A method is given for evaluating electromagnetic scattering by an irregular surface with spatially-varying impedance. This uses an operator expansion with respect to impedance variation and allows examination of its effects and the resulting modification of the field scattered by the rough surface. For a fixed rough surface and randomly varying impedance, expressions are derived for the scattered field itself, and for the coherent field with respect to impedance variation for both flat and rough surfaces in the form of effective impedance conditions.
A dual-mode dual-band bandpass filter with high cutoff rejection using asymmetrical transmission zeros technique is presented here. Two dual-mode filters are combined to form a dual-band filter by sharing the input and output coupled-feed line, which is more flexibility-designed and maintains a small circuit size. Controllable asymmetrical transmission zeros (TZs) at lower- and upper-sideband locations of dual-band filters are designed to achieve the high-selectivity dual-mode dual-band bandpass filter. Unwanted signals are suppressed by the places of the TZs between the first and second passband, which give much-improved signal selectivity for the dual-band bandpass filter. The two passbands are centered at 1.8 and 2.4 GHz, respectively. The first and second passbands' insertion losses are only 0.9 dB and 1.1 dB, and the measured return losses are better than 20 dB. Three transmission zeros are located between both passbands, which achieve the rejection levels about 40 dB attenuations from 1.9 to 2.3 GHz.
In this work, a numerical quasi-static approach is proposed to efficiently analyze symmetrical shielded broadside-coupled microstrip line (SBCML) structures. Based on the modified least squares boundary residual method combined with a variational technique, this approach allows accurate computation of the electrical/geometrical parameters of different SBCML configurations. The errors for the quasi-TEM electrical parameters range are less than 4%. The proposed technique was demonstrated through successful comparison with data from published works and results obtained from commercial EM simulators like CST-EMS and COMSOL.
To meet the growing requirements of Standard Positioning Services (SPS) and Precision Services (PS), more and more GNSS systems operating at conventional GPS frequencies and higher frequency bands are launched. The Indian NavIC system is one of such systems transmitting navigational signals at S1 (2492.028 MHz) and L5 (1176.45 MHz) frequencies. For GPS at L-band frequencies, comprehensive research work has been conducted to analyze the ionospheric delay to estimate precise user position, although very little research work is available in the public domain at the navigational S-band level. The NavIC program provides opportunities to explore the ionospheric delay effect on S-band navigational signals. The precise position determination demands accurate estimation of the vertical ionospheric delay which is generally obtained using Vertical Electron Content (VTEC) of the ionosphere. The VTEC can be obtained by multiplying a mapping function to the Slant Total Electron Content (STEC). Conventionally a thin shell (also known as a single shell) model is used to map STEC to VTEC, but it introduces error at low elevation angles. This error is significant for the NavIC receivers, located in the northern part of India, as they observe elevation angles below 50° for most of the time, and thus there is a need to investigate the suitability of the mapping function model for the NavIC system. As the ionospheric shell height modifies the mapping function and results in a change in VTEC, the height and thickness of the thick shell have been investigated based on the ionospheric data taken from IRI 2016 and were estimated as 300 km and 250 km, respectively. In the present work, the thick shell model has been compared to thin shell model mapping functions to improve the accuracy of VTEC estimation at the low elevation. The reduction in vertical delay using the thick shell mapping function at low elevation indicates its suitability for the locations like Dehradun, India, which lies in the mid-latitude region. Furthermore, the temporal variability of vertical delay at S and L band frequencies has also been investigated to understand the diurnal and seasonal characteristics of ionospheric vertical delay over a period of 12 months to cover all the seasons during the year 2017-18. The vertical delay at the S-band frequency was found to be less than that at the L-band frequency and is almost constant over a month. This finding will be beneficial for single-frequency users and could be used to develop the Grid Ionospheric Vertical Delay (GIVD) map for the NavIC system to enhance positional accuracy.
In this study, 1D Photonic Crystal (PhC) with Nematic Liquid Crystal (N-LC) central microcavity is analyzed and discussed using Rigorous Coupled Wave Analysis (RCWA) method. A microcavity is inserted into the 1D PhC by the Air Defect, making it ideal for measuring the properties of an N-LC contained inside the microcavity. Here simulation is considered for N-LC (E7) as a thermal sensor. The principle of photonic crystal thermal sensor operation is studied in the TE mode of the incident beam. We conduct a detailed study of the thermal sensor with differences in the width of central microcavity of N-LC. The sensitivity and quality factor are evaluated. Compared to other photonic crystal sensors mentioned previously, this thermal optical sensor has a much simpler structure and higher sensitivity.
A novel 4-element MIMO (multi-input multi-output) array antenna is proposed for DSRC, WLAN, and X-band applications. The proposed antenna is a microstrip antenna that consists of a simple square patch as radiating element with a defected ground structure (DGS). Dimensions of the proposed antenna are very compact with size 40 x 48 x 0.8 mm3. It operates from 5.6-6.1 GHz (DSRC/WLAN) and 8.7-10.8 GHz (X-band) with impedance bandwidths (S11 < = -10 dB) of 500 MHz and 2.1 GHz, respectively. The isolation between elements of MIMO is also greater than 25 dB in the operating bands. Antenna performance parameters are investigated at 5.9 GHz and 10.5 GHz center frequencies and computer-simulated, and experimentally measured characteristics are found to be satisfactory. A peak gain of 4.8 dB is achieved, and radiation efficiency is also greater than 75% in operating bands. ECC (Envelope Correlation Coefficient) is less than 0.05, and DG (Diversity Gain) is very close to 10. Group delay among the MIMO elements is below 2.7 ns, and CCL (Channel Capacity Loss) is also below 0.4 bits/sec/Hz. Therefore, the proposed 4-element MIMO antenna is suggestible for DSRC/WLAN and X-band applications.
In the paper, a filtering coupled-line trans-directional (CL-TRD) coupler with broadband bandpass response is presented for the first time. It is composed of three sections of coupled lines, four transmission lines and four shunt stubs. Design equations of the proposed filtering CL-TRD coupler are derived using the even- and odd-mode analysis. For demonstration, a prototype operating at 2.4 GHz is designed, fabricated and measured. Under the criterion of |S11| < -10 dB, the measured bandpass bandwidth is 41.7 %. In this bandwidth, the output port phase difference is within 90° ± 5°. Besides, two stopbands (0.91 GHz ~ 1.89 GHz and 3.36 GHz ~ 4.3 GHz) are obtained on both sides of the passband with sharp rejection. The measurements and comparisons results show that smaller size, wider bandwidth and easier fabrication than the reported filtering couplers are exhibited by the proposed filtering CL-TRD coupler. It indicates that a good candidate for filtering-coupling applications can be served by the proposed coupler.
An effective method to reduce grating lobes in linear scanning phased array antennas with large element spacing of one wavelength is presented. The proposed technique is based on employing self-nulling antenna elements by simultaneously exciting the first two modes in a circular microstrip patch antenna to partially nullify the grating lobes. More importantly, a modified amplitude tapering is optimized in the array level to facilitate the grating lobe reduction for relatively wide scan angles up to ±60°. Analytical results of a 21-element linear array are fully presented, and a -22.5 dB grating lobe reduction for up to ±60° scan angles is reported using the proposed method, followed by the results of a smaller array for validation purposes.
In this study, we present the experimental results of ultra-wideband (UWB) imaging oriented for detecting small malignant breast tumors at an early stage. The technique is based on radar sensing, whereby tissues are differentiated based on the dielectric contrast between the disease and its surrounding healthy tissues. The image reconstruction algorithm referred to herein as the enhanced version of delay and sum (EDAS) algorithm is used to identify the malignant tissue in a cluttered environment and noisy data. The methods and procedures are tested using MRI-derived breast phantoms, and the results are compared with images obtained from classical DAS variant. Incorporating a new filtering technique and multiplication procedure, the proposed algorithm is effective in reducing the clutter and producing better images. Overall, the methods and procedures registered a signal-to-clutter ratio (SCR) value of 1.54 dB when imaging the most challenging example involving the heterogeneously dense model in 8-antenna geometry. The SCR is slightly increased to 3.12 dB when the number of sensors is increased to 16.
Oscillation frequency in a plasma filled rectangular dielectric resonator antenna is computed. Perturbation method for solving differential equation is applied to find oscillation frequencies of dielectric cavity resonator. Equilibrium distribution function of collisionless Boltzmann equation is slightly perturbed. Distribution function of plasma is perturbed by altering external applied electromagnetic field. Perturbed Boltzmann equation satisfies with the relaxation time approximation used for the collision. The resulting Maxwell equations are subjected to appropriate boundary condition. Multilinear algebra tensor decomposition technique is done to find eigenfrequincies of cavity resonator antenna considered in this paper. A simulation study of a ionized gas plasma antenna is done on HFSS. Numerically calculated oscillation frequency is cross verified with HFSS result and found in good agreement.
The shielding cavity loaded with electronic equipment inside has a high Q value and is in overmode at relatively high frequency as a reverberation chamber (RC), but it does not have stirrers or paddles. However, the electromagnetic environment in the cavity is similar to that in the reverberation chamber working in frequency stirring mode or source stirring mode because of the certain bandwidth of the electronic equipment and the movement of the portable electronic equipment. Therefore, the electric field in the cavity can be predicted based on the theory of reverberation chamber. In order to predict the electric field in a given shielding cavity after loading additional electronic equipment, the determination method of the Q value of the cavity and the absorption cross section (ACS) of the electronic equipment, the influence of the ACS on the Q value of the cavity, and the relationship between the Q value and electric field are analyzed Firstly, the ACS and radiated emission power of the loading electronic equipment are measured in the RC. Then, the Q value of the cavity with the electronic equipment loaded inside is calculated by the known Q value of the cavity without the electronic equipment and the ACS of the electronic equipment. Finally, the electric field in the cavity loaded with electronic equipment is estimated by using the calculated Q value of the loaded cavity and the measured radiated emission power of the electronic equipment. The experimental results verify the effectiveness of the prediction method.
The electromagnetic vibration noise level of a permanent magnet synchronous motor (PMSM) directly affects the Noise, Vibration and Harshness (NVH) performance of an electric vehicle. Taking a permanent magnet synchronous motor (PMSM) for electric vehicle driving as an example, the electromagnetic noise characteristics were studied by combining ANSYS Workbench multi-physical field finite element analysis platform. The electromagnetic vibration force of the stator teeth of the motor is the main source of electromagnetic noise. The magnetic field of the motor can be optimized by changing the slot structure of the motor rotor, so as to improve the electromagnetic vibration force of the stator teeth and reduce the electromagnetic vibration noise of the motor. In order to optimize the magnetic field, three different rotor slot structures are proposed. The most suitable slot structure is found by comparing and analyzing the magnetic field, noise field and electromagnetic force with the structure before optimization. By comparing the results before and after optimization, it can be seen that the optimized motor can effectively reduce the vibration noise of the motor and ensure the electromagnetic performance of the motor.
This paper presents a humidity monitoring system with X band electromagnetic transmission. The verification is performed by comparing the gain and phase difference of intermediate frequency between 10.2 GHz and 10.4 GHz. Measurement data are analyzed to classify relative humidity levels and make decisions with ANNs. The system is simulated with electromagnetic field simulation software to analyze the ability of humidity monitoring. The structure from the simulation is developed to be a prototype system, including transmitter and receiver modules. Each module consists of an antenna, a frequency synthesizer, and a frequency mixer. The different operation frequencies of the two modules are -200 MHz and +200 MHz. The obtained intermediate frequency by mixing signals from each module is introduced into the circuit to find the gain and phase difference to compare with a relative humidity level. Humidity monitoring experiment is set in a closed plastic box to control the environment. The relative humidity level is from 55% to 95%. The decrease in gain is associated with increased relative humidity. Results found that the phase difference decreases clearly at the relative humidity from 75% to 95%. Both gain and phase difference data are used to train ANNs to optimize ANNs structure. Data are divided into 50% for training and 50% for testing. The proposed ANNs structure with a learning rate of 0.05 provides 98.8% accuracy. The optimized ANNs structure is composed of two input nodes, eight hidden nodes, and four output nodes. The four output node represents the relative humidity in 11 levels. The simulated and experimental results show that the system is able to monitor humidity effectively for applying in the greenhouse.
Although wireless power transfer systems suffer from splitting frequency conditions under strong coupling, this could create an opportunity for initiating other frequencies for power and data transfer. This paper introduces a model of an inductive transmitter containing a transmitter and many internal resonators to diversify the magnetic link to the receiver. Using the proposed architecture and solution, the efficiency and received power can be increased, and it also supports multiple frequency diversity.
Nonlinear effect on optical properties of one-dimensional photonic crystal (1D-PC) of the type (HL)n (LH)m (LLHH)k was investigated. It is an asymmetric hybrid Fabry-Perot resonator type of 1D-PC structure which is composed of linear (H layers) and nonlinear (L layers) materials. The linear and nonlinear transmission spectra are graphically illustrated using a numerical approach based on the Transfer Matrix Method (TMM). Results show the appearance of a Perfect Transmission Peak (PTP) in the photonic band gap which makes the structure constitute a monochromatic filter. By analyzing this PTP it is shown that the Full-Width at Half-Maximum (FWHM) depends not only on the number of symmetry layers of the studied 1D-PC but also on the refractive index of the nonlinear layers. The change of the refractive index (Kerr effect) causes a dynamically shift in the band gap including the resonance peak. As a result, such a structure has the potential to be used for designing optical filters and nonlinear optical devices.
Herein a circularly-polarized (CP) quad-band compact microstrip antenna is proposed. Its design involves one annular ring radiator having eight symmetrical slots along its boundary and three circular closed ring resonators (CRRs) on the bottom side of the substrate. Resonance frequencies of this antenna have been analyzed first and then tuned to excite desired modes via specially designed feed configuration by applying theory of characteristic modes (TCMs). Evolution process of the antenna geometry shows that the eight symmetrical slots in tandem with the CRRs generate wide impedance bandwidth (IBW), while measured quad CP bands are obtained through uses of an asymmetric ground plane resonating at 5.63 GHz (120 MHz), a cross-shaped slit at 7.69 GHz (650 MHz), a rectangular open loop at 9.91 GHz (1200 MHz), and a tuning stub in the feeding structure at 12.09 GHz (160 MHz). Series of parasitic strips augmented CP radiation and eliminate ripples in the radiation pattern. A low cost FR-4 substrate is used to fabricate the antenna with an optimized dimension of 35×30×1.6 mm3. The measured IBW ranges from 4.36-4.82 GHz, 5.50-5.78 GHz and 5.95 - beyond 14 GHz. The proposed antenna may find suitable applications in C band, X band, and 5 GHz WLAN devices.
A novel analytical method suitable for coupled electromagnetic field of a circuit is proposed in this paper. In a high frequency circuit and high-frequency converter, skin effects are obvious, and the variations in resistance and inductance values depend on frequency. In addition, the voltage and current distribution changes of a high frequency circuit generated with a high-frequency converter during dynamic switching process are complicated and depend on time. A novel analytical method suitable for coupled electromagnetic field of circuit in parameter optimization design of high-frequency circuit and high-frequency converter is proposed in this paper. The proposed method considers the influence of skin effect and coupled electromagnetic field on parameter variation simultaneously. According to the law between parameter variation and line length, the calculation process of parameter optimization will be simpler and more effective.
With the rapid development and in-depth research of non-contact bio-radar-based detection technology, researchers have recently been putting more emphasis on target identification. Living status identification, a hotspot of target identification research, is particularly useful in search and rescue missions. During such missions, in order to rescue victims and provide corresponding medical support in a timely manner, it is necessary to acquire the survival information of victims, especially when they are injured. Hence, the vital signs extracted from a radar signal should be considered as the crucial parameters to reflect the living status. To determine living status through analyzing vital signs, this study utilized a bio-radar system to continuously monitor hemorrhagic animals, which simulated injured persons with hemorrhagic symptoms. Moreover, we defined and classified three survival periods based on changes in vital signs combined with a K-nearest neighbor algorithm (KNN) classifier. Experimental results show that we can approximately determine the current living status of animals with this method, which can aid in providing information for on-site rescue and follow-up medical treatment.
The management of the current pandemic COVID-19 has been challenging and complex. The main and only successes have been achieved with non-pharmacological interventions (NPI). When tracking, monitoring, and early intervention at home have been delivered to citizens, the contagion can be controlled. In the current pandemic, various methods have been applied to track the COVID-19 virus, such as Korea's mobile phone tracking system. We propose a method based on a wearable bracelet prototype able to detect biomedical parameters, which can be very useful to monitor the virus infection when the patient develops symptoms, such as a high temperature or low blood oxygenation. In particular, the prototype bracelet can measure the blood oxygenation using an infrared optical sensor and measure the temperature of the patient. The bracelet can record the identification number of other bracelet devices that came in proximity. The bracelet is equipped with a built-in low power Bluetooth, aimed to send the recorded data to a smartphone or another device in order to connect them with proper geo-localization and to the web. The identification number of the patient device can be used to trace the number of people and whom he has been in contact with, immediately by the sanitary authorities. Moreover, the bracelet can be used for monitoring the patient's health at home, avoiding the hospital's overcrowding. The proposed system not only can effectively localize the trace path of patients positive to the COVID-19 virus or to other respiratory diseases, but also can provide an evolution of the patient symptoms and monitor people in-home quarantine. The system is simple and could be an efficient tool to track any other future pandemics.
A high impedance surface has far-reaching potential in wireless applications, but realization of the surface operating at sub-GHz ranges is challenging due to its size limits in practical applications. Here, we present a novel inductive technique based on multi-turn square spiral loops. The introduction of the spiral loops to a mushroom-shaped high impedance surface provides additional current path, thereby results in a dramatic increase in its total inductance at given dimensions, and therefore leads to a significant reduction in a resonant frequency of a high impedance plane. Electromagnetic simulation results reveal that a resonant frequency shifts downward 1 GHz at a given dimension, and they are in good agreement with results from an analytical model for the proposed structure. Experimental measurements suggest the feasibility of the proposed approach.
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