In this paper, an efficient wireless power transfer (WPT) system integrating with highly sub-wavelength metamaterials is proposed. The negative refractive index (NRI) and negative permeability (MNG) metamaterials for operation at radio frequencies are designed and applied to WPT system for improvement of power transfer efficiency. A dual-layer design which consists of a planar spiral on one side and a meander line touching with narrow metallic strips on the other side produces the properties of effective negative permittivity and permeability simultaneously, i.e., negative refractive index. In addition, the structure of double spirals produces a negative permeability. The cell size of the NRI and MNG metamaterials is about 253 times smaller than the operation wavelength. By integrating one, two, three or four metamaterial slabs between the two coupling copper rings, the transfer efficiency is improved significantly. The measured results show that the contribution of high transfer efficiency is due to the property of negative permeability which can make the WPT system work in the mechanism of magnetic resonance.
Based on the method of the vectorial angular spectrum, an analytical expression of the electric field of an elegant Laguerre-Gaussian beam in free space is derived beyond the paraxial approximation, and the corresponding magnetic field is obtained by taking the curl of the electric field. By using the expressions for the electromagnetic fields, the expression of the orbital angular momentum density of the elegant Laguerre.Gaussian beam is derived, which is applicable to both the near and far fields. The effects of the three beam parameters on the distribution of the orbital angular momentum density of the elegant Laguerre-Gaussian beam are studied. The distribution of the orbital angular momentum density of the elegant Laguerre-Gaussian beam is also compared with that of the standard Laguerre-Gaussian beam. The result shows that the distribution of the orbital angular momentum density of the elegant Laguerre-Gaussian beam is more simple and centralized than that of the standard Laguerre-Gaussian beam.
We create an invisible gateway simply by putting electric and magnetic superscatterers in a metallic waveguide. The characteristics of the electric and magnetic resonators are analyzed in a metallic hollow waveguide, and the dual-mode superscattering property is discussed in detail to broaden the bandwidth of the invisible gateway. Good agreement is achieved between the simulation and measurement for such an invisible gateway. The present work help readers understand easily how an invisible gateway works (or makes sense) in a classical way without using any complex metamaterial or complicated method of transformation optics.
A novel coupled-fed antenna with compact branch-structure for 4G mobile phone is proposed in this paper. In the proposed design, a driven monopole strip and coupled branch-strips are developed to produce different operation band. The prototype of the proposed antenna was fabricated, tested and discussed. Simulation and measurement results reveal that the proposed antenna can provide two wide frequency bands (698~960 MHz, and 1710~2690 MHz), which covers multi-band for LTE700/GSM850/GSM900/DCS1800/PCS1900/UMTS/LTE2300/LTE2500. The proposed antenna with compact size of 34×12×6.5 mm3 is suitable for today's mobile phone application.
In this paper, a complete model structure for propagation inside tunnels is presented by following the segmentation-based modeling thought. According to the concrete propagation mechanism, totally five zones and four dividing points are modeled to constitute three channel structures corresponding to large-size users and small-size users. Firstly, the propagation characteristics and mechanisms in all the zones are modeled. Then, from the view point of the propagation mechanism, the criterion of judging the type of a user is analytically derived. Afterwards, all the dividing points are analytically localized as well. Finally, a panorama covering all the propagation mechanisms, characteristics, models, and dividing pints for all types of users is presented for the first time. This panorama is very useful to gain a comprehensive understanding of the propagation inside tunnels. Validations show that by using the analytical equations in this paper, designers can easily realize a fast network planning for all types of users in various tunnels at different frequencies.
A novel reduced size three band Koch Pentagonal fractal antenna is presented. The proposed antenna uses pentagonal shape for the basic fractalization combined with inner sides etched with Koch fractal pattern of the first iteration providing reduction in the overall size of the antenna. For higher order of iterations, more size reduction is achieved, producing equal number of radiation bands. Optimization is done for achieving radiations in the S, C and X bands. Ansoft HFSS, CST Microwave Studio and Solid Works are used for the 3D Modeling, S11 frequency optimization and radiation pattern calculations. The proposed third iteration fractal configuration is fabricated on Rogers RT5870, and measured results are presented. Size reduction up to 43.26 percent in terms of its overall size and 75.18 percent in terms of copper cladding remaining is achieved for the third iteration proposed fractal antenna in comparison to pentagonal patch antenna operating in the first resonant frequency band.
Mass-lumped continuous finite elements allow for explicit time stepping with the second-order wave equation if the resulting integration weights are positive and provide sufficient accuracy. To meet these requirements on triangular and tetrahedral meshes, the construction of higher-degree elements for a given polynomial degree on the edges involves polynomials of higher degrees in the interior. The parameters describing the supporting nodes of the Lagrange interpolating polynomials and the integration weights are the unknowns of a polynomial system of equations, which is linear in the integration weights. To find candidate sets for the nodes, it is usually required that the number of equations equals the number of unknowns, although this may be neither necessary nor sufficient. Here, this condition is relaxed by requiring that the number of equations does not exceed the number of unknowns. This resulted in two new types elements of degree 6 for symmetrically placed nodes. Unfortunately, the first type is not unisolvent. There are many elements of the second type with a large range in their associated time-stepping stability limit. To assess the efficiency of the elements of various degrees, numerical tests on a simple problem with an exact solution were performed. Efficiency was measured by the computational time required to obtain a solution at a given accuracy. For the chosen example, elements of degree 4 with fourth-order time stepping appear to be the most efficient.
The polarization maintaining photonic crystal fiber (PM-PCF) with two zero dispersion wavelengths is designed and fabricated by the improved stack-and-draw technology in our laboratory. The broadband blue-shifted and red-shifted dispersive waves (DWs) are efficiently generated from soliton self-frequency shift (SSFS) along the slow axis of PM-PCF. By optimizing the pump parameters and the fiber length, the polarized DWs centered in the normal dispersion region can be used as the pump and Stokes pulses for the high resolution coherent anti-Stokes Raman scattering (CARS) microscopy. Moreover, it is demonstrated that the widely tunable relevant CARS wavelengths can be obtained by adjusting the pump wavelength. The CARS microscopy based on DWs can find important applications in detecting the biological and chemical samples with the C=N, S-H, C-H, and O-H stretch vibration resonances of 2100 to 2400 cm-1, 2500 to 2650 cm-1, 2700 to 3000 cm-1, and 3000 to 3750 cm-1.
A novel multi-band circular polarizer is proposed by using a bilayered chiral metamaterial (CMM). The unit cell of the CMM is composed of four Archimedean spiral structures, which are twisted 90° to each other in the upper and bottom layers. When a linearly polarized wave incidents on this circular polarizer, the simulation result shows that the transmission of right circularly polarized (RCP) wave can be obtained at 14.28 GHz and 15.96 GHz, while the transmission of left circularly polarized (LCP) wave is emitted at 15.3 GHz and 16.88 GHz. The retrieval results reveal that the effective refractive index of the CMM closes to zero or negative at the vicinity of four resonances. The experimental results are in good agreement with the numerical results.
This study investigated transdermal drug delivery mechanisms of pectin and pectin-oleic acid (OA) gels and their effects on skin barrier treated by microwave. Hydrophilic pectin-sulphanilamide gels, with or without OA penetration enhancer, were subjected to drug release and skin permeation studies. The skins were untreated or microwave-treated, and characterized by infrared spectroscopy, raman spectroscopy, thermal, electron microscopy and histology techniques. Unlike solid film, skin treatment by microwave at 2450 MHz demoted drug permeation especially from OA-rich pectin gel. The pectin-skin binding was facilitated by gel with freely soluble pectin molecules instead of solid film with entangled chains. It was promoted when microwave fluidized stratum corneum into structureless domains, or OA extracted endogenous lipid fraction and formed separate phases within intercellular lipid lamellae. This led to a remarkable decrease in transdermal drug permeation. Microwave-enhanced transdermal delivery must not be implemented with pectin gel. In skin treated by microwave, the penetration enhancer in gel can act as a permeation retardant.
The inverse synthetic aperture radar (ISAR) image can be very effective in target recognition because it provides 2-D image that uses frequency data measured at various observation angles. However, the jet engine modulation (JEM) that can occur in the received signal due to the rotation of the blade in the engine may result in image blurring in cross-range direction. In this paper, we propose an efficient method of removing JEM signals by using the existing chirplet basis function and an efficient method to estimate the initial values of the four parameters of the chirplet. Simulations using the measured data provided clear ISAR image of a real Boeing747 aircraft.
This paper investigates Ultra Wide Band (UWB) response of a self-actuated electromagnetic wave shield based on a diode grid both in frequency and time domain. The investigation is first carried out on a shield valid for an incident wave polarized at a specific direction only, then extended to a shield effective for an incident wave polarized at an arbitrary direction. In the frequency domain, two linear analysis methods are used to study the properties of the diode grid over the frequency range from 0.01 to 10 GHz. One method is the microwave network analysis. Another is simulating the diode grid by a linear equivalent circuit instead of a diode. In the time domain, the property of the shield is studied with respect to a broadband impulse, where the diode is described by its SPICE circuit model including the nonlinear property. The results show that the diode grid works well as a self-actuated electromagnetic power selective surface (PSS) in a certain frequency range. The diode grid is strongly frequency dependent. The operating frequency band relies on the reactive elements in the diode grid. In order to extend the operating frequency to a high band, smaller cell size and smaller junction capacitance should be employed.
In this paper, we present an UHF-RFID tag mountable on metallic surfaces and capable to operate in the assigned frequency bands in Europe (866-869 MHz) and USA (902-928 MHz). Due to the proximity of these frequency bands, the dual-band functionality can be achieved through a perturbation method applied to a single band tag designed to operate at the intermediate frequency. The tag consists of an integrated circuit, an impedance matching network (where the perturbation method is applied) and a patch antenna. The considered antenna has been chosen because it has high efficiency over metallic surfaces. The whole tag has been analyzed, designed and finally fabricated. The read ranges measured in free-space are 9.5 m and 7.5 m at the European and USA frequency bands, respectively. By placing the tag on a metal surface, the read ranges increase up to 14 m and almost 11 m, respectively.
The electromagnetic scattering mechanism of radar targets in the high-frequency domain can be characterized exactly by geometrical theory of diffraction (GTD) model. In this paper, we propose a novel parameter estimation method for GTD model based on compressed sensing. The sparse characteristic of radar echoes is analyzed, and the parameter estimation problem is converted to one of sparse signal reconstruction. Furthermore, clustering and linear least-minimum-squares algorithms are utilized to improve the accuracy of the result. Compared with several modern spectral estimation techniques, the proposed method gives a more precise estimation of the GTD model parameters, especially the scattering centers. Simulations with synthetic and measured data in an anechoic chamber confirm the effectiveness of the method.
A bidirectional circularly polarized array of the same sense is proposed. The implementation is a combination of end-fire array, crossed dipoles, and composite right/left-handed transmission line (CRLH-TL). The proposed array consists of four dipoles spaced at a distance equal to λ0/4 (λ0 is the wavelength in free space at the center frequency). For the bidirectional circular polarization of the same sense, the four dipoles are fed in-phase in a series-fed structure. A feed line that exhibits 0° phase shift every λ0/4 is needed. To satisfy the demand for the space distance and phase distribution in a series-fed array, the CRLH unit cell composed of lumped capacitors and inductors is employed and inserted in the feed line. Theoretical analysis is performed based on the balanced parallel stripline and design equations are presented for the determination of the lumped element parameters. The design method can be used in the design of the arrays with more elements. From the experimental results, the array offers a 4.2 dBic bidirectional circular polarization gain. The bandwidth between which the impedance matching is better than -10 dB and the axial-ratio is better than 3 dB is 300 MHz from 2.39 to 2.69 GHz.
Due to the fact that the imaging distance is similar to the dimension of synthetic aperture antenna in near-field, the Fourier imaging theory used in the traditional synthetic aperture imaging radiometer (SAIR), which is based on the far-field approximation, is invalid for near-field synthetic aperture imaging. This paper is devoted to establishing an accurate imaging algorithm for near-field millimeter wave SAIR. Firstly, the near-field synthetic aperture imaging theory is deduced and its relationship to the far-field imaging theory analyzed. Then, an accurate imaging algorithm based on the near-field imaging theory is established. In this method, the quadratic phase item and antenna pattern are taken into consideration, and the image reconstruction is performed by minimizing the Total-Variation norm of brightness temperature image, which reduces the influence of the visibility observation error and improves imaging precision. Finally, the effectiveness of the proposed imaging algorithm has been tested by means of several simulation experiments, and the superiority is also demonstrated by the comparison between it and the existing Fourier transform methods. The results demonstrate that the proposed method is an efficient, feasible imaging algorithm for near-field millimeter wave SAIR.
Azimuth multichannel is a promising technique of realizing high resolution and wide swath for synthetic aperture radar (SAR) imaging, which consequently leads to extremely high data rate on satellite downlink system and confronts serious ambiguity in subsequent processing due to its strict limitation of pulse repetition frequency (PRF). Ambiguity suppression performance of conventional spectrum construction is disappointing when the samples are approximately overlapped. To overcome these weaknesses, a novel sparse sampling scheme for displaced phase center antennas based on compressed sensing (CS) is proposed in this paper. The imaging strategy sparsely sampled in both range and azimuth direction, leading to a significant reduction of the system data amount beyond the Nyquist theorem, and then operated the CS technique in two dimensions to accomplish target reconstruction. Effectiveness of the proposed approach was validated through simulation and real data experiment. Simulation results and analysis indicated that the new imaging strategy could provide several favorable capability than conventional imaging algorithm such as less sampled data, better ambiguity suppression, higher resolution, and lower integrated side-lobe ratio (ISLR).
A major challenge in UWB signal processing is the requirement for very high sampling rate under Shannon-Nyquist sampling theorem which exceeds the current ADC capacity. Radar signal is essentially a delayed and scaled version of the transmitted pulse, determined by sparse parameters such as time delays and amplitudes. A system for sampling UWB radar signal at an ultra-low sampling rate based on the Finite Rate of Innovation (FRI) and the estimation of time delays and amplitudes to detect UWB radar signal is presented in the paper. This sampling scheme which acquires the Fourier series coefficients often results in sparse parameter extraction for UWB radar signal detection. The parameters such as time-delays and amplitudes are estimated using the total variation norm minimization. With this system, the UWB radar signal can be accurately reconstructed and detected with overwhelming probability at the rate much lower than Nyquist rate. The simulation results show that the proposed approach offers very good recovery performances for noisy UWB radar signal using very small number of samples, which is effective for sampling and detecting UWB radar signal.
In this paper, a novel triangular metamaterial (TMM) structure, which exhibits a resounding electric response at microwave frequency, is developed by etching two concentric triangular rings of conducting materials. A finite-difference time-domain method in conjunction with the lossy-Drude model was used in this study. Simulations were performed using the CST Microwave Studio®. The technique of specific absorption rate (SAR) reduction is discussed, and the effects of the position of attachment, the distance, and the size of the metamaterials on the SAR reduction are explored. The performance of the novel TMMs in cellular phones was also measured in the cheek and the tilted positions using the COMOSAR system. The TMMs achieved a 50.82% reduction for 1 gm SAR. These results provide a guideline to determine the triangular design of metamaterials with the maximum SAR reducing effect for a cellular phone.
In this paper, a novel dual-band RF-harvesting RF-DC converter with a frequency limited impedance matching network (M/N) is proposed. The proposed RF-DC converter consists of a dual-band impedance matching network, a rectifier circuit with a villard structure, a wideband harmonic suppression low-pass filter (LPF), and a termination load. The proposed dual-band M/N can match two receiving band signals and suppress the out-of-band signals effectively, so the back-scattered nonlinear frequency components from the nonlinear rectifying diodes to the antenna can be blocked. The fabricated circuit provides the maximum RF-DC conversion efficiency of 73.76% and output voltage of 7.09 V at 881 MHz and 69.05% with 6.86 V at 2.4 GHz with an individual input signal power of 22 dBm. Moreover, the conversion efficiency of 77.13% and output voltage of 7.25 V are obtained when two RF waves with input dual-band signal power of 22 dBm are fed simultaneously.
A novel double-ridge loaded folded waveguide (FWG) traveling-wave tube (TWT) amplifier for sheet electron beam working at 140 GHz is proposed in this paper. The dispersion relation and interaction impedance characteristics have been analyzed based on the equivalent circuit method. The transmission properties and nonlinear interaction are investigated. The simulation results reveal that the double-ridge loaded FWG-TWT with sheet electron beam can make full use of relatively large electronic fields, and the average output power can be over 110 W at 140 GHz when the electron beam voltage and the current of the sheet beam are set to 12.7 kV and 150 mA, respectively. Meanwhile, the maximum gain and interaction efficiency can reach 34 dB and 12%, respectively. Compared with the traditional FWG-TWT, the novel FWG-TWT has the advantages of much higher efficiency and bigger output power.
The selection of a near-field or far-field ground-penetrating radar (GPR) model is an important question for an accurate but computationally effective characterization of medium electrical properties using full-wave inverse modeling. In this study, we determined an antenna height threshold for the near-field and far-field full-wave GPR models by analyzing the variation of the spatial derivatives of the Green's function over the antenna aperture. The obtained results show that the ratio of this threshold to the maximum dimension of the antenna aperture is approximately equal to 1.2. Subsequently, we validated the finding threshold through numerical and laboratory experiments using a homemade 1-3 GHz Vivaldi antenna with an aperture of 24 cm. For the numerical experiments, we compared the synthetic GPR data generated from several scenarios of layered medium using both near-field and far-field antenna models. The results showed that above the antenna height threshold, the near-field and far-field GPR data perfectly agree. For the laboratory experiments, we conducted GPR measurements at different antenna heights above a water layer. The near-field model performed better for antenna heights smaller than the threshold value (≈29 cm), while both models provided similar results for larger heights. The results obtained by this study provides valuable insights to specify the antenna height threshold above which the far-field model can be used for a given antenna.
The dynamical properties of cos-Gaussian beams in strongly nonlocal nonlinear (SNN) media are theoretically investigated. Based on the moments method, the analytical expression for the root-mean-square (RMS) of the cos-Gaussian beam propagating in a SNN medium is derived. The critical powers that keep the RMS beam widths invariant during propagation in a SNN medium are discussed. The RMS beam width tends to evolve periodically when the initial power does not equal to the critical power. The analytical solution of the cos-Gaussian beams in SNN media is obtained by the technique of variable transformation. Despite the difference in beam profile symmetries and initial powers, a cos-Gaussian beam always transforms periodically into a cosh-Gaussian beam during propagation, and the transformation between the two beams revives after a propagation distance.
A coherent processing method for subband signals of distributed multi-band radar data is proposed and tested. The method uses de-noising cross-correlation (DNCC) algorithm and statistical method to obtain phase incoherent parameters (ICP) between subband signals. After compensating the phase ICP, a coherence function is defined and combined with statistical method to find amplitude ICP. Finally, data fusion method via two-dimensional gapped-data state space approach (2-D GSSA) is applied to subband signals and high-resolution imaging of target is achieved. The advantage of this method lies in that it can be used to process subband signals of different bandwidth and different gaps between them. To validate our work, electromagnetic calculation target and real target measured in microwave chamber are analyzed and used for testing different mutual-coherence and data fusion algorithms. Experimental results demonstrate the superiority of the proposed method over previous approaches in terms of improved imaging quality and performance.
Due to their very high integration density, echelle grating spectrometers based on silicon nanophotonic platforms have received great attention for their applications in many areas, such as optical sensors, optical communications, and optical interconnections. The design of echelle gratings requires an effective modeling and simulation technique. Though we have used a boundary integral method to accurately analyze the polarization-dependent performance of the echelle grating, it is complicated and time-consuming for the simulation due to its large size and aperiodic structure. In the present paper, we will present a faster simulation method for the grating with twice total internal reflection facets based on a modified Kirchhoff-Huygens principle with the influence of the Goos-Hachen shift considered. On the one hand, the presented simulation results agree well with our previous results obtained by the boundary integral method when the shift can accurately be calculated using a FDTD method. On the other hand, the biggest advantage of the new method over the existing methods is that it can also provide an insightful physical explanation for many numerical results. Finally, we will effectively apply the present method to design an on-chip spectrometer with very low noise floor.
In this paper, we propose a new method for Synthetic Aperture Radar (SAR) image despeckling via L0-minimization strategy, which aims to smooth homogeneous areas while preserving significant structures in SAR images. We argue that the gradients of the despeckled images are sparse and can be pursued by L0-norm minimization. We then formularize the despeckling of SAR images as a global L0 optimization problem with ratio-of-average operations. Namely, the number of pixels with ratio-of-average that are unequal to one is controlled to approximate prominent structures in a sparsity-control manner. Finally, a numerical algorithm is also employed to solve the L0 optimization problem. In contrast with existing SAR image despeckling approaches, this strategy is applied without necessity to consider the local features or structures. The performance of our method is tested on high resolution X-band SAR images. The experimental results show the effectiveness of the proposed method in SAR image filtering. It outperforms many typical despeckling techniques in terms of the equivalent-number-of-looks and the edge- preserve-index. It also has some advantages compared with the existing state-of-the-art despeckling filters.
A near-field three dimensional imaging algorithm for circular SAR is proposed in this paper. It adopts the theory of spherical wave decomposition to transform Green function to a superposition of plane wave components. Using this relation, the image-reconstruction can be implemented in frequency domain instead of in spatial domain, which simplifies the solving process of target reflectivity function, and allows for the target to be near to the radar. Through compensating phase factor and filtering at each elevation, we firstly get the ground CSAR signal of each elevation in frequency domain. Then, performing two dimensional inverse nonuniform fast Fourier transform and accumulating the results of all azimuth angles, the reconstructed two dimensional image corresponding to an elevation is achieved. Finally, using reconstructed image datum of all elevation, the three dimensional image of target is obtained. To demonstrate the imaging performance of our method, numerical simulations and experiments are conducted. By comparing the results with the focusing operator algorithm and the back-projection algorithm, it is found that the proposed algorithm is more efficient and can obtain a good imaging performance.
Damage on rail increasingly originates from the surface of the rail as a result of for example rolling contact fatigue (RCF). This is a major concern for track operators, who operate test regimes for flaw detection and monitoring. The paper aims to assess the feasibility of applying electromagnetic (EM) simulation techniques to high frequency magnetic induction sensing of flaws in a section of rail head using the Boundary element method (BEM). When the driving frequency is significantly high (~MHz), the rail with high conductivity can be treated as perfect electric conductors (PEC) with negligible errors. In this scenario, BEM based on scalar potential and integral formulations becomes an effective way to analyze this kind of scattering problems since meshes are only required on the surface of the object. A simple high frequency magnetic induction sensing system was chosen to inspect the surface flaw of the rail. Different kinds of flaws were tested with different sensor configurations. The simulations were carried out using an algorithm the authors have developed in MATLAB. The paper provides new insights into the application of magnetic induction sensing technique using BEM in non-destructive testing. Based on the simulation and mathematical analysis, hardware system can be built to verify the proposed detection strategy.
A shaped-beam series-fed aperture-coupled stacked patch array antenna at X-band is presented. To improve the array bandwidth, two-port aperture-coupled stacked patch antennas, which are suitable for the series-fed array configuration, are presented as the radiating elements. To offer the pattern design and optimization progresses more flexibility, a uniformly spaced array configuration is applied in the shaped-beam pattern design, instead of the conventional nonuniformly spaced array configuration. The experimental results show that, in a 7.6% bandwidth, the main beam shape of the array maintains in good agreement with the design goal, and the side lobe level maintains lower than -18 dB.
In this paper, the properties of anisotropic photonic band gaps (PBGs) in three-dimensional (3D) nomagnetized plasma photonic crystals (PPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in uniform nomagnetized plasma background with various lattices including the diamond, face-centered-cubic (fcc), body-centered-cubic (bcc) and simple-cubic (sc) lattices, are theoretically investigated by the plane wave expansion (PWE) method. The equations for calculating the anisotropic PBGs in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained as the uniaxial material introduced into 3D PPCs. The PPCs with diamond lattices consisting of isotropic dielectric have the larger PBGs compared to PPCs doped by the uniaxial material since its low symmetry structure. Furthermore, the PPCs with fcc, bcc, sc lattices will not exhibit a complete PBG unless the uniaxial material is introduced. The influences of the ordinary-refractive index, extrordinary-refractive index, filling factor and plasma frequency external magnetic field on the properties of anisotropic PBGs for 3D PPCs with fcc, bcc, sc lattices are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D PPCs with fcc, bcc, sc lattices, and the complete PBGs can be obtained compared to 3D PPCs doped by the conventional isotropic dielectric. It also is shown that the anisotropic PBGs can be tuned by the ordinary-refractive index, extrodinary-refractive index, filling factor and plasma frequency, respectively. The complete PBGs can be obtained by introducing the uniaxial material as 3D PPCs are with high-symmetry lattices. This also provides a way to design the tunable devices.
In this paper a novel synthesis procedure is presented to achieve optimum solution for UWB filter parameters. It is found that the narrowband approximation is not valid for any arbitrary powered rational type filtering function. For wider bandwidths frequency dependent terms have significant effects on the frequency response. Hence, extracted filtering function cannot be mapped to generalize Chebyshev polynomials. This paper will provide exact synthesis procedure for step impedance resonators (SIR's) type UWB bandpass filters. To validate the synthesis procedure prototypes are designed and fabricated. Simulated and measured results show good agreement with proposed theory.
In this paper, we propose a method to use 1-D dielectric slabs, instead of metallic Frequency Selective Surfaces (FSSs), to produce Partially Reflective Surfaces (PRSs) with positive reflection phase gradients. The structure is realized by a single kind of dielectric substrate. It is modeled as cascaded transmission lines and then analyzed by virtue of the Smith Chart from the perspective of impedance transformation. A PRS designed by this approach is then applied to the realization of a wideband EBG resonator antenna operating at Ku band which is fed by a slot-coupled patch antenna. The calculated results indicate that the antenna possesses a relative 3 dB gain bandwidth of 22%, from 14.1 GHz to 17.6 GHz, with a peak gain of 17 dBi. The impedance bandwidth for the reflection coefficient (S11) less than -10 dB, is from 14 GHz to 17.7 GHz, well covering the 3 dB gain bandwidth. A prototype has been fabricated and measured, and the experimental results well validate the simulation. The design method developed here is significantly effective, and can be easily adopted for antenna designs at other frequencies.
Dual-band metamaterial absorber (MA) with polarization independency based on omega (Ω) resonator with gap and octa-star strip (OSS) configuration is presented both numerically and experimentally. The suggested MA has a simple configuration which introduces flexibility to adjust its metamaterial (MTM) properties and easily re-scale the structure for other frequencies. In addition, the dual-band character of the absorber provides additional degree of freedom to control the absorption band(s). Two maxima in the absorption are experimentally obtained around 99% at 4.0 GHz for the first band and 79% at 5.6 GHz for the second band which are in good agreement with the numerical simulations (99% and 84%, respectively). Besides, numerical simulations validate that the MA could achieve very high absorption at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves. The proposed MA and its variations enable myriad potential applications in medical technologies, sensors, modulators, wireless communication, and so on.
Since the system-level package was proposed, the electronics industry has increasingly attached importance to both directly relevant and related issues, and the scope of system-level package use has increased. Creating more complex system-level package structures, thereby leading to the design of overall electrical effects, requires more electromagnetic simulation resources, and therefore a great deal of time in the design process. The main purpose of this paper is to analyze the effects of system-level packaging, and to establish systems-in-package in accordance with electrical specifications. Using a segmented approach, this paper also builds an overall model for designers to predict electrical characteristics, thus shortening the product development schedule. In this paper, the transmission effects of a substrate are analyzed by changing the length of the substrate transmission line, with or without a thermal ground ball and ground ring. Previously established package IP are cascaded to establish the model of the package substrate, which verifies the feasibility of the package IP. We then analyze the characteristics of the interference between chips and package using an integrated passive device, and propose a complete package equivalent circuit model.
One of the most promising alternative imaging modalities for breast cancer detection involved the use of microwave radar systems. A critical component of any radar-based imaging system for breast cancer detection is the early-stage artifact removal algorithm. Many existing artifact removal algorithms are based on simplifying assumptions about the degree of commonality in the artifact across all channels. However, several real-world clinical scenarios could result in greater variation in the early-stage artifact, making the artifact removal process much more difficult. In this study, a range of existing artifact removal algorithms, coupled with algorithms adapted from Ground Penetrating Radar applications, are compared across a range of appropriate performance metrics.
In this study, we suggest and experimentally validate a methodology for fast and optimized design of dual-band implantable antennas for medical telemetry (MICS, 402-405 MHz, and ISM, 2400-2480 MHz). The methodology aims to adjust the design of a parametric dual-band antenna model towards optimally satisfying the requirements imposed by the antenna-fabrication procedure and medical application in hand. Design is performed in a systematic, fast, and accurate way. To demonstrate its effectiveness, the proposed methodology is applied to optimize the parametric antenna model for intra-cranial pressure (ICP) monitoring given a specific antenna-fabrication procedure. For validation purposes, a prototype of the optimized antenna is fabricated and experimentally tested. The proposed antenna is further evaluated within a 13-tissue anatomical head model in terms of resonance, radiation, and safety performance for ICP monitoring. Extensive parametric studies of the optimized antenna are, finally, performed. Feasibility of the proposed parametric antenna model to be optimally re-adjusted for various scenarios is demonstrated, and generic guidelines are provided for implantable antenna design. Dual-band operation is targeted to ensure energy autonomy for the implant. Finite Element (FE) and Finite Difference Time Domain (FDTD) simulations are carried out in homogeneous rectangular and anatomical head tissue models, respectively.
The propagation of light in an anisotropic impedance-matched metamaterial is studied in the frame of geometrical optics. We prove that directions of fields D, B and v (ray velocity) are a triad of conjugate directions with respect to the inverse relative dielectric permittivity tensor and constitutes a local basis, whose reciprocal one is formed by directions of E, H fields and wave-vector k. Consequently, both dual bases are intrinsically related to the physical properties of medium. We have identified these bases with direct and reciprocal bases of a curvilinear coordinates system, showing that physics defines geometry. This identification provides a powerful tool to solve two kinds of problems (direct and inverse ones) that currently arise: In direct problems, medium properties are given and it suffices to know ε = μ tensor at every point, to obtain the wave structure. In inverse problems, medium properties must be found for the rays to propagate along prescribed trajectories. The procedure is applied to an illustrating example.
In this paper, the equivalent cable bundle method (ECBM), an efficient simplified modeling method of the complex cable bundles, is modified for crosstalk prediction of complex cable bundles within uniform structure with arbitrary cross section. The foremost attributes of the modified method are a) the cable bundle within uniform structure with arbitrary cross section can be mapped to equivalent cable bundle above an infinite perfect electric conductor ground plane during the equivalence procedure, b) the culprit and victim conductors are divided into two groups separately during the grouping process, denoted as the culprit group and victim one, which do not participate in the equivalence procedure compared with the original ECBM for crosstalk problem, c) an effective eight-phase procedure is established to define the electrical and geometrical characteristics of the reduced cable bundle model. Numerical simulations performed on a selected cable bundle surrounded by a rectangular cavity illustrate the efficiency and the advantages of the method. This method is considered as a key step for the ECBM to find wide applications in real systems.
This paper proposes a novel method to make large area metamaterials on arbitrary planar hard or flexible substrates, in-situ. The method is based on painting the desired substrate with metallic and dielectric paints through a patterned stencil mask. We demonstrate this painting approach to fabricate ultra-thin perfect electromagnetic absorbers based on metamaterials at X-band frequencies (8-12 GHz) with paper based stencils, silver ink and latex paint. Measurement results on absorber samples made with this process shows absorption of 95%-99%, in close agreement with simulation results. The proposed painting approach is a simple low cost additive manufacturing process that can be used to realize metamaterial based frequency selective surfaces and filters, radar absorbers, camouflage screens, electromagnetic sensors and EMI protection devices.
In this paper, we investigate an expectation-maximization (EM) maximum likelihood (ML) algorithm of direction finding (DF) for bistatic multiple-input multiple-output (MIMO) radar, where it is shown that the DF problem can be described as a special case of ML estimation with incomplete data. First, we introduce the signal and the noise models, and derive the ML estimations of the direction parameters. Considering the computational complexity, we make use of the EM algorithm to compute the ML algorithm, referred to EM ML algorithm, which can be applied to the arbitrary antenna geometry and realize the auto-pairing between direction-of-departures (DODs) and direction-of-arrivals (DOAs). Then the initialization is considered. In addition, both the convergence and the Cramer-Rao bound (CRB) analysis are derived. Finally, simulation results demonstrate the potential and asymptotic efficiency of this approach for MIMO radar systems.
This paper focuses on the fluctuating target detection in low-grazing angle using Multiple-input Multiple-output (MIMO) radar systems with widely separated antennas, where the multipath effects are very abundant. The performance of detection can be improved via utilizing the multipath echoes, which is equivalent to improve the signal-to-noise ratio (SNR) by using multipath echoes. First, the reflection coefficient considering the curved earth effect is derived. Then, the general signal model for MIMO radar is introduced for fluctuating target in low-grazing angle. Using the Neyman-Pearson sense, the detectors of fluctuating targets, i.e., Swerling 1-4, with multipath are analyzed. Finally, the simulation results show that the performance can be enhanced markedly when the multipath effects are considered.
A novel circular arc fractus named Arched Bow-shaped Fractal Curve (ABFC) is originally proposed. Four ABFCs are connected end-to-end, forming so called Arched Bow-shaped Fractal Loop (ABFL). The loop antenna peculiarly presents multiband multimode characteristics with resonance compression. The normal mode, which is pertinent to the loop area and circumference, is found improved with the iterative procedure. Thus, an eight-turned wire helix of small pitch angle (α=3 °) with a circular disc ground called Arched Bow-shaped Fractal Helix (ABFH) antenna is shaped from K2 ABFLs. It can unprecedentedly operate in multiband of axial and off-axial modes with dual-sensed circular polarizations and high gain. Four matched bands (|S11|≤-10 dB) are obtained within 2 GHz-8 GHz, of which f1=2.34 GHz (400 MHz, 17.09%; G=10.63 dBi; RHCP), f2=4.24 GHz (770 MHz, 18.16%; G=12.43 dBi; LHCP), f3=5.48 GHz (300 MHz, 5.47%; G=8.13 dBi; RHCP), and f4=6.98 GHz (960 MHz, 13.75%; G=15.89 dBi; RHCP). The unique multiband multimode property has been theoretically analyzed with illustrations and can be attributed to existence of the fractal boundary, which particularly encloses multiple equivalent loops with considerable areas. These peculiarities make K2 ABFH antenna a very attractive candidate for multiband circularly polarized antennas, especially for space applications, such as spacecrafts communication, remote sensing, and telemetry, where reduction of quantity, height and weight of antennas are urgently wanted. It can also be configured into large array for higher gain service like radars and radio astronomy.
In this paper, a compact tri-band impedance transformer by utilizing stubbed coupling line for matching a load at three arbitrary frequencies is proposed. The transformer is composed of two parts, and each part is constructed from parallel-coupled transmission lines. Two structures with different configurations of the proposed transformer have been given and analyzed. Then, the close-form equations for the transformer parameters are derived analytically, and the corresponding analytical design approach is verified by numerical examples. To certify the validity of design formulas, an impedance transformer is fabricated and measured at 0.9/1.8/3.2 GHz. Good experimental performances at each frequency are obtained, which are in good agreement with the simulated results.
A broadband gradient index (GRIN) metamaterial lens for gain enhancement of circularly polarized antennas has been automatically designed, fabricated and investigated. The GRIN metamaterial lens consists of an isotropic dielectric plate with a corresponding distribution of deep-subwavelength drill holes each with the same diameter. Such drill holes have a negligible influence on both the polarization state and the spectral response of the electromagnetic wave transmitting through the resulting GRIN metamaterial lens. Therefore, the GRIN metamaterial lens is polarization-insensitive and can efficiently transform spherical waves into planar waves over a very broad frequency range keeping the initial polarization states (e.g. linear or circular) scarcely changed. In the following we have derived analytical formulas that enable the setup of distribution rules for the drill holes on the plate. Based on these formulas, the GRIN metamaterial lens can be automatically designed and easily fabricated using circuit board engraving machines. The proposed GRIN metamaterial lens has been tested by placing it on the aperture of a circularly polarized conical horn antenna. The agreement between simulation and measurement results shows that the gain of the horn antenna has been significantly increased within the whole X-band (i.e. from 8 GHz to 12 GHz) and the largest gain enhancement reaches up to 5.7 dB. In particular, the axial ratio of the horn antenna with the GRIN metamaterial lens is less than 1.6 dB.
Pipelines made of dielectric materials such as Polyethylene (PE) are becoming increasingly popular. With no suitable inspection technique for dielectric pipes, there is an urgent need to develop new technology for their inspection. This paper presents a novel pipe inspection technique using Electrical Capacitance Tomography (ECT) imaging. Traditionally ECT is used for industrial process tomography as a low resolution but fast tomographic imaging technique. Typically commercial ECT can provide a resolution of approximately 10 percent of the imaging region. In this paper a limited region tomography technique is developed take into account prior knowledge about the geometry of the pipe. This has signicantly enhanced the imaging resolution of the ECT system, making it a viable pipe inspection solution. The experimental results in this study demonstrate an interior wall loss area as small as 0.195 percent of the ECT cross sectional imaging region is repeatable and can be reliably detected. A narrowband pass filter method (NPFM) is used as a means to limit the region for the ECT algorithm. This results in an unprecedented resolution, making ECT a viable non-destructive evaluation (NDE) technique for plastic pipes. The NDE application of the ECT for PE pipes is demonstrated in this paper with several experimental results. A wall loss of depth of 1.5 mm could be detected for an ECT sensor array of 150 mm in diameter, showing a high resolution and high definition ECT (HD-ECT) imaging that has not been reported before.