Doppler Ultrasound as the gold standard for noninvasive arterial pulsation monitoring has limitations such as dependency on the operator and absence of acoustic window in some patients. Recently, mm-wave has been propounded as an alternative modality for biomedical diagnostics. However, heartbeat monitoring using mm-wave modality has been experimentally investigated only for external carotid artery, and its usage for deeper arteries has not been proved, yet. This study investigates the feasibility of mm-waves in the monitoring of non-superficial arteries. A continuous-wave (CW) reflectometer sensor is used for sensing pulsations exploiting the Doppler effect. The artery mimicking tube passes through an artificial agar-oil skin phantom. A peristaltic pump circulates the liquid through a tube. An antenna is placed in direct contact with the phantom without any coupling liquid. First, we investigate the optimum frequency of the given antenna in its impedance bandwidth [16 GHz-20 GHz]. Using the optimum frequency, the pulsation of an ar-tery with a 1.6 mm diameter, placed in the depth of 16 mm, and has less than 0.02 mm radial oscillation amplitude was easily detectable.

A hexagonal cavity backed antenna based on HMSIW is proposed to operate at 5.2 GHz and 5.8 GHz frequencies. The TM₀₁₀ and TM₁₁₀ modes of the hexagonal cavity resonator have been chosen to excite the structure. Afterwards, an HMSIW hexagonal cavity is formed by splitting conventional hexagonal cavity resonator along a magnetic wall. This enables a 50% reduction in size without affecting the antenna operating frequency. A rectangular slot is etched at the centre of the magnetic wall to curtail TM₁₁₀ mode operating frequency. The dimensions of the slot are optimized to adapt TM₁₁₀ resonant frequency to the desired frequency. In free space, the resulting antenna accomplished a peak gain of 5.5 dB and 4.3 dB at centre frequencies of 5.2 GHz and 5.8 GHz respectively. In the vicinity of pork tissues, the antenna exhibits a peak gain of 4 dB at 5.8 GHz along with an efficiency of 87.2%.

A study is presented of several types of nondiffracting and slowly diffracting spatiotemporally localized waves supported by a simple dielectric medium moving uniformly with speed smaller or larger than the phase speed of light in the rest frame of the medium. The Minkowski material relations are not independent in the case that the speed of motion equals the phase speed of the medium; hence, the electric displacement and magnetic induction vectors cannot be uniquely determined from them. Following, however, a waveguide-theoretic approach, separate equations can be written for the longitudinal and transverse (with respect to the direction of motion) electromagnetic field intensities. The fundamental solutions associated with these equations provide a uniform transition between the cases of ordinary and Čerenkov-Vavilov radiation. The equation satisfied by the longitudinal field components in the absence of sources is examined in detail. In the temporal frequency domain one has an exact parabolic equation which supports accelerating beam solutions. The space-time equation supports several types of nondiffracting and slowly diffracting spatiotemporally localized waves. Comparisons are also made with the acoustic pressure equation in the presence of a uniform flow.

In this paper, the optimized results of multi-beam forming for an active phased array antenna are presented. In the case of a horn radiator, to implement equal main beamwidths and a low side-lobe level in the principal planes, a circularly polarized dual-mode horn antennawith the gain over 14.5 dBi is designed and fabricated at the Ka-band, which is composed of a conical horn, polarizer, and transducer. In the case of multi-beam forming, when several main beams are simultaneously generated within a limited scanning range, large side-lobes can be observed among the main beams. To overcome this phenomenon, an evolutionary technique, such as a genetic algorithm is applied to the optimization of a multi-beam pattern. It is shown that the proposed method can significantly reduce the outer side-lobe level as well as the inner side-lobe level of the simultaneous multi-beam pattern.

Compared to crystalline silicon solar cells, thin-film solar cells are inexpensive, but a weak absorption of sunlight at a longer wavelength is a significant issue. In this perspective, an efficient light trapping mechanism is needed to facilitate the light-guiding in enhancing light absorption. This paper presents a theoretical investigation of ultrathin amorphous silicon (a-Si) solar cells using the rigorous coupled-wave analysis (RCWA) method. We noticed broadband light absorption of the designed solar cell due to an efficient light trapping geometry. Our proposed design is composed of anti-reflection coating (ITO), an absorbing layer (a-Si), a back reflector (Ag-substrate), top-indium tin oxide (ITO), and bottom-silver (Ag) nanogratings. Using an Ag-back reflector with diffraction gratings demonstrated the improved diffraction and scattering of light, which enhanced light absorption within a 50 nm thick absorbing layer. Compared to the reference solar cell, the proposed ultrathin solar cell endorsed the enhanced photovoltaic conversion, i.e., 19% and 23%, corresponding to the transverse electric (TE) and magnetic (TM) polarization conditions. Furthermore, we explore the investigations of light absorption, current density, field distributions, reflection, transmission, and parasitic losses for the optimal design of ultrathin film (a-Si) solar cells.

Generalized Lorentz-Mie Theory (GLMT) provides analytical far-field solutions to electromagnetic (EM) scattering of an aggregate of spheres in a fixed orientation. One of the computational codes that implements the GLMT calculation is that provided by Xu, dubbed GMM which returns EM responses such as the extinction cross section, σ_ext, given the information of incident wavelength, particle arrangement, the common radius, and reflective indices of the aggregate. We have attempted to represent the GMM code in the form a neural network dubbed NNGMM. The NNGMM obtained was stress tested and systematically quantified for its accuracy by comparing the σ_ext predicted against that produced by the original GMM code. The σ_ext produced by the NNGMM for arbitrary aggregates at random wavelength yielded a good fidelity with respect to that calculated by the GMM calculator up to an R-squared value of above 99% level and mean squared error of ≈5.0. The realization of NNGMM proves the feasibility of representing the GMM code by a neural network. The optimally-performing NNGMM obtained in this work can serve as an alternative computational tool for calculating σ_ext in place of the original GMM code at a much cheaper cost, albeit with a slight penalty in terms of absolute accuracy.

In this article, we focus on metric space in Finsler geometry and propose a method of ship detection in synthetic aperture radar (SAR) amplitude image based on Finsler information geometry. This provides deep unified perspectives of Finsler geometric application. The proposed method consists of three stages: The Weibull manifold model is used to represent the statistical information of intensity SAR images; then the Finsler metric is constructed to realize the distance measurement between probability distributions in Weibull manifold space; finally, Finsler metric space is used to achieve saliency representation and detection of ships. Theoretical analysis and comprehensive experimental results demonstrate the robustness and effectiveness of the proposed approach using typical real SAR images.

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%.