Compact antenna with good performance characteristics is always preferred for small IoT (Internet of Things) sensor nodes. The novelty of this proposed work is not in terms of design but in terms of application as Log-Periodic antennas has been so far used for UHF/VHF (Ultra High Frequency/Very High Frequency) and TV reception applications, and in this paper, the advantages of Log-Periodic structure have been exploited for IoT applications. This antenna design consists of two Log-Periodic like structured radiating elements on an FR4 substrate of 1.6\,mm thickness. The compact antenna of size of 15 mm×17 mm covers a bandwidth ranging from 2.01 GHz to 4.04 GHz including the WiMAX (2.3 GHz-2.4 GHz, 2.5 GHz-2.7 GHz and 3.4 GHz-3.6 GHz) and WLAN (2.4 GHz and 3.6 GHz) frequency bands. This system employs Defected Ground Structure (DGS) technique to obtain the required range of bandwidth of operation, for improving the isolation and obtaining mutual coupling suppression between the two individual elements. This miniaturized cheap antenna has a very low ECC (Envelope Correlation Coefficient) value and all other MIMO (Multiple Input Multiple Output) parameters in acceptable range. The isolation obtained over the entire range of operation is below -30 dB, and the performance efficiency is as good as 92.8% with a maximum gain of 2.9 dB. The simulated and measured results of the antenna system are also found to be in good agreement. The MIMO system can be considered as a good candidate for medium range IoT applications for its small size and good performance.

In this paper, electromagnetic scattering from multi-impedance body of revolutions (BORs) is formulated using self-dual integral equations (SDIEs) and is solved numerically by the method of moments using BOR basis functions. Using the axial symmetry advantage of BORs, a 3D problem is converted to a 2D one, and a significant reduction in unknowns is obtained. This in turn leads to an increase in the speed of scattering problem solving. Numerical results show that monostatic and bistatic RCS calculation with the proposed method is about 85 and 18 times faster than the commercial software, respectively.

This study presents an effective solution on the basis of Discontinuous-Galerkin Time-Domain (DGTD) scheme for the injection of elliptically polarized plane wave through total-field/scattered-field (TF/SF) boundary. Generally, the elliptically polarized wave can be resolved into two linearly polarized waves in phase quadrature with the polarization planes at right angles to each other, but the proposed methodology is focused to utilize the principle of wave field formation to induce left-handed or right-handed elliptically polarized waves by regulating the phase and amplitude of the incident waves. The outcome of the proposed technique is achieved by deriving the EB-scheme equations and employing the explicit fourth order Runge-Kutta (RK4) time integration scheme in the DGTD methodology. An anisotropic Riemann solver and non-conformal mesh schemes are introduced for domain decomposition to allow efficient spatial discretization. Additionally, the proposed work is extended from single frequency to broadband elliptical polarized plane wave injection in the DGTD method, and the significance of this study is observed in the results. The experimental outcomes reveal that the proposed method is consistent with the analytical solution in free space and expected to provide efficient numerical solutions for analyzing scattering characteristics generated by various elliptically polarized waves.

This article aims at discussing computational approach to design magnet-free nonreciprocal metamaterial. Detailed mathematical derivation on Floquet mode analysis is presented for Faraday and Kerr rotation. Non-reciprocity in the designed metasurface is achieved in the presence of biased transistor loaded in the gap of circular ring resonator. Based on the derived mathematical model, co- and cross-polarized components have been extracted, which helps find Faraday and Kerr rotation and compare/contrast the reciprocal and nonreciprocal systems.

Recent advancement in ultra-low-power electronics and radio communications has significantly contributed to the development of miniaturized biomedical sensors capable of capturing and transmitting wirelessly physiological data. The characterization of signal and power transmission inside the human body is of great importance. This paper investigates the case of an intra-body wireless communication in the UHF frequency band. An implanted antenna (bent dipole) is designed to operate efficiently in a biological tissue model. Predictions of the performances obtained by 3D electromagnetic simulations are compared to measurements in a realistic environment (pork meat in a box of 18x10x7 cm³). The antennas show return loss matching of -12 dB at 1,2 GHz, in the presence of the meat. Then a characterization of the transmission link between two antennas is performed both numerically and experimentally at 1,2 GHz. At this frequency, the measured |S₂₁|² is around -35 dB at 6 cm, and -40 dB at 8 cm. The simulation of the |S₂₁|² highlights the impact of the conductivity of the tissues, driving to values of -25 to -55 dB at 6 cm, and -30 to -65 dB at 8 cm. The characterization of the pork meat is evaluated experimentally around 2 S/m. During the process of characterization, this value may be over-estimated due to the pressure applied on the sample. The simulations results are compared with measurements results, and also with retro-simulations results. The latter are considered as a worst case due to the losses implied by the over-estimated conductivity value.

This paper presents an optimal duty cycle model predictive current control (ODC-MPCC) strategy based on the internal model observer (IMO) for permanent magnet synchronous motor (PMSM). First, in order to be able to control the current quickly and better, the partial derivative of the cost function with respect to the optimal duty cycle is directly used. On this basis, a five-segment algorithm is used to allocate the optimal duty cycle, and output voltage with arbitrary amplitude and direction. In addition, to reduce the current static error under parameter mismatch, the IMO is designed to estimate the system disturbance caused by parameters variation, which is used for feedforward compensation. Finally, experiments show that the proposed method can effectively reduce the current ripple and static error and improve the steady-state performance of the system.

In this paper, a microstrip sensor based on a complementary split ring resonator (CSRR)-derived structure is proposed to characterize the permittivity and permeability of materials. By loading an etched meandered conductive ring and an interdigital capacitor structure, effective separation of the permittivity sensing area and permeability sensing area is realized, and the field strengths of the corresponding areas are improved. The relationship between the resonant response (resonant frequency and quality factor) of the sensor and the permittivity and permeability of the sample under test (SUT) is discussed, and the theoretical basis for measuring the material properties is given. By analyzing the measured resonant frequency and quality factor, the real and imaginary parts of the permittivity and permeability of the SUT can be determined. The sensor was fabricated on a Rogers 5880 substrate, and four standard dielectric and magnetodielectric (MD) samples were tested. The results show that the measured values of the real and imaginary parts of the permittivity and permeability are in good agreement with the reference data.

A high-selective wideband bandpass filter (BPF) with a notched-band and harmonic suppression is proposed in this paper. Firstly, a uniform impedance resonator with an embedded open-circuited stub square loop is applied in the filter design. By adopting parallel-coupling structure at I/O ports, such a resonator can generate a notched-band within the passband due to the counter-phase cancellation of two dissimilar signal paths. The width of the square loop can be adjusted to select the location of the notched-band. Secondly, by introducing an L-shaped open-circuited stub to one input feed line, a transmission zero (TZ) is created. It can be used to suppress higher harmonic passband. The filter is designed and fabricated with the notched-band centered at 8.1 GHz, and two TZs are implemented at the both sides of the passband. Simulated and measured results show that the filter has a good selectivity and a wider stopband characteristic.

In order to realize the maximum torque output (MTO) in the field-weakening region for the bearingless induction motor (BIM) stator vector control, a flux feedforward control strategy was proposed. Firstly, based on the restrictions of the stator flux oriented control and the dynamic characteristics of the current in the BIM field-weakening region, the optimal distribution of the torque current and the excitation current and the dynamic model of the maximum torque output strategy are analyzed. Then the field-weakening region could be divided into two parts according to the change of slip, it can be proved that the BIM works under the voltage and current limitations in the field-weakening region I, and works under the voltage and torque limitations in the field-weakening region II. By this way, the optimal flux mathematical model of the motor can be obtained. Finally, the maximum torque output in the field-weakening region is proved. The simulation and experiment results show that the proposed flux feedforward control strategy in the field-weakening region can make the output torque and current tracking effect improve significantly when the BIM runs beyond the rated speed. At the same time, the suspended rotor has good suspension performance, and high efficiency and stability of the BIM is realized.

A novel active metasurface which is switchable to accomplish dual band gain enhancement is reported. The metasurface is used as a superstrate above the dual band patch antenna working at 2.4 GHz and 4.6 GHz. The gain of the antenna is enhanced by 3.5 dB at both frequencies. Switching between the frequencies is enabled by a p-i-n diode. When the p-i-n diode is in OFF state, gain is enhanced at 2.4 GHz, while gain is reduced at 4.6 GHz and when the p-i-n diode is in ON state, gain is enhanced at 4.6 GHz, but reduced at 2.4 GHz. The diode is controlled by biasing with a regulated DC source. The efficiency of the antenna is 70% at 2.4 GHz and 85% at 4.6 GHz. The simulated and measured results show good agreement. The distance between the antenna and the superstrate is 6 mm, which is 0.048λ at 2.4 GHz and 0.092λ at 4.6 GHz. This superstrate can be used in WLAN and Sub-6 GHz 5G applications.

A filtering dielectric resonator antenna (FDRA) using an inductive CPW (coplanar waveguide) feed structure is proposed. Simultaneously, a pair of slotline stubs are respectively loaded on the signal line and ground of the CPW feed structure, which is used to generate radiation nulls near the edges of the passband. Furthermore, the two radiation nulls can be controlled independently by adjusting the length of the loaded two pairs of slotline stubs. In addition, it is interesting that TE₁₁₁ mode is split due to the different loading effects of slotline stubs in feed network, thereby three resonances in the passband are formed. Finally, an FDRA with quasi-elliptic function response is realized without additional filtering circuit. The prototype of the FDRA operating at 3.53 GHz was fabricated and measured to verify the design validity. The measured results show that the impedance bandwidth is 13.6% (3.29-3.77 GHz); the gain is basically stable at 5.7 dBi wihtin the passband; and the two radiation nulls are located at 3.05 GHz and 3.88 GHz, respectively.

A frequency- and pattern-reconfigurable cone antenna utilizing liquid metal is investigated. It contains a cone antenna, four reflectors, and a circular ground plane. The transparent resin is processed into a mold for the cone and reflective poles to store the liquid-metal. By controlling the poles height in the mold, the proposed antenna can realize four radiation patterns. Meanwhile, the cone height could be adjusted by the reflective poles, thereby achieving frequency tuning. The simulation and measurement results show that, by tuning and switching the liquid-metal radiator and reflectors, a wide frequency tuning bandwidth of 43.2% is achieved, and a pattern reconfigurable with five types of beam steering over 360° coverage is realized. The prototype is fabricated, assembled, and measured, with good agreement between the simulated and measured results. The design of indoor coverage antenna system must have comprehensive measurement indexes such as multi-bands, multi-beams, high gain, and low cost.

In the paper, a compact wideband power divider (PD) which consists of a λ/4 unequal width three-coupled-lines, four short-circuited stubs and an airbridge resistor is presented. By connecting the four short-circuited stubs to the input and output ports of the PD, two additional transmission poles are obtained, which results in enhanced bandwidth and improved selectivity. Rigorous design equations are given according to the even-odd mode analysis, and the design parameters are obtained based on particle swarm optimization. For validation, a prototype operating at 1 GHz is fabricated and tested. The experimental results indicate that the proposed power divider exhibits a return loss of more than 17.5 dB and an isolation of larger than 18.8 dB isolation in the fractional bandwidth of 91%.

A newly synthesis method of planar array antenna for wireless power transmission (WPT) is introduced in this paper. The whole array aperture is divided into several subarrays which can reduce the complexity of the feed network and the cost of the array antenna. Invasive Weed Optimization (IWO) algorithmis used to optimize the subarray division and the excitation amplitude of each subarray. The maximum beam collection efficiency (BCE) and maximum sidelobe level outside the receiving area (CSL) are considered as the evaluation index. The synthesis results show that the proposed method can obtain higher BCE and lower CSL.

We demonstrate the recovery of simple geometric and permittivity information of breast models in an experimental microwave breast imaging system using a synthetically trained machine learning workflow. The recovered information consists of simple models of adipose and fibroglandular regions. The machine learning model is trained on a labelled synthetic dataset constructed over a range of possible adipose and fibroglandular regions and the trained neural network predicts the geometry and average permittivty of the adipose and fibroglandular regions from calibrated experimental data. The proposed workflow is tested on two different experimental models of the human breast. The first model is comprised of two simple, symmetric phantoms representing the adipose and fibroglandular regions of the breast that match the model used to train the neural network. The second, more realistic model replaces the symmetric fibroglandular phantom with an irregularly shaped, MRI-derived fibroglandular phantom. We demonstrate the ability of the machine learning workflow to accurately recover geometry and complex valued average permittivity of the fibroglandular region for the simple case, and to predict a symmetric convex hull that is a reasonable approximation to the proportions of the MRI-derived fibroglandular phantom.

Pattern synthesis usually involves determining the strengths of the current sources in a given array that yield a specified pattern. Demonstrating that this pattern can be produced by an actual array of physical elements is a step that is rarely included in the discussion. The purpose of this article is to examine how well a numerical model of these sources will match the desired pattern when mutual interactions between the array elements are taken into account. An investigation of this process is described here using NEC (the Numerical Electromagnetics Code), although any wire-antenna computer code could be used. Modeling wire antennas in codes like NEC typically involves specifying the input or exciting voltage of the antenna to find the induced current from which the far field can be obtained. The pattern-synthesis problem for a specified array geometry, by contrast, requires instead finding the exciting voltages that will induce the synthesized currents needed to produce the pattern of interest. The radiation pattern that results can then be compared with the desired pattern to determine how well the physical array performs. Several examples of this approach are included here to demonstrate the process.

A novel low-profile GNSS microstrip circular polarization antenna is proposed and analyzed. Circular polarization is realized by asymmetric structure patch, and arc structure loaded on the main radiator can keep two modes orthogonal over a wide-angle range, so that the antenna has an extremely wide 3 dB axial ratio beamwidth (ARBW). The far-field AR beamwidths obtained are 232° and 212° respectively in the main plane of φ=0° and φ=90°. In φ=45° and φ=135°, 3 dB AR beamwidths are 241° and 244°, far exceeding the 120° required for satellite applications. In the whole CP band, 78.95% of the beam width exceeds 180°. The profile is only 0.0156λ₀, which is suitable, especially, for portable wireless systems or devices. The return loss bandwidth of -10 dB is 5.13% (1.52 GHz-1.6 GHz), which covers BeiDou Navigation System B1 (1.561 GHz). The axial ratio bandwidth is 1.28% (1.55 GHz-1.57 GHz), and the in-band peak gain is 4.09 dBi.

This paper presents a highly directive pattern reconfigurable antenna array capable of switching single or multiple beams of high directivity in multiple directions. Each element is individually capable of providing radiation pattern of directivity 12 dB and realized gain of 10.2 dB. Here, eight directive array elements are arranged in a circular fashion resembling a fan along with a switching arrangement to obtain beam switching in the horizontal plane. Two or more elements can be excited simultaneously to obtain patterns in multiple directions. In another configuration, the elements are arranged around a cylindrical support resembling an umbrella structure to obtain azimuthal switching at a desired tilt. The ability to reconfigure patterns in desired direction facilitates their usage as base station antennas providing desired angular coverage to intended users only, resulting in least signal interference.

A novel mid-infrared (MIR) biochemistry sensor using two suspended GaAs waveguides based on an asymmetric Mach-Zender Interferometer (MZI) is proposed. The propagation properties and refractive index (RI) sensing performances of MZI are investigated by the finite element method (FEM). The simulation results show that the maximum waveguide sensitivities (S_wg) of the TE and TM modes in the suspended GaAs waveguide are ~1.2 and ~1.0. This design of the GaAs waveguide using the suspension structure is to enhance the interaction between the vanishing field and the measured material. The RI sensitivity of the asymmetric MZI structure increases with the length of the sensing arm, which can reach 854.5 nm/RIU with a Q of 208.2 after parameter optimization. The two arms of the MZI are designed as width-asymmetric structures to make the sensor more sensitive to the measured material. The asymmetric MZI sensing structure has high RI sensitivity and compact structure, which provides a feasible scheme for biochemical sensing.

The article presents a compact size and high isolation with 2×2 MIMO, double flare horn shaped antenna for K and Ka bands of mm-wave applications. The overall size of the MIMO antenna 0.19λ×0.19λ×0.01λ mm³ at a lower frequency has been designed, simulated, fabricated and tested. The proposed MIMO antenna components are arranged parallel with identical shaped to provide a high level of inter-element isolation and 50 W micro strip line feed. The antenna covers 18.61-20.01 GHz in the K-band (18-26.5 GHz) and 21.52-33.91 GHz in the Ka-band (26.5-40 GHz) with impedance bandwidths of 7.2% and 44.5% respectively at port-1 and port-2. Maximum peak gain of 6.5 dBi & 8.1 dBi respectively at port-1 and 6.5 dBi&7.9 dBi at port-2 is observed respectively. Diversity characteristics such as envelope correlation coefficient, diversity gain, total active reflection coefficient and channel capacity loss are determined to validate the considered MIMO antenna's work qualities. The isolation of more than 35 dB indicates that the proposed structure is suitable to use a dual-port MIMO antenna. The recommended structure's investigation revealed a steady performance and a high degree of agreement between simulated and measured findings.