Quadrature feeding is an essential in magnetic resonance imaging radio frequency (MRI-RF) coils, to improve the homogeneity of the magnetic field of surface coil, the signal to noise ratio (SNR) of the image by a factor of √2 , and to create a circularly polarized magnetic field inside the volume coil. The quadrature feeding is incorporated, using hybrid coupler. However, at 63.87MHz the Larmor frequency of hydrogen proton, corresponding to 1.5 Tesla, the size of the hybrid coupler and other microwave circuits become large. So, to minimize its physical size, a coaxial cable transmission line with lumped capacitive loading has been proposed. The size of the proposed hybrid coupler is reduced by 68%, as compared to the conventional hybrid coupler. The proposed device is then fabricated as a both rigid and flexible structure, which provides isolation (S₄₁) of around 19 dB and a 900phase difference between coupled and the through ports. Both structures provide return loss S₁₁ > -15 dB and coupling at output ports S₂₁, S₃₁ around 3 dB.

Microwave testing is an area of research where material characterization is done using interrogating microwaves over a frequency band, and this technique can provide excellent diagnostic engineering, geophysical prospecting. Every material has a unique set of electrical characteristics that are dependent on its dielectric properties. Accurate measurements of these properties can provide valuable information about the material. This work presents a non-destructive technique for the detection of adulterants in food using the proposed RF sensor. The proposed RF sensor is operational at C-band with its resonant frequency at 5.7 GHz. The structure is designed using Ansys HFSS, and a predicted model of the proposed sensor is developed and fabricated. Some common food samples are tested using the fabricated sensor, and a shift in resonant frequency is obtained, which indicates the rate of adulteration. From the obtained results, a general conclusion is obtained on the dependency of the rate of adulteration and permittivity of the food sample. A precise correlation of permittivity of common food samples and its resonant frequency is obtained. The predicted model and the experimental results harmonize, which indicates that the model is proficient in real time testing.

We deploy the general momentum space theory developed in Part I in order to explore nonlocal radiating systems utilizing isotropic spatially-dispersive metamaterials. The frequency-dependent angular radiation power density is derived for both transverse and longitudinal external sources, providing detailed expressions for some special but important cases like time-harmonic- and rectangular-pulse-excited small dipoles embedded into such isotropic metamaterial domains. The fundamental properties of dispersion and radiation functions for some of these domains are developed in examples illustrating the features in nonlocal radiation phenomena, including differences in bandwidth and directivity performance, novel virtual array effects, and others. In particular, we show that by a proper combination of transverse and longitudinal modes, it is possible to attain perfect isotropic radiators in domains excited by small sinusoidal dipoles. The directivity of a nonlocal small antenna is also shown to increase by possibly four times its value in conventional local domains if certain design conditions are met.

In this paper, a compact modified hexagonal spiral resonator-based tri-band patch antenna with an octagonal slot is presented for Wi-Fi/WLAN applications. The proposed antenna is designed on a low-cost FR4 substrate with a dielectric constant of ε_r=4.4 and loss tangent δ=0.02. The tri-band operations have been achieved by the a Modified Hexagonal Complementary Spiral Resonator (MHCSR) and an Octagonal slot. The loading of the MHCSR at the bottom of the substrate is to cover the 900MHz (IEEE 802.11ah) band, and an Octagonal slot on top of the 5 GHz (IEEE 802.11a/h/j/n/ac/ax) rectangle patch is to cover the 2.4 GHz (IEEE 802.11b/g/n/ax)band. The prototype of the proposed antenna is fabricated and tested to validate the simulation results. The measured impedance bandwidth is 105 MHz at 900 MHz, 160 MHz at 2.4 GHz, 18 0MHz at 5 GHz. The designed antenna has a compact size with overall dimensions of 0.054λ₀ x 0.066 λ₀ x 0.0048 λ₀ (18 x 22 x 1.6 mm³). The 82.2% reduction in size has been accomplished as compared to a conventional patch antenna at 900MHz (lower resonance frequency). The waveguide setup method has been used to validate a negative permittivity property of the MHCSR. The parametric analysis of the proposed antenna had been carried out using the Ansoft HFSS19 software.

This paper focuses on an efficient antenna selection strategy for a distributed massive MIMO system. The objective of the proposed algorithm is to attain ergodic achievable rate as much as possible with antenna selection in a constrained capacity limited system. In this proposed work, the initial selection of antenna set is based on channel amplitude and correlation which then follows an iterative approach in order to select the best subset of transmit antenna elements from the overall antenna set. The proposed scheme significantly outperforms, in terms of ergodic rate with low complexity, the prevailing transmit antenna selection methods. Simulation results show that the performance of the proposed antenna selection method is close to select all transmission with a minimum throughput loss. Thus the proposed method is best suited for a large scale distributed Massive MIMO system without degradation in system performance and is of low computational complexity.

A new wideband 3-dB tandem coupler is presented that has wide bandwidth using four 90° short stubs. The proposed tandem coupler does not require a higher transmission line impedance or a narrower coupling gap than conventional couplers. Measurements of the fabricated tandem coupler operated at a center frequency of f₀ = 1 GHz are presented as verification of the design concept. The fractional bandwidth (FBW) at which the return loss is suppressed to a level better than 15 dB was 71%. Theoretical calculations and measurements of the tandem coupler were in good agreement

This article reports a very efficient Frequency Selective Surface (FSS) with Convoluted Square Loop (CSL) shape is designed for applications in the X-band. They are designed on the surfaces of an FR-4 substrate. Frequency selective surface (FSS) is a combination of a periodic structure designed to selectively absorb, reflect, and transmit the electromagnetic (EM) waves. FR-4 material provides durability and flexibility. A convoluted square loop structure reduces the size of the unit cell, and it also has a better stability with good gain. So, a CSL patch with a CSL FSS array with a slot on dual FR4 substrates is introduced for the improvement in overall gain and bandwidth. As per the design parameters, a structure is designed at 10GHz. This structure is designed with ANSYS HFSS. The proposed antenna structure has a return loss of -36.424 db, and VSWR value is 1.0307. The measurement results show a gain improvement of 6.266db and bandwidth of 5.882 db.

Nonlocal radiating systems are new functional structures composed of externally applied currents radiating in nonlocal material domains, for example hot plasma, optically active media, or nanoengineered spatially dispersive metamaterials. We here develope the requisite mathematical foundations of the subject needed for investigating how such new generation of radiating systems may be analyzed at a very general level (Part I), while radiation pattern constructions for applications are provided in Part II. A key feature in our approach is the adoption of a fully-fledged momentum space perspective, where the spacetime Fourier transform method is exploited to derive, analyze, and understand how externally-controlled currents embedded into nonlocal media radiate. In particular, we avoid working in the spatio-temporal domain popular in conventional local radiation theory. Instead, we focus on the basic but nontrivial problem of infinite generic (anisotropic or isotropic) homogeneous nonlocal domain excited by an external source and investigate this structure in depth by deriving the dyadic Green's functions of nonlocal media in momentum space. Afterwords, the radiated energy in the far-zone is estimated directly in the spectral domain using a generalized momentum space energy density concept after the use of a suitable power theorem. The derived expressions of the radiation power pattern of the source can be computed analytically provided that the medium dielectric functions and the dispersion relation data of the nonlocal metamaterial are available. Detailed examples and applications of the theory and its algorithm are given in Part II of the present paper.

A complete energy harvesting system via Radio Frequency (RF) is designed in a broadcast station where multiple frequency sources are readily available. These frequency sources are the Intermediate Frequency (IF), 70 MHz, Wi-Fi frequency band, 2.4 GHz, and the Ku-band frequency, 13 GHz. The RF source via the Wi-Fi band (2.4GHz) is harvested via a microstrip patch antenna designed with its matching network. The harvested RF energy is transformed into usable DC power via a 8-stage Villard voltage doubler circuit. The DC power is managed by a power management system handled by the BQ25570 circuit which gives a regulated output of 3V, powers up a low power motion sensor and charges a battery at the same time. This system comes with a backup source which is the battery and able to take over the system in case the incoming RF signal fails. The RF energy harvested from the IF 70 MHz and Ku-band at 13 GHz is derived from coupler outputs which are available in broadcast stations, transmission lines, etc. Both these RF signals are converted to DC signals via a 5-stage Villard voltage doubler circuit with different matching networks. The DC power is managed by a power mux via the TPS2122 which selects the highest available power. Over the years, no works on RF harvesting have focused on smart phone charging as its application, due to the limitation in power availability. This work strives to provide enough power to charge phones and effectively gives a 5V output to charge smart phones with a charging current of 0.5A which is similar to a USB charging port.

Aiming at the problem of look direction error in the desired signal, a novel robust adaptive beamforming method based on covariance matrix reconstruction is proposed. Firstly, the Sparse Bayesian Learning (SBL) is performed to acquire the true signal direction and the spatial spectrum simultaneously. Secondly, the SBL spatial spectrum is used to reconstruct the interference-plus-noise covariance matrix. Compared with other reconstruction algorithms, this approach can realize the position estimation without any optimization procedures. Theoretical analysis, simulation results and water pool experiments demonstrate the effectiveness and robustness of the propose algorithm.

In this manuscript, a porous one-dimensional Photonic Crystal (1D-PhC) based sensor is designed for bio-chemical sensing application (i.e. hemoglobin concentration). The alternate layers of silicon are considered for design optimization, where, the porosity is introduced to obtain the desired index contrast value. The sensing capability of the proposed design is enhanced by modifying the dispersion property of the structure. For this, a defect middle layer is deliberately introduced. The number of layers, defect layer optical thickness and porosity values are optimized to confine a defect mode of desired wavelength. Finally, the detailed analysis of proposed structure is carried out. This provides the average sensitivity of around 323nm/RIU (0.05nm/(g/L) along with considerably higher FOM of 517RIU^-1.

On the basis of serious electromagnetic interference (EMI) produced by power electronic equipment,coupling capacitance existing between transistor and transistor is considered as the main factor disturbing differential-mode(DM) loop. Calculation model of coupling capacitance is established by using FEM (Finite Element Method)and Moment method, and computing method is also derived.EMI improvement method for converter system is proposed by controlling the coupling capacitance impedance. Experimental results show that changing the placement distance and position of the transistor can reduce the conducted interference.

The sensitivity of dual-polarized Sentinel-1 backscatter towards biophysical parameters (height and biomass) of wheat and mustard crop was investigated. The plant height and biomass observations categorized into three groups, were useful in understanding the sensitivity across a particular biomass and height range whose significance was determined using a statistical measure (student's t-test). The crop parameters were retrieved only for the C-band sensitive biomass (< 5 Kg m^-2) and height (< 160 cm for mustard and < 80 cm for wheat) range considering the saturation of signals at advanced crop stages and based on the detailed investigation. The sensitivity towards the mustard plant height becomes very weak as the crop proceeds to a height > 190 cm. A low RMSE (11.50 cm) was observed when the retrieval was done for height < 160 cm. The cross-polarized responses were more sensitive to crop biomass than co-polarized responses mainly due to the dominant depolarization of the transmitted power. An early saturation was found at co-polarized VV (4 Kg m^-2) as compared to cross-polarized VH (6 Kg m^-2) particularly for planophiles like mustard and little later in the case of erectophile such as wheat. The backscatter response was found to be sensitive at early crop stages for both the crop geometry, and hence retrieval of biophysical parameters at these stages can yield better accuracy than the overall retrieval. The retrieval of wheat height resulted in a low RMSE of 9.25 cm when the retrieval was carried out for crop height < 80 cm. Retrieval was attempted using the simplistic logarithmic model which can find ways in the operational application using wide swath dual-polarized datasets.

This paper describes the design and development of a highly directive planar end-fire array using arc dipoles as the array elements. The inter element spacing, shape and size of the array elements are optimized for maximum directivity and gain. The array is printed on a substrate whose dimensions are also optimized for better performance. The overall length of the proposed six element array is 1.9λ, giving directivity and gain values as 12.0 dBi and 10.2 dBi respectively at 5.8 GHz.

In this paper, a highly directive small-cell waveguide antenna array for point to point wireless communication in E-band radio frequency systems is presented. The antenna array is designed and dedicated for the paired bandwidths 71-76 and 81-86 GHz. It is composed of 32 x 32 horn elements with a total surface of ~100 x 100 mm² to achieve a directivity ≥38 dBi, narrow beam (~2°) and low-level sidelobe ≤-26 dB. A compact stepped horn antenna element (SHE) (6.6 mm) is designed. It is 25% smaller than a standard horn element (in the same band) keeping the same aperture surface (3.4 x 3.4 mm²). Layer-by-layer micromachining process is employed for the fabrication. A compact feeding network (25 mm) is realized using ridged waveguide technique with a cut-off frequency of 55 GHz, much lower than standard WG one in the same band. A bow-tie multi-section waveguide polarizer rotator (±90°) is optimized and associated with the WG transitions to re-phase the fields applied to SHE elements. Electric discharge machining (EDM) process was used to manufacture a 4×4 sub-array prototype including the entire WG power-feed network. The antenna is characterized in an anechoic chamber, and experimental results are compared to 3-D electromagnetic simulations with good agreements over the two bands.

In this paper, the miniaturization of the slot antenna is presented for the first time with the use of high refractive index metamaterial. Based on the effective parameter extraction, the studies conducted on Single Ring Split Ring Resonator (SR-SRR) reveal that the unit cell can produce high values of positive refractive index. By taking the advantage of the principle of duality, the slot is loaded with two Complementary SR-SRRs (CSR-SRRs) on either side of it to create an effective HRI medium. With the partial loading of HRI metamaterial medium, the resonance frequency of the slot is brought down from 4.225 GHz to 2.5 GHz. The radiation characteristics of the loaded slot antenna were found to be almost similar to that of the conventional slot antenna. The simulated and measurement results were found in good agreement.

For the last half a century, neurophysiology relies on patch clamp which neutralizes the ions to sense a signal. The smaller the patch, the efficiency is better. However, the limit has not been reached yet, and we accomplish it here. We add a spiral and a ring antenna to a coaxial probe to significantly reduce its self-resonance as the tip filters the ultra-low vibrations of protein's sub-molecular parts (10^-18 watts to 10^-22 watts) in a living cell environment with 10-6-watt noise. A probe tip added by a cavity resonator & a dielectric resonator acquires four distinct ultra-low noise signals simultaneously from a biomolecule, which is not possible using a patch clamp. Protein transmits ions and small molecules. Our probe estimates the ionic content of the molecule. Simultaneously it also measures the dipolar oscillations of its sub-molecular parts that regulates ionic interaction. We experimentally measure signals over a wide frequency domain. In that frequency domain, we map the mechanical, electrical, and magnetic vibrations of the element and record the relationship between its electric and ionic conductions. Dimension wise it is the ultimate resolution, consistent both in silico & in real experiments with the neuron cells --- the atomic pen instantly monitors a large number of dynamic molecular centers at a time.

Characterization of the human body channel is a necessity to pave way for practical implementation of intrabody communication (IBC) in body area networks (BAN). In this paper, a circuit-coupled finite element method (FEM) based model is proposed to represent the galvanic coupling type IBC on human arm. In contrast with other models for IBC, both the finite element method and the parasitic capacitances between electrodes are taken into account in the modeling. To understand the characteristics of IBC, simulations with multiple frequencies, excitation voltages, channel lengths and values of parasitic capacitors are carried out using the model. The current density and electric field distribution in different human tissues reveal an insight into signal transmission path through the human body intuitively. The body channel gain presents a band-pass property after adding the parasitic capacitances into the model, while it performs an increasing characteristic with the frequency before the adding. Finally, a galvanic coupling IBC measurement setup is fulfilled, and the outcome shows a good agreement with the proposed model. It is indicated that the parasitic capacitances are the major factors to cause the band-pass and affect the bandwidth, and they should not be neglected in the real IBC applications.

This paper presents an overview and review of the fundamental implicit finite-difference time-domain (FDTD) schemes for computational electromagnetics (CEM) and educational mobile apps. The fundamental implicit FDTD schemes are unconditionally stable and feature the most concise update procedures with matrix-operator-free right-hand sides (RHS). We review the developments of fundamental implicit schemes, which are simpler and more efficient than all previous implicit schemes having RHS matrix operators. They constitute the basis of unification for many implicit schemes including classical ones, providing insights into their inter-relations along with simplifications, concise updates and efficient implementations. Based on the fundamental implicit schemes, further developments can be carried out more conveniently. Being the core CEM on mobile apps, the multiple one-dimensional (M1-D) FDTD methods are also reviewed. To simulate multiple transmission lines, stubs and coupled transmission lines efficiently, the M1-D explicit FDTD method as well as the unconditionally stable M1-D fundamental alternating direction implicit (FADI) FDTD and coupled line (CL) FDTD methods are discussed. With the unconditional stability of FADI methods, the simulations are fast-forwardable with enhanced efficiency. This is very useful for quick concept illustrations or phenomena demonstrations during interactive teaching and learning. Besides time domain, many frequency-domain methods are well-suited for further developments of useful mobile apps as well.

A periodic millimeter wave leaky-wave antenna (LWA), which has two different types of radiator elements that enable backward to forward radiation, is proposed. The unit-cell of the LWA consists of two quarter-wavelength microstrip lines and two corrugated substrate integrated waveguide (CSIW) cells with S-shaped quarter-wavelength open-circuit stubs. In addition to two parallel edge radiators, a single etched transverse slot with a tilt angle acts as an ancillary radiator, which ensures impedance matching in a large frequency range and achieves the backward to forward scanning. We analyze the proposed design through simulations, characterize a fabricated prototype and find it to have good radiation properties including broad impedance bandwidth. The measurement results show a high peak gain from 11 to 15.8 dBi with a large scanning angle range from -34° to +22° in the K-band operating frequency range.