Prestressed steel strands are critical components of prestressed structures, which determine the bearing capacity of the structures. The prestress loss of steel strands causes the bearing capacity to decline. To monitor the stress of prestressed steel strands, a stress monitoring method based on the magnetoelastic effect was proposed. The influence of the material strain was considered to improve monitoring accuracy. To do the monitoring, a coil-based sensor, using a small excitation current to generate a necessary magnetic field, was employed. The sensor converted the stress into inductance. An experimental system was set up and two batches of specimens were tested. The experimental results showed that the measured inductance was stable and repeatable. There was a nonlinear relationship between the inductance and the stress. Strands of different batches need to be calibrated separately to obtain the inductance-stress equation. Based on the calibration equation and the measured inductance, the stress of strands could be calculated. The difference between the calculated stress and the actual stress was small. Besides, to improve the accuracy and ease of the construction, the self-induction coil of the senor should be one layer and with moderate turns.

This paper presents the work of the LAPLACE Electromagnetism Research Group to build an experimental setup able to measure tiny forces that may appear in microwave cavities, in the context of EMDrive investigations. It is based on a commercial balance in the range of 0.1 mN sensitivity, a contactless feeding for more than 150~W RF power, and self calibrating device process. It requires a double cavity system in mirror configuration and is here experimented with frustum cavities, different from the NASA one [1]. The global setup can make force measurement and calibration in less than two seconds. Investigating two different cavities and various electromagnetic modes for the biggest, no force is reported while the 0.1 mN sensitivity is demonstrated.

Previously, an inverse microwave scattering model based on radiative transfer was developed for the retrieval of sea ice thickness using radar backscatter data. The model, called the Radiative Transfer Inverse Scattering Model (RTISM), is a combination of the Radiative Transfer-Dense Medium Phase and Amplitude Correction Theory (RT-DMPACT) forward model and the Levenberg-Marquardt Algorithm (LMA). In this paper, the LMA in the RTISM is replaced with Simulated Annealing (SA) as the optimizer to allow a wider range of inversion capability. SA is a global optimizer, and its settings make it convenient to switch between different target parameters to be optimized for inversion. In this study, the model will first be tested using different data sets to verify its applicability. Next, the model is used to estimate the sea ice thickness around Ross Island, Antarctica using data from ground truth measurements together with satellite data from Radarsat-1 from the year 2006. In order to further validate the model, the data collected from measurements performed during an experiment to grow an ice sheet within a refrigerated facility at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) are used to perform the retrieval of saline ice thickness. Preliminary results show that the new model performs as expected and shows potential. However, there are still limitations to the inverse model, and further improvements in the future need to be considered.

A novel single-layer band-pass frequency selective surface (FSS) is proposed in this letter. The unit cell is composed of a series of rotationally symmetrical fishbone-shaped structures surrounded by a modified octagonal loop. This fishbone-shaped FSS exhibits stable resonant frequency while the incident angle ranges from 0˚ to 60˚ for both TE and TM polarizations, which means that polarization insensitivity and angular stability are well demonstrated on the proposed FSS. A prototype is fabricated and measured in an anechoic chamber, and good agreements are obtained between measured and simulated results.

Electric dipoles are the fundamental components of a planar multi-layered circuit. Present work focuses on the theoretical investigations of radiation field due to a vertical electric dipole in a four-layered region composed of a perfect conductor covered with two dielectrics and the air above. Locating a vertical electric dipole (VED) on or near the air-dielectric boundary, approximate formulas are obtained. The resultant analytical formulas have the merit of offering unique insights about the characteristics of the radiation field including direct waves, reflect waves, lateral waves, and trapped surface waves. The amplitude of the field along the boundary exhibits the dependence of ρ^-1/2, which is an intrinsic characteristic of trapped surface waves, where ρ is the propagation distance. In addition, the radiation field is further examined for propagation distance and propagation characteristics of the interference phenomenon. Furthermore, when the observation angle Θ ≥ 88°, the lateral wave still exists; however, the trapped surface wave is a major component of the total field. The proposed formulas have potential to develop planar four-layered circuit structures.

A new compact ultra-wideband (UWB) bandstop filter with good performance is proposed. The proposed UWB bandstop filter is composed of two pairs of quarter-wavelength resonators, a high impedance main transmission line, a half-wavelength resonator, and an H-shaped multiple-mode ring resonator. The proposed H-shaped multiple-mode ring resonator is introduced to achieve three transmission poles appearing in the lower and upper passbands thus to improve the characteristics of selectivity. The proposed quarter-wavelength resonators and half-wavelength resonator are used to obtain four transmission poles showing up in stopband thus to improve the in-band suppression characteristics. To validate the design concept, a new compact UWB bandstop filter with high selectivity and good suppression is designed and fabricated. UWB stopband, low insertion losses, and good selectivity are achieved as demonstrated in both simulation and experiment.

Lenses can be used to focus and disperse the electric field emitted by the antenna. Sustainable and environmentally friendly lenses were made from lithium molybdenum oxide (LMO) glass composite. Half spherical lenses with a diameter of a 30 mm were fabricated from LMO composite, and the antenna properties were measured with a waveguide feed. The lens enhanced radiation pattern was measured at K_u band, and the improvement in the gain was found to be 2 dB.

There has been a presented modal approach for analyzing the scattering of plane waves that are incident on penetrable gratings with metallic fins lined over both exterior surfaces of each conducting bar to create flanged apertures, which altogether is covered on both sides by multiple dielectric layers. The new degrees of freedom afforded by the special complex geometry offer ways to improve the capabilities of various applications such as beam deflectors, resolution of spectroscopic gratings, grating couplers, and grating pulse compression/decompression, as shall be demonstrated herein for the latter two. All of these entail higher-order diffraction modes, which are advantageously studied by the aforementioned analytical tool. Outcomes of measurements on a fabricated prototype that agree well with expectations from theory are also presented.

A problem of electromagnetic wave diffraction by a longitudinal slot cut in a waveguide wide wall is solved by a generalized method of induced electro-magneto-motive forces (EMMF). The slot radiates in a half-space above a perfectly conducting plane where two vertical impedance monopoles are arbitrarily located. To control electrodynamic characteristics of the radiator, a passive impedance monopole is placed in the waveguide. The paper is aimed at the study of the electrodynamic characteristics of waveguide vibrator-slot structures, analogous to the known Clavin element, with two identical impedance monopoles on both sides of the narrow half-wave slot. The influence of the geometric structure parameters on the directional characteristic of Clavin type element: relative level of sidelobes in the E-plane and the RP width differences in the main polarization plane at 3 dB level was analyzed. It was shown that the directional and energy characteristics of the radiators: radiation and reflection coefficients, antenna directivity, and gain can be varied within wide limits by changing the electrical length and/or distributed surface impedance of the vibrators.

Wideband designs of nearly square microstrip antenna using two half U-slots and rectangular slots are proposed. The slots optimize the spacing in between the patch modified TM11, TM20, TM02, and TM30 resonant modes, to yield wideband response. The design with two half U-slots yields bandwidth of around 1000 MHz (~50%) whereas that with an additional rectangular slot yields bandwidth of 1345 MHz (~61%). Due to the presence of higher order modes, the proposed design offers higher cross polar radiation pattern across the entire bandwidth with the gain greater than 5 dBi. The formulations for the modified patch modes and subsequent redesign procedure are presented, which serve as a guideline in the designing of similar antennas around specific resonance frequency. With the given antenna characteristics, the proposed antennas will find applications in personal and mobile communication systems.

In this paper, we focus on the energy efficiency (EE) optimization for an amplify-and-forward (AF) relay network, where the energy-constrained relay harvests energy from a transmitter using power splitting (PS) scheme. We aim to maximize the EE of the network via jointly optimizing the transmit precoding, relay beamforming, and PS ratio, under the constraints of transmit power and the spectral efficiency. To solve the formulated fractional programming, we approximate the problem via two layer optimization, where the outer problem is handled by the Dinkelbach method, and the inner problem is solved by penalized difference-of-convex (DC) and constrained concave-convex procedure (CCCP). Finally, an iterative method is proposed. Simulation results demonstrate the performance of the proposed design.

This research work adopts an open-circuited-series stub-tuning in sequence with unmatched antenna radiator to bring out a small form factor. Thereby, the effective antenna radiator size has been shrunk up to 0.2λ, where similar efficiency and beam pattern has been maintained. The antenna is conceptualized with symmetrical slots, which indicates a multi-ring structure to contribute multiband miniaturization. This consists a loop based rectangular-ring connected with an E-shaped patch, which is excited through a microstrip stepper impedance transmission line followed by an equally distributed strip-line. It enables enhanced impedance-matching at 2.76 GHz and 6.34 GHz by a stepper impedance transmission line with stub-loading technique. The antenna aperture area miniaturization of 56% has been achieved by introducing slots on the radiator patch. Moreover, this miniaturized patch exhibits improved gain response of 4.43 dBi and 5.37 dBi in the broadside direction. The proposed design occupies a dimension of (0.22λ × 0.26λ) mm².

This paper presents the design and investigation of array antennas formed of two narrow rectangular slots. Two approaches for feeding the two slots by microstrip lines are investigated as well as the influence of changing the distance between the slots on the radiation pattern. The two slots are etched on one side of the substrate, while the feed network is placed on the other side. Two designs, depending on the feeding approach, are presented. In the first design, a simple T-shaped divider is used to feed the two slots, while the second design is based on a single microstrip line which feeds the two slots in series. Two antennas are for the first design, each with dimensions of 57.83 х 41.3 mm², while those of the second design have dimensions of 83.45 x 36.9 mm². The four proposed designs have been simulated and optimized using Computer Simulation Technology (CST-MWS) simulation program. Prototypes were fabricated and tested to verify the designs. The four antennas achieved -10 dB impedance bandwidths between 8.6% and 9.4%, while the gain values were between 4.7 dB and 5.7 dB. The comparisons between the fabricated and simulated antennas considered the reflection coefficient and radiation pattern showing good agreement.

This paper presents an axial flux permanent magnet (AFPM) synchronous generator that was manufactured for the reduction of cogging torque by considering the different angles of a rectangle-shaped permanent magnet (RSPM). The placement angle of RSPM was changed from 0 to 28 degrees to obtain total harmonic distortion, line voltage, and cogging torque. A numerical finite element model using Maxwell software was created. The model was validated by the experimental results, with and without a load. The optimum placement angle was obtained at 20 degrees, whose total harmonic distortion (Thd) and cogging torque (Tc) were improved by 41.6% and 71.4%, respectively.

In this manuscript, a high-performance beam-steerable phased array antenna is introduced for fifth-generation (5G) mobile handsets. The configuration of the design is arranged by employing eight dielectric-insensitive L-ring/slot-loop radiators in a linear form on the top edge of the handset mainboard. The beam-steerable array design exhibits high radiation performances even though it is implemented on a lossy FR-4 material. The proposed design exhibits an impedance bandwidth of 18-20 GHz with the center frequency of 19 GHz. It provides satisfactory characteristics such as wide beam-steering, high gain and efficiency characteristics indicating its promising potential for beam-steerable 5G smartphones. The characteristics of the antenna array are insensitive for different types of dielectrics. Furthermore, the designed antenna array offers quite good radiation behavior in the presence of hand phantom.

The present article shows the design, implementation, and measurement of a compact contactless electronic system for sensing small volumes of liquids. The system is based on two elements: an electronic reader and a passive sensor. The proposed sensor consists of a printed monopole antenna loaded with two Split-Ring Resonators. This results in a fully-passive and single-layer low-cost design. To allow the sensing of small volumes of liquids, a 1-mm-thick adhesive Kapton layer was attached on the top layer of the sensor, and two drop tanks were added to the structure. On the other hand, the reader was designed following a layered approach, which allows us to develop compact and low-cost electronic sensor readers for the Internet of Things. The resulting reader contains a Radio-Frequency interface for the generation of detection of signals, a minicomputer, and the radiating interface. This interface includes a patch antenna that allows us to interrogate the contactless sensor within a 1-cm range. The whole system was manufactured and tested. The total dimensions of the reader are 15 cm × 15 cm, and its weight is below 1 kg. These imply a dramatic form factor and weight reductions with respect to previous readers. Moreover, the manufactured system was used to measure the dielectric permittivity of different liquid drops. Results show that only 4 ml of liquid were needed to determine the dielectric permittivity with a 0.27% error. This volume means a 98.4% reduction compared to submersible sensors which can be found in the literature.

This paper investigates the effect of index finger position and distance on the radiated power of 4-element MIMO antenna, operating at 28 GHz. The antenna elements (AEs) are located at the top corner of the user terminal and separated at a distance of half a wavelength. Four different finger placements were investigated, one placement over each AE with six interaction distances between the AEs and the finger at each position starting from 0 up to 2.5 mm. When the finger is placed on an edge AE, the other edge AE maintained above 85 % of its free space radiated power irrespective of the interaction distance. However, the radiated power of each AE was severely affected when the finger was placed on it or on the AE adjacent to it. This effect ranged from total blockage at direct interaction with the element (with a distance of 0 mm) to maintaining more than around 60 % of free space radiated power after the interaction distance is increased to more than 2.0 mm. Besides the effects of the index finger on the amount of radiated power, this work also investigated the direction of radiated power resulting from the influence of this finger.

A problem of electromagnetic wave radiation by narrow slots cut in an end wall of a semi-infinite waveguide section into space above a perfectly conducting sphere is solved in a strict self-consistent formulation by the generalized method of induced magnetomotive forces (MMF). Inside the waveguide section, a reentrant cavity formed by the volume between a slotted diaphragm and the waveguide end wall is located. The waveguide is operating in the frequency range of a single-mode regime. The electrodynamic characteristics of this radiating system with the spherical screen of resonant dimensions are investigated numerically and ex-perimentally. The possibility to develop the spherical antennas with a narrow-band frequency, energy, and spatial characteristics is substantiated.

A wideband dual-mode band-pass filter (BPF) is proposed and implemented using a vertically stacked double-ring resonator (VSDR) and a pair of broadside-coupled input/output (I/O) feeding lines based on a 4-layer low temperature cofired ceramic (LTCC) substrate. The proposed BPF is required to cover the fifth generation (5G) N77/N78/N79 band (3.3-5 GHz), thus achieves a fractional bandwidth (FBW) of 40%. Furthermore, the proposed structure not only possesses a non-orthogonal I/O feeding style for convenient interconnection with neighboring devices, but also removes disturbing element for simpler layout. Comparison and discussion are implemented as well.

This paper presents Global Navigation Satellite System (GNSS) F-type and Bluetooth (BT) L-shaped antennas printed on flexible low loss substrate materials for smartwatch applications. The proposed printed antennas were designed along with the wristband of a smartwatch device with the main purpose of improving their electrical performance by using a new low loss polymer material and locating the antenna on the wrist strap. The antenna performances were simulated using CST Microwave Studio, and the prototypes were measured in a Satimo StarLab anechoic chamber. Silver printing and injection molding technologies were successfully utilized for fabricating new SEBS materials (styrene-ethylene-butylene-styrene) in wearable devices. The SEBS materials improved the radiation efficiency of the antennas by 1.6 dB for the GNSS and 2.2 dB for the BT over the previously used TPU (thermoplastic polyurethane) materials. The overmolded printed and hybrid integrated discrete antennas produced added-value for electronics fabrication thanks to its flexible and seamless integration technique. In addition, it is a low-cost mass manufacturing method. The research opens new perspectives for product definitions with a flexible, low loss material that enables better antenna performance.