Search

A new metamaterial based, circular polarized electromagnetic energy harvester is presented in this work. The structure, which is multilayer and utilises the well-known to the literature geometry of the spiral split ring resonator, operates at the Wi-Fi frequency band. Based on full electromagnetic analysis, the proposed harvester presents high efficiency (i.e., greater than 90%), adequate angle insensitivity (i.e., 44 deg.) and it is capable of absorbing circular polarised plane waves., This work will be presented in iWATT 2022, Dublin

An intelligent reflecting surface (IRS) at terahertz (THz) bands is expected to have a massive number of reflecting elements to compensate for the severe propagation losses. However, as the IRS size grows, the conventional far-field assumption starts becoming invalid and the spherical wavefront of the radiated waves should be taken into account. In this work, we consider a spherical wave channel model and pursue a comprehensive study of IRS-aided multiple-input multiple-output (MIMO) in terms of power gain and energy efficiency (EE). Specifically, we first analyze the power gain under beamfocusing and beamforming, and show that the latter is suboptimal even for multiple meters away from the IRS. To this end, we derive an approximate, yet accurate, closed-form expression for the loss in the power gain under beamforming. Building on the derived model, we next show that an IRS can significantly improve the EE of MIMO when it operates in the radiating near-field and performs beamfocusing. Numerical results corroborate our analysis and provide novel insights into the design and performance of IRS-assisted THz communication., To appear in 2021 IEEE International Conference on Communications Workshop

This paper summarizes an investigation around millimeter-wave (mmWave) multimode circular antenna array based beamformer capable of specially encoded data transmission in a wide coverage area. The circular antenna array is capable of an entire 360 deg. azimuth sector coverage where broadcast, uni-cast and multi-cast radio transmissions are possible. Orbital angular momentum (OAM) mode transmission along the elevation axis, i.e., perpendicular to the azimuth plane, can also be achieved. These two types of spatially encoded beamforming makes coverage in almost an entire hemisphere possible. The circular array is developed using twelve multilayer patch antennas with unique radiation performance aiding in both azimuth and elevation radiation. The proposed array architecture and its radiation performance makes it a good candidate for spatially encoded beamforming for mmWave 5G., 6 pages, 5 figures, this work will be presented in Eucap 2021

Nowadays, the monitoring of plant water stress is of high importance in smart agriculture. Instead of the traditional ground soil-moisture measurement, the leaf sensing is a new technology, which is used for the detection of plants needing water. In this paper, a novel, low-cost, and low-power system for leaf sensing using a new plant backscatter sensor node/tag is presented. The latter, can result in the prevention of water waste (water-use efficiency), when is connected to an irrigation system. Specifically, the sensor measures the temperature differential between the leaf and the air, which is directly related to the plant water stress. Next, the tag collects the information from the leaf sensor through an analog-to-digital converter, and then, communicates remotely with a low-cost software-defined radio reader using monostatic backscatter architecture. The tag consists of the sensor board, a microcontroller, an external timer, and an RF front-end for communication. The timer produces a subcarrier frequency for simultaneous access of multiple tags. The proposed work could be scaled and be a part of a large backscatter wireless sensor network. The communication protocol exploits the low-complexity Morse code modulation on a 868 MHz carrier signal. The presented novel proof-of-consent prototype is batteryless and was powered by a flexible solar panel consuming power around $20~\mu \text{W}$ . The performance was validated in an indoors environment where wireless communication was successfully achieved up to 2 m distance.

Nowadays, the explosive growth of Internet-of-Things-related applications has required the design of low-cost and ultra-low-power wireless sensors; backscatter communication has been introduced as a cutting-edge technology that could address the above constraints. For sensing applications, the monitoring of plant water stress is of high importance in smart agriculture. Instead of the traditional ground soil moisture measurements, leaf sensing is an old technology, which is used for the detection of plant water stress. Considering the above topics, this paper aims to provide a contemporary and literature review on fundamentals, applications and research efforts/progress on backscatter systems for leaf sensing applications. It is described how backscatter technology could be exploited for "one sensor per plant" applications in future precision agriculture.

A novel, polarization insensitive, wide-angle and broadband electromagnetic metamaterial absorber, which can cover either a flat or a bent geometry, is presented in this work. The periodic geometry has a unit-cell, which consists of four split ring resonators, which are sequentially rotated around the unit-cell axis progressively by 90 deg. First, the metallic parts of the geometry consists of low resistivity copper traces. Next, in order to increase the frequency bandwidth, resistively loaded traces, printed by conventional inkjet printer are used to replace the copper ones. For normal incidence, simulated and measurement results shown that the proposed flat absorber exhibits absorption efficiency higher than 0.8 for 6.9–29.9 GHz (i.e., bandwidth of 125%) regardless of polarization, while the curved absorber for 6.6–29 GHz (i.e., bandwidth of 126%) or for 10.5–29.6 GHz (i.e., bandwidth of 95%), depending the polarization. For oblique incidence and for TE or TM polarized incident wave it presents bandwidth of 118% (7.7–29.9 GHz) or 100.5% (9.9–29.9 GHz), respectively, for an incident angular range of 0–45 deg. Finally, the proposed absorber has thickness of 3.89 mm, corresponding to λ/11.7 at its lowest operation frequency.

This work presents a high efficiency, co-planar and low-complexity RF-to-dc rectifier of one diode, which is able to be directly connected, i.e., without a matching network, to a coplanar antenna, e.g., to a dipole or loop antenna. The rectifier was designed to optimally operate at 868 MHz and for low power input. Specifically, it presents 54.82% RF-to-dc efficiency for 20 dBm power input, while for −14.4 dBm the system is able− to supply continuously, i.e., with any boost converter, a backscatter sensor node with power consumption of 20 µW.

Within an increasingly connected world, the exponential growth in the deployment of Internet of Things (IoT) applications presents a significant challenge in power and data transfer optimisation. Currently, the maximization of Radio Frequency (RF) system power gain depends on the design of efficient, commercial chips, and on the integration of these chips by using complex RF simulations to verify bespoke configurations. However, even if a standard 50Ω transmitter’s chip has an efficiency of 90%, the overall power efficiency of the RF system can be reduced by 10% if coupled with a standard antenna of 72Ω. Hence, it is necessary for scalable IoT networks to have optimal RF system design for every transceiver: for example, impedance mismatching between a transmitter’s antenna and chip leads to a significant reduction of the corresponding RF system’s overall power efficiency. This work presents a versatile design framework, based on well-known theoretical methods (i.e., transducer gain, power wave approach, transmission line theory), for the optimal design in terms of power delivered to a load of a typical RF system, which consists of an antenna, a matching network, a load (e.g., integrated circuit) and transmission lines which connect all these parts. The aim of this design framework is not only to reduce the computational effort needed for the design and prototyping of power efficient RF systems, but also to increase the accuracy of the analysis, based on the explanatory analysis within our design framework. Simulated and measured results verify the accuracy of this proposed design framework over a 0–4 GHz spectrum. Finally, a case study based on the design of an RF system for Bluetooth applications demonstrates the benefits of this RF design framework.

Summarization: A low-cost (6 Euro per sensor), low-power (in the order of 200μ{W} per sensor), with high communication range (on the order of 250 m), scatter radio sensor network is presented, for soil moisture monitoring at multiple locations.The proposed network utilizes analog frequency modulation in a bistatic network architecture (i.e., the emitter and reader are not colocated), while the sensors operate simultaneously, using frequency-division multiple access.In contrast to prior art, this paper utilizes an ultralow-cost software-defined radio reader and offers custom microstrip capacitive sensing with simple calibration, as well as modulation pulses for each scatter radio sensor with 50% duty cycle; the latter is necessary for scalable network designs.The overall root mean squared error below 1% is observed, even for the range of 250 m.This is another small (but concrete) step for the adoption of scatter radio technology as a key enabling technology for scalable, large-scale, low-power, and cost environmental sensor networking. Presented on: IEEE Transactions on Microwave Theory and Techniques

This work presents a systematic study of dense rectenna-arrays using electrically small antennas and aims to the design of a high efficient for low power input (i.e., less than −20 dBm) and high sensitivity (i.e., less than 1 μW/cm2) RF energy harvester for IoT. Simulations shown that for power density of 0.1 μW/cm2 the RF harvester of size λ×λ delivers dc power output of 20.8 μW, while is able to power continuously a backscatter sensor node with power consumption of 100 μW at 1.6 V for power density of 0.2577 μW/cm2.

This work presents a systematic numerical analysis of the microstrip-grid antenna aiming not only to explore the antenna performance limits in terms of frequency impedance bandwidth and maximum gain, but also to use this analysis as a starting point for further optimization. The obtained antenna has dimensions 297 mm x 210 mm x 9.9 mm and at 2.41 GHz, has a maximum gain of 15.4 dB, which is very close to the directivity of an ideal, lossless aperture antenna with the same dimensions, at the same frequency. Measurements have shown that the antenna operates from 2.38 to 2.51 GHz (i.e., across the WiFi-band with a 5.32% frequency bandwidth relative to 50 Ohm), with maximum radiation efficiency 98.2%, while the latter remains over than 91% for the whole.WiFi-band, and finally has a measured half-power beamwidth of 18.5 and 34.5 deg. in the horizontal and vertical planes, respectively. Thus,the antenna is suitable candidate for long-range WiFi links.

In this paper, the effective parameters of diverse single-negative bulk structures are extracted in terms of first-principles homogenization techniques. Each metamaterial unit-cell is initially considered to be an electrically small scatterer, and under this assumption, its polarizabilities are derived via a dynamic approach. Also, the wavenumber of a normally incident propagating plane wave through the aforementioned single-negative structures is obtained by means of several algorithms. The retrieved polarizabilities of a single scatterer and the wavenumber of the periodic medium are, finally, incorporated in the homogenization formulas to compute the desired effective parameters. Numerical verification addressing the analysis of two different resonators and comparisons with the results of a popular homogenization method, reveals the merits of the proposed formulation and proves its overall efficiency.

The purpose of this paper is to present efficient models of new octagonal split ring resonant (O-SRR) periodic structures that can offer practical applications for electromagnetic compatibility (EMC) engineers in the area of absorbing materials. The model of an ultra-thin, compact O-SRR absorber for operation at microwave frequencies is introduced, exhibiting very high absorptive regions. The idea is extended to multi-band performance, where two different setups are demonstrated and analyzed. The physics behind the absorption mechanism for the multi-band structures is explained through the surface mechanism.

The scope of this paper is to present a systematic and versatile method, with minimal computational requirements, that incorporates the use of new electromagnetic bandgap (EBG) structures in stealth technology. Grounded structures are used to ensure zero transmittance resulting to angle independence of the incident radiation. A possible future realistic scenario is simulated and experimentally examined where a metallic plane is fully covered by EBG structures and the monostatic radar cross section is measured. Varying the angle of incidence from 0 ° to 90 °, it is observed that for the worst case scenario the reduction of the monostatic radar cross section (RCS) is almost 19 dB. Finally, to verify our idea, the RCS of a metallic cube also fully covered by EBG structures was examined. The assets of the proposed concept, applied to the design of different patterns, appear to be potentially beneficial for various electromagnetic interference/electromagnetic compatibility configurations.

A further example of multi-band absorption using ultra-thin, polarization-insensitive, wide-angled metamaterial absorbers that operate in multi-frequency bands within the microwave regime is presented in this work. The basic structure geometry is utilised to create multi-band highly absorbing structures by incorporating the scalability property of the metamaterials. Simulation results verify the structure’s ability for high absorption. The multi-band absorbers are promising candidates as absorbing elements in scientific and technical applications because of its multi-band absorption, polarization insensitivity, and wide-angle response. Finally, the current distributions for those structures are presented to gain a better insight into the physics behind the multiple absorption mechanism.

We present a series of designs for uniplanar electromagnetic bandgap structures for antennas and microwave circuits. The proposed, easy to fabricate configurations, are based solely on metallic surfaces on layer interfaces, without the use of vias or other kinds of vertical connections. Their use in low profile antenna applications and mutual coupling reduction of planar radiating elements is investigated through an efficient and versatile technique, since the only information needed is the reflection phase and the dispersion diagram of the unit cell.

The uniplanar cross-like compact EBG structure is thoroughly assessed by means of a computational FEM-based eigenvalue analysis. A careful inspection of the dispersion diagram reveals the existence of a nearly-TEM mode that compromises the bandgap behavior, a fact that is also confirmed in coupling performance investigations. The structure is then modified and optimized to maximize the resulting bandgap zone, for mutual coupling reduction in WiMAX MIMO arrays.

This work describes and proposes a new triple-band (GSM 900, DCS 1800, WiFi), highly efficient metamaterial harvester that is capable to operate in wide angles of plane wave incidence. The energy harvesting structure consists of a conventional metamaterial electric resonator, which employs a via that channels all the absorbed RF power to a resistive load. The latter represents the input impendance of a RF-to-DC rectifier. The metamaterial harvester is analyzed in terms of absorbance, power efficiency and power losses mechanism for normal as well as for wide angle incidence. The assets of the proposed model, could be proven to be potentially instructive for various electromagnetic RF energy harvesting configurations.

A controllable bowtie-like electromagnetic bandgap (EBG)-based microwave filter is proposed in this article. The device exploits EBG properties to form the desired stopband, whereas tunability is used by means of switching elements. Numerical analysis is performed by a finite element scheme revealing the DC-extending bandstop behavior of the structure. In addition, a prototype of the proposed filter is constructed and measured. Experimental data demonstrate the robustness of the conducted simulations, while an adequate tuning range is observed. The simple, yet efficient and easily fabricated, design promises operational reconfigurability combined with amplitude tunability. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2472–2474, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26316

—This work aims to improve the RFID RF front-end performance via microwave analysis. It is well known thatthe magnitude of the complex reflection coefficient difference,between two loads connected to the tag-antenna, is a crucialdesign parameter. On the other hand, the loads are usuallyconsidered ideal and there is no microwave analysis of electro-magnetic interference between the antenna and the load controlcircuit. This study demonstrates through measurements that theassumption of ideal loads is not realistic and magnitude ofreflection coefficient difference is reduced in practice, offeringdegraded backscatter radio performance (compared to the idealcase). A microwave analysis is utilized in order to assess couplingbetween the control circuit and the antenna/RF switch (thatselects the loads). As a collateral dividend, the magnitude ofreflection coefficient difference is increased with microwave anal-ysis and experimental measurements and a specific methodologyis proposed. Index Terms

The consistent retrieval of effective parameters for complicated single-negative structures is presented in this paper through a first-principles homogenization method. The proposed technique considers each metamaterial unit-cell as an electrically-small scatterer and evaluates its polarizabilities via a robust process. These outcomes and the extracted wavenum-bers are inserted in the homogenization relations to obtain the required medium parameters.

In this paper a new technique for mutual coupling reduction of uniplanar MIMO antennas is presented. The only necessary information needed, is the transmission coefficient of a plane wave which is propagating over a specific structure, of a new proposed geometry.

In this article, the authors introduce and study the performance of two novel parametric families of Nyquist intersymbol interference-free pulses. Using only two design parameters, the proposed pulses yield an enhanced performance compared to the sophisticated flipped-inverse hyperbolic secant (asech) filter, which was recently documented in the literature. Although the construction of parametric families originates from the work of Beaulieu and Damen, the authors' approach is based on the concept of ‘inner’ and ‘outer’ functions and for this reason a higher flexibility in the choice of the family members is achieved. The proposed pulses may decay slower than the original raised-cosine (RC) pulse outside the pulse interval, but exhibit a more pronounced decrease in the amplitudes of the two largest sidelobes and this accounts for their improved robustness to error probabilities. It is clearly shown, via simulation results, that a lower bit error rate (BER), compared to the existing pulses, can be achieved for different values of the roll-off factor and timing jitter. Moreover, a smaller maximum distortion as well as a more open-eye diagram are attained which further demonstrate the superiority of the proposed pulse shaping filters.

Summarization: This work presents an efficient and high-sensitivity radio frequency (RF) energy harvesting supply. The harvester consists of a single-series circuit with one double diode on a low-cost, lossy FR-4 substrate, despite the fact that losses decrease RF harvesting efficiency. The design targeted minimum reflection coefficient and maximum rectification efficiency, taking into account not only the impedance matching network, but also the rectifier microstrip trace dimensions and the load. The simulated and measured rectenna efficiency was 28.4% for-20-dBm} power input. In order to increase sensitivity, i.e., ability to harvest energy and operate at low power density, rectennas were connected in series configuration (voltage summing), forming rectenna arrays. The proposed RF harvesting system ability was tested at various input power levels, various sizes of rectenna arrays, with or without a commercial boost converter, allowing operation at RF power density as low as 0.0139 μ W/cm2. It is emphasized that the boost converter, whenever used, was self-started, without any additional external energy. The system was tested in supplying a scatter radio sensor, showing experimentally the effect of input power density on the operational cold start duration and duty cycle of the sensor. Presented on: IEEE Transactions on Microwave Theory and Techniques

In this article, a new two-parametric pulse that outperforms state-of-the-art pulses with the best performance in terms of BER is proposed, which is studied in terms of frequency and time domain characteristics. Specifically, the pulse is based on the inverse-hyperbolic functions acsch and asech which are used for the first time for an ISI-free pulse, and its design depends only on the roll-off factor and the timing jitter parameter (i.e. two-parametric design). Finally, the proposed pulse is shown to outperform most of the well-known pulses reported in the literature, since it presents lower error probability, smaller maximum distortion and wider eye-diagram.

The systematic design of size-conflned, polarization- independent metamaterial absorbers that operate in the microwave regime is presented in this paper. The novel unit cell is additionally implemented to create e-cient multi-band and broadband structures by exploiting the scalability property of metamaterials. Numerical simulations along with experimental results from fabricated prototypes verify the highly absorptive performance of the devices, so developed. Moreover, a detailed qualitative and quantitative analysis is provided in order to attain a more intuitive and sound physical interpretation of the underlying absorption mechanism. The assets of the proposed concept, applied to the design of difierent patterns, appear to be potentially instructive for various EMI/EMC conflgurations.