We present experiments of contact electrocardiograms (ECG) recording using copper and e-textile-based flexible dry electrodes. In this work, dry electrodes with different shapes, sizes, and materials were designed and fabricated. In cardiac monitoring using these flexible dry electrodes, three different conditions were considered, which are sitting, standing, and walking. To evaluate the performances of the fabricated dry electrodes, average-to-variation ratios (AVR) of the recorded ECG signals measured using the flexible dry electrodes were calculated and compared with those measured using the commercially-available wet electrodes in all three conditions. The AVR results demonstrate that the dry electrodes have a similar performance as the commercially-available wet electrodes in the sitting and standing conditions and a better performance in the walking condition. These results suggest that it is possible to weave dry e-textile-based electrodes in normal clothing and use them for continuous monitoring of ECG signals in different conditions.

A compact CPW-fed ultra-wideband monopole antennas with band notch characteristics using Split Ring Slots (SRSs) are proposed in this manuscript. Initially, the antenna is designed by using a rectangular shaped patch, and it has been modified to obtain enhanced impedance bandwidth (VSWR ≤ 2) throughout the entire UWB frequency range. Further, the notch band element (split ring slot) has been introduced in the geometry of proposed antenna to generate the band rejection at WLAN frequency centered at 5.3 GHz (5.15-5.81 GHz). Another antenna has been designed by varying the dimensions of SRS to get the rejection of frequency at an X-band satellite communication system centered at 7.4 GHz (7.16-7.71 GHz). The overall size of proposed UWB antennas is compact (18 × 18 mm²), and it is designed on a low cost FR4 glass epoxy substrate with 1.6 mm thickness and 4.4 dielectric constant. The proposed antennas with and without a notch filter are designed by using HFSS V13 simulator and fabricated for the validation of simulated results. Experimental and simulated results are compared and found in reasonable agreement with each other.

In order to solve the problem of the poor performance of the traditional microwave resonance method in multi-parameter fitting data processing, a permittivity measurement method based on Back Propagation (BP) Neural Network algorithm is proposed, which introduces the Neural Network algorithm in data processing of microwave resonance method for the first time. In order to verify the effectiveness of this method in measuring permittivity, a microstrip line structure is used as a microwave resonator. It achieves high sensitivity (4.62%) by loading periodically arranged open resonant rings. On this structure, the reflection coefficients S₁₁ of different material samples are simulated as the data of neural network. The amplitude and phase of S₁₁ and resonant frequency f are taken as the input layer of the neural network, respectively. The dielectric constant and dielectric loss are taken as the output to establish the neural network model. The simulated and measured results show that the dielectric constant and dielectric loss calculated by the model are basically consistent with the data provided by the manufacturer. The relative error of the dielectric constant is less than 0.6%, and the error of the dielectric loss is less than 0.0005. Compared with the traditional data processing of microwave resonance method, the introduction of BP neural network algorithm can significantly improve the accuracy of dielectric constant measurement.

In near-field energy transmission, it has been proved that magnetic coupling wireless power transfer (MC-WPT) is a promising energy transmission method. Traditionally, the MC-WPT system is established based on a linear resonant circuit. Recently, it has been reported that nonlinear MC-WPT system shows more advantages. However, nonlinear characteristics of the nonlinear MC-WPT system are not fully recovered. In this paper, a nonlinear MC-WPT system which can be described by Duffing equation is presented. The mathematical model of the equivalent circuit is developed. The related nonlinear characteristics under the impact of driving force are investigated. It is found that the driving force has a direct impact on the system performance. The operation of the nonlinear MC-WPT system varies from periodic sinusoidal state to periodic non-sinusoidal state even to chaotic state when the driving force increases. It should be mentioned that the chaotic state should be avoided. Generally, the MC-WPT system should be operated in periodic sinusoidal state which only covers a small range of driving force. For the system operated in periodic non-sinusoidal state, a waveform correcting circuit is designed. The simulated and experimental results show that the restriction of the driving force on the operation of the system is eliminated with a waveform correcting circuit added. It is possible for the nonlinear MC-WPT system to be operated in a much wider range.

A compact triple-band antenna of size 20×13×1.6 mm³ for WLAN (2.4/5 GHz) and WiMAX (3.5 GHz) applications and a metamaterial slab for Specific Absorption Rate (SAR) reduction are proposed in this paper. The antenna comprises a rectangular patch with two conjoint square split rings, attached along its top edge, to excite two resonances in the 2.5 GHz and 5.5 GHz range. The antenna is also backed with a slotted ground plane structure to achieve miniaturization. The radiator is subsequently slotted to yield the third tone around 3.5 GHz. Several parameters are tuned independently to achieve the desired bands of resonance around (2.2-2.6) GHz, (3.40-3.60) GHz, and (5.0-6.9) GHz with impedance bandwidths of 17%, 5.5%, and 46%, respectively. To validate the simulated results, the designed antenna is fabricated and measured experimentally. Later, a metamaterial slab composed of a 5×3 array of pentagonal split-rings printed on a 20×13×1.6 mm³ FR-4 substrate is placed above the antenna at a suitable distance to increase the gain as well as to reduce the SAR. Inclusion of this slab improved the maximum radiation efficiency and gain of the proposed antenna from 65% and 2.7 dB to 80% and 3 dB. A cubical tissue model is designed and used for simulation. SAR reduction of 84.5% is inferred with the metamaterial slab. This paper has taken a cubical tissue model for SAR calculation, which can be further enhanced by taking a human phantom model in future.

An ultra-wideband (UWB) flexible antenna with a dual band-notched property is designed in this letter. This antenna is fed by a coplanar waveguide (CPW) tapered transmission line to achieve an impedance bandwidth of 1.95-35 GHz for VSWR<3. A double C-shaped slot within the monopole radiation patch and two L-shaped slots etched on the ground are introduced to reject the bands of 3.5 GHz (3.1-3.9 GHz) and 5.5 GHz (4.7-5.74 GHz) respectively, which are assigned to WiMax and WLAN applications. A Rogers4350 substrate is used to realize a low profile (0.29λ_L×0.22λ_L×0.00065λ_L, where λ_L is the free-space wavelength of the lowest operating frequency). The measured results show that the antenna has a UWB omnidirectional radiation characteristic that is suitable for UWB wireless communications.

In this paper, we propose a laser monitor with a horizontally located observation area for studying laser initiation and combustion of thin layers of metal nanopowders. Three configurations of the optical scheme with different inputs of igniting laser radiation and different magnifications are considered. Visualization of combustion of a 0.4 mm layer of aluminum nanopowder demonstrated the possibility of studying the surface of a nanopowder thin layer during combustion using a laser monitor. The bright glowing of the sample and the bright radiation of the igniting laser do not interfere with the imaging of the surface. The proposed system allows us to study surface changes caused by the propagation of combustion waves. It is demonstrated that in the region of laser initiation, combustion proceeds in one-stage, and combustion products are formed during laser action. Outside the initiation area, combustion proceeds in two stages. The results reveal the prospects for designing a laser monitor for studying the combustion of thinner layers of metal nanopowders.

This paper proposes a novel wideband filter based on a quintuple-mode substrate integrated waveguide (SIW) resonator. Two metallic vias loading a rectangular SIW cavity diagonal line are used to excite five resonant modes. A pair of the complementary split ring resonators (CSRRs) etched on the top plane to further control the degenerating modes. A quintuple-mode filter is implemented based on this resonator. One transmission zero (TZ) at the lower frequency side and three TZs at the upper frequency side were obtained to improve the filter selectivity. A seven-order filter with wide stopband rejection is investigated under the use of a pair of microstrip low-pass filters (LPFs). The proposed SIW cavity filter has been designed, manufactured, and measured as an experimental example to verify the proposed concept. Simulation and measurement results agree with 49.8% of fractional bandwidth at 5.3 GHz central frequency.

A compact six elements MIMO antenna is presented for UWB applications. The proposed MIMO array consists of non-identical monopole antennas with distinctive ground planes so as to nullify mutual coupling amid side-by-side elements. Also, by properly placing the antenna elements exploiting cross polarization diversity, a good isolation throughout the operating bandwidth is achieved. Moreover, two parasitic inverted L stubs in combination with small rectangular stubs are employed near the middle-placed radiators and corner placed radiators, respectively, in order to extend the frequency band and enhance the impedance matching. Results show a good reflection coefficient about -10 dB, a high isolation >20 dB, an envelope correlation coefficients <0.15, a high diversity gain equal to 9.3, and finally, a maximum value of efficiency for both used antenna elements which is about 78% and 60% with 6 and 5 dBi of gain, respectively. They validate the proposed MIMO antenna efficiency for UWB diversity applications.

This paper introduces a low profile wideband Planar Inverted-F antenna (PIFA) for vehicular applications in the 5G systems (below 6 GHz) and Vehicle-to-Everything (V2X) communications. The antenna covers a wide range of bandwidth which operates from 617 MHz to 6 GHz while having an acceptable filtering on the GNSS bands. This design's physical dimensions and electrical performance make it suitable for low profile wireless applications in the automotive field. Measurement data on Ground plane (GND) and on vehicle are presented from a properly cut metal sheet prototype along with simulated results of the model design. Simulation and measurement results are discussed in terms of VSWR, surface current distribution, radiation patterns, antenna efficiency, and linear average gain (LAG).

Electrical impedance tomography (EIT) is a technique for reconstructing the conductivity distribution by injecting currents at the boundary of a subject and measuring the resulting changes in voltage. Many algorithms have been proposed for two-dimensional EIT reconstruction. However, since the human thorax has the characteristic of three-dimensions, EIT is a truly three-dimensional imaging problem. In this paper, we propose a three-dimensional imaging method using tensors for EIT. A tensor EIT model is established by EIT data and the Tucker decomposition is used to obtain the tensor basis. The tensor basis can form a new way to reconstruct image in three-dimensional space. Experiment results revealed that the data structural information of image can be fully used by the tensor method. A comparison of the peak signal to noise ratio (PSNR) shows that the newly proposed method performs better than other methods, i.e. the Dynamic Group Sparse TV algorithm and Tikhonov algorithm. The newly proposed method is closer to the ground truth, thus it can more accurately reflect the state of a lung than two-dimensional EIT. Finally, the EIT experiment is carried out to evaluate the proposed method. The experimental results show that the accuracy of reconstruction based on the new method is efficiently improved.

This letter shows 50 percent memory saving for a regular Hierarchal Matrix (H-matrix) by converting it to symmetric H-matrix for large electrodynamic problems. Only the upper diagonal near-field and compressed far-field matrix blocks of the H-matrix are stored. Far-field memory saving is achieved by computing and keeping the upper diagonal far-field blocks leading to compressed column block U and row block V at a level. Due to symmetry, the lower diagonal far-field H-matrix compressed column is the transpose of V, and the compressed row block is the transpose of U. Storage and computation of lower diagonal blocks are not required. Similarly, in the case of near-field, only the upper diagonal near-field blocks are computed and stored. Numerical results show that the proposed memory reduction procedure retains the accuracy and cost of regular H-matrix.

This work presents an overview of rainfall fading models over satellite links in South Africa using three years of rainfall data collected by the Joss-Waldvogel RD-80 disdrometer in Durban, South Africa (29˚52'S, 30˚58'E), alongside a colocated Ku-band satellite TV link. Different drop size distribution models, such as Lognormal, Gamma, Weibull, and the Optimised drop size distribution model for Equatorial Africa, are used to formulate the rainfall attenuation models used in this study. Thereafter, the formulated attenuation models are used to convert rainfall rate time series data to predicted rainfall attenuation time series. In addition, both the ITU-R model and the Synthetic Storm Techniques are applied for comparison with the above rainfall attenuation models alongside experimental measurements over the 12.6 GHz satellite TV link from Intelsat-20 (IS-20) located at 68.5˚E on the azimuth angle of 57.5˚ with respect to Durban.

In this article, a compact super wideband (SWB) monopole antenna with a wide-frequency is designed and analyzed for future handheld gadgets. The designed antenna is made by etching four slots on a round cornered rectangular patch which are connected through a 50-Ω triangular tapered microstrip transmission feedline (TTMTF) for broadband impedance matching. A triangular slot is etched on the semicircular partial ground plane, which helps to shift the lower frequency edge of 1.07 GHz to 1 GHz. The experimental results show that the proposed antenna operates over a wide frequency range of 1-30 GHz with a reflection coefficient of less than -10 dB. The antenna acquires a compact dimension of 25 x 16 x 0.787 mm³. Further, an equivalent circuit method is used to analyze the proposed structure, and its outcome is compared with the simulated and experimental results. The peak gain of the designed antenna is about 5.5 dBi. The proposed antenna has low cross-polarization even at higher frequencies. Finally, the time domain analysis is also carried out to see the distortion between transmitting and receiving modes. The designed antenna can be used for various wireless applications such as NB-IoT, GPS, Wi-BRO, ISM band, IRNSS, WiMAX, X-band, Ku-band, and K-band.

In this paper, the space-and-time structure of the output signal of the antenna array (AA) of a chirp pulse radar is investigated in dependence on the frequency sweep range of the probe signal. Expressions are derived for calculating the output signals of the AA of a chirp pulse radar after optimal filtering in the case of beamforming using phase shifters and/or time-delay lines. Distortions of the space-time power pattern pertaining to the phase scanning method are analyzed in dependence on the frequency chirp range and scan angle. It is shown that these distortions are similar to the effects observed in the case of using taper windows for sidelobe suppression in the time and space (angular) domains. Based on the results obtained an applicability condition is suggested for the phase scanning in AAs of chirp pulse radars. It is shown that minor violations of this condition result in decreasing the amplitude and broadening of the main lobe and sidelobes in the AA space-time power pattern. In the case of strong violations of the applicability condition for the phase scanning the sidelobes of the angular directional pattern degrade, merging with the main one into a single quite broad maximum. The considered effects lead to deterioration of the range and azimuth resolution capabilities of radars and should be taken into account when selecting the taper window parameters.

A design of a compact wideband harmonic suppressed rat-race coupler (RRC) is presented in this paper. The present coupler is obtained by replacing each quarter wave length transmission line of a conventional double section rat-race coupler with a triple stub M-shape unit. The M-shape unit with 3 stubs is used to enhance the bandwidth, suppress the harmonics, and reduce the size of the coupler. Design guidelines are established using the lossless transmission line model. Theoretical predictions are verified by fabricating a prototype coupler. The proposed double section RRC provides harmonic suppression up to seventh of operating frequency and 62.4% size reduction with wide bandwidth, which is useful for wireless communication systems.

The paper is focused on reliable modeling of the effects associated with the resonant transformation of the field of a plane, density modulated electron beam, flying over the periodically uneven boundary of a natural or artificial medium, in the field of volume outgoing waves. Here, the general information (analytical basis) is presented on the peculiarities and principal characteristics of electromagnetic fields arising in the situations under consideration, on the procedures for regularization of model boundary value problems describing these situations, and on possible eigenmodes of periodic structures. Without relying on this information, it is impossible to advance considerably effectively in solving numerous urgent physical problems(establishing the conditions providing anomalously high levels of Vavilov-Cherenkov and/or Smith-Purcell radiation; diagnostics of beams of charged particles, artificial materials and media) and in practical implementation of new knowledge aboutthe effects of diffraction radiation and their wave analogues in new devices and instruments of optoelectronics, high-power electronics, antenna, and accelerator technology.

This article discusses the design analysis of a wideband rectenna (Antenna + Rectifier). It empowers low power devices, battery-less power sensors, and many Internet of Things (IoT) devices. The main focus of this work is divided into two parts. First, to develop the power to operate the wideband frequency of operation without system complexity. To obtain rectifier bandwidth sufficiently, L-section impedance matching with dual Schottky diode HSMS270B is proposed. Second, to improve the rectenna efficiency and output DC power. Wideband rectenna harvests the maximum RF power of 30.590 dBm, 1145.51 mW, 10.703 Volts at 3.2 GHz. The harvested power is easily available to power up the low powered sensor such as gas sensor (500-800 mW), pressure sensor (10-15 mW), and temperature sensor (0.5-5 mW). The peak conversion efficiency of the rectenna is 88.58% at 0 dBm, 34.70% at 10 dBm, and 53.52% at 20 dBm under the load resistance of 100 KΩ. The proposed work shows a 20-25% improvement in conversion efficiency with this approach. For efficient RF energy harvesting applications, the proposed rectenna is capable of covering a wideband application from 1.975 to 4.744 GHz with a single radiation patch. This shows that the novel approach of the considered work and the proposed rectenna has the specialty to capture more energy from a wide area at once.

A band-pass filter using spoof surface plasmon polaritons (SSPPs) and half-mode substrate integrated waveguide (HMSIW) for Ka-band RADAR application is proposed. In order to achieve the band-pass response, an HMSIW structure with high pass response and SSPPs with band-stop response are combined. Moreover, to investigate effects of geometric dimensions on the frequency characteristics of the proposed band-pass filter are examined by parametric analysis. It has been observed that lower cut-off and upper frequencies can be individually controlled just by changing the structural parameters. High Frequency Structure Simulator (HFSS) software was utilized to simulate the proposed structure. HFSS is the simulation tool for complex 3-D geometries and uses the finite element method (FEM). To validate the functionality, the proposed band-pass filter is fabricated on the dielectric material RT duroid 5880 with the dielectric constant ε_r = 2.2, height h = 0.508 mm, and dissipation factor tanδ = 4 × 10^-4. The measured result shows return loss better than -10 dB and insertion loss less than 1.25 dB with the 3 dB fractional bandwidth (FBW) of 44.02% at the center frequency of 7.95 GHz.

An extremely close integration of a dual band sub-6 GHz 4G antenna with a 28 GHz 5G antenna is proposed in this article. Firstly, a dual band 4G LTE (Long term Evolution) antenna is designed on an inexpensive substrate. The proposed antenna operates in the 2.5 GHz and 3.5 GHz LTE bands. The antenna has dimensions of 63 x 5.6 x 0.5 mm³, indicating an electrically small design. As the width of the antenna is less than 7 mm, it could be easily mounted on commercial mobile devices. The patterns for both the bands are almost omnidirectional as desired by the low frequency antennas. The proposed antennas do not carry any additional miniaturization or tuning circuitry hence simplifying fabrication process. Secondly, an angled dipole with Yagi topology is proposed, which works in the 28 GHz mmWave 5G band. The angled dipole has dimensions 28.3 x 5.6 x 0.5 mm³, which is also electrically compact and has a high front to back ratio. The microwave and millimetre wave antennas are placed orthogonally for minimal mutual coupling. The characteristics of both the antennas are not affected by the presence of the other element. Detailed results are shown in this article.