Normal Mode Helical Antenna Research Articles

Performance regulation of high-precision wireless passive yarn sensor based on normal mode helical dipole antenna

Stable and reliable sensing performance was required for high-precision wireless passive yarn sensor based on normal mode helical dipole antenna (NMHDA). The actual helical pitch of NMHDA was non-uniform due to manufacturing process, and the previous equivalent impedance model for uniform NMHDA, i.e., wire-loop model, was oversimplified, resulting in inaccurate predicted reactance and sensing performance of yarn sensor. This work combined the circular polarization principle and the asymmetric structure of non-uniform NMHDA to build the wire-loop-wire model. Based on the wire-loop-wire model, the parametric expression of NMHDA impedance and resonant frequency were obtained, and the results predicted by wire-loop model and wire-loop-wire model were compared with the measured one. Furthermore, to demonstrate the practicality of wire-loop-wire model and parametric resonant frequency expression, the impact of helical pitch uniformity on resonant frequency was discussed in terms of the statistical characteristics of prototype helical pitch, and also the parametric expression was applied to design wireless passive yarn sensors with expected working property. It was found that the wire-loop-wire model incorporating the asymmetric structure accurately described the impedance characteristics of the NMHDA with non-uniform helical pitches, and the maximum predicted deviation of resonant frequency was reduced to 1 MHz. The steady long reading range (19.42 ± 0.09 m) of wireless passive yarn sensors prototype demonstrated the capacity of wire-loop-wire model in designing high-precision sensor. Generally, this paper successfully built the wire-loop-wire model for NMHDA with non-uniform helical pitches, and provided a practical tool for designing e-textile devices with NMHDA.

Design of Normal Mode Helical Antenna for Seawater Application

To overcome the substantial propagation loss in the ocean, a low frequency band should be chosen when contemplating radio wave communication.Then, the antenna used at the portable radio equipment should be very small compare to the wavelength. For the miniaturized antenna, the normal mode helical antenna(NMHA) is suitable because of achieving high efficiency. In this paper, design method of NMHA in the seawater condition (r=81, =4) is explained. The frequency bands of 100MHz and 15MHz are selected. The self-resonant structures are determined based on the theoretical equation. Electrical characteristics such as resonant frequency, input impedance, VWSR and antenna efficiency are obtained through simulation by FEKO simulator. Electromagnetic simulation model is formed by taking into account the practical experimental condition. At 100MHz and 15MHz, resonances are ensured for antenna diameter lengths of 6.83 cm and 12.2 cm respectively. Input resistance of 27.15and 94.14, antenna efficiencies of -14.88dB and -26.27dB are achieved at 100MHz and 15MHz respectively.

Novel tumor localization model and prediction of ablation zone using an intertwined helical antenna for the treatment of hepatocellular carcinoma.

Hepatocellular carcinoma has been the leading cause of death in recent centuries and with the advent of newer technologies, several thermal and cryo-ablation techniques have been introduced in the recent past. In this regard, microwave ablation has developed into a promising method for thermal ablation technique. However, due to clinical obligations, in-vivo analysis is not feasible and ex-vivo analysis is inaccurate due to changes in the electrical and thermal properties of the tissue. Therefore, in this study, temperature-dependent permittivity, electrical conductivity, and thermal conductivity along with phase change effect due to temperature reaching above 100°C are incorporated using finite element method model. Further, using an intertwined normal mode helical antenna ablation probe, a change in resonant frequency (Δf) and reflection coefficient (ΔS11 ) from the actual value (antenna parameter in the air at 5GHz) is modeled using second-order polynomial curve fitting to predict the surrounding permittivity in the range of 30-70. A maximum deviation of 0.8 value in permittivity from the actual value is observed. However, to obtain a generalized methodology, XG Boost and CAT Boost algorithms are used. Further, since ablation diameter plays a crucial role in achieving optimal tumor ablation, an artificial neural network (ANN) algorithm with three different optimizers is incorporated to predict ablation diameter using five critical parameters. Such an ANN algorithm which can predict the transversal and axial ablation zone may provide optimal ablation outcomes.

The influence of structure uniformity on resonant frequency of ultra-high frequency radio frequency identification tag thread With normal mode helix dipole antenna

The stable performance of ultra-high frequency radio frequency identification (UHF RFID) tag thread with normal mode helical dipole antenna (NMHDA) was required for industrialized application. The ununiform helical pitches and helical radiuses caused by the unstable tension in the preparation process and material properties of carrying yarn probably deteriorate the performance of UHF RFID tag thread with NMHDA, while previous work focused on the properties of UHF RFID tag thread with uniform structure by finite element simulation. This work conducted numerical experiments with the actual statistical distribution of helical pitch and helical radius, i.e. normal distribution, and discussed the influence of the distributed parameters on resonant frequency. And then, the relationship between structure uniformity and resonant frequency was explored. Furthermore, the relationship was put into practice of the design of UHF RFID tag thread with stable properties. The results show that the fluctuation of resonant frequency first decreases and then increases with the increase of the mean helical pitch ( S me), and the resonant frequency decreases with the increase of the standard deviation of helical pitch ( S st) and that of helical radius ( r st). When the reactance of helical coil linearly changes with helical radius, the mean helical radius ( r me) has a negligible effect on the fluctuation of resonant frequency. The importance of the factors for the resonant frequency conforms to the following order: r me> S st> S me> r st. Additionally, the stable reading range of prototype (14.13 ± 0.06 m) demonstrated the practice of these results in the design of UHF RFID tag thread with NMHDA.

Nearfield radio link of normal mode helical antenna for wireless capsule endoscopy

Wireless capsule endoscopy (WCE) is designed to monitor the physical data from inside human stomach and gastro intestine (GI) tract and transfer data to the receiver device. Normal mode helical antenna (NMHA) that has high efficiency at a small size is selected for WCE. To clarify the radio wave communication link budget in the dielectric environment is crucial. In this paper, NMHA for WCE system at 402 MHz along with a link budget analysis is presented. The transmitter uses NMHA embedded in a cylindrical phantom mimicking human stomach tissue, whereas the receiver uses another NMHA located outside the body. The NMHA dimension of height and diameter are 18 mm × 11 and 37 mm × 18 mm respectively. Through this study, a novel method of analytical equations for the radio wave communication link in human body are derived. From the good agreement between simulated and measured S21, the effectiveness of derived equations is ensured.

A compact normal-mode VHF/UHF dual-band helical antenna for lunar microsatellite

This paper has proposed a novel compact VHF/UHF dual-band helical antenna, which was used onboard Longjiang-2, the first independent Earth-Moon-transfer microsatellite. As a critical component of the first amateur radio communication system for a lunar satellite, the antenna requires small size and omnidirectional beam coverage. The structure of the resulted antenna is a combination of a helix and a loaded monopole, and has achieved a 56% size reduction for axial height compared to a conventional normal-mode helical antenna. Moreover, parametric studies were performed to explore the resonant characteristics. The radiation patterns of the proposed antenna installed on the satellite were simulated, which indicated that the antenna achieved a good beam coverage of more than 99.9% in space. Measurements in anechoic chamber and in lunar orbit were carried out to verify the effectiveness of the design.

Near field radio link design in fat phantom for Wireless Capsule Endoscopy application

Abstract Medical devices such as Wireless Capsule Endoscopy (WCE) that need wireless imaging and monitoring, operating at 402 MHz, is considered to be in the near field region due to the distance being shorter than the wavelength. In this paper, the radio link calculation method in the near field region is investigated. Normal Mode Helical Antenna (NMHA) is used as the transmitter antenna which is placed inside of a fat phantom of 11.6 F/m and the receiver antenna at distance 0.1 to 1.0 m apart. For link budget establishment, parameters such as power density, W and receiver antenna effective area, Ae are investigated through electromagnetic simulation. The distance dependency of W is examined and the result of W∝ 1/(distance)2 is obtained. The relation of Ae of the receiver antenna is found to be the size of the cross-section area of the antenna. A radio link equation is formed by employing W, Ae and other propagation loss factors of a medium and is then compared with the power received, PR and S21 obtained from simulation. The agreement between calculated and simulated results shows that this equation can be used in the near field region.

Design of a novel externally‐tapped intertwining helical antenna for microwave ablation and its statistical analysis on tissue model

Cancer is the leading cause of death in recent centuries and microwave ablation (MWA) has been evolving to thermally treat cancerous tissue through cell necrosis and is also a promising substitute to radio frequency ablation. In this article, a novel normal-mode helical antenna based MWA probe is investigated for the effect on ablation diameter in the presence of five critical parameters. The antenna consists of an intertwining helix structure mounted on a very small ground plane. An external tapping is used to match the antenna impedance. In the proposed design at the center frequency, a reflection coefficient of more than 23 dB without insertion into the tissue model and a reflection coefficient of more than 14 dB with insertion into the tissue model have been observed at 5 GHz frequency. The gain and percentage bandwidth of the antenna is 0.6 dB and 10%, respectively. At 20 W power, a maximum ablation diameter of 32 mm (transversal-T) and 44 mm (axial-A) is reached within 5 min of application time at a distance of 30 mm from the probe. Further, the L27 Taguchi's orthogonal array has been employed to study the effect on ablation diameter by varying five thermo-electrical parameters. The outcome of Taguchi's analysis has been ranked according to the contribution of each parameter. Further, F- and p-value test has been employed using analysis of variance to study the significance of each parameter on ablation diameter.

Wheeler Method for Evaluation of Antennas Submerged in Lossy Media

A Wheeler method for the evaluation of the radiation efficiency of submerged antennas within lossy media is presented and demonstrated for the first time in the literature. Extensive investigations have been devised by empirical and simulation methods. Normal-mode helical antenna (NMHA) was first designed and fabricated to exemplify a real-life application at the UHF band (0.3 to 3 GHz). The antenna under test (AUT) was evaluated within an artificial lossy material using a series of Wheeler caps featuring different radii to study the validity of this method. The error between the experimental and simulation radiation efficiency is below 3% near the theoretical radian length. The presented measurement method of radiation efficiency without any essential measurement facilities or accessories could be a promising candidate for fast and accurate evaluation for any wire-type antenna submerged within lossy media.

Normal-Mode Helical Antennas With Near-Field Coupling: Improving Design Flexibility [Antenna Applications Corner

The near-field coupling between closely placed metallic structures has been utilized to cope with the dilemma of a normal-mode helical antenna (NMHA) design. For small NMHAs, the impedance-matching difficulty is mitigated by designing appropriated coupling feeds, either electrically or magnetically. For long NMHAs, the radiation pattern distortion is rectified by dividing the complete helix into properly designed small sections. With mutual section coupling, the currents on all of the sections can be nearly in-phase, dictating an omnidirectional radiation pattern. The design principle has been described as two-element models and a corresponding equivalent circuit analysis. The simulated and measured results show that, compared to conventional NMHAs, it is possible to design an NMHA of simultaneous good matching and radiation properties but with a much more flexible helix length and size.

Increase of Input Resistance of a Normal-Mode Helical Antenna (NMHA) in Human Body Application

In recent years, the development of healthcare monitoring devices requires high performance and compact in-body sensor antennas. A normal-mode helical antenna (NMHA) is one of the most suitable candidates that meets the criteria, especially with the ability to achieve high efficiency when the antenna structure is in self-resonant mode. It was reported that when the antenna was placed in a human body, the antenna efficiency was decreased due to the increase of its input resistance (Rin). However, the reason for Rin increase was not clarified. In this paper, the increase of Rin is ensured through experiments and the physical reasons are validated through electromagnetic simulations. In the simulation, the Rin is calculated by placing the NMHA inside a human’s stomach, skin and fat. The dependency of Rin to conductivity (σ) is significant. Through current distribution calculation, it is verified that the reason of the increase in Rin is due to the decrease of antenna current. The effects of Rin to bandwidth (BW) and electrical field are also numerically clarified. Furthermore, by using the fabricated human body phantom, the measured Rin and bandwidth are also obtained. From the good agreement between the measured and simulated results, the condition of Rin increment is clarified.

Counter-Wound Normal-Mode Helical Antenna as an Electrically Small Electro-Quasi-Static Exciter

An electrically small electro-quasi-static exciter is demonstrated using a counter-wound normal-mode helical antenna. The arms are counter-rotated to cancel the generation of magnetic fields in the quasi-static regime. The field equations are derived and verified to show the degradation of magnetic fields with minimal effects to the electric field. The long wire lengths give sinusoidal current distribution and fields that are not strongly dependent on the feed structure. As a result, the measured electro-quasi-static field agrees well with the dipole behavior over long ranges. In addition, the circuit model for the antenna is presented and verified with measurements.

A Displacement Sensor Based on a Normal Mode Helical Antenna

This paper presents a passive displacement sensor based on a normal mode helical antenna. The sensor consists of an external helical antenna and an inserting dielectric rod. First, the perturbation theory is adopted to demonstrate that both the electric intensity and magnetic intensity have a noticeable gradient change within the in-and-out entrance of the helical antenna, which will cause the sensor to experience a resonant frequency shift. This phenomenon was further verified by numerical simulation using the Ansoft high frequency structure simulator (HFSS), and results show the linear correlation between the retrieved resonant frequency and the displacement. Two sets of proposed sensors were fabricated. The experiments validated that the resonant frequency shifts are linearly proportional to the applied displacement, and the sensing range can be adjusted to accommodate the user’s needs.

Effects of the permittivity and conductivity of human body for normal-mode helical antenna performance

Effects of the permittivity and conductivity of human body for normal-mode helical antenna performance

Normal Mode Helical Antenna on Small Circular Ground Plane

ABSTRACT In this paper, it has been shown that input impedance matching for the Normal Mode Helical Antenna (NMHA) can be obtained by using a small circular ground plane (radius λ/20) without any external impedance matching network. It also discusses the effect of the finite circular ground plane radius, the radius of wire on the input impedance, resonance frequency, and bandwidth of the NMHA. Further, the effects of different ground plane shapes and cupped shape ground plane bending in upward and downward directions on input impedance matching are presented. A prototype of NMHA has been fabricated to operate around 1.8 GHz and the measured results are in good agreement with the simulated results.

Deterministic Equation of Self-Resonant Structures for Normal-Mode Helical Antennas Implanted in a Human Body

Recently, helical antennas had been used as a very small implantable antenna in a capsule endoscopy system. For a helical antenna, a normal-mode helical antenna (NMHA) is promising because of its small size and the completeness of an antenna design method, which has already been established. However, in the human body, the effects of human tissues on the electrical characteristics of an NMHA were not clarified. The most important aspect is to determine the self-resonant structures. In this letter, a deterministic equation is derived for the self-resonant structures of an NMHA in the human body. By utilizing simulation results of an electromagnetic simulator, a capacitive reactance equation is deduced based on the electric field distributions around an antenna. An inductive reactance equation is obtained by modifying the equation of free space to the condition of inside a dielectric material. Finally, by equating the capacitive and inductive reactance equations, the self-resonant equation is determined. The accuracy of the equation is ensured through the agreements of the antenna structures given by equations and electromagnetic simulations. Moreover, by fabricating an NMHA and a human body phantom, the measured results are obtained. The self-resonant structure is ensured through the measured results.

Investigating Equations Used to Design a Very Small Normal-Mode Helical Antenna in Free Space

A normal-mode helical antenna (NMHA) has been applied in some small devices such as tire pressure monitoring systems (TPMS) and radio frequency identification (RFID) tags. Previously, electrical characteristics of NMHA were obtained through electromagnetic simulations. In practical design of NMHA, equational expressions for the main electrical characteristics are more convenient. Electrical performances of NMHA can be expressed by a combination of a short dipole and small loops. Applicability of equations for a short dipole and a small loop to very small normal-mode helical antennas such as antennas around 1/100 wavelengths was not clear. In this paper, accuracies of equations for input resistances, antenna efficiency, and axial ratios are verified by comparisons with electromagnetic simulation results by FEKO software at 402 MHz. In addition, the structure of the antenna equal to 0.021 λ is fabricated, and measurements are performed to confirm the design accuracy.

Design of a Small-Size, Low-Profile, and Low-Cost Normal-Mode Helical Antenna for UHF RFID Wristbands

Emerging RFID applications in the UHF band in some cases require very specific antenna solutions. This letter considers the identification and tracking of patients inside hospital facilities using wristbands, which impose strict tag size and cost limitations. We propose a solution for passive tags based on a normal-mode helical antenna as an alternative to bulky and/or expensive solutions that can be found in the literature. The robustness of the resulting wristband will be assessed in a particular implementation by measuring the maximum read range for a variety of subjects with different physical constitutions.

Low-Profile Helical Quasi-Yagi Antenna Array With Multibeams at the Endfire Direction

This letter presents a novel helical quasi-Yagi antenna array with low profile and multibeams at the endfire direction. First, a planar normal-mode helical quasi-Yagi antenna with top-hat loading for low profile is designed to achieve endfire radiation. It is mounted on a conducting plane, consisting of a top-loaded folded helix as the driven element and three top-loaded unfolded helices as parasitic elements. A broadband can be achieved by controlling the resonance difference between the driven and parasitic elements. Second, a microstrip beamforming network based on Butler matrix is designed to feed a 1 × 4 helical quasi-Yagi array. The proposed antenna array is fabricated and tested. Measured results show that three endfire beams at ϕ = 90°, (90 ± 47)° are obtained while the antenna has a very low profile of 0.054 λ at its center frequency, showing that the antenna may be useful in many airborne applications such as unmanned aerial vehicles.

A Very Compact Normal Mode Multiloop Helical Antenna with Enhanced Bandwidth

The physical size of an antenna becomes an important characteristic when receiving signals in bands with long wavelengths. Size determines two important aspects of antenna performance; impedance and efficiency. For example, the VHF antennas installed on radio sets that intended to receive FM or the latest technology Digital Audio Broadcasting (DAB) radio signals in Bands II, III respectively. Antennas that are installed on mobile platforms (i.e. portable receivers) require a receiver that utilizes a whip telescopic antenna with adjustable length which can operate as a λ/4 monopole antenna. Whereas, non-portable applications like a deck commercial receiver has no built in antenna due to the large size of the radiator needed and so must be connected with an external antenna. This paper presents a new design of a very small size Normal Mode Multiloop Helical Antenna (NMMHA) with superior performance developed for commercial receivers operate in band II, III. The major drawback which has been overcome with this design is the very narrow bandwidth of the Normal Mode Helical Antenna, which originally was optimized to provide the minimum Voltage Standing Wave Ratio VSWR response across Band II (87.5 - 108 MHz). The NMMHA’s size allows it to be a build in block of a deck commercial receiver.