Printed multi-turn loop antenna for RF biotelemetry

Abstract: This paper is about the optimization of a small circular loop antenna using a Genetic Algorithm (GA) to significantly enhance its radiation efficiency for operation at 38.22MHz. Traditional small loop antennas are known for their poor radiation characteristics due to extremely low radiation resistance and high conductor losses, rendering them unsuitable for practical RF communication without a complex matching network. This research applies a Genetic Algorithm implemented in MATLAB to optimize two critical design parameters: the loop radius and the wire radius (thickness). An analytical electromagnetic model was developed to compute radiation resistance, conductor loss resistance (accounting for skin effect and radiation efficiency. The objective function was designed to maximize efficiency by minimizing its negative value. Results from the GA were analysed using convergence plots and two-dimensional contour maps, revealing the efficiency distribution across the design space. The optimized antenna achieved a loop radius of 0.02458m and a wire radius of 0.0099m, leading to a dramatic improvement in radiation efficiency from 0.02% (traditional design) to 99.4%. Additionally, gain and bandwidth performance were significantly improved, making the antenna suitable for terrestrial RF applications. The study demonstrates that evolutionary optimization techniques like GA can overcome the inherent limitations of traditional small loop antennas, by intelligently navigating the design space, the Genetic Algorithm identified configurations that would be difficult to obtain through manual tuning. These findings highlight the practical potential of computational intelligence in modern antenna design particularly for compact efficient and broadband systems in wireless and communication technologies.

Demands for extremely small antennas to be used in radiofrequency identification tags for ubiquitous communication have increased. Examples of very small antennas utilizing meander line structures are seen. To date, important studies have been carried out on basic design and on improvement of the radiation efficiency by a folded configuration. Most of the structures studied have dimensions of more than 0.1 wavelength. For the demands of ultracompact antennas, this paper deals with meander line antennas whose dimensions are less than 0.1 wavelength. First, the parameters for resonant configurations are derived for antennas with dimensions of 0.1 to 0.025 wavelength. Next, the radiation resistance and the ohmic resistance are studied in the folded structures. First, through a transmission line model analysis, it is shown that the step‐up ratios of radiation and ohmic resistances in the case of folded structures are different. In addition, these resistances that are basic values of electrical performances are derived through electromagnetic simulations. Further, in order to confirm the validity of the numerical results and the realizable performance, antennas with dimensions of 0.1 and 0.05 wavelength were fabricated. Electrical characteristics are compared, and good agreements are found. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(8): 1–11, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20204

The fundamental effects of superstrate (cover) materials on printed circuits antennas are investigated. Substrate-superstrate resonance conditions are established which maximize antenna gain, radiation resistance, and radiation efficiency. Criteria are determined for material properties and dimensions for which surface waves are eliminated and a radiation efficiency due to substrate-superstrate effects of e_{s} = 100 percent is obtained. Criteria for nearly omnidirectional \bar{H} -plane patterns and nearly omnidirctional \bar{E} -plane patterns are presented. Finally, a general criterion is given for choosing a superstrate to optimize efficiency for the important case of nonmagnetic layers with the antenna at the interface.

Optical antenna collection efficiency is limited by material loss, particularly dissipation in optical metals. We investigate the radiation resistance and Ohmic resistance in transmitting infrared (IR) dipole antennas by considering the concepts of input impedance, radiation efficiency and dispersion of metals in the antenna. Then by applying antenna reciprocity, the receiving properties of IR antennas are explored. We analyze the power absorbed by a nickel (Ni) microbolometer load connected with a half-wave dipole antenna and a full-wave dipole antenna. By tuning the load impedance we are able to impedance match to IR dipoles in order to show enhanced absorption efficiency when radiation resistance dominates over Ohmic loss.

An electrically small planar passive UHF-RFID tag based on an edge-coupled split ring resonator (EC-SRR) antenna is presented in this work. In order to explore the potentiality and limitations of the SRR antenna and to aid the tag design, an analytical study of the SRR radiation properties at its fundamental resonance is presented for the first time. Radiation resistance, efficiency, polarization, bandwidth, and impedance matching with the radio-frequency identification (RFID) application-specific integrated circuit (ASIC) are treated in the study. Based on such analysis, the tag design process is presented, and a tag prototype of size $30\;\text{mm}\times30\;\text{mm} (\lambda_{0}/11\times\lambda_{0}/11)$ is designed to operate in the North-American UHF-RFID band (902–928 MHz) and manufactured. The measured read range is in good agreement with the simulation and reaches 9.3 m at 911 MHz. The tag also features a mitigation of the blind spots, providing a minimum measured read range of 4.2 m.

In this letter, an electrically small mu-negative (MNG) zeroth-order resonance (ZOR) antenna with multilayered conductor is presented. To improve the radiation efficiency, the structure of the MNG ZOR antenna is determined to increase radiation resistance by reducing the current cancellation between the conductor strip of the antenna. In particular, the multilayered conductor is employed to enhance the radiation efficiency by reducing ohmic loss. The MNG ZOR antenna using multilayered conductor (kr = 0.182) has a measured 3-dB fractional bandwidth of 0.846% and radiation efficiency of 18.66%.

Whistler wave radiation from a loop antenna located in a cylindrical duct with enhanced plasma density is considered in the case where the wave frequency is less than the lower hybrid frequency. Using the full-wave formulation, the total radiation resistance and the partial radiation resistances corresponding to guided eigenmodes of such a duct and unguided waves radiating to the background magnetoplasma are calculated and analyzed as functions of the plasma and source parameters. The emphasis is placed on the radiation characteristics of the considered source in the presence of an artificial near-antenna duct that can be created during active experiments in the ionosphere. Conditions are revealed under which the total radiation resistance is predominantly determined by the excitation of the eigenmodes of the duct. It is shown that the presence of an enhanced density duct can lead to a notable increase in the radiation resistance of a loop antenna in the discussed frequency range even if the duct is rather narrow and capable of guiding only a single low-order eigenmode. The results obtained can be helpful in understanding the basic features of excitation of the ducted whistlers and planning the related ionospheric and laboratory experiments.

The fundamental properties of carbon nanotube (CN) loop antennas have been determined using numerical modeling in both transmitting and receiving modes. The variation of the antenna impedance, reflection coefficient, radiation efficiency, Q-factor, and extinction cross section with varying loop radii was determined numerically using method-of-moment simulations incorporating the quantum mechanical conductivity of carbon nanotubes. Contrary to metallic loop antennas (well known for their inductive input impedance), the carbon nanotube loops with a large circumference show capacitive reactance over the entire frequency range. Therefore, one cannot make CN loop to act as an inductive radiator or even a simple inductor (when ka → 0) if the circumference is beyond ~56 μm. However, the carbon nanotube loops with circumference smaller than ~56 μm exhibit properties similar to ordinary loop antennas by going through antiresonance and then resonance regions. Despite the dispersive conductivity model, carbon nanotube loop antennas possess normalized dispersion relation, which is linearly related to the frequency.

A novel internal meandered loop antenna for multiband operation in the mobile phone has been proposed. Strong effects of the user's hand on the impedance and radiation characteristics of the antenna have been observed. Results indicate that, when the user's hand is close to or cover a certain portion of the antenna, large decrease in the antenna's radiation efficiency and great distortion in the antenna's radiation pattern for both the unbalanced and balanced modes will occur. On the other hand, when the user's hand holds the mobile phone with a large distance to the proposed antenna, smaller decrease in the radiation efficiency has been observed for the antenna's self-balanced mode than the antenna's two other unbalanced modes.

In this work, a versatile, low mutual coupling, circularly polarized Multiple-Input-Multiple-Output (MIMO) antenna is presented on a flexible polyimide substrate, specifically designed for multiband on-body wireless communication applications. The antenna is implemented on a compact 30 × 50 mm2 polyimide substrate, making it lightweight, conformal, and highly suitable for wearable and body-centric systems. The patch and ground planes are modified with several structural enhancements to improve the performance and to achieve circular polarization. The ring-shaped patch elements were developed for proper impedance matching, and the T shaped rectangular stub on the ground plane, along with a rectangular slot at the centre, are incorporated for enhanced isolation and mutual coupling suppression. The propounded antenna structure results in an efficient multiband performance at 1.4, 3.1, and 4.7 GHz operating at bands of On-Body Wireless Medical Telemetry, Fifth-Generation (5G), and Military Communication Applications. The presented MIMO has high radiation efficiency, good Total Active Reflection Coefficient (TARC) and very low Envelope Correlation Coefficient (ECC) and a Diversity Gain (DG) near 10 dB, which verifies the excellent MIMO performance. Furthermore, the low Specific Absorption Rate (SAR) of the antenna makes it safe for wearable body-centric applications. The mechanical flexibility of the proposed antenna enables its steady performance even under bending and deforming conditions, which suggests its reliability in practice. With the compact size, multiband, reduced mutual coupling, and reliable operation, the proposed antenna provides an efficient and technologically advanced solution for next-generation 5G systems, Internet of Things (IoT)-based biomedical sensing, military communications, and smart wearable devices.

A novel printed antenna configured with circular loop geometry of approximately one wavelength perimeter is designed for operation at 5.8 GHz with near omni-directional radiation pattern. The loop is partitioned into multiple segments and loaded with capacitive elements at selected locations so as to decrease phase variations in the current flow and thereby increase the radiation efficiency. A total of five capacitors are used to achieve stable current flow, resulting in phase variations of <; 12°. The performance of the loop antenna is first analyzed as a transmitter in free space using a method of moments (MoM) solver for thin-wire structures, and then validated using 3-D finite element method (FEM) and MoM solvers. The simulated radiation pattern for the thin-wire model in the plane of the loop is close to omni-directional with directive gain of 1.46 dBi. A printed circuit antenna model is then designed with alternating top- and bottom-layer conductors of annular geometry on a thin substrate, with regions of conductor overlap functioning as physical capacitors. Simulations of the printed antenna demonstrate omni-directional radiation in the azimuthal plane, with peak directive gain of 1.66 dBi, peak directivity of 1.69 dB, radiation efficiency of 0.98, and input impedance close to 50 Ω. Performance measurement data for a fabricated printed circular loop antenna (in process) will be shown during presentation for comparison and validation.

This letter presents the design and performance of an electrically small loop antenna standing on the compact ground in wireless sensor package. The loop antenna works at 434 MHz Industrial, Scientific, and Medical (ISM) band with the size 18 ×18 ×12 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The performance is simulated complied with measurement. Over 5 MHz of -10-dB impedance bandwidth and more than 22% radiation efficiency in the frequency are achieved. Moreover, one essential step for the electrically small loop antenna measurement is proposed. The small volume makes the proposed miniaturization technique possible for the sensor package, which would have significance for the rapidly increasing Internet of Things (IOT) industry.

The capability to assess the biomechanical properties of living bone is important for basic research as well as the clinical management of skeletal trauma and disease. Even though radiodensitometric imaging is commonly used to infer bone quality, bone strength does not necessarily correlate well with these non-invasive measurements. This paper reports on the design, fabrication and initial testing of an implantable ultra-miniature multi-axis sensor for directly measuring bone stresses at a micro-scale. The device, which is fabricated with CMOS-MEMS processes, is intended to be permanently implanted within open fractures, or embedded in bone grafts, or placed on implants at the interfaces between bone and prosthetics. The stress sensor comprises an array of piezoresistive pixels to detect a stress tensor at the interfacial area between the MEMS chip and bone, with a resolution to 100 Pa, in 1 s averaging. The sensor system design and manufacture is also compatible with the integration of wireless RF telemetry, for power and data retrieval, all within a 3 mm × 3 mm × 0.3 mm footprint. The piezoresistive elements are integrated within a textured surface to enhance sensor integration with bone. Finite element analysis led to a sensor design for normal and shear stress detection. A wired sensor was fabricated in the Jazz 0.35 µm BiCMOS process and then embedded in mock bone material to characterize its response to tensile and bending loads up to 250 kPa.

Vibration and sound radiation of a piano soundboard (6-ft grand) were studied using modal analysis and surface intensity methods in the frequency region below 210 Hz. The first mode (49.5 Hz) looked like a trampoline. The second (76.5 Hz) and third (85.3 Hz) modes were the first breakup modes in the length direction. The fourth mode (116.1 Hz) showed the first breakup mode in the width direction. There were seven major resonances below 210 Hz with an average modal density of 1/25 Hz. The radiation was very inefficient below 90 Hz and the surface intensity method was not adequately accurate below this frequency. The radiation pattern (intensity distribution) showed some similarity to the forced vibration pattern for the lower-order modes (but not for the higher-order modes). On an average basis, the radiation efficiency (the ratio of the power radiated from the upper side of the soundboard to the mechanical input power) was approximately 15% above 100 Hz. A normalized radiation resistance was also used to evaluate the efficiency of radiation. A comparison of the normalized radiation resistance to the volume velocity confirmed that the interaction among the sound radiated from different areas on the soundboard is the major cause of the large fluctuation in the normalized radiation resistance.

Efficiency is a critical antenna parameter that describes how well an antenna emits and accepts electromagnetic signals. When an antenna has poor efficiency, the input power is only partially radiated and is primarily wasted due to internal losses such as conduction, dielectric, mismatching, and several other losses within the antenna. In order to enhance signal quality, a communication system requires an antenna with high efficiency and gain. The fifth‐generation wireless system will use millimeter wave spectrum along with sub 1 GHz and sub 6 GHz bands to fulfill wide bandwidth, ultra‐high‐speed, and low latency requirements of 5G communication. Compact low‐profile antenna with high radiation efficiency, high gain, and wideband characteristics are required to support bandwidth requirements of 5G and mitigate the signal degradation due to high link losses caused by environmental absorptions at the millimeter‐wave (mm‐wave) spectrum. Compact planar antennas have become an important part of modern wireless communication equipment, but these antennas are associated with many issues like low efficiency, poor gain, small radiation resistance, and high cross‐polarization, which is due to the increased conductor and dielectric losses, surface wave losses and so forth. Various techniques need to be employed for the improvement of the efficiency of the antenna, which results in high gain low loss antenna characteristics. This article presents the survey of various efficiency enhancement techniques for 5G antennas and a review of structures that provides good radiation efficiency for 5G communications.