This paper presents a mini multi-band printed omni-directional antenna with v-shaped structure for radio frequency identification (RFID applications. The proposed multi-band antenna is developed from the initial v-shaped design which is only capable of working as a single-band antenna. By deploying a concept of dipole antenna to an initial design, the proposed antenna is accomplished to operate with two different modes of RFID system which are passive and active modes at frequencies of 915 MHz and 2.45 GHz respectively. The passive RFID tag is invented when a chip of UHF (Ultra High Frequency) is integrated with a proposed multi-band antenna. This passive tag, which is able to radiate with the measured signal strength, shows that the reading ranges are boosted almost two times compared to the conventional inlay antenna. The maximum reading range of passive RFID tag with inlay antenna is 5 m, though a reading range up to 10 m is achievable through the deployment of the proposed antenna at a measurement field. Implicitly, the measurements carried out on the antenna are in good agreement with the simulated values. Moreover, the size of the mobile passive RFID tag has been substantially as 100 mm x 70 mm, even though the antenna is fabricated with an inexpensive FR-4 substrate material. With the reasonable gain, coupled with cheaper material and smaller size, the proposed antenna has attractive potentials for use in RFID applications with multiple frequency antenna for active and passive tags.
In this paper, a parametric electromagnetic radiated emission model has been explored. Several mathematical improvements with respect to its extraction and computational performance have been deployed. The model, represented with an array of radiating electric dipoles, predicts the electromagnetic emission of components and systems. Core-level changes have been made in order to extract the model parameters: the dipole positions, their orientations and currents, and the effective relative permittivity from near-field measurements. Thresholding and windowing techniques are used to detect and optimize dipole positions, directly from the field data. A fast and memory efficient two-level optimization algorithm based on the Levenberg-Marquardt non-linear least squares technique is implemented for parametric extraction. All the constraints of the previous model have been overcome and the system is validated for mono-substrate and multi-substrate devices from measurements and/or simulations, with promising results. A tremendous improvement in modeling capability and performance has been obtained when compared with that of its erstwhile counterpart.
We present a new accurate node's renumbering method for minimizing the profile of stiffness matrix arising in finite elements problems. This method is suitable for cylindrical structures like electrical rotating machines and is especially intended for movement consideration by the moving band method. The structure is divided into sectors classified in a special way. The nodes contained in each sector are classified according to their radius value in regressing order. We show that the performances of the method are better than the most popular ones proposed in the literature. Application for a permanent magnet synchronous machine is presented. Application for finite elements analysis of a permanent synchronous machine in motion is achieved.
The present study discusses some numerical techniques on the simultaneous use of the Fast Multipole Method (FMM) and specialpurpose computer (MDGRAPE-3) to make the impractically expensive calculation feasible without the loss of numerical accuracy. In the present calculations, the impingement of two identical inclined vortex rings has been studied, and the computation time has been reduced by a factor of 1000 at N=1.18 × 106 where N is the number of vortex elements. The direct and MDGRAPE-3 calculations both have a scaling of O(N2), and the use of the FMM brings them both down to O(N). The global kinetic energy, enstrophy and energy spectra have been investigated to address the numerical accuracy and have good agreement with other similar works.
Communication technology is increasingly pervading everyday life. The rapid progress in wireless communication besides the increasing interest in wearable antennas and electronics in civil, medical, sport wear and military domains promises to replace wiredcommunication networks in the near future in which antennas are in more important role. Recently, there has been growing interest in the antenna community to merge between wearable systems technology, Ultra-Wideband (UWB) technology and textile technology. All these together have resulted in demand for flexible fabric antennas, which can be easily attached to a piece of clothing. In this paper, three different structures of UWB antennas using clothing materials and suitable for wearable application were fabricated and presented. The substrate of the designed antennas was made from jeans textile material, while radiating element and ground plane are made out of copper tape. The operating frequency of all three designs is between 3 GHz and 12 GHz. Measured results are compared with simulations and good agreement was observed.
We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25--3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (<5 mm×5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure. Numerical simulations were performed to test the design conceptsbefore building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed a superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.
The complete design of 35 GHz, 200 kW gyrotron for various material processing and heating applications is presented in this article. The components of the device, such as Magnetron Injection Gun, interaction cavity, collector and RF window, are designed for the TE03 mode. Various in-house developed codes (GCOMS, MIGSYN and MIGANS) and commercially available codes (MAGIC, EGUN and CST-MS) are used for the design purpose. A thorough sensitivity analysis of the gyrotron components are also carried out. The designed device shows the capability to generate more than 200 kW of output power with more than 40% of efficiency.
A complex image method is presented for the analysis of a subwavelength circular aperture in a perfectly conducting screen of infinitesimal thickness illuminated by a plane wave. The method is based on the Bethe-Bouwkamp quasi static model of the aperture field and uses the spectral domain formulation as the point of departure. Closed-form expressions are obtained for the electromagnetic fields valid for all observation points. Sample numerical results demonstrate the accuracy and efficiency of the method for both normal and oblique illuminations, including an evanescent wave. In the latter case, the results show a circulating power flux and enhanced field confinement near the aperture.
Design and development of a low profile, compact, wide beam and wide band printed double layered exponentially tapered slot antenna (DTSA) with a coplanar waveguide (CPW) feed meant for wide scan active phased array antenna in X-band has been presented. DTSA satisfies the requirements on the maximum reflection coefficient of Γ ≤ -10 dB for ±60o and ±45o scan from broadside in H- and E-planes, respectively with a moderate gain of 4-7 dBi. Realized antenna has shown a symmetric pattern together with moderately high gain, low cross-polarization and 3 dB beam width better than ±60o and ±45o in H- and E-planes, respectively. The designed structure is expected to find applications in mounting platforms with limited RF real estate available to it like in military aircrafts, owing to its easy integration with the uni-planar monolithic millimeter-wave integrated circuits.
A multi-scale (MS) approach combined to the generalized equivalent circuit (GEC) modeling is applied to compute the input impedance of pre-fractal structures with incorporated PIN diodes. Instead of treating the whole complex problem at once, the MS method splits the complex structure into a set of scale levels to be studied separately. The computation is done gradually from the lowest level. Each scale level is artificially excited by N modal sources to compute its input impedance matrix. The MS method is based on converting this input impedance matrix into an impedance operator to achieve the transition toward the subsequent level. The PIN diodes were easily integrated in the MS approach thanks to their surface impedance model. The main advantage of the MS-GEC method is the significant reduction of the problem's high aspect ratio since fine details are studied separately of the larger structure. Consequently, the manipulated matrices are well conditioned. Moreover, the reduced size of matrices manipulated at each level leads to less memory requirement and faster processing than the MoM. Values obtained with the MS-GEC approach converge to those given by the MoM method when a su±cient number of modal sources are used at each scale level. For frequencies between 1 GHz and 6.8 GHz, the agreement between the two methods is conspicuous.
We prove a theorem on the magnetic energy minimum in a system of perfect, or ideal, conductors. It is analogous to Thomson's theorem on the equilibrium electric field and charge distribution in a system of conductors. We first prove Thomson's theorem using a variational principle. Our new theorem is then derived by similar methods. We find that magnetic energy is minimized when the current distribution is a surface current density with zero interior magnetic field; perfect conductors are perfectly diamagnetic. The results agree with currents in superconductors being confined near the surface. The theorem implies a generalized force that expels current and magnetic field from the interior of a conductor that loses its resistivity. Examples of solutions that obey the theorem are presented.
Investigations are conducted into low-loss, low-dispersion fully shielded membrane-supported striplines designed for use in a millimeter-wave multi-chip-module. Two types of transmission line are studied: a membrane-supported shielded stripline and a novel variation of this where the membrane material is removed in areas of little mechanical importance to reduce attenuation and dispersion. The latter is possible through the exploitation of a versatile micromachining technique using SU-8 for both the membrane and the shielding. The micromachining techniques used for the fabrication of the micro-shielding allows for the conformal packaging of lines and devices, with the ultimate aim of the realization of novel components for 3D system-in-a-package type modules. Extensive simulated results obtained from rigorous electromagnetic modeling are presented that fully characterize both types of line and, where possible, are compared to measured results. Loss mechanisms are investigated for both line types and simulations suggest that losses as low as 0.39 dB/cm and effective relative permittivities of less than 1.05 are possible at a frequency of 100 GHz, comparing well with other demonstrated membrane supported transmission lines. The methods used for investigation of line characteristics and analysis of single-mode, non-leaky frequency range are applicable to any variety of membrane supported transmission line. The basics of line fabrication are given along with measurement results and de-embedding techniques used at V-band.
Three-dimensional (3D) axisymmetric invisibility cloaks with arbitrary shaped in layered-media background are presented using the transformation optics. The inner and outer boundaries of the cloaks can be non-conformal with arbitrary shapes, which considerably improve the flexibility of the cloaking applications. However, such kinds of 3D cloaks cannot be simulated using the commercial softwares due to the tremendous memory requirements and CPU time. By taking advantage of the rotationally symmetrical property, we propose an efficient finite-element method (FEM) to simulate and analyze the 3D cloaks, which can greatly reduce the CPU time and memory requirements. The method is based on the electric-field formulation, in which the transverse fields are expanded in terms of second-order edge-based vector basis functions and the azimuth components are expanded using second-order nodal-based scalar basis functions. The FEM mesh is truncated using the absorbing boundary condition. Excellent cloaking performance of the 3D cloaks in layered-media background has been verified by the proposed method.
An array processing algorithm based on artificial neural networks (ANNs) is proposed to estimate the directions of arrival (DOAs) of moving humans using a small sensor array. In the approach, software beamforming is first performed on the received signals from the sensor elements to form a number of overlapping beams. The received signals from all the beams produce a unique "signature" in accordance with the target locations as well as the number of targets. The target tracking procedure is handled by two separate ANNs in sequence. The first ANN determines the number of targets, and the second ANN estimates their respective DOAs. The ANNs are trained using simulation data generated based on a point scatterer model in free space. The proposed approach is tested using measurement data from two loudspeakers and two walking humans in line-of-sight and through-wall environments.
This paper aims to provide an effective solution to the problem of detecting a large number of densely stacked DVDs. The number is in the range of 2000. In order to achieve that goal, firstly the structure and the properties of materials comprising a DVD disc and a DVD case are investigated. The effect of the metal layer in the disc on the interrogating wave is evaluated via theoretical analysis and simulation. Based on that analysis and simulation, and on numerous experiments on either a single labeled DVD in free space or multiple labeled DVD in a DVD stack, two solutions are proposed whereby over 95% DVDs in a great portion of a 2000 DVD stack could be detected. Eliminating the tags which have weak performance, the percentage can be 100%. This paper not only expands the range of categories detectable by UHF RFID systems but also provides a process and method for item-level tagging in which the number of the items is in the range of thousands.
The modeling of the reverberation chamber with the use of deterministic techniques, one of which is the Ray Launching (RL) method, requires a careful tuning with measurements. A few factors that most severely influence the simulation results are: the minimum number of stirrer rotations to produce representative outcomes, the number of reflections of each traced ray and, finally, the size of the receive probe and the wall reflection loss. In the course of investigations it was demonstrated that these factors have a different, and in some instances --- even opposite, impact on the simulated results in the electromagnetic (EM) power domain and in the time domain (the time delay spread). A simple procedure consisting of a few steps has been proposed for tuning deterministic RL models to the measured data.
A novel procedure for estimating the Fresnel reflection coefficient of a transversally homogeneous half-space medium is introduced. GPR multistatic measurements are exploited as data whereas the Fresnel coefficient (as a function of the incidence angle) is retrieved by inverting a linear integral equation. Having estimated the reflection coefficient it can be exploited to determine the medium electromagnetic parameters. Numerical examples are used to show procedure effectiveness for different types of homogeneous half-space media within a two-dimensional scalar geometry. The case of a layered half-space is also discussed.
The reflection of linearly polarized light from an ultrathin biaxially anisotropic dielectric film on an isotropic transparent material is investigated in the long-wavelength limit. The approximate expressions for the reflection characteristics of s- and p-polarized electromagnetic plane waves are obtained. The analytical approach developed in this paper not only provides insight into the nature of reflection problem for biaxially anisotropic ultrathin films but also furnishes the methods for resolving the inverse problem for such anisotropic layers. It is shown that a key capability of the developed analytical method is to decouple the usual correlations in the index and the thickness of ultrathin films.
An original iterative method based on the conjugate gradient algorithm is developed in this paper to study electromagnetic scattering. The Generalized Equivalent Circuit (GEC) method is used to model the problem and then deduce an electromagnetic equation based on the impedance operator. For validation purposes, the developed method has been applied to various iris structures. Results computed using the new implementation of the conjugate gradient are similar to theoretical values. The field and current distribution are identical to the ones obtained with the moment method. Moreover, the memory resources required for storage are significantly reduced.
We present a novel approach for adjoint transient sensitivity analysis with respect to discontinuities with space-dependent materials exhibiting known distribution. Our approach integrates the Time Domain Transmission-Line-Modeling (TD-TLM) with the Adjoint Variable Method (AVM). Using only one extra TD-TLM simulation, the sensitivities of the observed response with respect to all the parameters of the Gaussian distribution are obtained. The accuracy of our sensitivity analysis approach is illustrated through a number of different 2D and 3D examples. Using the previous sensitivities, gradient-based optimization technique is applied to exploit in the location and profile of various inhomogeneous material Gaussian distribution for inverse problems. This method can be repeated for any continuous or discontinuous distributions that exist in electromagnetic imaging for space dependent materials like cancer detection.