S. Ivanov, N. Nikolaev, R. Thomae, H. Klein, F. Hilschert
Radio frequency created plasma is very promising for applications targets. Capacitively coupled plasmas is relatively well investigated (see e. g. [ID. Recently inductively coupled plasmas have foundm increasing interest due to their possible use for implantation [2] and etching devises [3]. In well progress are both the theory and the experiment of inductively coupled plasma, created by spud coil. There is only few experiments with helical coil among which in Frankfirrt Pm experiment [2]. Doing plasma measurements we surprisingly have encountered light bubbles at high current probe regime. The bubbles are due to two double layers. Double layers appear in thermionic emission devices or in such, “where a potential is applied between independently generated discharges, which are separated by grids” [6]. In our experiments there are neither thermionic emission, nor grids. The plasma bubbles have been observed experimentally on the probe in inductively coupled plasma, created by helical coil around the plasma source. The bubbles are the saturation stage of the Bunemann instability j4.51. At the appearance of the bubbles there is a jump of the current, which is accompanied by drastically drop of plasma resistant. A typical for double laym dynamics has been observed. This work has been supported by DAAD and grant F-408 of the Bulgarian National Fund for Scientific Research.
{"title":"Plasma bubbles on langmuir probe in inductively coupled plasma","authors":"S. Ivanov, N. Nikolaev, R. Thomae, H. Klein, F. Hilschert","doi":"10.1109/AEM.1996.873109","DOIUrl":"https://doi.org/10.1109/AEM.1996.873109","url":null,"abstract":"Radio frequency created plasma is very promising for applications targets. Capacitively coupled plasmas is relatively well investigated (see e. g. [ID. Recently inductively coupled plasmas have foundm increasing interest due to their possible use for implantation [2] and etching devises [3]. In well progress are both the theory and the experiment of inductively coupled plasma, created by spud coil. There is only few experiments with helical coil among which in Frankfirrt Pm experiment [2]. Doing plasma measurements we surprisingly have encountered light bubbles at high current probe regime. The bubbles are due to two double layers. Double layers appear in thermionic emission devices or in such, “where a potential is applied between independently generated discharges, which are separated by grids” [6]. In our experiments there are neither thermionic emission, nor grids. The plasma bubbles have been observed experimentally on the probe in inductively coupled plasma, created by helical coil around the plasma source. The bubbles are the saturation stage of the Bunemann instability j4.51. At the appearance of the bubbles there is a jump of the current, which is accompanied by drastically drop of plasma resistant. A typical for double laym dynamics has been observed. This work has been supported by DAAD and grant F-408 of the Bulgarian National Fund for Scientific Research.","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125760094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A spectral domain full-wave algorithm based on 4x4 transfer matrix and integral equation metbods is developed for the connected and periodic microstrip line on the multilayered anisotropic substrate.
{"title":"Transfer matrix method for the theory of microstrip lines on the multilayered anisotropic substrate","authors":"I. Nefedov","doi":"10.1109/AEM.1996.872869","DOIUrl":"https://doi.org/10.1109/AEM.1996.872869","url":null,"abstract":"A spectral domain full-wave algorithm based on 4x4 transfer matrix and integral equation metbods is developed for the connected and periodic microstrip line on the multilayered anisotropic substrate.","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125873832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A new statistical model for fast fading channel simulation for both line of sight (L.O.S.) and no L.O.S. cases, has been developed using the theory of statistics. Considering that there is a finite number of fixed or randomly moving scatterers in the propagation medium, then in proportion to the central limit theorem the received signal is a modified Student's process (eq. 1). Thus the amplitude variations of the recived signal (the channel's impulse response envelope variations), termed as fast fading, can be modelled by the new so called POCA distribution, which can be found by the following analysis.
{"title":"A general statistical model for fast fading channel simulation","authors":"D. Polydorou, C. Capsalis","doi":"10.1109/AEM.1996.872858","DOIUrl":"https://doi.org/10.1109/AEM.1996.872858","url":null,"abstract":"A new statistical model for fast fading channel simulation for both line of sight (L.O.S.) and no L.O.S. cases, has been developed using the theory of statistics. Considering that there is a finite number of fixed or randomly moving scatterers in the propagation medium, then in proportion to the central limit theorem the received signal is a modified Student's process (eq. 1). Thus the amplitude variations of the recived signal (the channel's impulse response envelope variations), termed as fast fading, can be modelled by the new so called POCA distribution, which can be found by the following analysis.","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125326385","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This report delivers to investigation of diffraction of a frequency-modulated (FM) pulses on a conductive screen in dispersive media. The problem has an important significance in non-stationary diffraction processes of FM signals on conductive elements of antenna systems and space constructions. There are different analytical and numerical methods calculating a space-time distribution of wave fields caused by diffraction processes under consideration. In this paper we shall consider the problem of diffraction of a semi-infinitive radiopulse on a conductive screen by means of methods of a space-time (ST) geometry theory of diffraction (GTD). The propagation of a radio signal with increasing frequency is known to result in the compression of signal and forming a ST caustic of cuspoid types (AN) which may be interpreted as envelope of ST geometric-optical (GO) rays. An account of space-time boundary rays connected with the beginning of radiopulse lead to utilizing of BN+~=(AN,A~) edge catastrophes. As follows the field in the neighborhood of limiting ST GO ray is described by the incomplete Airy's functions. In diffraction problem with the metal screen besides ST GO rays and ST boundary rays two additional rays families generated on a boundary of the screen by rays listed above must be confederated: a family of ST diffraction rays generated by ST GO rays and ST corner rays generated by ST boundary rays. Then in the neighborhood of limiting ST GO ray the (AN,A~ ,AN,A~) corner catastrophe arise. If the screen boundary is a straight line and the signal frequency is not modulate, then N=l and all rays diverge and don't form caustics. If the radiopulse is modulated which frequency increase linearly, then N=2 and in addition to the focusing of ST GO rays the same type focusing (A$ of ST diffraction rays arises. In the case when the frequency modulation law besides linear term has also quadratic one it is possible to arise the (A3,Ai ,A3,Al) and so on. The problem will be more complex if we shall take into account a curvature of screen boundary and nonhomogeneity of medium. In the paper we shall also present the uniform asymptotic describing space-time structure of radiosignal in the neighborhood of limiting ST rays and results of numerical simulation of amplitude-phase field structure. '
{"title":"Radio pulse diffraction in terms of the wave catastrophe theory","authors":"A. S. Kryukovsky, D. S. Lukin, D. Rastyagaev","doi":"10.1109/AEM.1996.872871","DOIUrl":"https://doi.org/10.1109/AEM.1996.872871","url":null,"abstract":"This report delivers to investigation of diffraction of a frequency-modulated (FM) pulses on a conductive screen in dispersive media. The problem has an important significance in non-stationary diffraction processes of FM signals on conductive elements of antenna systems and space constructions. There are different analytical and numerical methods calculating a space-time distribution of wave fields caused by diffraction processes under consideration. In this paper we shall consider the problem of diffraction of a semi-infinitive radiopulse on a conductive screen by means of methods of a space-time (ST) geometry theory of diffraction (GTD). The propagation of a radio signal with increasing frequency is known to result in the compression of signal and forming a ST caustic of cuspoid types (AN) which may be interpreted as envelope of ST geometric-optical (GO) rays. An account of space-time boundary rays connected with the beginning of radiopulse lead to utilizing of BN+~=(AN,A~) edge catastrophes. As follows the field in the neighborhood of limiting ST GO ray is described by the incomplete Airy's functions. In diffraction problem with the metal screen besides ST GO rays and ST boundary rays two additional rays families generated on a boundary of the screen by rays listed above must be confederated: a family of ST diffraction rays generated by ST GO rays and ST corner rays generated by ST boundary rays. Then in the neighborhood of limiting ST GO ray the (AN,A~ ,AN,A~) corner catastrophe arise. If the screen boundary is a straight line and the signal frequency is not modulate, then N=l and all rays diverge and don't form caustics. If the radiopulse is modulated which frequency increase linearly, then N=2 and in addition to the focusing of ST GO rays the same type focusing (A$ of ST diffraction rays arises. In the case when the frequency modulation law besides linear term has also quadratic one it is possible to arise the (A3,Ai ,A3,Al) and so on. The problem will be more complex if we shall take into account a curvature of screen boundary and nonhomogeneity of medium. In the paper we shall also present the uniform asymptotic describing space-time structure of radiosignal in the neighborhood of limiting ST rays and results of numerical simulation of amplitude-phase field structure. '","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122408676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The finite element method for the computation of electromagnetic fields is gaining popularity in recent times due to its ability to handle arbitrary geometries and its versatility in modeling inhomogeneities and material discontinuities. For electrically large and complex structures, massively parallel computers have to be used in order to obtain sufficiently accurate solutions in acceptable time fiames. In this paper we present the implementation details and the performance evaluation of a parallel three dimensional finite element code for open domain electromagnetic problems. In the finite element method the computational domain is divided into smaller nonoverlapping subvolumes, in our implementation tetrahedra. Within each tetrahedron the scattered electric field is represented using edge based vector basis hnctions. The finite element mesh is truncated artificially at some distance fiom the scatterer with the use of a second order absorbing boundary condition [ 11. The whole mathematical procedure leads to a linear system with symmetric complex sparse matrix. Only the nonzero elements of the upper triangular part of this matrix are stored using the compressed row storage format. The linear system is solved with the conjugate orthogonal conjugate gradient method. The parallel computer we use is the Parsytec We13612 of the Athens High Performance Computing Laboratory. It is a distributed memory machine with message passing architecture. It consists of 512 T805 transputers arranged on a two dimensional grid. In order to parallelize the finite element code using np processors, we divided the global matrix and the vectors into np sections, and assign one section to each processor. The data decomposition is performed in a manner that reduces interprocessor communication, while balancing the load on each processor. We organize the np processors in a virtual ring topology, and employ asynchronous communication that allows us to overlap message exchange with computations for better efficiency. We tested the parallel code for the case of a plane wave incident on a dielectric sphere. The near field values were in good agreement with those from a Me series solution, although the absorbing boundary surface was placed only a fraction of a wavelength away fiom the scatterer. We observed significant speedups for large numbers of processors. This means that the finite element method is well suited for parallelization in a massively parallel environment. We firther noticed that for a given problem size, we can always find an upper boundary of processors above which performance deteriorates, as the increased communication overhead exceeds the time saved by parallel execution of computations. However we can set this boundary arbitrarily high by scaling up sufficiently the size of the problem. References
{"title":"A parallel implementation of the finite element method for electromagnetic scattering","authors":"P. Atlamazoglou, G. Pagiatakis, N. Uzunoglu","doi":"10.1109/AEM.1996.873072","DOIUrl":"https://doi.org/10.1109/AEM.1996.873072","url":null,"abstract":"The finite element method for the computation of electromagnetic fields is gaining popularity in recent times due to its ability to handle arbitrary geometries and its versatility in modeling inhomogeneities and material discontinuities. For electrically large and complex structures, massively parallel computers have to be used in order to obtain sufficiently accurate solutions in acceptable time fiames. In this paper we present the implementation details and the performance evaluation of a parallel three dimensional finite element code for open domain electromagnetic problems. In the finite element method the computational domain is divided into smaller nonoverlapping subvolumes, in our implementation tetrahedra. Within each tetrahedron the scattered electric field is represented using edge based vector basis hnctions. The finite element mesh is truncated artificially at some distance fiom the scatterer with the use of a second order absorbing boundary condition [ 11. The whole mathematical procedure leads to a linear system with symmetric complex sparse matrix. Only the nonzero elements of the upper triangular part of this matrix are stored using the compressed row storage format. The linear system is solved with the conjugate orthogonal conjugate gradient method. The parallel computer we use is the Parsytec We13612 of the Athens High Performance Computing Laboratory. It is a distributed memory machine with message passing architecture. It consists of 512 T805 transputers arranged on a two dimensional grid. In order to parallelize the finite element code using np processors, we divided the global matrix and the vectors into np sections, and assign one section to each processor. The data decomposition is performed in a manner that reduces interprocessor communication, while balancing the load on each processor. We organize the np processors in a virtual ring topology, and employ asynchronous communication that allows us to overlap message exchange with computations for better efficiency. We tested the parallel code for the case of a plane wave incident on a dielectric sphere. The near field values were in good agreement with those from a Me series solution, although the absorbing boundary surface was placed only a fraction of a wavelength away fiom the scatterer. We observed significant speedups for large numbers of processors. This means that the finite element method is well suited for parallelization in a massively parallel environment. We firther noticed that for a given problem size, we can always find an upper boundary of processors above which performance deteriorates, as the increased communication overhead exceeds the time saved by parallel execution of computations. However we can set this boundary arbitrarily high by scaling up sufficiently the size of the problem. References","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116789971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Fresnel zone lens witb transparentlreflecting (absorbing) rings has inadequate focusing properties.The radiation efficiency of the corresponding lens antenna is less than 15 % [l]. To increase the lens focusing quality Wiltse (1976) replaced the teflecting (absorbing) rings by phase-reversing dielectric Ms. On the base ofthis dielectric zoneplate lens antennas have been developed and examiued for which the radiation efficiency is of about 25-30 % [2-4]. Recently, a new variety of quarter-wave Fresnel zone-plate lens with increased focusing quality was proposed [5]. Each full-wave zone of the Fresnel plate lens was divided into four quarter-wave subzones which were covered by dielectric rings having equal thickness but different pennittivities. To accomplish a quarter-wave stepwise phaseandon the relative permittivities has to obey the following sequence: E 1’1, E2=6.25, €3‘4, and Eq”2.25. This is evident from the computed “infinite” transmission phase-shift characteristics of the dielectric plates having the above sequence of permittivity values, and thickness of the ideal dielectric phase-shifter, i.e. l/2 for & 4. This lens configuration was used to design a tmsmissive-type Fresnel zone-plate antennas for DBS TV and millimeter-wave bands with a computed radiation efficiency higher than 50% [5-71. They were examined theoretically using the multiple reflection/transmission coefficients for low-loss dielectric plates and vectorial Kirchhoff diffraction antenna theory. With dielectric rings made in sandwich-type manner the Fresnel zone-plate antenna reaches about 60% theoretical aperture efficiency. References
{"title":"Dielectric fresnel zone-plate lenses and antennas","authors":"R.D. Hristoy","doi":"10.1109/AEM.1996.872875","DOIUrl":"https://doi.org/10.1109/AEM.1996.872875","url":null,"abstract":"The Fresnel zone lens witb transparentlreflecting (absorbing) rings has inadequate focusing properties.The radiation efficiency of the corresponding lens antenna is less than 15 % [l]. To increase the lens focusing quality Wiltse (1976) replaced the teflecting (absorbing) rings by phase-reversing dielectric Ms. On the base ofthis dielectric zoneplate lens antennas have been developed and examiued for which the radiation efficiency is of about 25-30 % [2-4]. Recently, a new variety of quarter-wave Fresnel zone-plate lens with increased focusing quality was proposed [5]. Each full-wave zone of the Fresnel plate lens was divided into four quarter-wave subzones which were covered by dielectric rings having equal thickness but different pennittivities. To accomplish a quarter-wave stepwise phaseandon the relative permittivities has to obey the following sequence: E 1’1, E2=6.25, €3‘4, and Eq”2.25. This is evident from the computed “infinite” transmission phase-shift characteristics of the dielectric plates having the above sequence of permittivity values, and thickness of the ideal dielectric phase-shifter, i.e. l/2 for & 4. This lens configuration was used to design a tmsmissive-type Fresnel zone-plate antennas for DBS TV and millimeter-wave bands with a computed radiation efficiency higher than 50% [5-71. They were examined theoretically using the multiple reflection/transmission coefficients for low-loss dielectric plates and vectorial Kirchhoff diffraction antenna theory. With dielectric rings made in sandwich-type manner the Fresnel zone-plate antenna reaches about 60% theoretical aperture efficiency. References","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117257400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
hvestigation of properties of fields, -acted on a system of scatterers, is an important problem of modem physics. Description of such phenomena m resonance fkequency range, where length of the wave close to the scatterers' dimensions, is possible only with a rigorous solution of corresponding diffraction problem. The significant difficulties arise while the scattered field is calculated in the case of an arbitrary scatterers' geometry. One of the ways to solve the problem of scalar sonic wave difEaction on scatterers in stratified medium is proposed below. Let the plane xOy forms the medium interface between coating (sonic wave velocity c1 and medium densitypl) and air. The plane y=-dis interface between coating and substrate with sonic wave velocity cz and medium density p,. A system of cylindrical W t e l y thin cracks with cross-section of L , k=m is arbitrary situated in the strip parallel to Oz-axis. We assume the arcs L, are the Lyapunov type contours of arbitrary curvature. Two-dimensional own mode of structure (time dependence exp(-iot)) with a scalar component (in plane xOy) excites the presented structure. The appeared =action problem is reduced to find the solution of twodimensional Helmholtz equation, that satisfies conditions: of continuity of pressure and normal component of velocity vector on the lower plane; of absence of waves propagated fiom infinity (except exciting one); of Dirichlet on the arcs L, k = n and on the upper plane; of M e h e r type near the scatterers' ribs (Lk arc end-points). Green h c t i o n method is used and a solution of initial problem is presented as siagle layer potential. Satismg condition on scatterers' contours the problem is reduced to system of integral equations that is salved by the mechanical quadrature method as Nazarchuk [l]. Note, the kernels of integral equations consist Sommerfeld type integrals and their calculation should be carem. For that purpose we propose to modify the integration path to avoid integrand oscillations at far zone. Taking into account we consider an own mode excitation, we introduce the coefficients of transmission, reflection and calculate dissipation energy that is dissipated in lower halfspace. Thus obtained Green function of the problem and its behaviour investigation at far zone allow us to solve effectively the problem and to enhance the solution to explore numerically the problem for wide range of its parameters.
研究作用于散射体系统的场的性质是现代物理学的一个重要问题。在谐振频率范围内，当波的长度接近散射体的尺寸时，只有对相应的衍射问题进行严格的解，才有可能描述这种现象。在任意散射体几何形状的情况下，计算散射场会遇到很大的困难。本文提出了一种解决分层介质中散射体的标量声波衍射问题的方法。让平面xOy形成涂层(声速c1，介质密度l)与空气的介质界面。在声速为cz，介质密度为p的情况下，涂层与基材之间的平面y=-dis界面。横截面为l, k=m的圆柱形裂纹系任意位于平行于z轴的带材上。我们假设弧L，是任意曲率的李雅普诺夫型轮廓。具有标量分量(在xOy平面上)的二维自身结构模式(时间相关exp(-iot))激发了所呈现的结构。将出现的作用问题简化为二维亥姆霍兹方程的解，该方程满足以下条件:压力和速度矢量法向分量在下面的连续性;没有从无限远处传播的波(除了激发波);在弧线L, k = n和上平面上的Dirichlet;在散射体肋(Lk弧端点)附近，M为r型。采用Green - h - t - n方法，将初始问题求解为单层势。在满足散射体轮廓的条件下，将问题简化为一个积分方程组，用机械正交法求解为Nazarchuk[1]。注意，积分方程的核是由索默菲尔德型积分组成的，它们的计算应该小心。为此，我们提出修改积分路径以避免远区积分振荡。考虑到我们考虑一个自模激励，我们引入了透射系数和反射系数，并计算了下半空间耗散的耗散能。由此得到的问题的格林函数及其在远区行为的研究，使我们能够有效地求解该问题，并加强对该问题在大范围参数范围内的数值求解。
{"title":"Sonic wave diffraction on scatterers in stratified medium","authors":"Z. Nazarchuk, O. Ovsyannikov, R.V. Drogobytsky","doi":"10.1109/AEM.1996.873047","DOIUrl":"https://doi.org/10.1109/AEM.1996.873047","url":null,"abstract":"hvestigation of properties of fields, -acted on a system of scatterers, is an important problem of modem physics. Description of such phenomena m resonance fkequency range, where length of the wave close to the scatterers' dimensions, is possible only with a rigorous solution of corresponding diffraction problem. The significant difficulties arise while the scattered field is calculated in the case of an arbitrary scatterers' geometry. One of the ways to solve the problem of scalar sonic wave difEaction on scatterers in stratified medium is proposed below. Let the plane xOy forms the medium interface between coating (sonic wave velocity c1 and medium densitypl) and air. The plane y=-dis interface between coating and substrate with sonic wave velocity cz and medium density p,. A system of cylindrical W t e l y thin cracks with cross-section of L , k=m is arbitrary situated in the strip parallel to Oz-axis. We assume the arcs L, are the Lyapunov type contours of arbitrary curvature. Two-dimensional own mode of structure (time dependence exp(-iot)) with a scalar component (in plane xOy) excites the presented structure. The appeared =action problem is reduced to find the solution of twodimensional Helmholtz equation, that satisfies conditions: of continuity of pressure and normal component of velocity vector on the lower plane; of absence of waves propagated fiom infinity (except exciting one); of Dirichlet on the arcs L, k = n and on the upper plane; of M e h e r type near the scatterers' ribs (Lk arc end-points). Green h c t i o n method is used and a solution of initial problem is presented as siagle layer potential. Satismg condition on scatterers' contours the problem is reduced to system of integral equations that is salved by the mechanical quadrature method as Nazarchuk [l]. Note, the kernels of integral equations consist Sommerfeld type integrals and their calculation should be carem. For that purpose we propose to modify the integration path to avoid integrand oscillations at far zone. Taking into account we consider an own mode excitation, we introduce the coefficients of transmission, reflection and calculate dissipation energy that is dissipated in lower halfspace. Thus obtained Green function of the problem and its behaviour investigation at far zone allow us to solve effectively the problem and to enhance the solution to explore numerically the problem for wide range of its parameters.","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129838770","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
At recent years there were find out some peculiarities of changes of angular spectrum of wave power with distance in random inhomogeneous medium, caused by strong dissipation [ 1,2]. They can be observed in such important for practical applications cases as light propagation in ocean, infrared light in clouds and near infrared light in biological tissues. The report is dewouted to investigations of peculiarities of angular spectrum of power of point source radiation, when the source is elevated above the layer of absorbing random medium. The results can be applied in development of new methods of remote sensing. Let us describe flat layer of absorbing random inhomogeneous medium of thickness Z by complex permitivity. Then we consider that deviations of the permitivity from the mean value are small and the inhomogeneties have a large scale. Suppose that medium above and below the layer is nonabsorbing and homogeneous . Denote the distances from the layer to the point source and receiver (below the layer) by LI and L2 respectively. The angular spectrum of scattered wavefield we investigate in small angle approximation. In the case of strong phase fluctuations the spectrum has gaussian shape. In this case shift of maximum and width squared of spatial spectrum of power are determined by derivatives of correlation hnction of phase fluctuations. After rather bulky calculations there can be derived expressions for the shift of maximum and width squared of the spatial spectrum. The expressions were analyzed both analytically and numerically for power spectrum of fluctuations. As the result we derived that in the case of small distances from the source and receiver to the layer of' turbid medium ( Z/Li>5, Z/L2>5 ) width of the angular wave power spectrum does not depend on absorption and is equal to the width calculated for point source in anabsorbing medium. Shift of the maximum in this case tends to zero [3]. Vice versa in the case of Z/L1<2 the width and shift of the maximum begin anomalously quick increase with the growing of imaginary part of the layer permitivity . When Z/Li tends to zero, the expressions agree with results of works [ 21 It should be noted that under condition Z/Li=const the increasing of distance L2 from receiver to the layer causes decreasing of the width and changing of sign of the shift of maximum of the angular spectrum.
{"title":"Peculiarities of propagation of point sourse radiation through layer of absorbing random medium","authors":"V. Gavrilenko, A.A. Semerikov","doi":"10.1109/AEM.1996.872840","DOIUrl":"https://doi.org/10.1109/AEM.1996.872840","url":null,"abstract":"At recent years there were find out some peculiarities of changes of angular spectrum of wave power with distance in random inhomogeneous medium, caused by strong dissipation [ 1,2]. They can be observed in such important for practical applications cases as light propagation in ocean, infrared light in clouds and near infrared light in biological tissues. The report is dewouted to investigations of peculiarities of angular spectrum of power of point source radiation, when the source is elevated above the layer of absorbing random medium. The results can be applied in development of new methods of remote sensing. Let us describe flat layer of absorbing random inhomogeneous medium of thickness Z by complex permitivity. Then we consider that deviations of the permitivity from the mean value are small and the inhomogeneties have a large scale. Suppose that medium above and below the layer is nonabsorbing and homogeneous . Denote the distances from the layer to the point source and receiver (below the layer) by LI and L2 respectively. The angular spectrum of scattered wavefield we investigate in small angle approximation. In the case of strong phase fluctuations the spectrum has gaussian shape. In this case shift of maximum and width squared of spatial spectrum of power are determined by derivatives of correlation hnction of phase fluctuations. After rather bulky calculations there can be derived expressions for the shift of maximum and width squared of the spatial spectrum. The expressions were analyzed both analytically and numerically for power spectrum of fluctuations. As the result we derived that in the case of small distances from the source and receiver to the layer of' turbid medium ( Z/Li>5, Z/L2>5 ) width of the angular wave power spectrum does not depend on absorption and is equal to the width calculated for point source in anabsorbing medium. Shift of the maximum in this case tends to zero [3]. Vice versa in the case of Z/L1<2 the width and shift of the maximum begin anomalously quick increase with the growing of imaginary part of the layer permitivity . When Z/Li tends to zero, the expressions agree with results of works [ 21 It should be noted that under condition Z/Li=const the increasing of distance L2 from receiver to the layer causes decreasing of the width and changing of sign of the shift of maximum of the angular spectrum.","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128387373","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Potential applications of high-power tunable microwave sources to plasma diagnostics, nonlinear spectroscopy and technology have motivated the efforts to improve the performance characteristics of tunable gyrotrons. In our previous study it has been shown that the band of electron frequency tuning of a conventional high-0 cavity gyrotron coincides approximately with the unloaded cavity pass band which does not exceed 0.1 % usually. To expand frequency tuning band we propose gyrotron circuit consisted of two coupled circular cavities. Nonlinear self-consistent gyrotron theory predicted 15-20 % efficiency and 1.3 % bandwidth in this oscillator. An experimental study of an oscillator with coupled cavities operating in the TE 011 mode at X-band has been carried out. Experimental results of about.1 % bandwidth with an saturated efficiency of about 20 % were achieved and shown to be in good agreement with the theory.
{"title":"Broadband electron tuning of frequency in gyrotron with coupled cavities","authors":"E. Zasypkin, M. Moiseev, L. L. Nemirovskaya","doi":"10.1109/AEM.1996.873106","DOIUrl":"https://doi.org/10.1109/AEM.1996.873106","url":null,"abstract":"Potential applications of high-power tunable microwave sources to plasma diagnostics, nonlinear spectroscopy and technology have motivated the efforts to improve the performance characteristics of tunable gyrotrons. In our previous study it has been shown that the band of electron frequency tuning of a conventional high-0 cavity gyrotron coincides approximately with the unloaded cavity pass band which does not exceed 0.1 % usually. To expand frequency tuning band we propose gyrotron circuit consisted of two coupled circular cavities. Nonlinear self-consistent gyrotron theory predicted 15-20 % efficiency and 1.3 % bandwidth in this oscillator. An experimental study of an oscillator with coupled cavities operating in the TE 011 mode at X-band has been carried out. Experimental results of about.1 % bandwidth with an saturated efficiency of about 20 % were achieved and shown to be in good agreement with the theory.","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"6 6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129312481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A mechanism for small-scale structuring of patches in the ionospheric F region","authors":"L. M. Kagan","doi":"10.1109/AEM.1996.873173","DOIUrl":"https://doi.org/10.1109/AEM.1996.873173","url":null,"abstract":"","PeriodicalId":445510,"journal":{"name":"Trans Black Sea Region Symposium on Applied Electromagnetism","volume":"103 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130528680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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