Operating Frequency Bandwidth Research Articles

Barium titanate–silicon elastomer based body coupled antenna for wearable microwave head imaging applications

This paper presents a flexible monopole antenna fed by a coplanar waveguide (CPW) feeding line with a barium titanate (BaTiO3) silicon-elastomer impedance matching layer for microwave head imaging applications. The operating frequency bandwidth of the proposed antenna is 614 MHz which is from 0.475 GHz to 1.089 GHz. In biomedical microwave sensing and imaging applications, the major challenge is the high power loss due to reflection between the BaTiO3 and the antenna due to impedance mismatch. Therefore, the proposed BaTiO3 silicon-elastomer composite is designed to have dielectric property of 20 which acts as an impedance matching layer for the monopole antenna. The proposed antenna has dimensions of 70×30×6 mm. The flexibility of the antenna is provided by the use of the silicon elastomer. It has been shown that the power radiated into an artificial head phantom improved by almost 160% as compared to antenna without impedance matching layer. Moreover, the SAR level is 0.0286 W/kg when 1 mW of power is transmitted, which is well below the limit set by the regulation. This makes the antenna suitable for wearable biomedical applications due to its wideband characteristic and improved power penetration into human head.

Improving the output performance of magnetic energy harvesters through coupling beam

We propose a novel magnetic energy harvester (MEH) with multiple resonance modes. The MEH consists of low-frequency and high-frequency piezoelectric cantilevers connected by a coupling beam. Theoretical modeling, simulation, and experiments were conducted to validate the multiple resonance phenomenon. The results from these investigations are consistent with each other. It is evident that the internal coupling (IC) effect resulting from the coupling beam facilitates significant voltage outputs from both cantilevers at their respective resonant frequencies, i.e. the low-frequency beam (LFB) resonates at the resonant frequency of the high-frequency beam (HFB), resulting in a remarkable 122% increase in the output voltage. Conversely, the HFB resonates at the resonant frequency of the LFB, leading to an astounding 1200% increase in the output voltage. As a result of the IC phenomenon, the operating frequency bandwidth for harvesting an output voltage of more than 1 V in the LFB has been extended by 35.3%, while that of the HFB for capturing an output voltage of more than 0.5 V has been extended by 62.5%. Additionally, the coupling effect significantly enhances the power output of the MEH.

A lumped-parameter model of the free-flooded ring transducer array.

The free-flooded ring (FFR) transducer is an extensively used ring-type acoustic transducer in underwater environments owing to its broad operating frequency bandwidth and small size. However, achieving high sound pressure levels with a single FFR transducer is often difficult, thus necessitating the construction of vertically arranged FFR transducer arrays. This study presents a comprehensive analysis of the electrical and acoustic characteristics of an FFR transducer array by considering the mutual radiation load and the effects of gaps between adjacent piezoelectric rings. The lumped-parameter models of the piezoelectric ring, cylindrical cavity, cylindrical gap, and radiation impedance constitute an entire impedance matrix. The radiation impedance matrix for the FFR transducer array is calculated using the Helmholtz-Kirchhoff integral formula by considering the interaction of the FFR surfaces with the surrounding fluid medium. The proposed model predicts the resonance peaks in the admittance and transmitted voltage response (TVR) with a relative error of 5%, and the TVR level within a 3 dB range. Detailed analyses of a four-FFR transducer array reveal that a wider gap between each FFR leads to a decreased chance of negative conductance and broader operating bandwidth. The proposed model offers valuable insights into the design of FFR transducer arrays.

Two-dimensional honeycomb lattice structure for underwater acoustic cloaking using pentamode materials

This research article presents an innovative and novel approach to achieve underwater acoustic cloaking using a two-dimensional honeycomb lattice structure with pentamode materials in the kHz frequency range. Underwater acoustic cloaking holds substantial importance in various applications, such as marine engineering, imaging, and military operations, making the development of an efficient underwater acoustic shell imperative. The proposed cloak consists of a pentamode titanium material honeycomb lattice embedded in an air background, submerged in water. To attain effective camouflage and regulate the phase and energy flow, impedance matching was applied to the overall geometry of the structure. By fine-tuning the structural parameters of the cloaking shell, derived from the effective mass velocity and density for recovering reflected waves, impedance matching with water was ensured. Through simulation calculations and optimization design, the average total scattering cross-section of the acoustic cloak is determined to be 0.1. The results demonstrate that the pentamode material-based cloaking approach is not only suitable and efficient in achieving the cloaking phenomenon but also enhances operator flexibility. The operating frequency bandwidth of the acoustic cloaking system is approximately 8 kHz for lattice constant a = 5 mm. These findings pave the way for further advancements in underwater acoustic cloaking technologies.

A 77 GHz Power Amplifier with 19.1 dBm Peak Output Power in 130 nm SiGe Process.

This article reports a two-stage differential structure power amplifier based on a 130 nm SiGe process operating at 77 GHz. By introducing a tunable capacitor for amplitude and phase balance at the center tap of the secondary coil of the traditional Marchand balun, the balun achieves amplitude imbalance less than 0.5 dB and phase imbalance less than 1 degree within the operating frequency range of 70-85 GHz, which enables the power amplifier to exhibit comparable output power over a wide operating frequency band. The power amplifier, based on a designed 3-bit digital analog convertor (DAC)-controlled base bias current source, exhibits small signal gain fluctuation of less than 5 dB and saturation output power fluctuation of less than 2 dB near the 80 GHz frequency point when the ambient temperature varies in the range of -40 °C to 125 °C. Benefiting from the aforementioned design, the tested single-path differential power amplifier exhibits a small signal gain exceeding 16 dB, a saturation output power exceeding 18 dBm, and a peak saturation output power of 19.1 dBm in the frequency band of 70-85 GHz.

Broadband Continuous Transverse Stub (CTS) Array Antenna for High-Power Applications.

A continuous transverse stub (CTS) array antenna with broad bandwidth and high-power handling capacity is proposed in this paper. The technologies of multi-step impedance matching and T-shaped electromagnetic band-gap (EBG) loading are utilized, which improved the antenna operating frequency bandwidth. An H-plane lens horn is used to feed the CTS array. As a result, a good bandwidth capability of more than 32% is achieved, with a gain variation less than 3.0 dB. The measured sidelobe level (SLL) is below -18 dB in the entire frequency range. Moreover, the power handling capacity of the antenna is more than 80 MW and can reach the GW level after arraying, which indicates that this antenna has application potential in the high-power microwave (HPM) field.

Dual-Band Nested Circularly Polarized Antenna Array for 5G Automotive Satellite Communications

Currently, 5G low-earth orbit satellite communications offer enhanced wireless coverage beyond the reach of 5G terrestrial networks, with important implications, particularly for automated and connected vehicles. Such wireless automotive mass-market applications demand well-designed compact user equipment antenna terminals offering non-terrestrial jointly with terrestrial communications. The antenna should be low-profile, conformal, and meet specific parameter values for gain and operational frequency bandwidth, tailored to the intended applications, in line with the aesthetic design requirements of passenger cars. This work presents an original concept for a dual-band nested circularly polarized automotive user terminal that operates at the S-band frequencies around 3.5 GHz and Ka-band frequencies around 28 GHz, namely within the 5G new-radio bands n78 and n257, respectively. The proposed terminal is designed to be integrated into the plastic components of a passenger vehicle. The arrays consist of 2 × 2 aperture-coupled corner-truncated microstrip slot patch antenna elements for the n78 band and of 4 × 4 single-layer edge-truncated microstrip circular slot patch antenna elements for the n257 band. The embedded arrays offer, across the two bands, respectively, 9.9 and 13.7 dBi measured realized gain and 3-dB axial ratio bandwidths of 100 and 1500 MHz for the n78 and n257 bands along the broadside direction. Detailed link budget calculations anticipate uplink data rates of 21 and 6 Mbit/s, respectively, deeming it suitable for various automotive mobility and Internet-of-Things applications.

An improved lumped parameter model of the single free-flooded ring transducer using Helmholtz–Kirchhoff integral solution

The Helmholtz-Kirchhoff integral (HKI) may be considered as the boundary element method (BEM) used to calculate the acoustic pressure at any position in the 3D-radiation problem from a vibrating surface. This method provides valuable insights into the radiation characteristics of vibrating structures, which may offer significant information and tools to underwater transducer design engineers during the early stages of development. It may save considerable computational costs in the design processes for the underwater transducer such as Hull Mount Sonar. This study illustrates usefulness of the HKI-based approach by developing a simple model of the Free Flooded Ring (FFR) transducer using a piezoelectric ring model and the HKI solution on the surface acoustic pressure of the ring through their physical conditions on their connected interfaces. The FFR transducer is widely utilized as a low-frequency acoustic source in underwater environments due to its broad operating frequency bandwidth and relatively small size. The developed approach aims to construct a precise model that considers the sound-structure interactions between the piezoelectric ring and the acoustic medium around it. To validate the accuracy of the proposed method, the acoustic pressure and electrical admittance are compared with those obtained through finite element method (FEM) simulations.

Indoor Non‐Line‐of‐Sight Millimeter‐Wave Coverage Enhancements by Field‐Reorganizable Passive Digital Coding Metasurfaces

Digital metasurfaces define a novel methodology for metasurface designs by adopting discrete coding meta‐atoms to engineer electromagnetic waves in programmable ways. Herein, a novel field‐reorganizable digital metasurface (FRDM) that can be used to enhance the indoor non‐line‐of‐sight (NLOS) millimeter‐wave (mmWave) signal coverage is presented. The passive binary supercells which can be reorganized with an in situ optimization characteristic to deflect the incoming mmWaves into the blind area with adjustable angles are proposed. The indoor L‐shaped corridor signal coverage simulated by the ray‐tracing technique confirms that the NLOS blind area is effectively communicated using the passive FRDM. Practical environment experiments using FRDMs with different coding sequences are conducted, indicating that the averaged signal intensity is increased by over 10 dB in the NLOS blind area in a wide operating frequency band from 26 to 30 GHz by reorganizing the passive digital metasurfaces. The results suggest that the proposed FRDM enabled by the reorganizable binary supercells is a highly flexible, low‐cost, and extensible solution for B5G and 6G mmWave wireless communications.

Channel Estimator and Nonlinear Detector for mmWave Beamformed OTFS Systems in High Mobility Scenarios

Real-time data-intensive applications in highly mobile environments with high data rates and low latency are one of the key requirements for beyond fifth-generation (5 G) communications. Towards this end, a combination of the millimeter wave (mmWave) band with large available spectrum and orthogonal time-frequency space (OTFS) modulation, which offers robust performance in high mobility scenarios, can be envisioned as a promising solution. However, employing OTFS in the mmWave frequency band is challenging in presence of nonlinear distortions attributed to radio frequency (RF) power amplifier (PA) and complex equalization involved in OTFS receiver in the delay-Doppler domain. The nonlinearity effect of PA is inevitable in mmWave systems due to the high operating frequency and large bandwidth. The nonlinear distortions induce interference and make the target distribution analytically intractable. In this paper, we propose a receiver design for mmWave OTFS systems that aims to address the challenges posed by the nonlinear distortions of the RF PA. The proposed receiver design leverages the use of a large-scale antenna array to decouple the received signal into multiple branches through beamforming. Specifically, we first derive the input-output relation in the delay-Doppler domain with nonlinearity. Then, a combination of maximal-ratio combining (MRC) and iterative particle filter (PF)-based nonlinear detector is proposed to address the issue. We also design a pilot pattern considering the additional interference from the PA impairment. Furthermore, we reformulate the threshold-based channel estimation to incorporate the nonlinearly distorted pilot in its estimation process. Extensive numerical results demonstrate the proposed algorithm's reliability and superiority over existing digital predistorters (DPD) and conventional linear detectors.

An Optical Fiber Acceleration Sensor Based on a V-Shaped Flexure Hinge Structure

This paper proposes a novel vibration sensor based on fiber Bragg grating (FBG) technology. The sensor employs a V-shaped flexure hinge structure, which is theoretically and experimentally demonstrated to enhance sensitivity for vibration sensing. The proposed design utilizes the V-shaped flexures hinge to focus the acceleration-induced strain, resulting in improved performance for vibration sensitivity. The implementation of the FBG sensor was evaluated through theoretical computations using MATLAB. The simulation software was also used to simulate the proposed structure and assess the parameters affecting its sensing performance. The experimental results of this work sensor demonstrate a sensitivity of 79.46 pm/G and a resonant frequency of 1140 Hz. The sensor’s operating frequency bandwidth was 30–320 Hz, while the temperature influence was measured at 8.5 pm/°C. In addition, the amplitude in the transverse direction was only 3% of the amplitude in the working principle, indicating that the presented sensor has solid lateral immunity. The experimental results were consistent with the simulation findings, demonstrating the presented vibration sensor’s good performance. The given work provides an opportunity to apply the FBG acceleration sensor in the high-dependability detection of low- and medium-frequency vibration signals.

A wideband and compact Quasi-Yagi antenna based on spoof surface plasmon polaritons

In this paper, a novel wideband end-fire antenna, based on a spoof surface plasmon polaritons (SSPP) transmission line, is proposed. Periodically modulated corrugated metal strips are used as a transmission line for quasi-TEM conversion in the microstrip line to the state of SSPP and the best impedance matching. Due to the strong confinement of the field in the SSPP waveguide and its high transmission performance, it has been used as a transmission line. The antenna consists of SSPP waveguides for the transmission line, a metal plate on the ground as the reflector of the antenna, a metal strip director, and two half-rings to realize the radiation, reaching a wide bandwidth in the range of 4.1 to 8.1 GHz. The simulation results show that this antenna achieves a gain of 6.5 dBi, a bandwidth of 65%, and an efficiency of 97% across a wide operating frequency band, from 4.1 to 8.1 GHz. The proposed end-fire antenna has been fabricated, and the measured results agree well with the simulated results. The end-fire antenna implemented on a dielectric layer also has the advantages of high efficiency, good directivity, high gain, a wide bandwidth, easy fabrication, and a compact size.

A Novel Low‐Loss Planar PRGW Crossover Design for 5G Applications

AbstractIn this paper, a planar 0‐dB crossover using printed ridge gap waveguide (PRGW) technology is proposed and designed for millimeter‐wave applications. PRGW as a quasi‐TE mode is considered as the modern guiding technology at high frequencies and for the 5G and other upcoming communications. A prototype of the proposed PRGW crossover working around 30 GHz is fabricated and measured to validate the simulated results. Comparing simulated with measured results, a good agreement is observed. The measured results demonstrate that the designed crossover offers an insertion loss of better than 0.5 dB over the whole operating frequency bandwidth from 29 to 31 GHz where the return loss level is better than 15 dB and the isolation level is less than −13 dB. Compared with the other reported crossover structures, the designed PRGW crossover features a wider bandwidth with a smaller and planar configuration.

Low-Profile Planar Ultrawideband Modular Antenna Array Loaded With Parasitic Metal Strips

A low-profile dual-polarized planar ultrawideband modular antenna (PUMA) array is proposed in this paper. The overall profile is as small as 11.4 mm (0.228λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> is the free-space wavelength at the highest operating frequency) based on element sizes 25 × 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.5 × 0.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and a large operating frequency bandwidth achieved by loading lossless parasitic metal strips between the dipole patch and the ground plane. The loop-mode resonance that causes deterioration of the port isolation around the lowest operating frequency is comprehensively analyzed and suppression methods are proposed. To further reduce the overall profile, a metasurface-based wide-angle impedance matching (MS-WAIM) layer is introduced. The surface waves guided by the MS-WAIM layer during wide-angle scanning in H-plane are suppressed by cutting properly-sized square holes at critical positions. The calculated results show that the proposed infinite array can scan up to ±60° in E/H-planes with active VSWRs below 2.9 within 2–6 GHz and orthogonal port isolations beyond 20 dB. A 12 × 11 array prototype is fabricated and reasonable agreement is achieved between the calculated and measured results.

A Novel Design of G-Band Broadband Low-Gain Fluctuation Slow-Wave Structure With Improved Folded Waveguides

The design method for ultrawideband amplification with low-gain fluctuation is explored for the terahertz folded-waveguide traveling-wave tube (TWT). Although the folded-waveguide circuit has a large cold bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 30%), effective amplification with a flat gain characteristic can only be achieved in a limited range due to sharply reduced interaction impedance. The situation further deteriorates in the design of a terahertz TWT where an oversized beam tunnel has to be used to facilitate the transport of the beam. Through careful analysis of the folded-waveguide (FWG) design characteristics, a modification to the geometry of the circuit has been proposed, leading to a significant enhancement in design capability. As a result, the interaction impedance is increased by 26% over a wide operation frequency band in comparison to the normal folded-waveguide circuit. This makes it possible to use the phase velocity tapering technology to increase efficiency and balance the gain at the same time. A design example in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{G}$</tex-math> </inline-formula> -band is presented. The interaction circuit is capable of producing 18-W output power over 30 GHz from 202 to 232 GHz with a gain fluctuation of less than 1.5 dB.

Design of Novel Ultrabroadband Printed Antenna and Its Efficient Optimization Using Self-Adaptive Hybrid Differential Evolution Algorithm

A novel compact ultra-broadband-modified fork-shaped printed antenna is optimized efficiently by using a self-adaptive hybrid differential evolution (SHDE) algorithm. Firstly, a novel compact ultra-broadband-modified fork-shaped printed antenna structure is proposed. The antenna with more compact size consists of a modified fork-shaped radiator and a modified ground plane, which can cover a very wide operating frequency band. The antenna is fed by a step-shaped microstrip line, and the modified ground plane consists of some rectangular slots and an L-shaped stub. Then, the SHDE algorithm is used to determine structural dimensions of the proposed antenna, and the antenna’s performance is optimized while maintaining a cost-effective computation time. The optimized antenna with only 11.8 mm × 19.7 mm size covers -10 dB reflection coefficient bandwidth of 147.6% from 3.08 to 20.46 GHz. Finally, the antenna prototype is fabricated, and the measured results basically agree with the simulated ones. The proposed antenna can be viewed as an excellent candidate for realizing ultrabroadband transmission technology.

Increasing bandwidth of orthogonally polarised omnidirectional antenna composed of halo and sleeve antennas

AbstractIn this study, we developed and investigated a small‐diameter, low‐profile, wideband orthogonal‐polarisation multiple‐input multiple‐output (MIMO) antenna. A polarisation MIMO antenna is a combination of a modified sleeve antenna for vertical polarisation and a halo antenna with four parasitic elements for horizontal polarisation. Four parasitic elements vertically were loaded above and below the halo antenna, and a sleeve antenna with an upper sleeve structure was inserted inside the halo antenna to achieve a low profile, wideband antenna with a small diameter. Simulation and measurement results showed that the proposed antenna achieved a relative bandwidth of 10.1% (|S11| and |S22| ≤ −10 dB). For the lower frequency wavelength (λmin) in the required bandwidth, the diameter and height of the proposed antenna are 0.14λmin and 0.57λmin respectively. Additionally, it is capable of orthogonal‐polarisation isolation of approximately 20 dB within the operating frequency bandwidth.

Magnetic Bistability for a Wider Bandwidth in Vibro-Impact Triboelectric Energy Harvesters.

Mechanical energy from vibrations is widespread in the ambient environment. It may be harvested efficiently using triboelectric generators. Nevertheless, a harvester's effectiveness is restricted because of the limited bandwidth. To this end, this paper presents a comprehensive theoretical and experimental investigation of a variable frequency energy harvester, which integrates a vibro-impact triboelectric-based harvester and magnetic nonlinearity to increase the operation bandwidth and improve the efficiency of conventional triboelectric harvesters. A cantilever beam with a tip magnet was aligned with another fixed magnet at the same polarity to induce a nonlinear magnetic repulsive force. A triboelectric harvester was integrated into the system by utilizing the lower surface of the tip magnet to serve as the top electrode of the harvester, while the bottom electrode with an attached polydimethylsiloxane insulator was placed underneath. Numerical simulations were performed to examine the impact of the potential wells formed by the magnets. The structure's static and dynamic behaviors at varying excitation levels, separation distance, and surface charge density are all discussed. In order to develop a variable frequency system with a wide bandwidth, the system's natural frequency varies by changing the distance between the two magnets to reduce or magnify the magnetic force to achieve monostable or bistable oscillations. When the system is excited by vibrations, the beams vibrate, which causes an impact between the triboelectric layers. An alternating electrical signal is generated from a periodic contact-separation motion between the harvester's electrodes. Our theoretical findings were experimentally validated. The findings of this study have the potential to pave the way for the development of an effective energy harvester that is capable of scavenging energy from ambient vibrations across a broad range of excitation frequencies. The frequency bandwidth was found to increase by 120% at threshold distance compared to the conventional energy harvester. Nonlinear impact-driven triboelectric energy harvesters can effectively broaden the operational frequency bandwidth and enhance the harvested energy.

Analysis of Influencing Parameters Enhancing the Plucking Efficiency of Piezoelectric Energy Harvesters.

The integration of energy harvesting systems into sensing technologies can result in novel autonomous sensor nodes, characterized by significant simplification and mass reduction. The use of piezoelectric energy harvesters (PEHs), particularly in cantilever form, is considered as one of the most promising approaches aimed at collecting ubiquitous low-level kinetic energy. Due to the random nature of most excitation environments, the narrow PEH operating frequency bandwidth implies, however, the need to introduce frequency up-conversion mechanisms, able to convert random excitation into the oscillation of the cantilever at its eigenfrequency. A first systematic study is performed in this work to investigate the effects of 3D-printed plectrum designs on the specific power outputs obtainable from FUC excited PEHs. Therefore, novel rotating plectra configurations with different design parameters, determined by using a design-of-experiment methodology and manufactured via fused deposition modeling, are used in an innovative experimental setup to pluck a rectangular PEH at different velocities. The obtained voltage outputs are analyzed via advanced numerical methods. A comprehensive insight into the effects of plectrum properties on the responses of the PEHs is attained, representing a new and important step towards the development of efficient harvesters aimed at a wide range of applications, from wearable devices to structural health monitoring systems.

Power Generation by a Limestone-Contained Putty.

A novel contact-separation triboelectric generator concept is proposed in this paper, which consists of a limestone-based mounting putty and a metallized polyester (PET/Al) sheet. This is an attempt to explore tacky materials for power generation and extend the operational frequency bandwidth compared to existing TriboElectric NanoGenerators (TENGs). Moreover, the proposed design is very cost-effective and easy to build. Unlike traditional TENGs, which generate power solely due to a charge developing on the surface, the putty also replies on charge developed inside the material. Parametric study was conducted to determine the optimal putty thickness in a shaker test at 40 Hz. It was found that a putty layer at 0.6 mm thick yielded maximum power generation. During the separation phase, the electrical breakdown between triboelectric layers allows most existing electrons to flow back from the ground due to rapid charge removal at the interface. We are able to achieve a peak power of 16 mW in a shaker test at 40 Hz with an electrical load of 8 MΩ, which corresponds to a power density of 25.6 W/m2. A peak power of 120 mW in a manual prototype generator is achieved, which operates at approximately 2 Hz. Since putty material has less tackiness than double-sided tape, we are able to expand the frequency bandwidth up to 80 Hz, which is significantly higher than a TENG (typically <10 Hz). The mounting putty material contains limestone with approximate 31 nm of mean grain size mixed with synthetic rubber materials. Elasticity from rubber and the nanohardness of calcite crystallites allow us to operate a putty generator repeatedly without the concern of grain fracture. Also, a durability test was conducted with up to 250,000 contact-separation cycles. In summary, comparable performance is achieved in the proposed putty generator to benefit energy harvesting and sensor applications.