Focusing Of Electromagnetic Waves Research Articles

Double-Band Metasurface Infrared Optics for Integrated Multichannel Spectral Sensors

Simultaneously identifying the composition of mixtures and determining their concentration levels has aroused much attentions recent years to meet the large demands of compact and low-cost infrared spectral sensors to replace their conventional bulky counterparts with costly separated infrared components. In this work, we propose a design method for multi-channel metasurface infrared array optics covering two bands (MWIR/LWIR) for construction of integrated infrared gas sensors. The use of metasurface microstructures with same height realizes the effective filtering and focusing of electromagnetic waves at multiple wavelengths in the both infrared bands, which is beneficial to decrease the manufacturing costs. Four-channel metasurface lens arrays and filter arrays with operating wavelengths of 3.5 μm, 9.7 μm, 10.6 μm and 3.9 μm corresponding to the infrared absorption peaks of three gases of ethanol, ammonia, ethylene and one reference wavelength respectively, were designed and produced by photolithographic patterning and dry etching processes on silicon substrates. The multi-channel metasurface infrared optics have the advantages of easy fabrication and integration with wide-band infrared detector array to form a compact infrared spectral detector, which meets the requirements of small volume and low cost to advanced infrared spectral sensors for applications in portable smart sensing systems and internet of things.

On-fiber high-resolution photonic nanojets via high refractive index dielectrics.

In this manuscript, we present high spatial resolution focusing of electromagnetic waves at telecommunication wavelengths (λ0 = 1.55 µm) by using high-refractive index mesoscale dielectrics placed at the end of an optical fiber. Our approach exploits photonic nanojets (PNJs) to achieve high-intensity, spatially narrow focal spots. The response of the device is evaluated in detail considering 2-dimensional (2D) and 3-dimensional (3D) configurations using high-index mesoscale cylindrical and spherical dielectrics, respectively, placed on top of an optical fiber. It is shown how the PNJs can be shifted towards the output surface of the mesoscale high-index dielectric by simply truncating its 2D/3D cylindrical/spherical output profile. With this setup, a PNJ with a high transversal resolution is obtained using the 2D/3D engineered mesoscale dielectric particles achieving a Full-Width at Half-Maximum of FWHM = 0.28λ0 (2D truncated dielectric), and FWHMy = 0.17λ0 and FWHMx = 0.21λ0 (3D truncated dielectric). The proposed structure may have potential in applications where near-field high spatial resolution is required, such as in sensing and imaging systems.

Electromagnetic energy focusing technology with GPR array transmitting antenna for high resolution detection

To accurately detect complex objects in urban underground space, an electromagnetic energy focusing technology is proposed in this paper with Ground penetrating radar (GPR) array transmitting antenna. The proposed GPR system with the four-element array synchronous excitation antenna is realized based on Wilkinson power divider, so as to improve the gain and directivity of antenna system. The simulation and measurement results have shown that the designed array GPR system has a bandwidth of 600 MHz ∼ 3 GHz, a maximum gain of 15 dBi and a half-power beam width of 32°. The gprMax forward simulation and sand trough experiment results have verified that the proposed system has obvious electromagnetic wave focusing effect, greater sounding and higher spatial resolution. It can provide technical support for non-destructive precise detection of urban shallow underground complex targets.

Electromagnetic wave focusing with 2-D gridded parabolic reflector made of parallel circular PEC wires at oblique incidence

We consider the two-dimensional (2-D) scattering of the TE- and TM-polarized plane electromagnetic waves from a discrete grid-like parabolic reflector consisting of parallel circular perfectly electrically conducting (PEC) wires at oblique incidence. Our analysis is performed in the exact formulation, fully taking into account the wave interactions between the wires. We use the method of separation of variables in the local cylindrical coordinate systems in combination with Graf’s addition formulas for cylindrical functions. The near field in the vicinity of the reflector is calculated at different angles of incidence. The dependences of the maximum field amplitude in the focal area and the position of this maximum on the angle of incidence are plotted. The far field scattered patterns, total scattering cross-sections and backward scattering cross-sections are calculated and discussed.

Enhancing microwave heating uniformity using reconfigurable diffractive beamforming surface

AbstractConventional microwave oven suffers nonuniform electric field distribution due to standing wave inside the cavity, requiring improved heating uniformity. Multimode ovens, which are regarded as the most popular method, suffer from relatively limited accuracy and dependency on experimental validations. In this paper, a new class of microwave heating methodology is proposed to achieve heating uniformity improvements through the suppression of undesired standing waves. Microwave absorbers and focusing of electromagnetic waves using reconfigurable diffractive surface are devised, validated, and discussed. Numerical and experimental studies ascertain that the heat uniformity is improved by more than three factors compared to conventional microwave applicators, indicating its potential application and feasibilities.

시간 역전을 기반으로 한 지능적 원거리 무선전력전송

In this paper, we demonstrate electromagnetic wave focusing and rectification based on time reversal as a smart method for far-field wireless power transfer. Time reversal in a complex propagation environment allows for transmission of high peak power pulses by focusing the electromagnetic waves selectively regardless of the receiver position. We demonstrate wave focusing and radio frequency (RF) to direct current (DC) rectification via numerical simulation of a complex propagation environment. The results reveal that time reversal can ensure peak power up to 12 dB greater compared to a narrowband continuous wave signal, thereby enhancing the rectified DC voltage with better efficiency.

A near zero refractive index metalens to focus electromagnetic waves with phase compensation metasurface

Metamaterials have been widely used to enhance radiation characteristics of antennas thanks to their ability to manipulate the electromagnetic waves. Recent progress has shown that flat metasurfaces with reduced tunable dimensions are capable to provide a near zero refractive index and a phase compensation mechanism which are responsible for the focusing of electromagnetic waves. Here, we present a study, about two types of flat metasurface lenses operating at the frequency of 5.9 GHz for the improvement of a patch antenna radiation properties and bandwidth at the same time. The proposed structures can be used in wireless point to point communication and especially for WAVE applications.

Modeling of Antenna for Deep Target Hydrocarbon Exploration

Nowadays control source electromagnetic method is used for offshore hydrocarbon exploration. Hydrocarbon detection in sea bed logging (SBL) is a very challenging task for deep target hydrocarbon reservoir. Response of electromagnetic (EM) field from marine environment is very low and it is very difficult to predict deep target reservoir below 2km from the sea floor. This work premise deals with modeling of new antenna for deep water deep target hydrocarbon exploration. Conventional and new EM antennas at 0.125Hz frequency are used in modeling for the detection of deep target hydrocarbon reservoir. The proposed area of the seabed model (40km ´ 40km) was simulated by using CST (computer simulation technology) EM studio based on Finite Integration Method (FIM). Electromagnetic field components were compared at 500m target depth and it was concluded that Ex and Hz components shows better resistivity contrast. Comparison of conventional and new antenna for different target depths was done in our proposed model. From the results, it was observed that conventional antenna at 0.125Hz shows 70% ,86% resistivity contrast at target depth of 1000m where as new antenna showed 329%, 355% resistivity contrast at the same target depth for Ex and Hz field respectively. It was also investigated that at frequency of0.125Hz, new antenna gave 46% better delineation of hydrocarbon at 4000m target depth. This is due to focusing of electromagnetic waves by using new antenna. New antenna design gave 125% more extra depth than straight antenna for deep target hydrocarbon detection. Numerical modeling for straight and new antenna was also done to know general equation for electromagnetic field behavior with target depth. From this numerical model it was speculated that this new antenna can detect up to 4.5 km target depth. This new EM antenna may open new frontiers for oil and gas industry for the detection of deep target hydrocarbon reservoir (HC)

Electromagnetic Modeling of Human Body Using High Performance Computing

Realistic simulation of electromagnetic wave propagation in the actual human body can expedite the investigation of the phenomenon of harvesting implanted devices using wireless powering coupled from external sources. The parallel electromagnetics code suite ACE3P developed at SLAC National Accelerator Laboratory is based on the finite element method for high fidelity accelerator simulation, which can be enhanced to model electromagnetic wave propagation in the human body. Starting with a CAD model of a human phantom that is characterized by a number of tissues, a finite element mesh representing the complex geometries of the individual tissues is built for simulation. Employing an optimal power source with a specific pattern of field distribution, the propagation and focusing of electromagnetic waves in the phantom has been demonstrated. Substantial speedup of the simulation is achieved by using multiple compute cores on supercomputers.

Near field focusing for nondestructive microwave testing at 24 GHz – Theory and experimental verification

This paper describes the development of different novel antenna concepts for improving the spatial resolution of microwave based non-destructive testing (NDT) at 24 GHz. In a great number of applications the antenna of the sensor can be brought very close to the device under test. In these cases, the near field characteristics of the antennas are crucial for a high resolution. However, common sensor heads offer either a high image resolution or a high penetration depth. In order to combine both of the characteristics different antenna concepts have been developed. The objectives were to obtain a high return loss combined with a sufficient high dynamic range and a near field focusing of electromagnetic waves in order to yield a high resolution. Altogether, three antennas have been set up. Each antenna has been calculated analytically, followed by a FEM simulation, near field measurements and an experimental verification.

Optimization of electromagnetic wave focusing in heterogeneous biological tissue model

Optimization of electromagnetic wave focusing in heterogeneous biological tissue model

Focusing system of burst electromagnetic waves for medical applications

Bioelectrics has attracted much attention. Inducing apoptosis in malignant cells using subnanosecond pulses has previously been investigated; these results have encouraged the authors to develop a burst electromagnetic wave focusing system for cancer treatment through the induction of apoptosis to cells. Burst electromagnetic waves are characterized by a high-frequency and narrow band signal over a very short duration. This system consists of a radiating antenna and an ellipsoidal reflector which focuses radiation waves. The ellipsoidal reflector has the characteristic of focusing burst electromagnetic waves radiated from the first focal point to the second focal point, thus enhancing the electric field at the second focal point. This system is immersed in heated water to avoid permittivity mismatch between living tissue and the water in which electromagnetic waves propagate, thus reducing reflection and refraction at the surface of biological tissue. This paper presents experimental and simulated results purposed on narrowing focusing point area. The focusing of burst electromagnetic wave at the second focal point was confirmed by preparing a distribution map of electric fields. The experiment and simulation compared three types of transmitting antenna: sleeve, brown and discone antennas. The discone antenna was found to give the shortest FWHM of the electric field distribution. Attenuation of burst electromagnetic waves by biological tissue was investigated using pig tissue: skin, fat and muscle. Attenuation by muscle was found to be greatest. Thicker tissue was found to lead to greater attenuation.

Metamaterials Controlled with Light

We suggest and verify experimentally the concept of functional metamaterials whose properties are remotely controlled by illuminating the metamaterial with a pattern of visible light. In such metamaterials arbitrary gradients of the effective material parameters can be achieved simply by adjusting the profile of illumination. We fabricate such light-tunable microwave metamaterials and demonstrate their unique functionalities for reflection, shaping, and focusing of electromagnetic waves.

Negative refraction and partial focusing with a crossed wire mesh: Physical insights and experimental verification

We experimentally verify that a flat metamaterial lens formed by nonconnected crossed metallic wires enables the partial focusing of electromagnetic waves, as a consequence of the phenomenon of all-angle broadband negative refraction in such media. We prove that the strength of the negative refraction effect can be controlled by adjusting the angle between the crossed wires.

MOVING TARGET TRACKING USING TIME REVERSAL METHOD

Time reversal focusing of electromagnetic waves is investigated in case of source motion. We extract analytical formulation of uniformly moving source in presence of ideal time reversal cavity (TRC) and a more realistic model, time reversal mirror (TRM). Similar to the acoustic case, it has been observed that in case of moving point source spatial focusing is still achievable. Furthermore, we also investigate super resolution efiects on time reversal (TR) focusing of moving source in continuous random media. Results shows that an increase in (multipath) leads to better focusing resolution of the time-reversed signals.

Modeling of Antenna for Deep Target Hydrocarbon Exploration

Nowadays control source electromagnetic method is used for offshore hydrocarbon exploration. Hydrocarbon detection in sea bed logging (SBL) is a very challenging task for deep target hydrocarbon reservoir. Response of electromagnetic (EM) field from marine environment is very low and it is very difficult to predict deep target reservoir below 2 km from the sea floor. This work premise deals with modeling of new antenna for deep water deep target hydrocarbon exploration. Conventional and new EM antennas at 0.125 Hz frequency are used in modeling for the detection of deep target hydrocarbon reservoir. The proposed area of the seabed model (40 km ′ 40 km) was simulated by using CST (computer simulation technology) EM studio based on Finite Integration Method (FIM). Electromagnetic field components were compared at 500 m target depth and it was concluded that Ex and Hz components shows better resistivity contrast. Comparison of conventional and new antenna for different target depths was done in our proposed model. From the results, it was observed that conventional antenna at 0.125 Hz shows 70%, 86% resistivity contrast at target depth of 1000 m where as new antenna showed 329%, 355% resistivity contrast at the same target depth for Ex and Hz field respectively. It was also investigated that at frequency of 0.125 Hz, new antenna gave 46% better delineation of hydrocarbon at 4000 m target depth. This is due to focusing of electromagnetic waves by using new antenna. New antenna design gave 125% more extra depth than straight antenna for deep target hydrocarbon detection. Numerical modeling for straight and new antenna was also done to know general equation for electromagnetic field behavior with target depth. From this numerical model it was speculated that this new antenna can detect up to 4.5 km target depth. This new EM antenna may open new frontiers for oil and gas industry for the detection of deep target hydrocarbon reservoir (HC).

Experimental verification of subwavelength acoustic focusing using a near-field array of closely spaced elements

A linear array of closely spaced sound transducers is presented that can produce a subwavelength-focused intensity profile at a distance of a quarter wavelength. This work is related to research on super-resolution using metamaterials in both the acoustic and optical domains. It is designed using the principle of shifted beams, a near-field antenna array theory developed for the subwavelength focusing of electromagnetic waves. Once the spatial sound pattern is characterized for each source, the optimal weights for a minimum beam width can be calculated. An experiment operating at 4 kHz was able to successfully construct a super-focused beam.

Surface wave holography on designing subwavelength metallic structures

We report a method in the framework of surface wave holography to manipulate the electromagnetic wave on the metallic surface for realizing complicated electromagnetic wave transport functionalities in three-dimensional (3D) space. The method allows for direct determination of the metallic surface structure morphology for a given transport functionality, by means of writing desirable object information on the metallic surface via interference with a reference surface wave. We have employed the analytical approach to design and build metallic surface structures that realize arbitrary single-point focusing, arbitrary single-direction beam collimation, and simultaneous two-point focusing of electromagnetic wave in 3D space. Good agreement between numerical simulations and microwave experimental measurements has been found and confirms the power of the method in conceptually understanding and exploiting the surface electromagnetic wave on subwavelength metal structures.

Influence of line defects on focusing in a two-dimensional photonic-crystal flat lens

We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a line defect in the lens is introduced along the light transmission direction and the width of the line defect is less than λ/2. However, there appear two focusings when the width of the line defect is more than λ/2. When the line defect is introduced along the direction perpendicular to the transmission, there is always one focusing.

FOCUSING OF ELECTROMAGNETIC WAVE FROM HYPERBOLIC LENS INTO A UNIAXIAL CRYSTAL WITH AN ARBITRARY ORIENTATION OF THE OPTICAL AXIS IN THE PRESENCE OF ABERRATIONS

We derive integral representations suitable for studying the focusing of electromagnetic waves through a symmetrically hyperbolic focusing lens into uniaxial crystal in the presence of cylindrical and coma aberrations using Maslov's method. The uniaxial crystal used is the negative crystal LiNbO3. Numerical computations are made to obtain the results for focused flelds inside negative uniaxial crystal with several difierent orientations of the optical axis in the plane of incidence. The efiects of aberrations inside uniaxial crystal and isotropic medium are also noted. The results are compared with those obtained by Kirchhofi-Huygens integral and Maslov's method which are in good agreement.