Ected Waves Research Articles

УСТРОЙСТВО И СПОСОБ УПРАВЛЕНИЯ СВЧ-ОБРАБОТКОЙ СЕМЯН НА КОНВЕЙЕРНОЙ ЛЕНТЕ

The sowing qualities of seeds – such as germination, germination energy, weight of 1000 seeds, etc., are the factors ensuring high yields of agricultural crops. Technological methods of seed and grain treatment with the UHF MEMF (microwave electromagnetic fi eld of ultrahigh frequency) energy involve the use of various types of microwave devices, diff ering both in operating principle and in design. In fact, the process of microwave treatment of seeds is similar to the process of heat treatment of dielectric materials. Therefore, depending on the goal of treatment, microwave devices should provide some kind of selectivity of microwave heating, a high conversion factor of microwave energy into thermal energy, uniformity of microwave treatment of the bulk of material, protection of the microwave generator and electromagnetic safety. During the microwave treatment of seeds, it is important to ensure uniform treatment of the bulk of seeds and automatically maintain optimal treatment modes (microwave heating modes). An installation design is proposed for microwave treatment of seeds. A specifi c feature of the proposed design is that seeds are processed on a moving belt under an emitter with the process control and regulation according to the speed and fi nal heating temperature. Moreover, the microwave source intensity depends on the load (a layer of seeds on the conveyor belt). The authors also propose an algorithm for the microprocessor control of the device. Thus, the proposed design of the installation for treating seeds in a layer under the emitter on a moving conveyor belt, as well as the technological algorithm for matching the microwave source with the load ensure the compliance with the processing modes in strictly specifi ed ranges of the fi nal temperature and microwave heating rate of the material, as well as protect the microwave source from refl ected electromagnetic waves.

NOVEL SHORT TAPERED LEAKY WAVE ANTENNAS WITH COMPLEMENTARY SPLIT RING RESONANTOR FOR BACK LOBE SUPPRESSION

Two novel short tapered leaky wave antenna (LWA) designs with a complementary split ring resonator (CSRR) structure are proposed in this paper. The CSRR structure is positioned at 1=4‚g away from the open-end edge of the LWA. For one of the antenna designs, the CSRR is placed at the ground plane; for the other one, the CSRR is placed on the antenna plane. The re∞ected wave caused by the open-end edge of the LWA is cancelled by the re∞ected wave caused by the CSRR, thus, the back lobe can be efiectively suppressed. The length of these two short tapered LWAs with CSRR design is only 1:2‚g at 4.3GHz. According to the measurement results, the impedance bandwidth is 650MHz for 7dB return loss, which covers the range from 4.3GHz to 4.95GHz. The back lobe can be suppressed efiectively about more than 12dB at the whole operating frequency band. The scanning range of the main beam is about 34 - , which cover the scanning angle from 10 - to 44 - .

REDUCTION OF RADAR CROSS SECTION BASED ON A METASURFACE

A metasurface for Radar Cross Section (RCS) reduction is proposed. The surface is composed of the same type of metamaterial units with difierent geometric dimensions, leading to various re∞ection phases under the incidence of plane waves. By carefully choosing the phase distributions, difiusion will be produced for the re∞ected waves which may redistribute the scattering energy from the surface toward all the directions, and hence it can be applied as the coating of metallic targets with ultra-low RCS. Both the simulated and experimental results have validated the proposed method.

WAVE PACKETS SCATTERED BY NON-PERIODIC BRAGG-TYPE LAYERED STRUCTURES

The time delay, space shift and widening of wave packet transmitted and re∞ected by structures with Bragg mirrors have been investigated. The speciflc structures such as Bragg mirrors, resonators, and structures with chirp variation of thickness of the \period have been considered. The calculation has been carried out under the conditions that carrier frequency, and incidence angle is in the vicinity of the Bragg resonance. Integral (mass center) and difierential (group) estimates of the delay time and space shift have been compared. The conditions for the appearance of anomalous (negative) mass center delay or mass center shift (Goos-Hanchen shift) of the re∞ected wave packet have been determined. The shape transformations of the wave packet illuminating periodic and quasiperiodic apodized Bragg re∞ectors have been under consideration. Spatial apodization of permittivity contrast yields much smaller shape deformation of the transmitted wave packet upon incidence at angles and carrier frequency near the edges of re∞ection band, as well in Bragg re∞ection band, in comparison with phenomena in similar periodic structures. The values of group delay for layered structures with a small chirp variation of optical (electrical) thickness of the period along longitudinal coordinates have been experimentally obtained in microwave range.

WCIP APPLIED TO SUBSTRATE INTEGRATED WAVEGUIDE

This article presents an e-cient method for characteriza- tion of substrate integrated passive circuits. The analysis is based on the wave concept formulation and the iterative resolution of a system of two equations between incident and re∞ected waves. Simulations ob- tained are compared with analytical references and HFSS simulations. A good agreement is achieved with computation time saving.

ELECTROMAGNETIC INTERFERENCE IMPACT ON FRONT-END RECEIVERS OUTSIDE THE ANTENNA BANDWIDTH

Impact of electromagnetic interference on front-end receiver behaviour is theoretically and experimentally studied outside the bandwidth of the antennas. Microwave chaotic generation is observed. Under certain conditions, re∞ected waves combined to the non linearity of the front-end receiver leads to a chaotic signal generation between the antenna and the front-end receiver. Difierent antennas, such as patch, loop, monopole and horn, are tested. Theoretical and experimental results are presented for each antenna. When an intentional or an unintentional electromagnetic interference is applied outside of the bandwidth of an antenna, re∞ection waves are generated between the antenna radiation impedance which is in the case of a few ohms and the nonlinear impedance of the front-end circuit of the receiver which is interconnected to the antenna via a transmission line. Under certain conditions, the efiects of the re∞ected waves due to antenna mismatch combined to those of the nonlinear impedance of the front-end circuits lead to chaos generation. This can have an impact on the electrical behaviour of the receiver particularly for high speed receiver systems and short electromagnetic interference wave lengths. The chaotic behaviour has already been observed in a microwave limiter circuit (1), in 'R-L-diode' circuits (2{7) and also in VHF microstrip oscillator (8). The doubling period has been observed

ELECTROMAGNETIC FIELD OF A HORIZONTAL INFINITELY LONG MAGNETIC LINE SOURCE OVER THE EARTH COATED WITH A DIELECTRIC LAYER

In this paper, the electromagnetic fleld of a horizontal inflnitely long magnetic line source over the dielectric-coated earth is treated analytically, and the complete approximate solution for the radiated fleld under the far-fleld conditions is outlined. The total fleld is composed of four modes: the direct wave, the ideal re∞ected wave or image wave, the trapped surface wave, and the lateral wave. In particular, the complete analytical formulas are obtained for both the trapped surface wave and the lateral wave. The trapped surface wave is determined by the sum of residues of the poles. When the inflnitely long magnetic line source or the observation point is away from the planar surface of the dielectric-coated earth, the trapped surface wave decreases exponentially with height, and the total fleld is determined primarily by the lateral wave. When the conductivity of the earth is large, and both the inflnitely long magnetic line source and the observation point are on or close to the air-dielectric boundary, the total fleld is determined primarily by the trapped surface wave.

NEAR-FIELD AND PARTICLE SIZE EFFECTS IN COHERENT RAMAN SCATTERING

Nonlinear optical processes have been used for sensitive detection of chemicals, optical imaging and spectral analysis of small particles. We have developed an exact theoretical framework to study the angular dependence of coherent anti-Stokes Raman scattering (CARS) intensity in the near fleld and far fleld for nanoparticle and microparticle. We obtain exact analytical solution for the CARS signal valid for arbitrary detection distance. Interesting angular dependence is found for nanoparticle, especially with near fleld detection. The study includes the efiects of focused lasers and particle size on the CARS intensity distribution. We flnd that the detection distance and particle size do not afiect the spectroscopic peaks of CARS. However, interference of re∞ected waves in nanoparticle can produce a dip in the backscattered spectrum.

UNIFORM PLANE WAVE REFLECTION FROM PEC PLANE EMBEDDED IN A NONLINEAR MEDIUM

Re∞ection from a perfect electric conductor (PEC) plane of inflnite dimensions embedded in a second order nonlinear medium is studied. The re∞ected wave has two parts, one due to linear behavior, the other due to nonlinear behavior of the medium. The expressions of the re∞ection coe-cients for parallel and perpendicular polarization cases are obtained. The reduction of re∞ection coe-cient to a linear medium case is also reported. Dependence of the said coe-cients on incident electric fleld intensity and the angle of incidence is also plotted.

DESIGN OF A PERFECT ELECTROMAGNETIC CONDUCTOR (PEMC) BOUNDARY BY USING PERIODIC PATCHES

Perfect electromagnetic conductor (PEMC) is a novel concept in electromagnetic flelds of interesting properties and many potential applications. This paper introduces a new technique to design an artiflcial surface that has equivalent PEMC properties. The proposed PEMC boundary is based on a periodic structure composed of two conducting patches on a grounded dielectric slab. One of them is embedded inside the substrate and the other lies on the surface of the substrate. A conducting via is used to connect the two patches. In the resulting PEMC boundary, the polarization of the re∞ected wave is controlled by the tilting angle between the two patches.

QUANTITATIVE ESTIMATION OF SCATTERING WAVES IN CYLINDER-BODY MODEL FOR BODY AREA NETWORKS: COMPARISON OF ANALYSES WITH UNIFROM CYLINDER- AND SLAB-BODY MODELS

This paper estimates separately the components of scattering waves generated in cylinder-body model for body area networks. For the evaluation, scattering fleld formulations in relation to uniform cylinder- and slab-body models are provided, and the reliability of the analyses is testifled by the comparison with results computed by the flnite-difierence time-domain (FDTD) method. Creeping waves, cylinder leaky waves, and cylinder guided waves, which are created only in cylindrical structure, are extracted quantitatively by contrasting the scattering waves that are calculated with the two body models. In addition to the extracted waves, other components of scattering waves such as re∞ected waves, transmitted waves, surface waves, leaky waves, and guided waves also are examined. From evaluations with various operating frequencies and thicknesses of the body model, it is conflrmed that re∞ected waves have the most in∞uence on electrical characteristics of a source. Moreover creeping

A NOVEL APPROACH FOR RCS REDUCTION USING A COMBINATION OF ARTIFICIAL MAGNETIC CONDUCTORS

A thin Artiflcial Magnetic Conductor (AMC) structure for Radar Cross-Section (RCS) reduction applications is presented. The manufactured prototype, which combines two unit-cell metallization sizes, presenting two resonant frequencies, shows broad AMC operation bandwidth, polarization angle independency, and its angular margin when operating under oblique incidence is also tested. It is shown that signiflcant RCS reduction can be achieved with the proposed AMCs combination even if a 180 - phaseshift between re∞ected waves is not met. Two designs are considered: the already mentioned design combining AMCs with overlapped frequency bands and the second one combining Perfect Electric Conductor (PEC) and AMC surfaces. A comparison between these two designs regarding RCS reduction, supported by measurements in an anechoic chamber, is presented.

DISCUSSION ON VALIDITY OF HADAMARD SPECKLE CONTRAST REDUCTION IN COHERENT IMAGING SYSTEMS

Hadamard speckle contrast reduction (SCR) is considered to be an efiective approach to deal with speckle problems in coherent imaging systems. A Hadamard SCR system is divided into two sub- systems, which implement phase patterns projection and re∞ected waves imaging respectively. The performances of both sub-systems are discussed with numerical simulations and linked to certain parameters so as to give more insights of this approach. For generality, both optical and millimeter wave imaging systems are discussed. To distinguish from former literature based on Fourier optics, the simulation is implemented via wave optics, which is more physical and more accurate. Moreover, considering the fact that the Hadamard method originates from statistics, the efiectiveness of Hadamard SCR is in the flrst place linked to the texture of the object's surface. Statistical optics is also adopted during qualitative analysis of the results. It is shown that the ratio between the dimension of a resolution cell and the granular size of the object's randomly rough surface is closely linked to the performance of Hadamard SCR. Difierences in the roughness model in imaging cases of optical and millimeter waves are discussed, which would help to evaluate the validity of the Hadamard SCR approach in practice. The purpose of this paper is to clarify the misunderstandings of Hadamard SCR in previous literature and to give a guideline to apply this approach.

FURTHER STUDY OF RAINFALL EFFECT ON VHF FORESTED RADIO-WAVE PROPAGATION WITH FOUR-LAYERED MODEL

In this paper, rainfall efiect on the VHF radio-wave propagation in a tropical forest is further studied in details. Theoretical study and experimental investigations are performed with the help of a four-layered model for forested environment. It is found that the lateral wave traveling along the air-canopy interface, the direct waves, and the ground re∞ected waves are the main modes for VHF radio-wave propagation in forest. The rainfall can afiect these propagating waves to difierent extents. Especially, due to the increase in the dielectric permittivity of the wet canopy layer by rain water, the time of arrival of the direct wave traveling through the canopy layer can be delayed signiflcantly. Finally, the dielectric permittivity for the wet canopy layer under difierent rain events is evaluated empirically.

TUNABLE LATERAL SHIFT THROUGH NONLINEAR COMPOSITES OF NONSPHERICAL PARTICLES

The Goos-Hanchen (GH) shifts of the re∞ected waves from nonlinear nanocomposites of interleaved nonspherical metal and dielectric particles are investigated both theoretically and numerically. First, based on spectral representation theory and efiective medium approximation, we derive the fleld-dependent efiective permittivity of nonlinear composites. Then, the stationary phase method is adopted to study the GH shifts from nonlinear composites. It is found that for a given volume fraction, there exist two critical polarization factors Lc1 and Lc2, and bistable GH shifts appear only when L Lc2. Moreover, both giant negative and positive GH shifts accompanied with large re∞ectivity are found, hence they can be easily observed in experiments. The reversal of the GH shift may be controlled by adjusting both the incident angle and the applied fleld. Numerical simulations for Gaussian-type incident beam are performed, and good agreement between simulated data and theoretical ones is found especially for large waist width.

High Reflection Coatings with Negative and Positive Refractive Indexes

In this paper, we intend to create a stratifled coatings comprised of negative and positive refractive indexes, NRI and PRI, to achieve high re∞ection. Generally, quarter wave length longs of high and low refractive index media are applied to the substrate to form NRI-PRI multilayer stacks. By choosing the proper indexes, the various re∞ected wave fronts can be made to interfere gainfully to generate a well-organized re∞ector. The coatings and computations are performed and determined using the theory of transfer matrix method. Numerical results of this work show that the coatings are efiective for both parallel and perpendicular polarization components, and can be designed for a wide frequency range. In addition, this paper also provides to be able to decrease/increase the frequency range to the desired band and to make size reduction in the layer number.

Acoustic-Wave/Blade-Row Interactions Establish Boundary Conditions for Unsteady Inlet Flows

T HE computation of unsteady  ows in high-speed airbreathing inlets requires a compressor-faceboundarycondition (CFBC). The physical basis for the analytical or numerical formulation of a realistic CFBC is the acoustic re ection coefŽ cient of the operating compressor. In Ref. 1 an approximate, one-dimensionalmethod is offered to calculate this information for a single blade-row compressor, when the total approach velocity (vector sum of axial and tangentialcomponents, relative to the rotor blades) is subsonic.The present Note extends the calculation to the practically important case where the total approach velocity is supersonic and the axial component is subsonic. (In this Note, the term “supersonic” refers to this limited range.)The background,motivation,physicalmodel, method of analysis, and nomenclature described in Ref. 1 apply to thisNote without change and are not repeatedhere. Familiaritywith Ref. 1 is essential to the understandingof this Note. In supersonic cascade  ows expansion and compression waves can propagate upstream and can modify the approach  ow, which makes them considerablydifferent from subsonic cases. It has been well established that a steady, uniform, supersonic ow upstream of an inŽ nite, linear cascade of blades can exist only for a unique incidence angle. The existence of such an incidence implies that an upstreammoving acoustic disturbance (which might be initiated by a downstream-movingdisturbancearrivingto thebladerow) cancels the initial disturbance,restoring the undisturbedupstream  ow. The unique incidence angle can be determined in the knowledge of the blade geometry and the upstream Mach number (methods given in Ref. 2). The unique incidence angle is generally small, several degrees only. In the following,the exitMach number is assumed to be subsonic, which is a practically common situation. This assumption also deŽ nes a unique steady  ow when using the simplemean  owmethod of Ref. 1. The choice of subsonic out ow implies the presence of shocks (and, hence, a total pressure loss) in the blade passage. The effect of total pressure losses on the re ection coefŽ cient is demonstrably small and a reasonableestimate is sufŽ cient. Shock lossmay be estimated as that associatedwith a normal shock at the upstream Mach numberMu . The estimationof viscous lossesmay be made on the basisof empiricalinformationvalid for similar bladegeometries. The analysis deals with a transient initiated by the arrival of an acoustic step change to the blade row, the goal being the prediction of the magnitude of the re ected wave, which is also a step change. The equations used in the present analysis are the same as those of Ref. 1, with one exception. In the subsonic case, it was assumed that the direction of the exit  ow, after completion of the transient, is the same as the direction of the undisturbed exit  ow [Eq. (25)

Impedance and Its Time-Domain Extensions

The classical concept of impedance as a means to characterize the ree ectivity and absorption of a surface to the incident waves has always been a complex-valued quantity akin to plane harmonic waves and the analysis of their ree ections. A new look at this classical quantity irrespective of the type of incident waves is presented. It points out that a direct operational inversion of impedance into time-domain boundary operators will, in general, lead to an unstable system, whereas the inversion of the corresponding ree ection coefe cient will result in stable, easily implementable boundary operators for time-domain prediction of wave ree ection. It reveals the equivalent, pulselike, causal process of time convoluting the incident wave into the ree ected wave. Excellent agreement with analytical solutions derived here and from other sources supports the validity of the approach and demonstrates the accuracy of the implementations.

Optical parametric oscillator with non-ideal mirrors and single- and multi-mode pump beams

Residual re ections of the idler wave in nominally singly resonant optical parametric oscillators can lead to uctuations in the output because the parametric conversion process is sensitive to the phases of the re ected waves. The energy fluctuations in a pulsed optical parametric oscillator are studied experimentally and numerically for single- or multi-longitudinal mode pump beams. We find that the fluctuations are reduced by a multi-mode pump so this may be preferable when unwanted re ections are present. We also observe that the parametric conversion process leads to serious self-focusing of the pump beam, and this limits the maximum safe pump energy.