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This paper discusses the design of a cross-slotted waveguide array structure to be adopted for W-band communication between 84 86 GHz. Each array waveguide element contains 16 cross-slots along the broad wall to enable circularly polarized radiation behavior with a gain reaching up to 14 dBi and a cross-polarization isolation of more than 20 dB in the elevation plane. The design of the cross-slots is implemented with bent arms in order to accommodate them at an offset position from the waveguide narrow wall. Such position ensures the radiation of a circularly polarized wave. A waveguide-based feeding network with serpentine shaped transitions is implemented to feed the eight-element cross-slotted array topology. The design of the feeding network ensures an equal power split and in-phase distribution between the eight elements with a phase deviation that does not exceed 20°. The overall cross-slotted waveguide array is prototyped as a proof of concept. The measured results show a maximum gain of 24.5 dBi for both polarization schemes. The measured half power beam width (HPBW) is 8° in the elevation plane and 12° in the azimuthal plane. The measured cross-polarization between the two circularly polarized schemes at both ports reaches a level of more than 26 dB. The comparison between the simulation and measurement results proves the validity of the proposed approach in achieving a high-gain dual circularly polarized structure for millimeter-wave communication.

This letter describes the design of a right-hand circularly polarized planar filtenna (filter + antenna) that can reconfigure its operation between two center frequencies in the Ka-band. The filtenna structure is composed of a four-element array radiator and a reconfigurable bandpass filter, occupying an area of 31 × 14 mm. The circularly polarized array elements are fed by a sequential power divider for an enhanced polarization purity. The filter is based on a ring resonator loaded with a variable open stub. The length of the stub extends through a p-i-n diode switch, resulting in a change of the loaded reactance into the ring, and consequently tuning the filter's operating center frequency from 30.3 to 29 GHz. The proposed low-loss filtenna structure exhibits a reconfigurable fractional bandwidth up to 7.74%, a peak realized gain that can reach up to 11.5 dBic, an axial ratio of less than 1 dB, and a sidelobe level that can go as low as −12 dB. The prototype filtenna is fabricated and tested, where the measured results verify the simulated data. A figure of merit is proposed to highlight the superior performance of the presented Ka-band structure in terms of the polarization, size, reconfiguration ability, and radiation characteristics as proven by the comparison with other works in the literature.

Response to environmental thermomechanical inputs in applications that range from wearable electronics to aerospace structures necessitates agile communication systems driven by reconfigurable electromagnetic structures. Antennas in these systems must dynamically preserve acceptable radiation characteristics while enabling on-demand performance reconfiguration. However, existing reconfiguration mechanisms through stretchable conductors rely on high-strain behavior in soft substrates, which limits their applicability. Herein, this work demonstrates the use of mechanical metamaterials for stretchable conductors and dielectrics in antennas. Metamaterials allow conductor stretching up to 30% with substrate base material tensile moduli ranging from 26 MPa to 44 GPa. It is shown, through several antenna designs, that mechanical metamaterials enable similar frequency reduction upon stretching as monolithic conductors, while simultaneously providing a miniaturization effect. The conductor patterning, furthermore, provides control over coupling between mechanical stretching and electromagnetic reconfiguration. This approach enables designing reconfigurable antenna functionality through metamaterial geometry in response to arising needs in applications ranging from body-adapted electronics to space vehicles., Advanced Science, 10 (6), ISSN:2198-3844

This communication proposes the reconfiguration of a coplanar-fed single arm bowtie antenna structure by relying on the integration of a digital tunable capacitor (DTC). The coplanar-fed single arm bowtie antenna is presented in two configurations. The first configuration is a 2-D topology with a modified ground plane arrangement. The second configuration employs vertical folding for the ground plane as well as the radiating arm. In addition, vertical copper inserts are embedded within the bowtie single arm to further enhance the compactness of the structure and transform it into a 3-D topology. Both antennas are initially designed to operate at 868 MHz for Internet of Things (IoT) applications, with a digitally reconfigurable frequency operation for wireless communication. The 2-D antenna structure exhibits a 77% size reduction at the IoT operational frequency of 868 MHz in comparison with a similar rectangular patch antenna operating at the same frequency. On the other hand, the 3-D antenna structure reaches 84% of size reduction at the same frequency. A figure of merit (FOM) is derived to prove the superior performance of the presented antenna structure.

We report the construction of Polaris, a new linear plasma device with an axial magnetic field dedicated to research and education at the American University of Beirut in Lebanon. The goal is to initiate the investigation of topics related to basic magnetized plasma physics and nuclear fusion. We discuss the novel technical solutions found to set up various components of the device. We start with the magnetic coils where we use power cables to generate the required axial magnetic field. They are included in a stainless steel case for water-cooling. Then, we present the vacuum and the gas inlet systems with which we control the neutral pressure. The way we manufacture the water-cooled radio frequency (RF) antenna allows the production of a variety of designs. Polaris is thus built to operate in a steady state. Using a reciprocating Langmuir probe, we determine the plasma properties as a function of the various control parameters. As the plasma remains in the “blue mode,” we show that the increase in the main magnetic field leads to an increase in the density but a decrease in the plasma temperature. The increase in neutral pressure yields the same effects. However, the increase in RF power leads to an increase in both density and temperature. Finally, plans for future investigations are briefly described.

In this letter, waking-up wireless sensors is achieved by solely relying on existing ambient radio frequency signals from commercial Wi-Fi routers. The wake-up is accomplished based on the captured Wi-Fi signal that is received by an antenna and then fed into a rectifier circuit. A novel packet injection algorithm is developed to enable the rectifier to efficiently convert the captured Wi-Fi signal into a dc power. This algorithm can be implemented on any commercial router with no modifications to the router's hardware or protocol stack and without compromising the performance of the Wi-Fi network. The design is experimentally validated under controlled conditions.

In this study, a reconfigurable, two-element, multiple-input multiple-output (MIMO) printed inverted-F antenna (PIFA) is presented with an enhanced isolation ability. The MIMO antenna system is designed using three different reconfiguration techniques that are based on positive-intrinsic-negative diodes, radio frequency micro-electromechanical switches and varactors. Their impact on the performance of the PIFA and the MIMO system is evaluated in terms of radiation characteristics, gain, power dissipated, radiation efficiency, linearity, biasing requirements and MIMO performance. Isolation between the two MIMO antenna elements is enhanced by integrating a reconfigurable band-reject filter within the ground plane between the radiating elements. The band-reject filter is reconfigured simultaneously with the radiating elements, hence resulting in less coupling and better isolation. The MIMO system along its various components is fabricated for the three different reconfiguration techniques and the comparison with predicted data shows great agreement.

This article presents a new compact lightweight radio frequency (RF) energy harvesting system. The system relies on a dual-tapered transmission line-based matching network that stretches the rectification capability of an integrated Schottky diode. This topology is demonstrated on a 2.4 GHz rigid harvesting system with a resulting power conversion efficiency that reaches up to 58% over 0 dBm input RF power. Its performance is compared with a reference rectifier that relies on a typical open circuit shunt-stub matching network. The rectifier along with a miniaturized monopole antenna is then tailored for a flexible substrate with a resulting efficiency around 50% at 0 dBm input power. The rectifier exhibits an almost flat efficiency over the 2.3–2.5 GHz frequency span despite wide load variations. The system is characterized in multiple bent configurations featuring high and stable performance. It is demonstrated that for different bent states, the proposed flexible harvester does not display large variations in harvested power. Thus, the presented rectenna demonstrates the remarkable combination of compactness, flexibility, and stability. Equipped with these features, such rectifier can be plugged into a variety of sensors, even on wearable surfaces, which makes it ideal for Internet of Things (IoT) applications.

This letter investigates the incorporation of support vector machines (SVMs) to predict the time and location of maximum Wi-Fi coverage for energy harvesting. Such incorporation of machine learning, along with radio frequency energy harvesting systems, improves the proposed rectenna efficiency especially when scavenging wireless routers and access points. Experiments showed that the proposed framework that uses SVM was able to predict the time and location of maximum Wi-Fi coverage. Such prediction constitutes the basis of a scheduling mechanism for directed harvesting of Wi-Fi signals.

Power splitting of the input radio frequency (RF) signal is used to improve the efficient power range of a RF rectifier. Direct current (dc) power at the output of every rectifying branch is then combined over a resistive load and thus resulting in a single dc output. The enhancement in efficient power range, over which the power conversion efficiency (PCE) remains ≥ 50%, is determined to be 2.8 dB. The article starts by a theoretical analysis that addresses the negative effects of the diode's breakdown voltage, formulates an equation that predicts the maximum output dc voltage at saturation, and introduces a method that can improve the PCE of a typical shunt-type diode rectifier at low power levels. As a result, a rectifying system is designed and tested as a proof of concept. The proposed circuit, with the enhanced power range, is designed to operate within the power span from -10 dBm up until 10 dBm. Such system is suitable for operation in RF wireless energy transfer and energy harvesting applications.

In this paper, a digitally tuned flexible antenna is proposed for integration onto devices within the Internet of Things (IoT) paradigm. The antenna design caters for the various IoT communication standards by reconfiguring its operating frequency. Accordingly, the antenna reconfiguration allows operation at 868 MHz, 915 MHz, 1.8 GHz and 2.1 GHz. The reconfiguration is achieved digitally by resorting to a digitally tunable capacitor (DTC). The DTC changes its capacitance, and hence its frequency operation, by relying on 5-bit sequence commands through a microcontroller. The proposed antenna is coplanar waveguide fed with its ground plane surrounding the radiating structure. The gain of the antenna varies between 4 dB and 6 dB for different frequencies of operation. Its radiation efficiency varies between 78% and 92%. The antenna is fabricated and tested on a flexible substrate, where the resulting reconfigurable prototype maintains its performance characteristics for different bent states.

In this paper, the effect of sequential rotation on the beam steering capabilities of a circularly polarized phased antenna array is analyzed. Two different topologies for a phased antenna array operating at Ka-band between 28 GHz and 40 GHz are studied where each structure is tailored to produce a maximum gain of almost 19 dB with an axial ratio below 0.5 dB. The individual elements of both topologies are dual fed with a differential phase shift of 90° respectively. This paper proves that the steering capability of a phased antenna array is doubled when sequential rotation is omitted from its feeding network.

A wearable, continuous electromagnetic sensing system provides 96% glucose estimation accuracy when tested on healthy individuals., Painless, needle-free, and continuous glucose monitoring sensors are needed to enhance the life quality of diabetic patients. To that extent, we propose a first-of-its-kind, highly sensitive, noninvasive continuous glycemic monitoring wearable multisensor system. The proposed sensors are validated on serum, animal tissues, and animal models of diabetes and in a clinical setting. The noninvasive measurement results during human trials reported high correlation (>0.9) between the system’s physical parameters and blood glucose levels, without any time lag. The accurate real-time responses of the sensors are attributed to their unique vasculature anatomy–inspired tunable electromagnetic topologies. These wearable apparels wirelessly sense hypo- to hyperglycemic variations with high fidelity. These components are designed to simultaneously target multiple body locations, which opens the door for the development of a closed-loop artificial pancreas.

In this paper, we propose an extension for the Nicolson-Ross-Weir (NRW) method that enables the retrieval of the electrical parameters of low-loss materials that are thicker than one-half wavelength $(\lambda g/2)$. The proposed extension overcomes the NRW intrinsic limitation that causes a divergence of results at frequencies where the material thickness is an integer multiple of $\lambda g/2$. The method is tested on different sample materials, and is proven to provide a stable permittivity estimation, with no divergence at frequencies corresponding to integer multiple of $\lambda g/2$.

This paper presents novel dual tapered helical antenna structures that are 3D printed and nested within each other for size reduction. Each tapered helical antenna element is designed to operate at a distinct span of frequencies. The two helical antennas are nested together and wrapped in opposite direction to each other in order to satisfy orthogonal polarization. The two helical elements are fabricated using a laser based 3-D printing process where good measured radiation behavior is obtained.

This article proposes a new rectenna system that is based on a radio frequency (RF) rectifying circuit with enhanced power handling capabilities. The rectenna consists of an antenna that receives the RF signal and a rectifying circuit that converts it into a direct current (dc) output. The rectifier's power handling capability is improved by delaying the breakdown effect of a Schottky diode, resulting in higher maximum dc output power. The power handling capability enhancement is attained by splitting the received RF signal and directing it to feed multiple rectifying branches. The dc outputs from all branches are then combined across an optimized load. This topology results in a single-input single-output rectifier. The designed rectenna is fabricated and tested. The results indicate a 1.9 times increase in input power at which breakdown occurs. The rectenna system is proposed for use in wireless energy transfer applications, where dedicated power is transmitted towards the rectifier. This rectifier can be integrated into nodes of a wireless sensor network, where the enhanced power handling capabilities contribute to enhance the breakdown characteristics.

This letter discusses an antenna system that steers its radiation pattern to personalize coverage in a wireless local area network scenario. The change in the pattern occurs either by mechanically rotating or electrically switching the feeding network toward the appropriate antenna structure. The user controls the personalized coverage using an Android-based voice recognition application on a mobile device. Each antenna structure operates at 5.28 GHz with 110 MHz bandwidth and an increased gain around 7.5 dB. The antenna's radiation insures a redistributed sector coverage of two diametrically opposite geographical zones that are 180° apart from each other. A multiple-input–multiple-output (MIMO) implementation is also proposed with a discussion on the various possible coverage zones. The various antenna concepts are measured, and the results validate the predicted data.

This article discusses the design and dual functionality of two antenna arrays that operate from 1.8 to 2.4 GHz. Each antenna array is composed of two elements and proposed for either communication or radio-frequency (RF) energy harvesting. The antenna arrays are integrated vertically on top of a solar panel. Copper-based and transparent inverted-F antennas constitute the elements of both arrays. The transparent array has the same dimensions and topology as the copperbased one. Its purpose is to verify that the integration of the copper-based inverted-F antenna arrays on top of the solar panel does not majorly impact the solar panel's efficiency. A rectifying circuit that is positioned at the output of both arrays is also designed and tested. The rectifying circuit converts the collected RF energy into dc power that can supplement the solar panel's supply during the absence of solar energy. The measured performance results of the fabricated system, which is composed of the two array antennas in addition to the rectifying circuit, show good agreement with the simulated data.