Small Antenna Research Articles

A Small Implantable Compact Antenna for Wireless Telemetry Applied to Wireless Body Area Networks

Wireless Body Area Networks (WBANs) are human-centric wireless networks, and implantable antennas represent a vital communication component within WBANs. The dielectric properties of human tissue are highly complex, with each layer exhibiting distinct dielectric constants that significantly influence the performance of implanted antennas. It is therefore imperative that a compact broadband implantable antenna be designed in order to address the instability in communication of medical implant devices. The antenna, coated in silicone, is a single-layer structure fed by a coaxial cable, with a volume of just 6 mm × 6 mm× 0.53 mm. A metallic patch is etched on the upper surface of the substrate, and the compact antenna design is enhanced with the introduction of S-shaped, F-shaped, and rectangular slots on the patch. The bottom side of the substrate is etched with rectangular ground planes, which broaden the impedance bandwidth of the antenna. The simulation results demonstrate that the antenna attains an impedance bandwidth of 23.8% (2.08–2.64 GHz), encompassing the entirety of the Industrial, Scientific, and Medical (ISM) band (2.4–2.48 GHz). In order to simulate the working environment of the antenna within the human body, physical tests were conducted on the antenna in pork tissue. The test results demonstrate that the antenna exhibits a measured bandwidth of 28% (2.3–3.03 GHz), with a radiation pattern that displays omnidirectional radiation characteristics. The antenna’s impedance matching and radiation characteristics remain essentially consistent in both bent and unbent states, indicating structural robustness. In comparison to other implantable antennas, this antenna displays a wider impedance bandwidth, a lower Specific Absorption Rate (SAR), and superior implant performance.

Design of a Small Slotted Partial Grounded Fifth-Generation Patch Antenna at 3.5 GHz with Improved Performance

Design of a Small Slotted Partial Grounded Fifth-Generation Patch Antenna at 3.5 GHz with Improved Performance

A Distributed Energy-Throughput Efficient Cross-Layer Framework Using Hybrid Optimization Algorithm

Magnetic induction (MI)-operated wireless sensor networks (WSNs), due to their similar performance in air, underwater, and underground mediums, are rapidly emerging networks that offer a wide range of applications, including mine prevention, power grid maintenance, underground pipeline monitoring, and upstream oil monitoring. MI-based wireless underground sensor networks (WUSNs), utilizing small antenna coils, offer a viable solution by providing consistent channel conditions. The cross-layer protocols address the specific challenges of WUSNs, leading to improved network performance and enhanced operational capabilities in real-world applications. This work proposes a distributed cross-layer solution, leveraging the hybrid marine predator naked mole rat algorithm (MPNMRA) for MI-operated WUSNs. The solution, called DECMN (distributed energy-throughput efficient cross-layer network using MPNMRA), is designed to optimize the MI communication channels, MI relay coils (MI waveguide), and MI waveguide with 3D coils to fulfill quality of service (QoS) parameters, while achieving energy savings and throughput gains. DECMN utilizes the interactions between various layers to develop cross-layer protocols based on MPNMRA. Simulation results demonstrate the effectiveness of DECMN, offering energy savings, increased throughput, and reliable transmissions within the performance limits.

Resonant Conversion of Wave Dark Matter in the Ionosphere

We consider resonant wavelike dark matter conversion into low-frequency radio waves in the Earth’s ionosphere. Resonant conversion occurs when the dark matter mass and the plasma frequency coincide, defining a range mDM∼10−9–10−8 eV where this approach is best suited. Owing to the nonrelativistic nature of dark matter and the typical variational scale of the Earth’s ionosphere, the standard linearized approach to computing dark matter conversion is not suitable. We therefore solve a second-order boundary-value problem, effectively framing the ionosphere as a driven cavity filled with a positionally varying plasma. An electrically small dipole antenna targeting the generated radio waves can be orders of magnitude more sensitive to dark photon and axionlike particle dark matter in the relevant mass range. This Letter opens up a promising way of testing hitherto unexplored parameter space that could be further improved with a dedicated instrument. Published by the American Physical Society 2024

Tunnelling escape of waves

AbstractApplications of waves in communications, information processing and sensing need a clear understanding of how many strongly coupled channels or degrees of freedom exist in and out of volumes of space and how the coupling falls off for larger numbers. Numerical results are possible, and some heuristics exist, but there has been no simple physical picture and explanation for arbitrary volumes. By considering waves from a bounding spherical volume, we show a clear onset of a tunnelling escape of waves that both defines a limiting number of well-coupled channels for any volume and explains the subsequent rapid fall-off of coupling strengths. The approach works over all size scales, from nanophotonics and small radiofrequency antennas up to imaging optics. It gives a unified view from the multipole expansions common for antennas and small objects to the limiting plane and evanescent waves of large optics, showing that all such waves can escape to propagation to some degree, by tunnelling if necessary, and gives a precise diffraction limit.

Design of Electrically Small Intraocular Antenna for Retinal Prosthesis System and Its Validation.

This paper presents an ultra-miniaturized circular-shaped triple band microstrip antenna as an intraocular unit applicable for retinal prosthesis. The reported antenna is developed by modifying a conventional circular-shaped patch with a pair of open-ended circular annular rings and a semicircular ring-loaded rectangular stub. Additionally, a shorting pin is used at the periphery of the patch to achieve the frequency bands of interest. Further, to make the structure electrically small and accommodate highly dense electrodes, the circular ground plane is modified by making symmetrical slots over the four quadrants and edges. Specific absorption rate distribution for 1g and 10g of different tissue layers over three operating frequencies has been studied by placing electromagnetic sources at different locations. With these arrangements, the proposed strip antenna offers multiband operation within the frequency band of 1.25 GHz (1.13-1.46 GHz), 2.45 GHz (2.24-2.66 GHz), and 3.32 GHz (3.09-3.50 GHz). Besides, circularly polarized radiation has also been achieved at 1.25 GHz with a 3-dB axial ratio bandwidth of 10 MHz. Finally, the proposed antenna structure is fabricated, and its measured performance metrics are in close aggreement with the simulated parameters. The proposed antenna's performance inside a customized canonical eye model (DMCM) and anthropomorphic Zubal head model is studied and compared with the prior studies.

High-Gain, Endfire Electrically Small Antenna Based on Near-Field Resonant Parasitic Fan Strips

High-Gain, Endfire Electrically Small Antenna Based on Near-Field Resonant Parasitic Fan Strips

Performance of antenna-based and Rydberg quantum RF sensors in the electrically small regime

Rydberg atom electric field sensors are tunable quantum sensors that can perform sensitive radio frequency measurements. Their qualities have piqued interest at longer wavelengths where their small size compares favorably to impedance-matched antennas. Here, we compare the signal detection sensitivity of cm-scale Rydberg sensors to similarly sized room-temperature electrically small antennas with active and passive receiver backends. We present and analyze effective circuit models for each sensor type, facilitating a fair sensitivity comparison for cm-scale sensors. We calculate that contemporary Rydberg sensor implementations are less sensitive than unmatched antennas with active amplification. However, we find that idealized Rydberg sensors operating with a maximized atom number and at the standard quantum limit may perform well beyond the capabilities of antenna-based sensors at room temperature, the sensitivities of both lying below typical atmospheric background noise.

Optimizing photosynthetic light-harvesting under stars: simple and general antenna models

In the next 10–20 years, several observatories will aim to detect the signatures of oxygenic photosynthesis on exoplanets, though targets must be carefully selected. Most known potentially habitable exo-planets orbit cool M-dwarf stars, which have limited emission in the photosynthetically active region of the spectrum (PAR, 400<λ<700\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$400< \\lambda < 700$$\\end{document} nm) used by Earth’s oxygenic photoautotrophs. Still, recent experiments have shown that model cyanobacteria, algae, and non-vascular plants grow comfortably under simulated M-dwarf light, though vascular plants struggle. Here, we hypothesize that this is partly due to the different ways they harvest light, reflecting some general rule that determines how photosynthetic antenna structures may evolve under different stars. We construct a simple thermodynamic model of an oxygenic antenna-reaction centre supercomplex and determine the optimum structure, size and absorption spectrum under light from several star types. For the hotter G (e.g. the Sun) and K-stars, a small modular antenna is optimal and qualitatively resembles the PSII-LHCII supercomplex of higher plants. For the cooler M-dwarfs, a very large antenna with a steep ’energy funnel’ is required, resembling the cyanobacterial phycobilisome. For the coolest M-dwarfs an upper limit is reached, where increasing antenna size further is subject to steep diminishing returns in photosynthetic output. We conclude that G- and K-stars could support a range of niches for oxygenic photo-autotrophs, including high-light adapted canopy vegetation that may generate detectable bio-signatures. M-dwarfs may only be able to support low light-adapted organisms that have to invest considerable resources in maintaining a large antenna. This may negatively impact global coverage and therefore detectability.

Performance Analysis and Optimization of Switch Device for VLF Communication Synchronous Tuning System Based on Coupled Inductors

The very low frequency (VLF) communication system is characterized by a limited transmit bandwidth. Due to the low operating frequency, the dimensions of VLF antennas are significantly smaller than the corresponding wavelength. Therefore, VLF antennas are considered electrically small antennas (ESAs) with high Q values and narrow bandwidth. To achieve broadband VLF communication, synchronous tuning technology is commonly employed. In this study, we focus on analyzing the performance of the switching device in the synchronous tuning system using coupled inductors and IGBT as core components. By considering the equivalent circuit of the controlled source associated with coupled inductors, we propose an adaptive input impedance optimization algorithm based on the variable capacitor (hereinafter referred to as VC-ADIO) to address issues arising from coupling coefficient variations and internal parameters within IGBTs that affect primary loop input impedance. The radiated power of the VLF antenna is improved effectively.

Miniaturized Antenna Design for Wireless and Powerless Surface Acoustic Wave Temperature Sensors.

This paper presents the introduction, design, and experimental validation of two small helical antennae. These antennae are a component of the surface acoustic wave (SAW) sensor interrogation system, which has been miniaturized to operate at 915 MHz and aims to improve the performance of wireless passive SAW temperature-sensing applications. The proposed antenna designs are the normal-mode cylindrical helical antenna (CHA) and the hemispherical helical antenna (HSHA); both designed structures are developed for the ISM band, which ranges from 902 MHz to 928 MHz. The antennae exhibit resonance at 915 MHz with an operational bandwidth of 30 MHz for the CHA and 22 MHz for the HSHA. A notch occurs in the operating band, caused by the characteristics of the SAW sensor. The presence of this notch is crucial for the temperature measurement by aiding in calculating the frequency shifting of that notch. The decrement in the resonance frequency of the SAW sensor is about 66.67 kHz for every 10 °C, which is obtained by conducting the temperature measurement of the system model across temperature environments ranging from 30 °C to 90 °C to validate the variation in system performance.

Design of an electrically small printed square loop antenna for closely spaced Tx/Rx systems

AbstractA highly miniaturised electrically small square loop antenna has been designed for operation at 2.5 GHz. The antenna is loaded using a simple series combination of two lumped inductors and two interdigitated capacitors in order to realise inherent impedance matching at a given miniaturisation level with respect to a specified source impedance, without using any external matching network. The designed antenna has an overall size of 0.061λ0 × 0.061λ0, which is approximately 75.6% miniaturised in terms of total loop length and 94% miniaturised in terms of overall footprint. The designed antenna is fabricated and the corresponding impedance matching and radiation patterns are measured, which are found to be in reasonable agreement with their simulated counterparts. Moreover, an investigation with two closely spaced electrically small SLAs, one for transmitting and the other for receiving, is carried out in this work in pursuit of maximising the isolation, which plays a crucial role in the Tx/Rx systems.

Development and analysis of small Multi Input Multi Output antenna with better isolation for Frequency Range‐2 5th Generation band applications

SummaryA simple planar wideband four‐port MIMO antenna of size 2.75𝜆l × 2.75𝜆l × 0.04𝜆l (𝜆l is the wavelength when fl is 24.26 GHz) with high isolation that offers the 24.26 to 30.2 GHz bandwidth covering the 5G FR‐2 spectrums is proposed in this work. Total fractional bandwidth of 21.8% has been achieved that covers the n257 (26.5 to 29.5 GHz), n258 (24.25 to 27.5 GHz), and n261 (27.5 to 28.35 GHz) 5G spectrums. Popular rectangular radiator‐based 4‐port MIMO antenna with symmetric stubs loaded parallel to feed line and tapered semi‐circular cut in the lower corners of patch is incorporated that exhibits an excellent isolation that is below −27 dB through the entire spectrum and the extreme realized separation is −40 dB. The projected MIMO radiator is premeditated on RT/duroid 5880 of 0.508 mm depth and permittivity (εr) of 2.2. The maximum radiation efficiency and gain of the proposed antenna are 93.07% and 6.48 dBi, respectively. The MIMO antenna parameters such as envelope correlation coefficient (ECC) were achieved lesser than 0.003, diversity gain (DG) was achieved around 10 dB, channel capacity loss (CCL) was achieved lower than 0.15 bits/s/Hz, and mean effective gain (MEG) was achieved between −3.6 dB and −3 dB throughout the impedance band, which exhibit the excellent MIMO properties, and thus, the projected antenna is appropriate for 5G/beyond 5G wireless technologies.

3D‐structure coupled monopole designs with lower frequency resonance

AbstractIn this study, we investigated three‐dimensional configurations involving a monopole‐coupled wired ring, a hollow metallic cylinder, and wired helix spring to achieve resonance lower than quarter‐wave resonance. The resonance frequency of a quarter‐wave monopole, originally 2.05 GHz, was significantly lowered by 54.53% through effective coupling with a wired ring, and a quarter‐wave monopole properly coupled with a hollow metallic cylinder experienced a large decrease of 64.34%. The primary incentive for connecting a wired ring to a hollow metallic cylinder is to significantly reduce resonance frequency. Efforts were also made to lower resonance frequency in a wired helix spring with a length close to that of the wired ring, resulting in a substantial 78.83% reduction in resonance frequency. The −10 dB bandwidth was 14.63% for the quarter‐wave monopole, 27.21% for the monopole‐coupled wired ring, 33.71% for the monopole‐coupled hollow metallic cylinder, and 4.69% for the monopole‐coupled helix spring. The ka values for the monopole‐coupled wired ring, hollow metallic cylinder, and helix spring were 0.35, 0.27, and 0.16, respectively. Hence, these antennas can be classified as electrically small antennas. The achieved resonant frequencies have applications in various wireless communication scenarios. The experimental results from the fabricated prototype agree well with the simulation results.

Polarization conversion metasurface enabled broadband circularly polarized patch antenna

AbstractAssembling polarization conversion metasurface (PCM) and a simple patch antenna to realize a circularly polarized (CP) antenna with over 10% fractional bandwidth (BW) is a challenging task. A kind of PCM composed of S‐ring and grating structure that converts linearly polarized (LP) wave into CP wave in a broadband frequency from 8.74 to 12 GHz can address the challenge. The universality of the PCM in realizing antenna polarization conversion is verified by using a standard LP horn antenna. Then, we design a broadband LP rectangular patch antenna to demonstrate that the present PCM can be integrated with small antenna devices to achieve CP antenna. A broadband CP patch antenna with a 12.4% −10 dB BW and 11.3% 3 dB axial ratioBW is obtained. The antenna gain reaches 8.1 dB with the enhancement gain of 4.1 dB. The findings are very attractive for wireless communication, radar monitoring, and satellite systems because the proposed antenna has excellent broadband CP performances, simple structure, and easy fabrication.

Integrative implementation of scattering reduction and radiation enhancement for an electrically small antenna by subwavelength plasmas

The integrative design of scattering and radiation characteristics of antennas is of great practical significance for modern wireless communication. In this work, from the perspective of separate and cooperative modes, we comprehensively discussed the possibility of simultaneously and harmoniously implementing scattering suppression and radiation enhancement for an electrically small antenna by subwavelength plasmas. For the separate mode where the two functions are decoupled based on a two-layer structure, it is shown that an overdense–underdense core–shell density profile is preferred to achieve the optimal synergism between radiation enhancement and plasmonic-cloaking-induced invisibility, where the angular frequency of detecting waves (ωd) is supposed to be lower than that of communication signals (ωc). For the cooperative mode where the two functions are coupled within one plasma shell, the collaborative strategies between plasmonic-cloaking/Fano-resonance-induced invisibility and radiation enhancement are analyzed. The results show that the plasmonic-cloaking type requires ωd &amp;gt; ωc, while for the Fano-resonance type, ωd is larger/less than ωc when radiation enhancement is dominated by the symmetrically/asymmetrically coupled plasmon modes. Also, we provided clearer perspectives to distinguish the physical differences between plasmonic-cloaking and Fano-resonance-induced invisibility and between radiation enhancement underlying the two modes. Our results provide promising solutions for designing next-generation plasma-based tunable and intelligent stealth antennas.

Microwave ablation on ex vivo porcine pancreas: The influence of ablation parameters on ablation results and fat liquefaction.

The pancreas is adjacent to critical organs; excessive microwave ablation (MWA) can result in serious complications. The purpose of this paper is to provide the reference data of pancreas MWA for clinicians, analyze the ablation outcomes under different ablation parameters, and determine the critical temperature of pancreatic surface fat liquefaction outflow. Combinations of two power levels (30 W and 55 W), three antenna diameters (1.3 mm, 1.6 mm, and 1.9 mm), and three ablation times (1 min, 1.5 min, and 2 min) were applied to an ex vivo pig pancreas. Temperature measurements were taken at four thermocouple points. The center point is located 5 mm horizontally from the antenna slot, with a temperature measurement point located 5 mm above, below, and to the right of the center point. Main effect analysis and variance analysis were used to quantify the influences of each factor on the ablation outcomes. At 30 W, the antenna diameter contributing the most at 48.5%. At 30 W-1.3 mm-1 min, the spherical index (1.41) is closest to 1. At 55 W, the coagulation zone size was almost only affected by the ablation time, with a contribution rate of 28.7%, the temperature at point C exceeds point B. On the surface of the ex vivo porcine pancreas, the fat outflow temperature was 54ã. Ablation combinations with low power, short duration, and small antenna diameter results in a more nearly spherical coagulation zone. When performing MWA on the pancreas, it is advisable to avoid areas with higher fat content, while keeping the pancreatic surface temperature below 54°C.

An Electrically Small Antenna With Wide Tuning Capability for UHF Applications

An Electrically Small Antenna With Wide Tuning Capability for UHF Applications

Class-E, active electrically small antenna with enhanced bandwidth-efficiency product and high radiated power at the high-frequency (HF) band

Antennas operating at the high-frequency (HF) band (3–30 MHz) are frequently electrically small due to the large wavelength of electromagnetic waves (10–100 m). However, the bandwidth-efficiency products of passively matched electrically small antennas (ESAs) are fundamentally limited. Wideband HF waveforms using bandwidths of 24 kHz or more have recently received significant attention in military communications applications. Efficiently radiating such signals from conventional passive ESAs is very challenging due to fundamental physical limits on bandwidth-efficiency products of ESAs. However, active antennas are not subject to the same constraints. In this work, we present the design and experimental characterization of a high-power, class-E active ESA with enhanced bandwidth-efficiency product compared to that of passively matched ESAs. Specifically, the proposed class-E active ESA can radiate wideband HF signals with bandwidths of 24 kHz or more at 3 MHz (fractional bandwidths of ≈1%–4%), with total efficiencies ranging from 40% up to 80% depending on the modulation type and radiated power levels approaching 100 W. Our approach uses a highly efficient, integrated class-E switching circuit specifically designed to drive an electrically small, high-Q HF antenna over a bandwidth exceeding 24 kHz at 3 MHz. Using a high-Q RLC antenna model, we have successfully demonstrated wideband binary ASK, PSK, and FSK modulations with the proposed class-E active ESA. Experimental results indicate that the bandwidth-efficiency product of this class-E active ESA is 5.4–9.8 dB higher than that of an equivalent passive design with the same data rate and bit-error-rate.

Rapid construction of electrically small spherical and cylindrical antennas

Using three-dimensional (3D) printing technologies, two of the folded electrically small antennas (FESAs) are simulated, fabricated, and evaluated. A folded spherical helix and a cylindrical helix are chosen as a part of the verification of this fabrication process. FESAs are constructed on the polylactic acid (PLA) material-based 3D printed support and the effect of this extra support on antenna performances are discussed. The similarity index between measured and simulated performance parameters of both spherical helix and cylindrical helix shaped FESAs is high. The fabrication process is faster, dependable and provides the design flexibility of any complex-shaped spiral antenna.