An analysis is presented of a three-layer tapered core liquid crystal optical fiber (TLCF) having the outermost clad section made of radially anisotropic liquid crystal. TE mode propagation through TLCF is demonstrated with maximum distribution of power in the liquid crystal section under the situation that the TLCF core and the inner clad regions are constructed of homogeneous and isotropic dielectric materials. Such a propagation feature is attributed to the radial anisotropy of the liquid crystal outer region, and attracts useful applications of TLCFs in evanescent field optical sensing and other coupling devices primarily used in integrated optics.
We present a new RADAR system able to perform Phase Conjugation experiments over the ultrawideband [2-4] GHz. The system is equipped with a transmit/receive linear array made of eight antennas connected to a 2-port Vector Network Analyzer through eight independent couples of digitally-controlled RF attenuators and phase shifters. Thus, each channel can selectively transmit or receive and can as well attenuate and phase shift the RF signal. For each frequency, either the Phase Conjugation or the Decomposition of the Time Reversal Operator (DORT) is applied to the received signal and the appropriate amplitude and phase law is coded into the prototype; the focusing wave is then experimentally re-emitted by the array. The quality of the achieved backpropagation is evaluated both in frequency and time domain: in this sense we can speak of Time Reversal. The excellent agreement between measured and theoretical results validates the potential of our system.
Strong interests are recently emerging for development of solid-state devices operating in the so-called "terahertz gap" region for possible application in radio astronomy, industry and defense. To fill the THz gap by using conventional electron approach or transit time devices seems to be very difficult due to the limitation that comes from the carrier transit time where extremely small feature sizes are required. One way to overcome this limitation is to employ the traveling wave type approach in semiconductors like classical traveling wave tubes (TWTs) where no transit time limitation is imposed. In this paper, the analysis method to analyze the properties of drifting plasma waves in semiconductor-insulator structure based on the transverse magnetic (TM) mode analysis is presented. Two waves components (quasi-lamellar wave and quasisolenoidal wave), electromagnetic fields (Ey, Ez and Hx) and ω-and k-dependent effective permittivity are derived where these parameters are the main parameters to explain the interaction between propagating electromagnetic waves and drifting carrier plasma waves in semiconductor. A method to determine the surface impedances in semiconductor-insulator multi-layered structure using equivalent transmission line representation method is also presented since multi-layered structure is also a promising structure for fabricating such a so-called plasma wave device.
Electromagnetic scattering by conducting bodies of revolution (BOR) coated with homogeneous chiral media above a lossy half-space is formulated in terms of the Poggio-Miller-Chang-Harrington-Wu surface integral equation combined with combined field integral equation. A field decomposition scheme is utilized to split a chiral media into two equivalent homogeneous media. The spatial domain half-space Green's functions are obtained via the discrete complex image method. Due to the rotational symmetry property of BOR, the method of moment for BOR (BORMoM) is applied to the linear system solved by the multifrontal direct solver. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed method.
Synthetic aperture radar (SAR) imagery technology is one of most important advances in space-borne microwave remote sensing during recent decades. Completely polarimetric scattering from complex terrain surfaces can be measured. Polarimetric SAR (POLSAR), and its relevant technologies, such as POL-interferometric SA (POLINSAR), bistatic SAR (POL-BISAR), high resolution (in m and dm resolution) SAR, inverse SAR (ISAR) etc., have been providing rich all-weather, all-time and high resolution data and images of active miscrowave remote sensing. Fully understanding and retrieving information from polarimetric scattering signatures of natural media and SAR images have become a key issue for the SAR remote sensing and its broad applications. Many researches on polarimetric scattering and SAR imagery technology have been carried out (e.g., [1-6]). This paper presents a review of the research works in Fudan University (FDU) during recent years on theoretical modeling of the terrain surface for polarimetric scattering simulation and Mueller matrix solution, mono-static and bistatic SAR image simulation, new parameters for unsupervised surface classification, DEM inversion, change detection from multi-temporal SAR images, and reconstructions of buildings from multi-aspect SAR images, etc. [7-46]. Some applications are briefly reported.
We study the characteristics of nano-optical antenna made of two gold nano-particles by three dimensional numerical calculations in visible and near infrared bands. To carry the computational burden and guarantee the precision and speed of a three dimensional FDTD calculation, adaptive mesh refinement technology is used. In this paper, we first highlight the concrete way of controlling the emitter position and orientation to fulfill the requirements of larger spontaneous emission enhancement. Then, we analyze the far field distribution and find that the far fied directivity is strongly influenced by surface plasmon polaritons (SPPs). Choosing the incident wavelength of 600 nm, we compute the decay rates and radiant efficiency as a function of antenna geometry limitations. Next, the particle aspect ratio is optimized, and we obtain that L/R = 4 is the best for our optical-antenna. Furthermore, we present a spectrum analysis. Around 5000 fold spontaneous emission enhancement is successfully achieved. Finally, we find a piecewise linearity relationship between the particle length and resonant wavelength.
This paper presents a phase-resolved optical coherence tomography (OCT) system that uses the polarization quadrature encoding method in a two-channel Mach-Zehnder interferometer. OCT is a powerful optical signal acquisition method that can capture depth-resolved micrometer-resolution images. In our method, a complex signal is optically generated, and its real and imaginary components are encoded in the orthogonal polarization states of one sample beam; absolute phase information can then be acquired instantaneously. Neither phase modulation nor numerical Fourier or Hilbert transformation to extract phase information is required, thereby decreasing data acquisition rates and processing time. We conducted signal post-processing to select data from the instabilities of reference scanning delay lines; the measured phase sensitivity was as low as 0.23°, and the corresponding path-difference resolution was 265 pm. A localized surface profile measurement of a chromium-coated layer deposited on a commercial resolution target surface was conducted. The results confirmed that successful images can be obtained even with very small optical path differences using the proposed method.
Design of array antennas for satellite applications is always a trade-off between physical constrains and pattern requirements. In this paper, the focus is on the design of a large array antenna for earth coverage applications using spot beams. The array antenna has a diameter of 1 m and consists of circular polarized horn antennas positioned in a non-uniform grid. By using a binary coded genetic algorithm (BCGA) the desired element positions and their excitations are optimized to fulfill the pattern requirements. In addition thinning has been used to study the possibility of maintaining good antenna performance when reducing the number of elements. The proposed antenna design has robust side lobe level, beam width and gain; all remain virtually unchanged under a change of operating frequency ±7% and under lobe steering over earth ±8.8o.
This paper proposes an efficient and automatic means of achieving a reduced model of a transfer function for UWB antenna design. According to the formulation of a transfer function, we have derived two factors, which are critical in determining the radiation pattern and input impedance respectively. Their special formula allow us to establish a reduced model automatically using the Model Order Reduction (MOR) techniques of a second order system. The process is free of any human factors and suitable to any antenna systems, thus enabling a direct and efficient interface with the optimization process in the design of a UWB antenna system. In addition, the proposed way of establishing a transfer function of the whole antenna system has successfully cascaded the entire system into separate subsystems, thus offering deeper insights in analyzing a UWB antenna system.
The energy conservation of lossless network reflects a series of novel symmetry in S parameter. This paper presents the generalized modulus symmetry, spurious reciprocity, constant characteristic phase and determinant of the lossless block network. The perfect matching condition of block load network [Γl] and the invariable lossless property of S parameter of generalized block network are developed. Application examples are given to illustrate the application and validity of the proposed theory.
The technology of metallized foam offers a new approach to the design of wire-like, flat, and 3D antennas. Only the necessary metal skin depth (some microns in UHF band) is deposited over arbitrary shaped structures. Thanks to this technology new antenna designs have been possible offering low weight, possible shaping, and innovative architectures. To demonstrate these possibilities, a monopole inspired in the Sierpinski fractal carpet is built. The proposed design is suitable for a pico-cell base station antenna since the antenna operates at GSM850, GSM900, GSM1800, GSM1900, UMTS, Bluetooth/WLAN, WIMAX, and WIFI featuring omni-directional radiation pattern and an average total efficiency of 79%.
Multifractal dimensions Dq for real q are a more general parameter than the fractal dimension in describing geometrical properties. It has been shown that the four multifractal dimensions D-1, D0, D1 and D2 are able to extract different surface information of SAR images. In this paper, we investigate the dimension properties of multifractal dimensions. For land use classification where the textural information on the surface is important, it is necessary to look into the properties of multifractal dimensions with the geometrical properties of terrain. In order to extract the surface information from SAR images, the optimum number of multifractal dimensions to be used in the classification process is considered. To address the suitability of these parameters, these parameters are applied on a multi-band SAR image with regions of different textural information and the results are studied. The abilities of multifractal dimensions in extracting information for different land use classes are considered. In general, although multifractal dimensions provide additional information about the land use classes, there is no clear relation among the land use classes, image polarization and multifractal dimensions.
In this paper, a novel dual-band active filter topology is presented. The non-linear phase response of a composite right/left-handed cell is used to achieve the desired dual-band performance. Additionally, the proposed structure based on coupled ring resonators yields a very compact solution in which high-order implementations can be easily obtained by cascading multiple rings. The theoretical principles of this type of filters are analyzed in detail. Finally, three prototypes based on first-, second- and third-order structures validate the feasibility of this type of filters. Good agreement between simulations and measurements has been achieved.
Co-frequency interference problem is severe in shared-spectrum multistatic radar system, leading to detection problems in applications. In order to mitigate the co-frequency interferences, an adaptive pulse compression algorithm based on Maximum Signal Minus Interference Level criterion(MSMIL) is proposed in this paper, the main idea of which is to adaptively design an appropriate filter at each range cell, maximizing the result of signal power minus interference power, so that both range sidelobes and cross-correlation interference can be suppressed. Simulation results show that the algorithm outperforms the traditional multistatic adaptive pulse compression (MAPC) method in interference suppression. Compared with MAPC method, after one iteration step, the output SIR of the proposed algorithm is increased by about 10 dB. And after two iteration steps, it is increased by more than 40 dB. Moreover, it also outperforms the MAPC in convergence speed.
Partial dischagre is the precursor of insulators breakdown. In this work the propagation of electromagnetic radiation emitted from partial discharge in high voltage insulating materials is investigated. Three common dielectric materials used in power industry: polymer, epoxy resin and ceramics are studied. The results obtained are envisaged to support the development of appropriate sensors for partial discharge detection. The radiation pattern is dependent on a multitude of parameters. Among these, the intensity distribution of the source as well as the dielectric material and its geometry are the main parameters. Significant differences in the radiation spectra are obtained for insulators made of ceramic material compare to non-ceramic insulators.
Agriculture waste has potential to be used as an alternative material for the microwave absorber used in the anechoic chamber. Compared to the current materials used, such as polystyrene and polyurethane, agricultural waste has low cost and is environmental friendly. In this paper, rice husks from paddy are used as the material in the pyramidal microwave absorber design, to operate effectively in the frequency range from 1 GHz to 20 GHz. Urea Formaldehyde (UF) and Phenol Formaldehyde (PF) are the resins investigated, and are used to make the rice husk particle board. There are four main stages in designing the rice husk pyramidal microwave absorber. They are fabricating the rice husk particle board, deriving the dielectric constant value of the resin-rice husk mixture particle board, simulating the rice husk pyramidal microwave absorber using CST Microwave Studio software, and analyzing the performance of the rice husk pyramidal microwave absorber. Various parameters that affect the performance of the pyramidal microwave absorber are investigated, such as the dielectric constant of the material used, mixed resin percentages, source-port distance and angles between the signal source and the surface of the pyramidal microwave absorber. The excellent reflection loss results show that the rice husks can be potentially used as the material in a microwave pyramidal absorber.
Hadamard speckle contrast reduction (SCR) is considered to be an effective 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 reflected 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 effectiveness of Hadamard SCR is in the first 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. Differences 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.
A new type of microwave transmission line structure is proposed in order to reduce the crosstalk between transmission line circuits. In this structure, the edge of the metal strip line is periodically corrugated with subwavelength grooves of appropriate geometric parameters, and thus the transmission lines can support highly localized spoof surface plasmon polaritons (SPPs) at microwave frequencies. The theoretical simulation shows that the crosstalk between such a transmission line and a conventional strip line is very low at microwave frequencies, and this is further verified experimentally. This type of transmission line structures has great potential applications in high speed circuit systems.
This paper presents a six-section multi-layer asymmetric 10 dB directional coupler based on offset broadside coupled striplines, using Low Temperature Co-fired Ceramic (LTCC) technology, which operates over a decade bandwidth from 1.8 to 18 GHz. It features high performance transitions between the external signal layer and the buried signal layers, as well as a novel mixed first section to solve the limitations of the coupler access bends. A prototype was manufactured that exhibits a return loss of better than 15 dB, isolation of better than 23 dB and a high coupling accuracy of 10.3±0.6 dB over the 1.8-18 GHz band. This design outperforms previously reported results in terms of bandwidth and shows excellent potential for microwave measurement applications.
A novel hybrid adaptive iterative physical optics-method of moments (AIPO-MoM) technique is presented for the electromagnetic analysis of jet engine structures that are both electrically large and complex in both stationary and dynamic cases. In this technique, the AIPO method is used to analyze the smooth inlet region, and the MoM method is used to analyze the electrically complex compressor region, including blades and a hub. It is efficient and accurate by virtue of combining the respective merits of both methods. In the dynamic case, a concept for modified impedance equation is proposed to reduce computational load. Numerical results are presented and verified through comparison with Mode-FDTD and measured and commercial simulation packages results.
According to the derived transfer function using different orders of approximation, stability and signal transmission analysis of a driven metallic single-walled carbon nanotube (SWCNT) bundle interconnect are performed. It is shown that as the length of SWCNT bundle interconnect increases, the poles will be closer to the imaginary axis, which causes the transmitted signal response tends to be more damping. Using the fourth-order approximation of the transfer function, the transmitted pulse waveform along the SWCNT bundle interconnect is captured accurately, with signal overshoot and time delay examined. Further, a complete physical model for the transient response of carbon nanotube bundle interconnect is derived, which can also accurately predict the transient response of carbon nanotube bundle interconnect including time delay and crosstalk.
Microwave inverse scattering approaches have shown their effectiveness in imaging inaccessible regions. Unfortunately, the problem at hand is strongly non-linear and ill-posed and therefore it is often solved by seeking for the global minimum of a proper functional. Nevertheless, it is also necessary to introduce suitable regularizations in order to improve the convergence of the reconstruction process toward a reliable solution. In this context, the paper presents a method that exploits an energetic constraint to define a regularization term of the cost functional. A numerical validation with single and multiple inhomogeneous lossless targets demonstrates that an improvement of the reconstruction accuracy is achievable without introducing significant computational complexity to the inverse scattering problem.
This paper proposes magnetostatic analysis of Switched Reluctance Motor (SRM) under angular misalignment fault to evaluate the performance of the motor under different operating conditions. In this analysis three-dimensional finite element method (FEM) is used to simulate reliable and precise model by considering the complex motor magnetic geometry, end effects, axial fringing effects as well as nonlinear properties of the magnetic materials. The FE analysis is performed to obtain the static magnetic characteristics of SRM including flux density, flux linkages, terminal inductance and mutual inductance profile under different rotor positions for different varying degree of faults. Consequently, it presents assessing the features of mutual inductance in inactive phases to study the variations of diagnosis index. The results obtained present useful information regarding the detection of fault and its direction as well as the amount of angular misalignment fault in the motor. To the best knowledge of the authors, such an analysis has not been carried out previously.
Reverberation chambers are widely used in electromag-netic compatibility test facilities because they provide a large working volume and are cheaper than other types of test facilities. In addition, they provide a statistically uniform field and generate a high maximum electric field within a relatively large volume. The volume of the cavity, the structure of the stirrer, and high tested frequency must be used in the reverberation chamber appropriately. Changing a volume of cavity dimensions and test frequency can be difficult in the reverberation chamber because they were determined already in the design process. In these cases, the stirrer should be changed. We investigated of the effects of various stirrer angles and heights on a reverberation chamber. The optimization of the stirrer with respect to various stirrer parameters was investigated; these parameters are related to field uniformity, the quality factor, stirred efficiency, and electric field polarity. Our results suggest that a reverberation chamber can be successfully operated if careful decisions are made regarding the stirrer design.
The study of a planar circular slot antenna for Ultrawideband (UWB) communications is presented. The integration on this antenna of a notch filter, to reduce the possible interferences with the 5 GHz WLAN communications, has been discussed in detail. Four different structures, achieved by etching a suitable pattern on the antenna circular stub, have been considered, and their features have been compared. The antenna with symmetrical and inverted-L cuts shows the best performance, and it has been therefore realized and fully characterized. It shows very good matching features over the UWB band, and notable rejection of the 5 GHz WLAN band.