In this article we give an analytical formula for calculating the self-inductance for circular coils of rectangular cross-section which has a non-uniform current density. Recently, the formula for calculating this important electromagnetic quantity was published in the form of the single integral whose kernel function was asum of elementary functions. However, a new formula is obtained in the form of elementary functions, single integrals, and the complete elliptic integral of the first, second and third kind. Although its development looks tedious, we obtain a rather user-friendly expression for the calculation. From the general case, the self-inductance of the thin disk coil (pancake coil) with the nonuniform current is obtained in a remarkably simple form. The results of this work are compared with different known methods, and all results are in the excellent agreement. Our approach has not been found in the literature.

This paper presents a new design concept of dual bandpass filter. Based on the strong coupling between two resonators, a dual 1-pole band-pass filter is designed and is used as the basic building block. By providing appropriate weak coupling between these building blocks, a higher-order dual bandpass filter can be realized. In addition, these building blocks can be stacked vertically and/or horizontally to construct a compact filter. In this way, by using 3D full wave EM and circuit co-simulation, the simulation time required in the design stage can be reduced. In addition, it also provides a way to post-tune each building block individually and further reduces the time required in prototype post tuning process. For demonstration, an L-band dual 4-pole bandpass filter is designed with passband frequencies of 1.23 GHz~1.255 GHz and 1.55 GHz~1.6 GHz. In order to reduce the size of the filter and obtain a wide stopband bandwidth, a suitable evanescent mode cavity is used to realize the resonant structure. The measurement result shows that the insertion losses of the low passband and high passband are 1.03 dB~2.00 dB and 1.02 dB~1.75 dB, respectively; the return loss of both passbands is better than 15 dB. Furthermore, up to 5 GHz (> 3fo, where fo is at 1.39 GHz), the stopband rejection level is better than 80 dB.

In this work, a novel 4 element Multi-Input Multi-Output (MIMO) antenna is reported. The proposed antenna has a size of 50x50x1.6 mm³ is printed on the FR-4 substrate having dielectric constant ε_r = 4.4 and loss tangent (tan δ = 0.02). The four antenna elements are positioned in each corner of the PCB board in an orthogonal manner such that they can provide better isolation between antenna elements. The proposed MIMO antenna is designed to operate in frequency bands of 2.25 GHz to 2.4 GHz and 4.7 GHz to 6.3 GHz. The lower band ranges from 2.25 GHz to 2.4 GHz and covers 2.3 GHz WiBro applications while the upper band ranging from 4.7 GHz to 6.3 GHz is useful for Hiper LAN and Wi-MAX applications. The proposed antenna acquires return loss less than -10 dB and isolated by more than 16 dB throughout the dual operating bands. The structure exhibits stable gain and radiation patterns. Various diversity performance metrics including envelope correlation coefficient (ECC), diversity gain (DG), and mean effective gain (MEG) are evaluated and are within acceptable limits.

A frequency reconfigurable microstrip patch antenna with two asymmetric L-slots is proposed in this article. Two RF pin diodes inserted on the asymmetric L-slots are used to switch the operating frequency over the C band. Design and optimization of different physical parameters of the antenna viz. slot dimensions, feed location, notch size and pin diode positions are carried out using High Frequency Structure Simulator Version 13.0. The design is implemented on an FR4 substrate (ε_r = 4.4) of dimension (35×40×1.6) mm³. DC bias circuitry for RF PIN diode activation is also integrated with the antenna. Switching combinations of two PIN diodes offer four reconfiguration modes of operation at 4.75, 5.05, 5.11 and 5.18 GHz. In all the states, the -10 dB bandwidth shows minimal changes with average variations of 15.8% with respect to the state when both PIN diodes are OFF. The gains of the antenna for different modes of operation are found almost stable with an average of 6.64 dBi.

Monitoring the prestress of prestressed steel strands is important but difficult. The magnetoelastic inductance (MI) method is used to monitor the prestress. A coupling model was established to describe the correlation among stress, magnetism, and inductance. A prestress monitoring system based on the MI effect was proposed. To verify the feasibility of the method, experiments were carried out. The results showed that influenced by the hydration heat of the grouting materials, the fluctuation range of the inductance was 1.033%. When the hydration came to an end, the inductance approached the initial inductance. For internal steel strands, the obtained inductance-prestress relationship was similar to the relationship of external steel strands. Thus, the prestress of the internal steel strands could be monitored by the MI method.

In this letter, a surface-mount planar inverted-F antenna (PIFA) is proposed for the 5G mmWave system using ball grid array packaging (BGA). To meet the requirement of cost-effectiveness, the proposed antenna element is designed on a single FR4 layer to achieve low cost. To achieve a compact size, the BGA packaging is used on the proposed antenna element. Finally, the size of the antenna prototype is only 4.5 mm × 4.5 mm × 1.3 mm. Besides, the surface-mount feature allows the proposed antenna to be integrated with other devices in the same system package. The simulation and measurement results are discussed in detail. The measurement results show that the impedance bandwidth of - 10 dB is 15.3 % (24.7-29.6 GHz), and the peak gain is 5.85 dBi at 28 GHz. The proposed PIFA can be used in the 5G NR bands N257 (26.5-29.5 GHz), N258 (24.25-27.5 GHz), and N261 (27.5-28.35 GHz).

This paper describes the ramifications in the capacity of Multiple Input Multiple Output (MIMO) wireless links when the antenna systems involved are mischaracterized and contain phase errors. Errors in simulated as well as measured radiation patterns are considered. Also, simple deterministic Line of Sight and stochastic propagation environments are examined. The analyses are carried out on a 2×2 MIMO system. Results show that the resultant error in capacity depends on the degree of the phase error between the antenna ports, the type of propagation environment, as well as the degree of the illumination Signal to Noise Ratio (i-SNR).

Transparent conducting materials with the ability of broadband electromagnetic shielding have a widespread range of applications in aerospace, medical equipment and electronic communications. Achieving enhanced electromagnetic shielding effect without sacrificing much optical transparency is the technical trend in both academia and industries. Here, we experimentally propose a flexible hybrid film constructed by nano-printing based metal meshes and a graphene coating for the transparent electromagnetic shielding application. Numerical analysis is carried out to investigate optimal balance between electromagnetic shielding and optical transparency. In the experiment, enhanced shielding ability of hybrid film is observed without excessively sacrificing optical transmittance, compared to the reference group (the case only with metal mesh). Our work provides a hybrid platform for the high-performance optically transparent shielding materials for electromagnetic environment safety protection.

A low loss propagating electromagnetic wave is shown to exist at a gradual interface between two lossy conductive media. Such a surface wave may be guided by a seafloor-seawater interface and it may be used in radio communication and imaging underwater. It should allow communication distances of the order of 500 m at 10 kHz along a sandy seabed. Similar surface waves may also be guided by various tissue boundaries inside a human body. For example, such surface wave solutions may exist at planar interfaces between skull bones and grey matter inside a human head at 6 GHz.

A direct synthesis approach is presented to realize in-line topology filters with adjacent frequency-variant couplings implementing a transmission response with the same number of finite transmission zeros as poles. The proposed method starts with an N-order fully canonical filter response definition. A non-resonant node (NRN) is incorporated into the transversal network to make room for an extra coupling, and as a consequence of the extended similarity transformation applied, the NRN is transformed into a resonant node. The result is a network with N poles and N transmission zeros implemented with N+1 resonant nodes and N FVC, being able to describe a fully canonical response with an inline network without cross couplings.

In this paper, a compact tri-band flexible MIMO antenna based on liquid crystal polymer (LCP) is designed to operate in WLAN and WiMAX bands. The antenna consists of two identical antenna elements. The isolation structure includes a ground slot, two I-shaped branches, and a parasitic strip. The measured results show that the impedance bandwidth (S₁₁ < -10 dB) covers three frequency bands of 2.38-2.55 GHz, 3.37-3.60 GHz, and 4.92-5.37 GHz, and the S₂₁ of working bands is basically better than -19 dB. Moreover, the flexibility of the MIMO antenna is analyzed at different bent cases. The specific absorption ratio (SAR) values are obtained by simulating the model of antenna approaching human body. The simulated results show that the SAR value of the antenna meets the European Union (EU) standard. The proposed antenna demonstrates the characteristics of satisfactory radiation, high isolation, sound gain in working bands and flexibility, which has good application prospects in the wearable field.

A problem of electromagnetic waves radiation diffracted at a narrow rectilinear arbitrarily oriented slot cut in an end wall of a semi-infinite rectangular waveguide is solved by an asymptotic averaging method. The slot radiates into a half-space over an infinite perfectly conducting plane. An influence of slot inclination angle upon energy and spatial characteristics is numerically studied. Theoretical results are compared with experimental data. A numerical-analytical problem of a narrow rectilinear slot radiating into the space above an infinite impedance plane is also presented. The asymptotic solution for the slot magnetic current was obtained by a generalized method of induced magnetomotive forces (MMF) by using Green's functions of a space above the impedance plane. The effect of the plane with impedance coating on the slot is reduced taking into account an additional term to the slot external conductivity, for which the expressions were obtained in an analytical form.

Over the past few years, the continuous evolution of embedded electronic systems has increased electromagnetic interferences problems. It has also generated a new design constraint on electromagnetic compatibility. Hence, predicting the electromagnetic field behavior in the vicinity of the electronic components and systems becomes a priority to avoid the potential for unwanted coupling occurrence, as well as to ensure the electromagnetic compatibility compliance for those components and systems which are embedded in a confined space. As a result, the designers of electronics' equipment are extremely interested in radiated emission models. This paper reports a comparative study in which two different methods will be applied: the equivalent source method and plane wave spectrum method. These two methods will be used to predict the magnetic field behavior in the vicinity of a microstrip patch antenna. The latter works in ISM band for Wi-Fi and Bluetooth applications. The two applied models are constructed from the tangential magnetic fields cartographies of the antenna obtained from HFSS® at 3.5 mm and validated by comparing the HFSS® results with those of the models at a higher elevation. Furthermore, the relative error between the simulated field of the antenna and those of the equivalent source model according to the dipoles number is presented to determine the minimum number of dipoles that allow users to obtain the results with better accuracy. Subsequently, the relative error as function of different elevations along the z axis together with the two methods comparison results is presented.

In this paper, a modified circular loop FSS with a slot antenna is proposed for sub-6 GHz 5G applications. The proposed FSS reduces the resonant frequency to towards lower bands of conventional circular FSS without change in its size. The operating bandwidth (-10 dB) of proposed antenna loaded with polarization insensitive single-layer FSS varies from 3.6 GHz to 6.1 GHz with an average gain of 7-7.5 dB and a maximum realized gain of 7.87 dB. An FSS superstrate is loaded onto a slot antenna to increase the realized gain of 4 dB, where the FSS shows desirable electromagnetic wave reflection characteristics over operating bandwidth and can be used in 5G sub-6 GHz band applications.

A low-loss dual-band negative group delay circuit (NGDC) with a flexible design is proposed. The proposed NGDC consists of a transmission line coupled asymmetrically with two step-impedance open-loop resonators. The negative group delay (NGD) times and center frequencies of the lower and upper bands can be tuned independently. To verify the design concept, two dual-band NGDC prototypes I and II are fabricated and measured. The measured NGD times of prototype I are -4.9 ns and -4.8 ns at the center frequencies of 1.949 GHz and 2.054 GHz, respectively. The insertion loss is lower than 2.7 dB and the return loss larger than 11.2 dB in both NGD bands. For prototype II, the NGD times at 1.949 GHz and 2.086 GHz are -4.7 ns and -3.3 ns, respectively. The measured insertion loss is better than 2.4 dB with the return loss larger than 11.9 dB.

A fast solution for electromagnetic (EM) scattering problems over a wide incident angle based on compressed sensing (CS) has been proposed in recent years. Since current expansion coefficients are not known in advance, the parameters of this solution (e.g., the times of measurements, the selection of sparse transforms) for different scattering objects are difficult to determine. In order to solve this problem, this paper presents a prior parameter extraction method based on the principle of on-surface discretized boundary equation (OS-DBE), in which an approximate distribution of current expansion coefficients at any given point of the scatterer is first obtained with low-coverage and low-complexity, and then the prior parameters can be determined by CS tests for the approximate result. The implementation method is elaborated, and its effectiveness is verified by numerical results.

Despite the advancements in the field of glucose monitoring sensors, the development of noninvasive, wearable, continuous and comfortable systems is still a real challenge. New technologies are required for noninvasive, continuous and effective measurements remaining discreet, painless, comfortable to the patient and avoiding additional costs.This article presents a truly noninvasive microwavetomography prototype designed for glucose monitoring. The system is based on an array of dipole antennas placed in a circular configuration.The transmitted field data are collected using a switchmatrix connected to a vector network analyzer. A heterogeneous 3-D arm model and a 3-D electromagnetic solver have been used to model the human arm and to characterize the system. Blood electromagnetic properties are affected by the glucose concentration, a promising correlation between the dielectric properties of blood and glucose level should be investigated. By simulating the antenna array on the arm phantom, the characteristics of the S-Parameters were interesting at the frequencies of interest. The transmission coefficient amplitude decreases as the dielectric constant decreases from 63 to 40, and the conductivity increases from 1.5 S/m to 3.5 S/m. For each value of dielectric properties, a given transmission coefficient value can be clearly identified. Experimental measurements validated the arm phantom and confirmed the relationship between the response of the system and the dielectric properties of blood tissue. The armband sensor is designed as an inexpensive, noninvasive, and light weight device suitable for all patients with a high level of discretion. This work, under optimization for preclinical and clinical testing, demonstrates the proof of concept of an innovative microwave tomography system for noninvasive glucose monitoring. Compared to studies with a similar aim, this research may achieve distinct advances and offers promising hope in the field of noninvasive glucose sensors.

A high-gain wide-band planar antenna with H-Shaped Resonators (HSRs) for Self-Powered wireless systems is proposed in this paper. The proposed antenna consists of four major parts, namely, a grating Vivaldi electrical dipole, a half-ring magnetic dipole, HSRs, and a solar panel reflector. The dipoles are etched from both antenna substrate sides by each half on one side. The HSR structures are etched on a single side of the used substrate to avoid the capacitive coupling effects which cause the radiation efficiency reduction. HSR inclusions are designed and tested numerically to have the desired electromagnetic properties at frequency band of interest. After introducing the HSR inclusions to the antenna structure, the antenna performance is tested numerically and compared to that without HSR inclusions. The fabricated prototype based HSR structure shows an enhanced gain bandwidth product to cover the frequencies from 1.75 GHz up to 7.43 GHz with a gain varying from 9.52 dBi up to 16.71 dBi over the entire frequency range. Finally, an excellent agreement has been achieved between the gathered numerical results and those from the experimental measurements.

The paper is focused on reliable modeling and analysis of the effects connected with the resonant transformation of the field of a plane and density-modulated electron beam flying over the periodic rough boundary of a natural or artificial medium. In the paper such a medium occupies a part of the half-space, limited in thickness. Therefore, the numerous effects appeared due to transverse (in the thickness of the periodic structure) resonances, and the coupling of eigen regimes of two different periodic interfaces also contributes to the anomalies appearing due to excitation of the surface eigen waves of the periodic boundary interface that had been discussed in previous papers of this series.

This paper proposes an improved mathematical formulation of Johnston's approach to measure the radiation efficiency of an antenna, based on the Wheeler Cap (WC) technique. The proposed modifications allow the measurement of the radiation efficiency of small antennas matched to complex loads implemented on Radio Frequency IDentification (RFID) tags. The studied structure is a low-cost, silver-printed, differentially-fed RFID dipole antenna. The antenna is printed on a flexible PET (polyethylene terephthalate) paper that is conformable on various objects. Link budget measurements validate the accuracy of the formulation, which can be applied to any dipole antenna matched to an RFID chip with a complex input impedance.