A novel embeddable miniature near-field reader antenna is designed for Ultra-High Frequency (UHF) Radiofrequency Identification (RFID) applications in the healthcare sector. The antenna spans 45 mm (length) x 20 mm (width) x 1.6 mm (thick) in size. The antenna is tuned for UHF RFID region-2 frequencies, 902 to 928 MHz. The antenna's -15 dB return loss bandwidth is 140 MHz. The antenna has very low far-field gain, and thus false reads of undesired tags are eliminated. The antenna can read both near-fields, and far-field tags as its magnetic field distribution on its surface are uniform with no dead zones. This miniature, light weight antenna is easy to embed and suitable for niche applications like surgical instrument tracking, dental instrument inventory, etc. The antenna's immunity towards proximity metal assets makes it more suitable for healthcare applications.
In this paper, an efficient Transmission Line Matrix (TLM) approach based on the shift operator (SO) has been developed to model electromagnetic wave interactions with gyroelectric media. The main idea of this technique is to formulate the electric current density vector components by introducing the equivalence between time differential operator ϑ/ϑt and discrete time shift operator z. A concise formulation of voltage sources modeling the frequency dispersive properties of gyroelectric media is then deduced and implemented. Numerical simulations illustrate the Faraday rotation phenomenon in time domain, and in the frequency domain, reflection and transmission coefficients of left hand circular polarization and right-hand circular polarization waves are also calculated. A comparison of SO-TLM scheme with five other approches according to the criteria of accuracy and CPU time is presented. Numerical experiments show that SO-TLM provides the most accurate and fastest results.
A computationally efficient, integrated and dynamic model has been developed for the design of a planar Slow Wave Structure (SWS) and beam-wave interaction analysis of a planar THz Traveling Wave Tube (TWT) with sheet beam. A Staggered Double Vane-Slow Wave Structure (SDV-SWS) is used for its numerous advantages over other types of SWSs. The integrated model determines RF performance of a planar TWT directly from the given beam voltage and center frequency by performing three different tasks, (i) determining geometrical parameters of a SDV-SWS of maximum possible bandwidth and high interaction impedance, (ii) determining RF circuit parameters of a SDV-SWS, and (iii) performing beam-wave interaction analysis of a planar TWT. The model was developed by adopting numerically computing environment, MATLAB. Also, highly accurate numerical techniques with double precision were used, e.g. Sixth Order Runge Kutta Method was used for electron beam dynamic. The model was used to design and simulate a 0.22 THz Sheet Beam TWT of 100W output power. The energy balance factor was achieved within ±0.001% over a very wide dynamic range from even 100 dB below saturation to more than 10 dB above saturation. The power growth of the forward wave was achieved with exactly 1 dB/dB. The program is fast enough for interactive use on a standard computer with a basic configuration. The model has been compared with the published works using 3D electromagnetic field simulator for demonstrating its accuracy.
The possibility of application Clavin type radiators in combined two-frequency antenna arrays with diode switching of vibrator and slot elements is validated. The conventional Clavin elements with passive monopoles operating at the main frequency and two active monopoles operating at the alternative frequency are used as the combined array radiator. Radiation fields of combined arrays at both frequencies are analyzed. It is shown that the alternative wavelength should not exceed the main wavelength by more than 25%.
In the installation of a dynamic wireless power transmission system of rail transit, the distance change among coils causes large power loss under high power conditions. Due to the limitation of detection surface and Doppler effect as well as other deficiencies, the traditional ranging methods cannot be adapted to fast, continuous, and large-area dynamic ranging in the wireless power transmission of rail transit. Therefore, the paper proposes a single coil dynamic wireless power efficiency optimization method based on electromagnetic induction for the first time. The distance between the transmitter and receiver is taken as the intermediate quantity, and the relationship between the detection coil amplitude and the wireless power transmission efficiency is constructed. Firstly, based on electromagnetic field theory, a quantitative relationship among the detection coil amplitude, wireless power transmission efficiency, and coil distance is established. Then detection experimental platform is designed. Finally, relevant experiments are accomplished through the established experimental platform. The experimental results show that for the area with low power transmission efficiency on the whole dynamic wireless power transmission line, relevant ranging data can be obtained by detecting the amplitude.
This article presents a bandstop Frequency Selective Surface (FSS) prototype based on square split ring resonators (SSRRs) and a square loop (SL) structure for Ultra Wide Band (UWB) frequency range. Triple band notches are obtained at WiMAX (3.3-3.6 GHz), WLAN (5-6 GHz) and Satellite communication X-band (7.2-8.4 GHz). To make this proposed design work as a band-stop filter, two SSRRs are positioned at the top layer of the substrate to resonate at WiMAX and WLAN frequency band respectively. A single SL is located at the bottom of the substrate that resonates at Satellite communication X-band. Attenuation more than 20 dB is observed at all notched frequencies. An angular stability from 0˚ to 40˚ is obtained. Compact size, simple structure, low cost material, single layer, easy fabrication, and wide coverage are some of the feathers of this proposed FSS. The dimension of proposed unit cell of FSS is 10x10 mm2.
In this paper, the radar target recognition is given by frequency-diversity RCS (radar cross section) together with kernel scatter difference discrimination. The frequency-diversity technique means to collect electromagnetic signals by sweeping the operation frequencies. Such a technique is usually utilized in inverse scattering and radar target recognition because different frequencies each may contain important information of a target. By using the frequency diversity RCS technique, one can reduce the times of spatial measurement. This is an important contribution since it is always difficult to build a spatial radar measurement in practical battlefield environments. To enhance the pattern recognition, the collected RCS data are processed by the kernel scatter difference discrimination, which is improved from the Fisher discrimination. To investigate the capability of tolerating environmental fluctuation, each simulated RCS data is added by a random component prior to implementing pattern recognition. Numerical simulation shows that our recognition scheme is still very accurate even though the RCS contains a random component.
This paper investigates a low-profile Multiple Input Multiple Output (MIMO) antenna with enhanced gain based on Defected Ground Structure (DGS). The proposed antenna consists of two sets of four elements (2 x 2), and it is yielded at the central frequency of 5.5 GHz for Wireless Local Area Network (WLAN) applications. Being on RT5880 with height of 1.575 mm, the overall dimensions of MIMO antenna and single array are 145 x 88 x 1.575 mm3 and 75 x 82 x 1.575 mm3, respectively. To get high gain and low mutual coupling for antenna, a Defected Ground Structure (DGS) is proposed and integrated on ground plane. At 5.3 GHz, the gain of antenna achieves approximately 9.5 dBi while mutual coupling level is under -20 dB. Besides, the MIMO antenna witnesses a radiation efficiency of 93%. The measurement results are compared to simulation ones to verify the performance of the proposed antenna.
In this article, the body shape and complex permittivity determination employing inverse electromagnetic scattering problem solution for two-dimensional cases is considered. The method of auxiliary sources (MAS) is used as a mathematical apparatus. Several body shape cases are considered, and the efficiency of the approach is shown. The program package is created based on this method, and the numerical experiment results are presented.
A dual-band circularly polarized (CP) patch antenna with wide 3-dB axial ratio beamwidth (ARBW) is presented for BeiDou Navigation System (BDS). Simple stacked circular patches are used as the main radiations for achieving dual-band operation. To enhance the ARBW for the two operation bands, an annular metal strip loaded ground plane (AMSL-GP) is presented. Besides, edge resistors are inserted to the GP for further ARBW enhancement at the lower band. In realization, a compact single-input feed network based on a coupled-line trans-directional (CL-TRD) coupler is designed to provide two orthogonal modes at the two frequency bands simultaneously. Experimental results show that the bandwidth for 10-dB return loss is from 1.15 GHz to 1.65 GHz, which covers BDS B1 (1.561 GHz) and B2 (1.207 GHz). The 3-dB axial ratio (AR) bandwidths for the lower and upper bands are 9.6% and 7.1%, respectively. At 1.207 GHz, the antenna has 3-dB ARBWs of 185° and 187° in the xoz and yoz planes, respectively. And the values are 192° and 194° at 1.561 GHz.
Available of multiple illuminators in a multistatic airborne passive synthetic aperture radar (SAR) system can enhance SAR imaging quality. In this paper, a new imaging algorithm based on two-level block sparsity for a multistatic airborne passive SAR system is proposed. The proposed imaging algorithm named by two-level block matching pursuit (BMP) algorithm utilizes both the spatially clustered property of observed targets and joint sparsity of the multistatic observation, i.e. two-level block sparsity to achieve imaging reconstruction of an observed scene. The simulation results show that the proposed two-level BMP imaging algorithm for the multistatic airborne passive SAR system can reduce imaging reconstruction time and provide enhanced imaging reconstruction quality compared to the state-of-the-art structured sparse imaging algorithm.
In this paper, a novel nested array is proposed for direction of arrival (DOA) estimation of noncircular signals. By using the noncircular property, the resulting virtual array is composed of difference coarray (DCA) and sum coarray (SCA). Specifically, we first give the properties of DCA and SCA for generalized translational nested array. Then, based on the relationship between DCA and SCA, an optimal translational nested array with increased degrees of freedom (DOFs) is constructed. To extend the physical array aperture, we move part of sensors in the translational nested array to the mirrored locations. Accordingly, the novel nested array with increased DOFs and physical array aperture is obtained. Finally, superiority of the proposed array is demonstrated by simulation experiments.
In this paper, a dual unmanned aerial vehicle (UAV)-enabled secure communication system with simultaneous wireless and information and power transfer (SWIPT) has been investigated. Specifically, assuming that the energy receivers (ERs) may be potential eavesdroppers (Eves), we aim to maximize the minimum secrecy rate among multiply legitimate receivers (LRs) within each period by jointly adjusting the UAVs' trajectories and power control (PC). Since the resulting optimization problem is very difficult to solve due to highly non-convex objective and constraints, we equivalently transform it into a more tractable problem via successive convex approximation (SCA) and constrained concave-convex procedure (CCCP), then propose an iterative method. The simulation results show that the proposed joint optimization algorithm achieves significantly better performance than the conventional algorithms.
In this paper, in order to meet the requirements for miniaturizing a microwave frequency conversion module, an L-band filter with narrow band and high out-of-band rejection is designed based on LTCC technology. The values of each element in the simplified schematic diagram are used with Chebyshev type function being the prototype, and the shapes and layout of the elements are reasonably designed for effectively utilizing the electromagnetic coupling effect inside the structure. The actually processed filter has a bandwidth of 20 MHz, and its out-of-band rejection reaches 39 dB and 42 dB at 1 GHz and 1.6 GHz, respectively.
A method is proposed for calculating the radiation characteristics of a reflector antenna in the resonant wavelength range. The method uses the solution of the problem of electromagnetic field scattering from a well-conducting non-closed screen of finite thickness. This problem is solved by an E-field integral equation and on approximate boundary conditions by Leontovich, which are applied onto a surface of a well-conducting screen.
An optimized microfluidic sensor for extracting volume ratio of binary mixture comprising of ethanol and methanol using electrical resonance technique has been presented in this work. In order to detect small changes in composition of binary mixture, a split-ring resonator structure with enhanced sensitivity was designed to operate around 2.5 GHz. A resonator was designed using HFSS, which possessed enhanced sensitivity. A novel algorithm for optimization was devised for binary mixture of the two liquids. The resonator was fabricated and tested for validation of results. Samples of ethanol and methanol mixture in different volume ratios were prepared and filled in micro-capillary tubes. These tubes were placed inside the resonant structure to perturb electric field. Variations in resonant properties due to change in volume ratio of liquid mixtures were analyzed. Resonant frequency, s-parameters and quality factor of structure were measured. It was observed that change in volume fraction as small as 1/100 resulted a shift of 0.25 MHz in resonant frequency (relatively high level of sensitivity). Measured results were utilized by mathematical model to compute volume fraction of liquid in these mixtures.
A metamaterial absorber in the Terahertz (THz) range is simulated and experimentally investigated in this work. The desired absorption frequency, efficiency and bandwidth can be tuned by changing the metal and dielectric geometric parameters. An absorption greater than 85% for TM polarized light with an incident angle up to 70˚ at any azimuthal direction is observed in a circular disc THz metamaterial structure. By adjusting the dielectric silicon dioxide (SiO2) thickness to 4 μm, an optimal absorption greater than 95% can be achieved at a resonance frequency of 0.97 THz. The experimental results also indicate that using Titanium (Ti) as a metamaterial metal layer provides four times broader absorption bandwidth than Aluminium (Al). This study, which works on polarization-insensitive and wide-angle metamaterial absorbers, can be fundamentally applied tomany THz applications including THz spectroscopy, imaging, and detection.
A single semicircle shape Complementary Split Ring Resonator (CSRR) is designed to enhance isolation by suppressing mutual coupling between MIMO antennas. Furthermore high level of mutual coupling by introducing circular slot in-between patch antennas on the substrate which creates additional coupling path between the patch antennas also opposes the some leakage signals coming back from the opposite coupling path after CSRR is etched from ground plane. The proposed patch antenna dimensions are chosen as 37.26 x 28.13 mm for operating at 2.51 GHz frequency, and the low-cost dielectric material, FR-4 (εr = 4.4), is chosen as the dielectric substrate with 1.6 mm height. The S parameters of proposed antenna prototype are characterized by using VNA. The measured return loss (S11) and isolation (S21) are -23.13 dB & -56.8 dB respectively. The results show that by introducing semicircle CSRR and circular slot, the structure provides a 33.2 dB improvement in mutual coupling for MIMO antenna. Hence, the proposed structure provides a better isolation between two antennas without affecting antenna performance.
Aiming at the problems of low gain, low efficiency at lower frequency and warping in pattern at higher frequency of 10-meter high frequency (HF) whip antenna, the whip antenna is loaded and matched with the network in different bands using Grasshopper Optimization Algorithms (GOA) and antenna reconfiguration technology, so a new frequency reconfigurable broadband whip antenna is designed in this paper. According to the electrical characteristics of 10-meter HF whip antenna, this paper divides short wave frequency into three bands and designs its radiation structure, loading, and matching network for each band of antenna, respectively. GOA is introduced into the research and design of antenna to optimize the component parameters of loading network and matching network. The results show that the antenna in lower frequency band can be improved at most, the maximum gain growth up to 5.8 dB (from -10.3 dB to -4.5 dB) and the maximum efficiency growth up to 8.5% (from 3% to 11.5%); the gain and efficiency in high frequency band are greatly improved too, and the phenomenon of warping in the pattern is effectively avoided.
A low-profile, decoupled two-monopole system with its two parasitic grounded strips conjoined, forming a very compact structure is demonstrated. Each of the two identical antennas comprises a driven coupling strip and a parasitic grounded strip, operating respectively in the 2.4 GHz (2400-2484 MHz) and 5 GHz (5150-5825 MHz) wireless local area network (WLAN) bands. The two parasitic strips are further joined together, becoming a central, grounded T monopole. By loading a capacitor between the T monopole and the antenna ground, the mutual coupling in the 2.4 GHz band can be reduced by about 12 dB. The capacitor in this design is used to control Ant2 monopole mode to cancel out opposite-phased currents of the dipole mode on the T monopole when Ant1 is excited, such that isolation enhancement can be attained. The proposed two-monopole system occupies a compact size of 5 mm × 40 mm (about 0.04λ × 0.32λ at 2.4 GHz) and is favorable for applications in the narrow-bezel notebook computers owing to its low profile of 5 mm.
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