An eye-shaped segmented (ESS) antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed antenna shows in-phase current even though the perimeter of the eye-shaped loop is comparable to the operating wavelength. The ESS antenna is fabricated on a FR4 printed circuit board (PCB) and embedded in a metal cavity with an overall size of 250×180×50 mm3. The measured bandwidth is around 11MHz (860-871 MHz) under the condition of VSWR less than 2.0, which covers the Europe standard (865MHz-868MHz) and agrees well with the simulated results. Finally, as a reader antenna in the RFID system, the measured read distance and read width can achieve 16.1 cm and 8 cm, respectively. The ESS antenna is desirable for UHF near-field RFID reader applications.
A correlation spectroscopy (COSPEC) based on a multi-wavelength fiber laser is first proposed for the detection of gas concentration. The lasing wavelengths are selected to match several characteristic absorption peaks of the gas under test, and the gas concentration is easily measured by correlating it with the reference gas. The present method is immune from the instability of the light source and the influence of other gases. The concentration measurement of C2H2 is demonstrated in the experiment in its near-infrared dominant absorption region. The technique has prospects for simultaneous detection of multiple gases, and the measurement of mixed gases of C2H2 and CO2 is also analyzed.
In this paper, design and fabrication of a quad-band microstrip bandpass filter (BPF) using multi-layered stepped impedance resonators (SIRs) structure is proposed. One pair of SIR on the top layer is designed to operate at the 1st and 3rd passbands (1.56/3.57 GHz), and the other pair is at 2nd and 4th passbands (2.42/5.23 GHz) by tuning the impedance and length ratios of the SIRs. In order to find the desired coupling location between the SIRs located on different layers and the input/output (I/O) lines, the voltage, current and power wave on the I/O lines are analyzed. It is verified that the proposed quad-band filter has good passband performances with an excellent isolation between adjacent bands for GPS, WLAN, and WiMAX applications.
This work deals with an exact solution of cylindrical wave equation for electromagnetic field in fractional dimensional space. The obtained fractional solution is a generalization of the cylindrical wave equation from integer dimensional space to a fractional dimensional space. The resulting theoretical framework can be used to study the phenomenon of electromagnetic wave propagation in any fractal media because fractal media can be described as an ordinary media in a fractional dimensional space. The classical results are recovered from fractional solution when integer dimensional space is considered.
A subwavelength array of planar triangle monopole antennas is proposed and discussed in this paper. Each element of the array is etched with many cross slots which bring no effects to the element's performances of voltage standing wave ratio and far-field radiation patterns. An important property of this antenna is that if multiple such planar antennas are placed face to face, the proposed array can perform time-reversal far-field focusing with a super-resolution as small as one twentieth of a wavelength. The proposed subwavelength array is easy to design and convenient for integration.
In this paper, to calculate the salient pole machine inductances under radial and axial non-uniformity, a new method is developed. The method, an extension of the modified winding function theory to 3D, allows studying salient pole machines with radial and axial non-uniform air gap considering more realistic mean radius of the air gap. By using the developed method and a precise geometrical model, inductances of a salient pole machine with inclined rotor are calculated. Inductances are evaluated and effects of several asymmetries on inductances are shown. Calculated inductances are used in a coupled electromagnetic model, for simulation of a salient pole machine under healthy and different inclined eccentricity conditions. Simulation results show that the 19th stator current harmonic can be detected to alarm for inclined rotors. Experimental results that validate the theoretical and simulation results are presented.
Planar microstrip filters are designed to have a quasi-elliptic function passband and extended upper stopband with a rejection level of 40 or 50 dB. The design employs stepped-impedance resonators in a compact 2×2 cross coupled configuration. The geometric parameters of the resonators are planned to shift the third resonance as high as possible, and then the transmission zeros created by the structure are devised to suppress the second resonance, so that a wide upper stopband up to more than 4.5 times the passband frequency can be achieved. By employing the skew-symmetric input/output feeds, three transmission zeros in the frequency band of interest can be created. The leading two zeros are allocated on the both sides of the passband, generating a quasi-elliptic function response with enhanced roll-off rate in the transition bands, and the last zero incorporating with a zero created by anti-coupled-line at higher frequencies are employed to extend the rejection bandwidth. The measurement data agree very well with the simulation responses.
A seven ports network is proposed to act as a six-way power divider/combiner. The proposed network structure consists of a set of λ/4 planar transmission lines at the design frequency and does not require any isolating resistor. The power divider is capable of providing various power ratios by judicious choice of the transmission lines characteristic impedances. Design equations are derived for arbitrary power ratios. Simulation results obtained from the ADS software proved the possibility of achieving preset power ratios with fairly linear phase response over a certain bandwidth. The latter depends on the chosen power ratios. Measured results of manufactured power dividers agree well with simulations and theory.
In this paper we develop an empirical approach to the design of Ultra Wideband (UWB) antennas employing the Inverse Parabolic Step Sequence (IPSS). The relationships developed can be used to miniaturize the antenna and achieve a good impedance match over the UWB bandwidth. The overall aim of this process is to give a good starting point for detailed numerical optimizations. We will illustrate the use of these formulae in three different designs of IPSS-based antennas. A low loss duroid substrate of loss tangent, tan δ, 0.0009, relative permittivity 2.2 and thickness 1.575 mm is used to simulate these planar monopole antennas in Ansoft High Frequency Structure Simulator (HFSS).
A new four-parameter modified refractivity profile (M-profile) model for the evaporation duct is introduced in this paper. In the estimation of radio refractivity structure from sea clutters, a parametric M-profile model is normally employed. The conventional M-profile model for evaporation ducts is the one-parameter log linear model, which has some potential disadvantages in describing the observed M-profiles which would result in rough results of evaporation duct estimation. Based on this model, three new parameters are introduced and a four-parameter M-profile model is proposed here. This model has the ability to (a) more accurately match real-world M-profiles, (b) well replicate the observed clutter field, and (c) show clutter power or path loss sensitivity to each model parameter. All these abilities are necessary for robust refractivity estimations. The performance of this model is tested and validated through the estimation for two truly measured M-profiles.
Based on the Helmholtz integral equation and series expansion theory, a high order integral small perturbation method (HISPM) for studying electromagnetic wave scattering from the finite conducting rough surface with tapered transverse electric (TE) wave incidence is presented. The high order scattering coefficients are obtained by the series expansion, the validity and accuracy of HISPM is verified through numerical evaluation with classical small perturbation method (CSPM) and the method of moments (MOM). By comparing with CSPM for the infinite rough surface case with plane wave incidence, the presented HISPM can greatly reduce the edge diffraction effect. HISPM also shows advantages in the memory requirement and computational time, especially in calculating scattering coefficients with low grazing angle incidence. Numerical examples are given to show that with the increasing of the length of the rough surface, the memory requirements and the computation time of HISPM are dramatically reduced compared to those of MOM.
The present contribution is concerned with an exact frame-based pulsed-beams expansion of planar aperture time-dependent electromagnetic fields. The propagating field is described as a discrete superposition of tilted, shifted and delayed electromagnetic pulsed-beam waveobjects over the frame spectral lattice. Explicit asymptotic expressions for the electromagnetic pulsed-beam propagators are obtained for the commonly used pulsed-quadratic windows.
This paper presents an efficient hybrid simulation technique for analysis of the electromagnetic field interactions between multi-transmitters and receivers located within a closed environment. The Method of Moments/circuit method is first used for modeling of the transceivers and their nearby surrounding to obtain the equivalent sources/receivers. Then, an approach that combines the asymptotic method and the ray tracing technique is deployed to calculate the long-distance coupling between a pair of transmitter and receiver. The acceleration algorithms for ray tracing have been developed to deal with more complex scenarios. The seamless combination between the circuit, numerical, and asymptotic approaches is the key to get accurate simulation results. Several numerical examples and experimental results are presented to demonstrate the efficiency of the proposed technique.
Accurate and effective system-level modeling has become necessary to address electromagnetic compatibility (EMC) issues in modern circuit and system design. Model order reduction (MOR) techniques provide a feasibility to approximate complex circuit models with compact reduced-order models. In this paper, an effective MOR technique entitled multi-point moment matching (MMM) is implemented for the partial element equivalent circuit (PEEC) modeling. Moment information at multiple frequency points is used in this method in order to accurately estimate a given system over an entire frequency range of interest, and for each frequency an enhanced asymptotic waveform evaluation (AWE) is applied to obtain a reduced-order model by constructing a pole-residue representation of the original transfer function. The improvements of conventional AWE in aspects of both moment computation and moment matching can avoid ill-conditioned moment matrices and unstable dominant poles. The complex frequency hopping (CFH) technique is employed to select the multiple expansion points by using a newly developed upwardsearch algorithm. Numerical simulations of coupled microstrip lines in both frequency and time domain indicate the effectiveness of the proposed method.
In this work, we theoretically investigate the tunable photonic band gap (PBG) in a semiconductor-dielectric photonic crystal made of highly doped n-type silicon (Si) layers alternating with silicon oxide layers. The tunable characteristic is studied by changing the donor impurity concentration in Si layer. The PBG is numerically analyzed in the near infrared frequency region from the reflectance calculated by the transfer matrix method. The effect of filling factor in Si layer on the photonic band gap is also illustrated. These tunable properties in such a photonic crystal provide some information that could be of technical use to the semiconductor optoelectronics, especially in communication applications.
The present study deals with a novel approach for fractional space generalization of the differential electromagnetic equations. These equations can describe the behavior of electric and magnetic fields in any fractal media. A new form of vector differential operator Del, and its related differential operators, is formulated in fractional space. Using these modified vector differential operators, the classical Maxwell equations have been worked out for fractal media. The Laplace, Poisson and Helmholtz equations in fractional space are derived by using modified vector differential operators. Also a new fractional space generalization of the potentials for static and time varying fields is presented.
This paper studies the excitation of a physical leaky mode in a covered microstrip structure at low frequencies. We calculate the current excited in the line by a delta-gap voltage source via a full wave analysis based on a mixed potential integral equation scheme. The current in the line is decomposed into its bound mode and continuous spectrum components. The bound mode component is associated with the propagation effects whereas the continuous spectrum component is associated with reactive and/or radiative effects and contains the contribution of the leaky mode. Our analysis also includes a detail study of the dispersion relations of the bound and leaky modes along with their corresponding electric fields. At low frequencies, in the covered microstrip structure with a low top cover height, we have found that the bound mode role is superseded by the leaky mode, in the sense that it is the leaky mode which partially or totally carries the signal energy. Therefore, the spurious effects associated with the excitation of a leaky mode, which usually appear at high frequencies in open microstrip lines, appear here in the low frequency range. This effect may have very relevant practical consequences in the performance of such systems.
Power transformers in service are subjected to a wide variety of electrical, mechanical and thermal stresses capable of producing insulation faults. This type of failure figures amongst the most costly faults in distribution networks since it produces both machine outage and electrical supply interruption. Major research effort has therefore focused on the early detection of faults in the insulating systems of large high voltage power transformers. Although several industrial methods exist for the on-line and off-line monitoring of power transformers, all of them are expensive and complex, and require the use of specific electronic instrumentation. For these reasons, this paper will present the On-Line analysis of transformer leakage flux as an efficient alternative for assessing machine integrity and detecting the presence of insulating failures during their earliest stages. An industrial 400 kVA-20 kV/400V transformer will be used for the experimental study. Very cheap, simple sensors, based on air core coils, will be used to measure the leakage flux of the transformer, and non-destructive tests will also be applied to the machine in order to analyse pre- and post-failure voltages induced in the coils.
This paper proposes a novel approach for the spatial microwave power combining. Anisotropic metamatierials are employed to trim the combined electrical fields and form a single beam radiation pattern. The radiation characteristics of a binary horn antennas array are investigated both numerically and experimentally at 12 GHz. The results show that much higher combining efficiency can be achieved. Given a designed combining efficiency, the strict relative position requirements in each transmission unit are reduced in this scheme.
The dielectric pyramid loaded and the dielectric cone loaded diagonal horn working at 150 GHz are investigated by using Gaussian beam mode analysis. With extremely low cross-polarized and axially symmetrical field distribution in the horn aperture, the calculated fundamental Gaussian mode coupling achieves about 98%. The far field radiation patterns of the two antennas are analyzed using fundamental Gaussian mode aperture-field distribution model whose results agree with high-accuracy CSTTM software computations, indicating that the dielectric loaded horns radiate fine Gaussian beams. The dielectric loaded geometry may be used to modify the diagonal horns with distorted beam.
This paper presents a geometrically based method for the calculation of the node-to-node distance distribution function in circular-shaped networks. In our approach, this function is obtained from the intersection volume of a sphere and an ellipsoid. The method is valid for both overlapping and non-overlapping networks. Simulation results and comparisons with methods in the literature demonstrate the efficacy of the approach. The relation between networks geometric parameters and distance statistics is explored. As an application example, we model distance-dependent path loss and investigate the impact of channel characteristics and networks size on signal absorption. The aforementioned model is a useful and low-complexity tool for system-level modeling and simulation of mobile communication systems.
A highly birefringent four-hole fiber (FHF) with a pair of large air holes and a pair of small air holes are proposed for air/hydrostatic pressure sensing. The birefringence of the FHF can be up to 0.01 due to the rectangle-like fiber core surrounded by four air holes. Therefore, a FHF with a length of only several centimeters is required for high-sensitivity pressure sensing based on a Sagnac interferometer. Optical properties of the FHF such as effective index and birefringence are investigated. Pressure sensor based on the FHF depends on the pressure-induced refractive index change or pressure-induced birefringence. The stress distribution of the FHF subjected to an air/hydrostatic pressure is represented. Simulations show that the principal stress component parallel to the slow axis of the of the FHF under the air/hydrostatic pressure is greatly enhanced due to the existence of two large air holes, which consequently results in a high sensitivity of the FHF-based pressure sensor. Relationships between the pressure-induced birefirngence and the radius of the large air hole, the external diameter of the FHF, or the ellipticity of the elliptical FHF are investigated. The polarimetric pressure sensitivity of the FHF can be up to 607 rad/MPa/m.
Planar multiband bandpass filters are implemented based on the versatile multimode stepped-impedance resonators (SIRs). The resonant spectrum of a SIR can be calculated as functions of the length ratios for various impedance ratios of the high- and low-impedance sections. Thus, by properly selecting the geometric parameters and designing the input/output coupling structure, the SIRs are feasible to realize multiband multimode filters. Using a single SIR, a dual-mode dual-band, a dual-mode triple-band or a hybrid dual-/triple-mode dual-band bandpass filter can be realized. Emphasis is also placed on designing specified ratios of center frequencies and fractional bandwidths of the passbands. To extend the design flexibility, extra shunt open stubs are used to adjust the ratio of the passband frequencies. In addition, sharpness of the transition bands is improved by designing the input/output stages. Simulation results are validated by the measured responses of experimental circuits.
The double and triple Langmuir probe diagnostic systems with their necessary driving circuits are developed successfully for the characterization of laboratory built low pressure inductively coupled nitrogen plasma, generated by 13.56 MHz radio frequency (RF) power supply along with an automatic impedance matching network. Using the DC properties of these two probes, the discharge plasma parameters like ion saturation current (Iio), electron temperature (kTe) and electron number density (ne) are measured at the input RF power ranging from 250 to 400 W and filling gas pressures ranging from 0.3 to 0.6 mbar. An increasing trend is observed in electron temperature kTe and ne with the increase of input RF power at a fixed filling gas pressure of 0.3 mbar, while a decreasing trend is observed in kTe and ne with the increase of filling gas pressure at a fixed input RF power of 250 W.
Spaceborne synthetic aperture radar (SAR) systems operating at lower frequencies, such as P-band, are significantly affected by Faraday rotation (FR) effects. This paper presents a novel algorithm for measuring system errors (channel imbalance and cross-talk) in the presence of Faraday rotation for spaceborne polarimetric SAR data. It uses four polarimetric selective calibrators (four polarimetric active radar calibrators [PARCs] or possibly two PARCs and two gridded trihedrals). Theoretical analysis and simulations demonstrate that the optimized calibration scheme puts tight constraints on the accuracy of the associated Faraday rotation if the cross-talk is to be accurately measured. There are also strong constraints on the allowable signal-to-noise ratio and average polarimetric noise associated with the calibration devices. The analysis suggests that, unless the calibration sites are at the magnetic equator, independent measurements of total electron content (TEC) from a direct ground-satellite line-of-sight dual-frequency system are also needed.
The method of connected local fields (CLF), developed for computing numerical solutions of the two-dimensional (2-D) Helmholtz equation, is capable of advancing existing frequency-domain finite-difference (FD-FD) methods by reducing the spatial sampling density nearly to the theoretical limit of two points per wavelength. In this paper, we show that the core theory of CLF is the result of applying the uniqueness theorem to local EM waves. Furthermore, the mathematical process for computing the local field expansion (LFE) coefficients from eight adjacent points on a square is similar to that in the theory of discrete Fourier transform. We also present a theoretical analysis of both the local and global errors in the theory of connected local fields and provide closed-form expressions for these errors.
The operation of a slab antenna with low-index metamaterial substrate is affected by a cluster of metallic cylinders positioned in the near-field area. A semi-analytical solution of the defined boundary value problem is obtained based on the small size of the rods. Several different configurations are found to possess beneficial features concerning the total radiated power and the angle of directive emission. The deduced diagrams are independently validated and discussed, revealing certain conclusions.
Extraction of vegetation water content and soil moisture from microwave observations requires development of a high fidelity scattering model. A number of factors associated with the vegetation canopy and the underlying bare soil should be taken into account. In this paper, we propose an electromagnetic scattering model for a corn canopy which includes coherent effect due to the corn structure and takes advantage of recently advanced scattering models for dielectric cylinder of finite length, for thin dielectric disk with elliptical cross section, and for rough surface. The model results are validated at both L and C bands. At C band we acquired some RADARSAT-2 data of several test fields of corn canopy in Jiangsu Province, China, in 2009, and carried out simultaneous measurement campaigns to collect the in situ ground truth. A comparison is made between theory and RADARSAT-2 data. At L band because high quality AIRSAR measurement data are available along with detailed ground truth in the literature, a comparison is also made between theory and AIRSAR data.
Image formation from squinted sliding spotlight synthetic aperture radar (SAR) is limited by azimuth spectral folding and severe two dimension coupling. This paper presents an Extended Wavenumber Domain Algorithm (WDA) for highly squinted sliding spotlight SAR data processing. This algorithm adopts azimuth deramping approach to overcome the azimuth spectral folding phenomenon. The chirp rate for azimuth deramping and the principle of choosing pulse repetition frequency (PRF) is presented to accommodate the characteristic of Doppler history. Subsequently, the full focusing is implemented by WDA. Instead of the conventional Stolt mapping in WDA, a modified Stolt mapping is introduced in order to enlarge the range extension of focused image and enable to update the Doppler parameters along range. To confirm the correctness of the implementation of modified Stolt mapping and the azimuth position of target in focused image, related compensation terms are developed. Point target simulation results are presented to validate the effectiveness of extended WDA to process highly squinted sliding spotlight SAR data.
An end-fire linear tapered slot antenna is presented in the terahertz band. The operation frequency goes from 0.6 THz to 2 THz, with symmetric radiation patterns from 1 THz to 1.7 THz, and gains up to 15 dB. The gaussicity of the beam is over 80% in the whole operation band and an efficiency at 1THz of 85%. This antenna gives enough directivity avoiding the use of a typical substrate lens, which introduce 30% of losses. This new design is a good candidate for new applications in the THz range in Radioastronomy and Imaging.