Loop Antenna Research Articles

Series-fed Loop Antenna Arrays with an Expanded Bandwidth of Circular Polarization

Series-fed Loop Antenna Arrays with an Expanded Bandwidth of Circular Polarization

A Leaky-Wave Analysis of Resonant Bessel-Beam Launchers: Design Criteria, Practical Examples, and Potential Applicationsat Microwave and Millimeter-Wave Frequencies.

Resonant Bessel-beam launchers are low-cost, planar, miniaturized devices capable of focusing electromagnetic radiation in a very efficient way in various frequency ranges, with recent increasing interest for microwave and millimeter-wave applications (i.e., 3-300 GHz). In recent years, various kinds of launchers have appeared, with different feeding mechanisms (e.g., coaxial probes, resonant slots, or loop antennas), field polarization (radial, azimuthal, and longitudinal), and manufacturing technology (axicon lenses, radial waveguides, or diffraction gratings). In this paper, we review the various features of these launchers both from a general electromagnetic background and a more specific leaky-wave interpretation. The latter allows for deriving a useful set of design rules that we here show to be applicable to any type of launcher, regardless its specific realization. Practical examples are discussed, showing a typical application of the proposed design workflow, along with a possible use of the launchers in a modern context, such as that of wireless power transfer at 90 GHz.

IMPROVING THE EDDY CURRENT IDENTIFIER OF METALS BASED ON THE CORRELATION APPROACH

Context. The article considers the problem of improving the eddy current device for metal identification on the basis of the correlation approach. This approach is convenient for the accumulation of a database of known leading materials, as well as for the comparison of the signal from an unknown metal object with the available standards in the database. The proposed approach allows to determine the type of metal from which the sample is made, without damaging its surface.
 Objective. The aim of the work is the identification of metals by type on the feedback signals from the eddy current converter, due to the identification of new informative features and the creation of a database of images of metals.
 Method. The paper presents the results of an experimental study of the proposed approach to increase the reliability of identification of metal objects that are detected using an eddy current device. These studies are conducted on the basis of a radio system that operates on the eddy current principle and has low-frequency magnetic loop antennas. The eddy current method allows the identification of metals by type remotely and without damaging their surface, in contrast to X-ray fluorescence, optical emission or chemical methods. A correlation approach for processing the response signal spectrum from a hidden metal object is proposed. The correlation approach allows to increase the reliability of the identification of metals by type when processing the signal in the spectral region based on the Fourier transform. Studies have been conducted on the example of metals that have similar spectral characteristics (silver, gold, lead). The updated approach allowed to increase the percentage difference between the information parameters of signals – responses from 1.87% to 5.02% for silver and gold, from 2.24% to 4.34% for silver and lead and from 0.36% to 0.7% for gold and lead.
 Results. The developed radio system is a laboratory model, which consists of an analog part and a digital one. The analog part is an antenna unit, a signal amplifier and a bandpass filter, a digital part – a microcontroller with an ADC for digitizing and transmitting data to a laptop, which software implements the proposed approaches to signal processing. The paper experimentally confirmed the possibility of using a radio engineering system to solve the problem of metal identification within a subset of nonmagnetic and magnetic materials.
 Conclusions. The development of modern eddy current devices is aimed at increasing the reliability of the identification the hidden metal objects, which is relevant in geophysical exploration, archeology, and law enforcement agencies in the search for hidden non-ferrous metals. The development and improvement of such systems includes both the development the hardware and the discovery new information parameters in the feedback signals from metals. One such direction may be the correlation approach to signal processing in the spectral region.

Assessment of the effectiveness of fish passage through the vertical-slot fishway at the main dam on the longest Baltic River

Abstract In 1969, a dam was constructed on the Vistula River, the longest in the Baltic drainage basin, 276 km from its estuary, which resulted in the collapse of migratory fish populations throughout the drainage basin. The existing, ineffective fishway was rebuilt in 2014. Monitoring at the new fishway indicated that 24 fish species used it, and over a period of five years the number of individuals fluctuated from nearly 4,000 to over 23,000. Radio frequency identification (RFID) technology was used to investigate 12 fish species, mostly vimba and bream, passing through the fishway. Fish caught in a trap in the upper part of the fishway were tagged with PITs and then released below the dam. Returning fish were recorded by four loop antennas. Of the 877 fish that were tagged, 13% returned to the fishway mostly on the first and fourth days following release. Of the fish that returned, 30% turned back while passing through the fishway: 30% vimba and 52% bream. The transit time of vimba and bream did not depend on fish size or the time after which they returned. Overall, estimated fishway efficiency based on the migration of the tagged fish was high.

MICS-Band Helical Dipole Antenna for Biomedical Implants

This letter presents the design, analysis, and measurement of a miniaturized ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{7}\!\times\!\text{7.5}$</tex-math></inline-formula> mm) electrically small helical dipole antenna with the introduction of a flexible magnetic sheet of high permittivity and permeability for biomedical implants. The proposed helical dipole, operating at 402–405 MHz Medical Implant Communication Services (MICS) band, supports wider bandwidths (10 dB bandwidth: simulated 33 MHz; measured 49.5 MHz) compared to the state-of-the-art designs. In addition, as a hybrid between a magnetic loop antenna and an electric dipole antenna and operating in the normal mode with small radian (ka < 0.36), enhanced radiation efficiency has been achieved as a result of the magnetic sheet. Measured in-body to on-body transmission verifies the antenna performance.

Enhancing Spin-Based Sensor Sensitivity by Avoiding Microwave Field Inhomogeneity of NV Defect Ensemble.

The behavior of the magnetic field sensitivity of nitrogen-vacancy (NV) centers as a function of microwave power and the inhomogeneous distribution of MW fields was systematically studied. An optimal structure for exciting spin structures by MW signals was designed using two parallel loop antennas. The volume of the homogeneous regions was approximately 42 mm3, and the associated diameter of the diamond reached up to 5.2 mm with 1016 NV sensors. Based on this structure, the detection contrast and voltage fluctuation of an optically detected magnetic resonance (ODMR) signal were optimized, and the sensitivity was improved to 5 nT/√Hz. In addition, a pulse sequence was presented to fully eliminate the MW broadening. The magnetic field sensitivity was improved by approximately one order of magnitude as the π-pulse duration was increased to its coherence time. This offers a useful way to improve the sensitivity of spin-based sensors.

The role of ion magnetization on plasma generation in a magnetic nozzle rf device

Two dimensional mappings of the floating potential, Ar II emission and ion saturation currents are used to characterize an 80 cm long magnetized rf plasma column. The data brings new evidence supporting that the level of ion magnetization under the rf loop antenna plays an important role for the efficient generation of plasma over an extended region when the magnetic nozzle is sufficiently separated from the antenna. Densities up to 10^{18} m^{-3} and a blue core are observed for an rf power of 200 W and magnetic fields above 400 G when ions are magnetized. The local wall charging under the antenna is probed and observed to change coherently with the local ion magnetization and seems critical to the global creation and transport of energetic electrons, which are indirectly observed far from the antenna when the ion Larmor radius is much smaller than the glass tube radius over the entire region of investigation.

915 MHz Miniaturized Loop Conformal Antenna for Capsule Endoscope

High-performance miniaturized antennas are one of the goals that have been pursued in the design of wireless communication systems for implantable medical devices. In this article, a 915 MHz novel-shape loop antenna conforming to the inner wall of the capsule is developed by comprehensively adopting meander and symmetrical structure patch, folding technique, and vector current reversal technique. Through electromagnetic simulation, testing, and experimentation, the antenna shows good characteristics such as small size, ultra-wideband, circular polarization, strong robustness, and safety. Specific performances include the following: 1) the size of the developed miniaturized loop conformal antenna is only 30.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 0.05 mm and the maximum gain is −21.5 dBi at 915 MHz, which solves the problem of low gain due to the small antenna radiation area; 2) the antenna has a 4.5 GHz ultra-wideband impedance matching bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10$ </tex-math></inline-formula> dB) from 0.5 to 5 GHz. Even if the parameters such as the implantation depth and the thickness of the capsule shell change, or there exists a wireless power transfer system, the antenna can still cover the required frequency band with strong robustness; and 3) the specific absorption rate (SAR) of human tissues radiated by the antenna is far lower than the safety limit in IEEE standards and ICNIRP guidelines. The experimental platform using pork to simulate human tissues was built for antenna performance testing and communication testing. The measurement results verified the good resonance performance, radiation characteristics, and omnidirectionality of the developed antenna. The antenna link loss model is also given, which has been used in wireless communication and localization.

Effects of feed gap arrangements of loop antennas on site validation for EMI measurements below 30 MHz

Effects of feed gap arrangements of loop antennas on site validation for EMI measurements below 30 MHz

A Loop Antenna Array With an Enlarged Near-Field Interrogation Zone for UHF RFID Near-Field and Far-Field Applications

This letter presents a loop antenna array for ultrahigh frequency near-field and far-field radio frequency identification (RFID) reader applications. The antenna array consists of several microstrip collinear loop antennas, and each loop antenna is composed of several periodic radiating units. By deploying microstrip collinear radiating units, a novel loop antenna with in-phase radiating currents is realized, which generates a strong and uniform magnetic field over a large interrogation area and a horizontally polarized omnidirectional radiation. By configuring the array antenna, the magnetic fields distribute on the entire antenna array and create an enlarged near-field reading area. The far-field coverage is enlarged by the superposition of omnidirectional radiation. The antenna array is simulated and validated with a four-element prototype made on FR-4 substrates. The antenna array is measured to have a −10 dB impedance bandwidth from 802 to 963 MHz with an enlarged near-field reading volume of 280 × 280 × 540 mm and a far-field gain of 6.66 dBi at the UK RFID band.

Basic characteristics of magnetic field antenna factor of loop antennas for EMI measurements

Basic characteristics of magnetic field antenna factor of loop antennas for EMI measurements

High-fidelity quantum information transmission using a room-temperature nonrefrigerated lossy microwave waveguide

Quantum microwave transmission is key to realizing modular superconducting quantum computers and distributed quantum networks. A large number of incoherent photons are thermally generated within the microwave frequency spectrum. The closeness of the transmitted quantum state to the source-generated quantum state at the input of the transmission link (measured by the transmission fidelity) degrades due to the presence of the incoherent photons. Hence, high-fidelity quantum microwave transmission has long been considered to be infeasible without refrigeration. In this study, we propose a novel method for high-fidelity quantum microwave transmission using a room-temperature lossy waveguide. The proposed scheme consists of connecting two cryogenic nodes (i.e., a transmitter and a receiver) by the room-temperature lossy microwave waveguide. First, cryogenic preamplification is implemented prior to transmission. Second, at the receiver side, a cryogenic loop antenna is placed inside the output port of the waveguide and coupled to an LC harmonic oscillator located outside the waveguide. The loop antenna converts quantum microwave fields to a quantum voltage across the coupled LC harmonic oscillator. Noise photons are induced across the LC oscillator including the source generated noise, the preamplification noise, the thermal occupation of the waveguide, and the fluctuation-dissipation noise. The loop antenna detector at the receiver is designed to extensively suppress the induced photons across the LC oscillator. The signal transmittance is maintained intact by providing significant preamplification gain. Our calculations show that high-fidelity quantum transmission (i.e., more than 95%) is realized based on the proposed scheme for transmission distances reaching 100 m.

Battery-Less NFC Potentiostat for Electrochemical Point-of-Care Sensors Based on COTS Components.

This work studies the feasibility of using a battery-less Near-Field Communication (NFC) potentiostat for the next generation of electrochemical point-of-care sensors. A design based on an NFC microchip, a microcontroller, and a custom potentiostat based on an operational amplifier is presented. A proof-of-concept prototype has been designed and used to quantify glucose concentration using commercial glucose test strips from chronoamperometry measurements. The device is harvested and the sensor is read using a mobile phone. The prototype uses an antenna loop covered with ferrite sheets to ensure stable operation of the electronics when the mobile phone is used as reader. The use of ferrite reduces the detuning caused by the proximity of the metal parts of the mobile phone. A comparison with a commercial glucometer device is provided. Results obtained using a commercial glucometer and those provided by the proposed potentiostat show an excellent agreement.

Closely arranged self‐decoupled MIMO antenna group using orthogonal mode and pattern diversity for 5G mobile terminals

In this article, a novel self-decoupling method for closely arranged multi-unit antenna array design is proposed. The orthogonal mode and the pattern diversity are adopted to weaken the electromagnetic coupling between the multi-antenna elements. To verify the proposed self-decoupling concept, a closely arranged 4-port antenna group consisting of dual antenna pairs is designed. One of the antenna pairs is composed of overlapping loop antenna and monopole, and the other antenna pair shares a radiator, which are arranged on the upper and lower sides of the metal ground respectively. The proposed 4-port antenna group exhibits good isolation and complementary patterns without adding any extra decoupling structures. Based on the proposed self-decoupled 4-port antenna group, a 16 × 16 multiple-input multiple-output (MIMO) antenna array is constructed. The simulated and measured results show that the proposed 16 × 16 MIMO array has good antenna performance, such as isolation better than 15 dB, efficiency higher than 51% and channel capacity about 73 bps/Hz with 20 dB SNR. The proposed design concept is a great choice for highly integrated multi-antenna array and 5G mobile terminal.

Multibeam antennas with customized elevation angles based on near-field magnetic field coupling of metamaterials

In this paper, we propose the design of multibeam antennas with customized elevation angles based on near-field magnetic field coupling of metamaterials. The antenna consists of a monopole feed and four identical metamaterial transmission-line (MTL) structures surrounding the feed. The MTL structure is composed of two pairs of broadside-coupled omega rings (BCORs) that are connected by two straight strip-lines. Under such a framework, magnetic fields within the near-field zone of the monopole feed can be coupled efficiently by the inner BCOR, converted to travelling waves along the double strip-lines, guided toward the outer end of the MTL structure, and radiated by the outer BCOR like a loop antenna. Due to travelling wave nature of the MTL structure, there is phase lag along the MTL structure and the radiation main lobes are tilted towards the outward direction. By arranging several MTL structures around the feed monopole, multi-beam directional radiation can be realized. More interestingly, by adjusting structural parameters and pitch angles of the MTL structures, elevation angle of the radiation main lobes can be customized. To validate the design, we simulated, fabricated and measured four prototypes with pitch angles 0°, 15°, 30° and 45°. Both the simulated and measured results verify the design and show that multiple-beam radiation with customized elevation angle can be obtained. This work provides an alternative method of designing multi-beam antennas and may find applications in communication, surveillance, etc.

Characterization of a 2 MHz-radiofrequency-driven magnetically expanding plasma source

A radio frequency (rf) plasma source is operated at 2 MHz under an expanding magnetic field. The source consists of a 14-cm-diameter and 25-cm-long source tube wound by a seven-turn rf loop antenna powered via an impedance matching circuit. The efficient rf power transfer to the plasma is demonstrated, and the high-density plasma above 1012 cm−3 is successfully obtained for a kW level of the rf power. The radial density profile having a center peak is observed both in the source and in the expanding magnetic field; it does not show the conical density structure previously observed in 13.56 MHz rf sources. This implies that the electron heating layer is changed by lowering the driving frequency. Even in the source operated at 2 MHz, the measurement of the ion energy distribution shows the presence of the supersonic ion beam as well as the sources operated at higher frequencies, e.g., 13.56 MHz in the previous studies.

Dynamic analysis of the effect of mesh tension on the deployment process of loop antenna

In orbit deployment and profile maintenance are the most important functional requirements in the development of loop antenna If the antenna cannot be deployed in orbit, it will lose the signal transmission function, and the profile in orbit holding function is related to whether the antenna can stably transmit electromagnetic signals. The mesh tension (main mesh tension, rear mesh tension and tension arrays tension) is the key means to maintain the profile stability in orbit. At the same time, it is also closely related to the rod load and the maximum motor driving force in the process of antenna deployment. Based on the theory of flexible multi-body dynamics, the dynamic modeling of the deployment process of ten meter loop deployable antenna is established in this paper On this basis, the influence of mesh tension on the deployment dynamics of loop antenna is analyzed by using the control variable method, and its related variation law is obtained. This study can provide guidance for the tension adjustment in the profile adjustment stage of the ring antenna, so as to shorten the development cycle, and can also predict the deployment of the antenna in orbit.

Small-Size Planar WWAN/LTE Range Loop Antenna Manufactured Using a New Composite Material for 5G-Technology Applications

Small-Size Planar WWAN/LTE Range Loop Antenna Manufactured Using a New Composite Material for 5G-Technology Applications

A Planar Bidirectional Circularly Polarized Antenna Using Orthogonal Magnetic Dipoles Without Extra Phase Shift Line

A planar bidirectional circularly polarized (CP) antenna using orthogonal magnetic dipoles (OMDs) without an extra phase shift line is proposed in this work. It consists of a rectangular microstrip magnetic dipole antenna (MMDA) and a loop radiator with two arms directly connected to the open edge of MMDA. The working principle is revealed by the equivalent sources model to provide a clear physical insight at first. The theoretical investigations imply that by controlling the width and the feed locations of the loop antenna on the aperture, the phase and magnitude for CP radiation can be realized in both endfire and backfire directions without introducing an additional phase shift line structure. For demonstration, one antenna prototype is designed and fabricated. The experimental results indicate that an overlapping bandwidth of 5.91% from 2.30 to 2.44 GHz is attained. Compared with the counterpart using OMDs, the proposed antenna exhibits a low design complexity and improved gains of 3.56/1.83 dBic in the endfire/backfire directions.

Wideband self-decoupled MIMO antenna element based on coupled-loop antenna for 5G smartphones

A novel wideband self-decoupled loop-coupled antenna element is proposed for the fifth-generation (5G) multiple-input multiple-output (MIMO) smartphones. The proposed loop-coupled antenna element generates two resonance modes of 0.75 and 1 λ. With the help of these two resonance modes, a wide bandwidth is achieved. The self-decoupled performance is realized by loading the loop antenna element with coupled lines. The common/differential mode theory is used to analyze and guide the antenna design to clarify the self-decoupling principle. At the same time, miniaturization of the proposed antenna element is also studied. The antenna element provides good isolation and diversity/multiplexing performances over N77/N78/N79 bands. An 8-port MIMO antenna is constructed using the proposed antenna element. The MIMO antenna is simulated, manufactured, and tested to verify and evaluate the performance metrics, such as isolation, envelope correlation coefficient, efficiency, and spatial multiplexing efficiency. The test results are in good agreement with the simulated ones.