a thermal-null medium (TNM), is proposed that leads to the design of various thermal functionalities such as thermal bending devices, arbitrarily shaped heat concentrators, and omnidirectional thermal cloaks. In contrast to the conventional transformation-thermodynamics-based conductivities, which are inhomogeneous and anisotropic, TNMs are homogeneous and easy to realize. It is shown that the TNMs obtained are independent of the desired device shape, meaning that if the geometry of the desired device is changed, there is no need to recalculate the conductivities required. This consequently makes the designed devices suitable for scenarios where reconfigurability is of the utmost importance. Several numerical simulations are carried out to demonstrate the capability of TNMs and their application in directional bending devices, concentrators, and cloaks. In order to validate the concept, by using effective-medium theory, a TNM with an aluminum-air multilayer structure is designed and fabricated. The structure realized is then used to implement an elliptically shaped thermal concentrator. It is observed that the experimental results exhibit good agreement with the results obtained from the numerical simulations, which corroborates the effectiveness of the proposed materials.

Feasible Thermodynamics Devices Enabled by Thermal-Null Medium

Based on the negative permittivity properties of a two-dimensional (2D) textured perfect electric conductor (PEC) cylinder, we design a spoof surface whispering gallery mode (WGM) sensor at microwave band. The sensitivity of the proposed sensor is much higher than that of the traditional dielectric sensor in the same geometry size. Importantly, we show that the physical origin for the improvement of sensitivity is the evanescent-wave amplification and local field enhancement effects. This may open up an avenue for designing metamaterial sensors with superior sensitivity.

https://iopscience.iop.org/article/10.1209/0295-5075/103/44001/pdf

A spoof surface WGM sensor based on a textured PEC cylinder

Converging heat transfer in completely arbitrary profiles with unconventional thermal concentrator

Arbitrarily shaped homogeneous concentrator and its layered realization

The dispersion equation of a layered cylindrical dielectric waveguide operating in the whispering gallery mode (WGM) is derived. We demonstrate that when the waveguide is coated with a negative permittivity layer, a surface WGM can be generated. It exposes a strong evanescent field to the ambient substance, rendering the negative permittivity material assisted microring sensor much more sensitive to a slight change in surrounding medium. This opens up an avenue towards designing optical WGM sensors with superior performance.

http://iopscience.iop.org/article/10.1088/1612-2011/10/1/015901/pdf

Fu Chun Mao

Papers

Arbitrarily shaped homogeneous concentrator and its layered realization

Surface WGM sensor based on a cylindrical dielectric waveguide