Experimental verification of effect of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation

The evaporation duct which forms above the ocean surface has a significant influence on electromagnetic wave propagation above 2 GHz over the ocean. The effects of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation are investigated, both in numerical simulation and experimental observation methods, in this paper. Firstly, the features of the horizontal inhomogeneity of the evaporation duct are discussed. Then, two typical inhomogeneous cases are simulated and compared with the homogeneous case. The result shows that path loss is significantly higher than that in the homogeneous case when the evaporation duct height （EDH） at the receiver is lower than that at the transmitter. It is also concluded that the horizontal inhomogeneity of the evaporation duct has a significant influence when the EDH is low or when the electromagnetic wave frequency is lower than 13 GHz. Finally, experimental data collected on a 149-km long propagation path in the South China Sea in 2013 are used to verify the conclusion. The experimental results are consis- tent with the simulation results. The horizontal inhomogeneity of evaporation duct should be considered when modeling electromagnetic wave propagation over the ocean.

Influence of obstacle on electromagnetic wave propagation in evaporation duct with experiment verification

In this paper, the influence of obstacle on electromagnetic wave propagation in an evaporation duct is investigated, both from numerical simulation and experimental observation. A comparison of electromagnetic wave propagation in evaporation duct with and without obstacle for a typical case is presented. The presence of obstacle causes a significant increase in path loss. The obstacle has significant impact on electromagnetic wave propagation when the frequency is higher than 5 GHz and when the evaporation duct height is higher than 10 m. The influence of an island on electromagnetic wave propagation was observed in the experiment held in the South China Sea, October 2012. The experiment result shows that the island causes about 30-40 dB increase in path loss. The discrepancy between model and measurement is analyzed and the errors of transmitting antenna height and relative humidity are the possible causes of the discrepancy.

Impact of Evaporation Duct on Electromagnetic Wave Propagation During a Typhoon

The evaporation duct,a result of evaporation from the ocean,is a region above the sea surface in which radio waves are refracted downward.This duct has strong effects on microwave instruments.Typhoons cause huge anomalies in marine meteorological parameters that influence the evaporation duct distribution and structure,which in turn affects the propagation of electromagnetic(EM)waves.However,EM wave propagation under the typhoon process has seldom been reported.Thus,taking Typhoon Phanfone(201929)as an example,this study uses a dataset from the European Centre for Medium-Range Weather Forecasts,combined with the Naval Atmospheric Vertical Surface Layer Model and the parabolic equation model,to study the evaporation duct’s impact on EM wave propagation during a typhoon.The spatial and temporal path loss distributions reveal that large amounts of EM wave energy are emitted from the evaporation duct when the EM wave passes through a typhoon eye.On average,a typhoon eye causes an approximately 20 dB increase in path loss for EM wave propagation at low antenna height.Furthermore,the effects of a typhoon eye on EM wave propagation at different signal frequencies and antenna heights are studied.The results show that a typhoon has a larger impact on EM wave propagation with low signal frequency and high antenna height.

Modeling of Electromagnetic Wave Propagation and Its Applicationin Virtual Test

With the development of virtual test,the computation of the effect of different weather conditions on electromagnetic wave propagation is required in many simulation systems. Firstly,this paper presents a unique point of view for computing the electromagnetic wave attenuation ratio under different weather conditions by means of an independent electromagnetic wave propagation component that can be directly implemented in virtual test, and is easy to configure and easy to reuse. We present an analysis of the principles of electromagnetic wave propagation and the algorithms designed for realization of various propagation models within the electromagnetic wave propagation component. Secondly,this paper presents a use-case analysis and outlines the design of the component,verifies the developed models under various weather conditions,and obtains equivalent values as those obtained theoretically. Finally,we build a virtual test system,verify the system in different weather conditions,and again obtain equivalent values to those obtained theoretically. The algorithms in the electromagnetic wave propagation component are developed in the C language, which substantially improves the computational speed,and meets the real-time requirements of the virtual testing platform.

Influences of Turbulent Reentry Plasma Sheath on Wave Scattering and Propagation

The randomness of turbulent reentry plasma sheaths can affect the propagation and scattering properties of electromagnetic waves.This paper developed algorithms to estimate the influences.With the algorithms and typical reentry data,influences of GPS frequency and Ka frequency are studied respectively.Results show that,in terms of wave scattering,the scattering loss caused by the randomness of the turbulent plasma sheath increases with the increase of the ensemble average electron density,ensemble average collision frequency,electron density fluctuation and turbulence integral scale respectively.Also the scattering loss is much smaller than the dielectric loss.The scattering loss of Ka frequency is much less than that of the GPS frequency.In terms of wave propagation,the randomness arouses the fluctuations of amplitude and phase of waves.The fluctuations change with altitudes that when the altitude is below 30 km,fluctuations increase with altitude increasing,and when the altitude is above 30 km,fluctuations decrease with altitude increasing.The fluctuations of GPS frequency are strong enough to affect the tracking,telemetry,and command at appropriate conditions,while the fluctuations of Ka frequency are much more feeble.This suggests that the Ka frequency suffers less influences of the randomness of a turbulent plasma sheath.

Numerical Analysis of EM Wave Propagation in Free Space and Chiral Media

In this paper, an implicit finite difference scheme of Box method is presented for analyzing the electromagnetic (EM) wave propagation in the case of axial symmetry. Typical numerical examples, which are about EM wave propagation in free space and chiral media, are presented. Such method has the advantage of high accuracy and easy boundary handling.

A Predictive 6G Network with Environment Sensing Enhancement:From Radio Wave Propagation Perspective

In order to support the future digital society,sixth generation(6G)network faces the challenge to work efficiently and flexibly in a wider range of scenarios.The traditional way of system design is to sequentially get the electromagnetic wave propagation model of typical scenarios firstly and then do the network design by simulation offline,which obviously leads to a 6G network lacking of adaptation to dynamic environments.Recently,with the aid of sensing enhancement,more environment information can be obtained.Based on this,from radio wave propagation perspective,we propose a predictive 6G network with environment sensing enhancement,the electromagnetic wave propagation characteristics prediction enabled network(EWave Net),to further release the potential of 6G.To this end,a prediction plane is created to sense,predict and utilize the physical environment information in EWave Net to realize the electromagnetic wave propagation characteristics prediction timely.A two-level closed feedback workflow is also designed to enhance the sensing and prediction ability for EWave Net.Several promising application cases of EWave Net are analyzed and the open issues to achieve this goal are addressed finally.

Waveguide resonance of subwavelength metallic slits

The transmission characteristics of a metallic film with subwavelength periodic slits are investigated by using the two-dimensional finite-difference time-domain method （2D-FDTD）. Two models are constructed to show the dependance of the transmission spectrum on the slit structure. A sandwiched structure is used to exhibit the contribution of the metallic wall inside slits to the extraordinary high transmission. And a filled slit structure is employed to reflect the relation between the average refractive index inside the slits and the transmission spectrum of the structure. The transmission characteristics of two structures can be explained well with the waveguide resonance theory.

ANALYSIS ON CHARACTERISTICS OF ATMOSPHERIC DUCT AND ITS EFFECTS ON THE PROPAGATION OF ELECTROMAGNETIC WAVE

On the basis of introducing the basic categories of atmospheric refraction and their existing conditions,the forming processes of three kinds of atmospheric ducts are expounded.Several main characteristics of atmospheric duct are summarized and analyzed,and field sounding data from the WEstern North-Pacific cloud-radiation EXperiment(WENPEX)and meteorological data around the Xisha sea area are used to validate these characteristics.Meanwhile the sensitivities of the evaporation duct height to the variations of atmospheric humidity.the air-sea temperature difference.and horizontal wind speed are examined.With the analysis of the effect of atmospheric duct on the propagation of electromagnetic wave.the maximum trapped-wavelength and the critical emitting angle of elevation for electromagnetic wave which can form duct propagation are derived. At the same time the four kinds of necessary conditions for electromagnetic wave to form duct propagation are brought forward.The effects of atmospheric duct on ultrashort wave propagation, radar observation.short wave communication etc.are also discussed.

RF characteristics of wireless capsule endoscopy in human body

The wireless capsule endoscope,as a small electronic device,has conquered some limitations of traditional wired diagnosing tools,such as the uncomfortableness of the cables for the patient and the inability to examine the very convoluted small intestine section.However,this technique is still encountering a lot of practical challenges and is looking for feasible improvements.This work investigates the RF performance of the wireless capsule endoscope system by studying the electromagnetic(EM) wave propagation within the human body.A wireless capsule endoscopy transmission channel model is constructed to serve the purpose of investigating signal attenuations according to the relative position between the transmitter and the receiver.Within 300-500 MHz,the S_(21) results are regular and do not display any sudden changes,which allows a suitable expression to be derived for S_(21) in terms of frequency and offset.The results provide useful information for capsule localization.

Remote sensing of atmospheric duct parameters using simulated annealing

Simulated annealing is one of the robust optimization schemes. Simulated annealing mimics the annealing process of the slow cooling of a heated metal to reach a stable minimum energy state. In this paper, we adopt simulated annealing to study the problem of the remote sensing of atmospheric duct parameters for two different geometries of propagation measurement. One is from a single emitter to an array of radio receivers （vertical measurements）, and the other is from the radar clutter returns （horizontal measurements）. Basic principles of simulated annealing and its applications to refractivity estimation are introduced. The performance of this method is validated using numerical experiments and field measurements collected at the East China Sea. The retrieved results demonstrate the feasibility of simulated annealing for near real-time atmospheric refractivity estimation. For comparison, the retrievals of the genetic algorithm are also presented. The comparisons indicate that the convergence speed of simulated annealing is faster than that of the genetic algorithm, while the anti-noise ability of the genetic algorithm is better than that of simulated annealing.

IMPROVEMENT TO THE EVAPORATION DUCT MODEL BY INTRODUCING NONLINEAR SIMILARITY FUNCTIONS IN STABLE CONDITIONS

Modified refractivity (M) profile is an important parameter to describe the atmospheric refraction environment,as well as a key factor in uniquely evaluating electromagnetic propagation effects.In order to improve the model-derived M profile in stable (especially very stable) conditions,three nonlinear similarity functions,namely BH91,CB05,SHEBA07,are introduced in this paper to improve the original Babin_V25 model,and the performances of these modified models are verified based on the hydrometeorological observations from tower platforms,which are finally compared with the original Babin_V25 model and Local_HYQ92 model.Results show that introducing nonlinear similarity functions can significantly improve the model-derived M profile;especially,the newly developed SHEBA07 functions manage to reduce the predicted root mean square (rms) differences of M and M slope (for both 0-5m and 5-40m) by 64.5%,16.6%,and 60.4%,respectively in stable conditions.Unfortunately,this improved method reacts little on the evaporation duct height;in contrast,Local_HYQ92 model is capable of reducing the predicted rms differences of M,M slope (for both 0-5m and 5-40m),and evaporation duct height by 76.7%,40.2%,83.7%,and 58.0% respectively.Finally,a new recommendation is made to apply Local_HYQ92 and Babin_SHEBA07 in very stable conditions considering that M slope is more important than evaporation duct height and absolute M value in uniquely determining electromagnetic propagation effects.

Role of the aperture in Z-scan experiments: A parametric study

In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing effect. In this work, by numerically solving the Fresnel-Kirchhoff diffraction integrals, the amount of transmitted power through apertures has been evaluated and a parametric study on the role of the various parameters that can influence this transmitted power has been done. In order to perform a comprehensive analysis, we have used a nonlinear phase shift optimized for nonlocal nonlinear media in our calculations. Our results show that apertures will result in the formation of symmetrical fluctuations on the wings of Z-scan transmittance curves. It is further shown that the appearance of these fluctuations can be ascribed to the natural diffraction of the Gaussian beam as it propagates up to the aperture plane. Our calculations reveal that the nonlocal parameter variations can shift the position of fluctuations along the optical axis, whereas their magnitude depends on the largeness of the induced nonlinear phase shift. It is concluded that since the mentioned fluctuations are produced by the natural diffraction of the Gaussian beam itself, one must take care not to mistakenly interpret them as noise and should not expect to eliminate them from experimental Z-scan transmittance curves by using apertures with different sizes.

Photonic crystal structures:Beam deflector and beam router

We investigate the optical characteristic,transverse magnetic（TM） and transverse electric（TE） band of twodimensional（2 D） square lattice photonic crystal structure,which is composed of cylindrical air regions positioned at the corners of the square shaped dielectric rods.We obtain the wide photonic bandwidths between TM1–TM2 and TM3–TM4 bands.According to the results,we demonstrate the band gaps close to each other in the TM and TE frequencies for proposed structures.The resulting photonic gaps are formed to be about 8% at the higher frequencies of TE modes（TE4–TE5）and TM modes（TM7–TM8 and TM9–TM10）.In addition,we examine isotropically generated structures for light guiding properties and observe that the light is directed in a particular route without using any deflection.We also investigate the self-collimation effect with the designed structure.The obtained results reveal the influences of the radius of cylindrical air holes and the angle between these air holes on absolute and partial photonic band gaps.Moreover,we observe the TM and TE band gaps that overlap.It is thought that the obtained band overlap will provide an easy way to produce the photonic crystals in practical applications like photonic insensitive waveguide.It is also believed that these results can provide the photonic crystal structures to work as a beam deflecting and beam router in integrated optical circuit applications.

Superimposed orbital angular momentum mode of multiple Hankel–Bessel beam propagation in anisotropic non-Kolmogorov turbulence

Mathematical models for the superimposed orbital angular momentum （OAM） mode of multiple Hankel-Bessel （HB） beams in anisotropic non-Kolmogorov turbulence are developed. The effects of anisotropic turbulence and source parameters on the mode detection spectrum of the superimposed OAM mode are analyzed. Anisotropic characteristics of the turbulence in the free atmosphere can enhance the performance of OAM-based communi- cation. The HB beam is a good source for mitigating the turbulence effects due to its nondiffraction and self-focusing properties. Turbulence effects on the superimposed OAM mode can be effectively reduced by the ap- propriate allocation of OAM modes at the transmitter based on the reciprocal features of the mode cross talk.

Photonic crystal waveguides and their applications Invited Paper

Two-dimensional （2D） slab photonic crystal waveguides （PCWGs） on silicon-on-insulator （SOI） wafer were designed and fabricated. Full photonic band gap, band gap guided mode, and index guided mode were observed by measuring the transmission spectra. Mini-stop-bands in the PCWG were simulated with different structure parameters. Coupling characteristics of PCWG were investigated theoretically considering the imperfections during the fabrication process. It was found that suppressing power reservation effect can realize both short coupling length and high coupling efficiency.

An analog of double electromagnetically induced transparency with extremely high group indexes

An asymmetric metamaterial exhibiting an analog of double electromagnetically induced transparency （EIT） in the middle-infrared region is reported. The metamaterial consists of two-layered arrays of Ushaped rings embedded in a medium, with the lower layer rotated by 90°. Our simulations demonstrate that both maximum group indexes are extremely high at the two EIT-like positions. The group index reaches about thrice the currently reported maximum value at the high-frequency EIT-like position. The transmittance at the two transparency positions also possesses extremely high Q factors, which is conducive to controlling the propagation of electromagnetic waves.

A novel biosensor with enhanced sensitivity based on grating coupled double-layered porous silicon waveguide

The enhanced sensitivity of a guided mode biosensor is analyzed by employing double-layered porous silicon grating structures. The grating-coupled waveguide structure consists of two porous silicon grating layers with different refractive indices. simulations are carried out by changing the refractive index, which is due to the binding of biological molecules on the porous silicon pore can increase the refractive index of porous silicon. The numerical results show that this novel guided mode biosensor with a double-layered grating can provide not only a very high sensitivity but also a better reflectivity characteristic.

A New Evaporation Duct Climatology over the South China Sea

The climatology of evaporation ducts is important for shipborne electromagnetic system design and application. The evaporation duct climatology that is currently used for such applications was developed in the mid 1980s; this study presents efforts to improve it over the South China Sea （SCS） by using a state- of-the-art evaporation duct model and an improved meteorology dataset. This new climatology provides better evaporation duct height （EDH） data over the SCS, at a higher resolution of 0.312°×0.313°. A comparison between the new climatology and the old one is performed. The monthly average EDH in the new climatology is between 10 and 12 m over the SCS, higher than that in the old climatology. The spatiotemporal characteristics of the evaporation duct over the SCS in different months are analyzed in detail, based on the new climatology.

Design of guided mode resonant filters for authentication applications through azimuthal angles varying

Guided mode resonant filters （GMRFs） for authentication application with low sideband reflection at 0^o and 90^o azimuthal angles were designed. Using rigorous coupled-wave analysis, the diffractive characteristics of this kind device with different illumination angles, groove depths, and thicknesses of cover SiO2 layer were investigated. The structure of GMRF which satisfies the requirements for authentication applications was obtained. Illuminated at 30^o for a definite polarization mode, the filter presents symmetrical reflectance shape, low sideband reflectance, two separate reflectance peaks, and definite full-width at halfmaximum （FWHM） at 0^o and 90^o azimuthal angles.