Small Helical Antenna Research Articles

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.

Helical and Spiral Antennas as Electric Small Antennas

The simplest form of a classical antenna is the dipole antenna, which is essentially two pieces of wire placed end to end with a feed point in the middle. The length of this antenna is typically half the wavelength of the signal that is being received or transmitted.&nbsp; An “electric small” antenna is defined as an antenna of much shorter dimensions than the wavelength of the signals it is designed for. Small electric antennas have an advantage when space is the most essential factor. Satellites and mobile communication apparatuses for example can use small antennas in order to free up more space for other components. The problem with classical electric small antennas is that their bandwidth and radiation efficiency shrink as they get shorter. Although such antennas have been in use for decades, they remain difficult to design and limited in their applicability. However, the classic approach of studying metal antennas using only Maxwell equations limits the real internal nature of them as metal lattice structures and thus as quantum wells of free electrons. When interpreted this way, free electrons are obeying the Schrodinger wave equation and this view can give new ideas for designing effective curvilinear electric small antennas.&nbsp; Such a class of electric small helical and spiral antennas is proposed in the following paper.

A fiber based diamond RF B-field sensor and characterization of a small helical antenna

We present a microwave B-field scanning imaging technique using a diamond micro-crystal containing a nitrogen vacancy center that is attached to a fiber tip. We propose a pulsed modulation technique, enabling the implementation of a variety of pulsed quantum algorithms for state manipulation and fast readout of the spin state. A detailed mapping of the magnetic B-field distribution of a helical antenna with sub-100 μm resolution is presented and compared with numerical simulations. This fiber based microwave B-field probe has the advantages of minimized invasiveness and small overall size and will boost broad interest in a variety of applications where near field distribution is essential to device characterization, to name a few, antenna radiation profiling, monolithic microwave integrated circuit failure diagnosis, electromagnetic compatibility test of microwave integrated circuits, and microwave cavity field mode mapping.

The Development and Application of a Live Transmitting Head Camera for Video Feedback in Rugby Decision Making

Previous studies have explored the use of head cameras in different scenarios, including sport training [1–4]. Until recently, athletes had their practice recorded and such recording was used for feedback purposes. This approach is problematic as it does not allow for immediate feedback and does not provide a similar perspective to those athletes have when training. To overcome this a head camera was developed to record first-person perspective during real-life training situation. This camera consisted of 3 main components: a miniature camera with wide angle lens (140 degrees) and transmitter running on a 2.4GHz frequency with a small helical antenna, a video relay device for increased line of sight between the transmitter and receiver, signal receiver device connected to a laptop computer with video review software. The camera components were mounted within a protective casing and inserted into a custom made rugby soft helmet, commonly known as headgear. The vantage point of the wearer is very different to conventional grandstand camera views and shows that different visual information [5] is presented to an individual making decisions. Case study: A randomised control trial is to be performed consisting of three groups; a group using and viewing footage from the head mounted camera, a group viewing coaches’ perspective, side of field footage and a control group with no video feedback. The players will complete a decision making drill and video feedback will be reviewed with players observing the movements of their teammates and surrounding opponents. Data will be recorded throughout the session measuring which video vantage point is associated with improvements in decision making.

Spherical Helices for Resonant Wireless Power Transfer

The capabilities of electrically small spherical helical antennas for wireless power transmission at small and moderate distances are analyzed. Influence of design on antenna radiation resistance, efficiency, and mode ratio is examined. These are the factors that, according to the theoretical considerations depicted herein, govern the maximum transfer performances. Various designs and configurations are considered for the purpose, with accent on small-size receivers suitable for implementation in powering common-sized gadgets. It is shown that spherical helix design is easily manipulated to achieve a reduced antenna size. Good radiation characteristics and impedance match are maintained by multiple-arm folded antenna design and by adjusting the separation between the arms.

Fundamental Aspects of Near-Field Coupling Small Antennas for Wireless Power Transfer

A physical limitation on the power transfer efficiency between two electrically small antennas in the near-field range is presented. By using a Z-parameter which describes the interaction between two antennas for spherical modes in connection with antenna parameters, the maximum power transfer efficiency and the optimum load impedance are shown as functions of the distance between two antennas, the radiation efficiency and the input impedance of the isolated antenna. The theory is verified by a simulation with a small helical antenna, which generates and modes, simultaneously.

Low-Loss Composite Material Containing Fine Zn–Ni–Fe Flakes for High-Frequency Applications

A low-loss magnetic composite material consisting of Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">75</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> fine flakes dispersed in a polymer has been developed for miniaturization and performance improvement of high-frequency devices. Fine flakes are produced by a new mixing procedure that prevents cohesion of particles, thereby enhancing the dispersibility of the particles. The complex relative permeabilities of the developed material are mu' = 2.4, mu" = 0.09, and tan deltamu( = mu"/ mu') = 0.04 at 1 GHz. The low-loss properties of the developed magnetic composite material are confirmed by measured and simulated results of the basic characteristics of a small helical antenna loaded with the developed material.

PARAMETRIC STUDY OF POWER ABSORPTION PATTERNS INDUCED IN ADULT AND CHILD HEAD MODELS BY SMALL HELICAL ANTENNAS

A comparative assessment of power absorption in adult and child heads exposed to a small helical antenna at 1710MHz, is presented, emphasizing the efiect of age related parameters. Finite Difierence Time Domain simulations are employed to study the interaction between MRI-based head models and a mobile communication terminal equipped with a small helical monopole. A semi-analytical method, based on Green's function theory and the Method of Moments, is used to study the absorption in three- layer spherical head models exposed to a small helical dipole. SAR patterns in child head models derived by non-uniform scaling of adult ones were assessed against SAR patterns computed in child heads derived by uniform downscaling procedures. In both realistic and canonical exposure scenarios, comparable levels of absorbed power

No effect of an UMTS mobile phone‐like electromagnetic field of 1.97 GHz on human attention and reaction time

Several studies in the past reported influences of electromagnetic emissions of GSM phones on reaction time in humans. However, there are currently only a few studies available dealing with possible effects of the electromagnetic fields emitted by UMTS mobile phones. In our study, 40 healthy volunteers (20 female, 20 male), aged 26.0 years (range 21-30 years) underwent four different computer tests measuring reaction time and attention under three different UMTS mobile phone-like exposure conditions (two exposure levels plus sham exposure). Exposure of the subjects was accomplished by small helical antennas operated close to the head and fed by a generic signal representing the emissions of a UMTS mobile phone under constant receiving conditions as well as under a condition of strongly varying transmit power. In the high exposure condition the resulting peak spatial average exposure of the test subjects in the cortex of the left temporal lobe of the brain was 0.63 W/kg (min. 0.25 W/kg, max. 1.49 W/kg) in terms of 1 g averaged SAR and 0.37 W/kg (min. 0.16 W/kg, max. 0.84 W/kg) in terms of 10 g averaged SAR, respectively. Low exposure condition was one-tenth of high exposure and sham was at least 50 dB below low exposure. Statistical analysis of the obtained test parameters showed that exposure to the generic UMTS signal had no statistically significant immediate effect on attention or reaction. Therefore, this study does not provide any evidence that exposure of UMTS mobiles interferes with attention under short-term exposure conditions.

Electrically small antenna with frequency tuning circuit for wideband applications

This study proposes the concept of frequency tuning for an electrically small antenna to be used in wideband applications in low frequencies. An electrically small antenna has too narrow bandwidth to be utilized for wideband systems. However, in such mobile TV services that the band is composed of each sub channel in VHF band, the narrow bandwidth can be appropriately utilized with wideband frequency tuning. That is, each service channel is covered by the narrow resonant band of a small sized radiator and the entire service band is satisfied by moving its frequency. To prove the idea of this study, a small helical antenna with the size of less than λ/10 is chosen as a sample and the T-DMB service, a kind of the mobile TV services allocated to 200-MHz band, is selected for testing. With the designed tuning circuit constituted of lumped elements and a varactor, a low impedance of the small radiator is matched to about 50 Ω and the wide bandwidth is satisfied by moving its narrow resonant frequency. The validity of the proposed antenna is also proved by the receiving measured result. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 244–247, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23049

A feeding method for small helical antennas

AbstractA feeding method is proposed for small helical antennas with diameters of about 1/80 to 1/20 wavelength. The present feeding method consists of excitation of a helix with a total length of about 1/4 wavelength and with its lower edge grounded by an open‐ended center conductor oriented coaxially to the helix. In this paper, it is shown that matching with a 50‐Ω feed system can be accomplished even when the helical diameter is varied in the same feeding method. The gain and the bandwidth characteristics of the ground plane versus diameter are discussed. As an example, a gain of −7.2 dBd (with respect to the dipole antenna) on the ground plane is obtained when the helical diameter is 1/46 wavelength and the height is 1/56 wavelength. Like the monopole antenna, the main radiation pattern is omnidirectional vertical polarization in the horizontal plane and figure‐eight in the vertical plane. When this antenna is installed on a transmitter case, the gain is about −4 dBd. When installed on the transmitter case, the antenna radiates the orthogonal polarization component. The null of the main radiation pattern in the zenith direction can be compensated by this polarization. The radiation characteristics of the antenna are numerically calculated by the method of moments and are verified experimentally. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(3): 33–41, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20324

Closely wound small helical antennas

With a view to applications to base stations for mobile communication, the results of experimental and conventional analysis of a small antenna are reported. The present antenna consists of a closely wound coil-shaped external conductor and a coaxially placed inner linear conductor. The bottom of the linear conductor is connected to the center conductor of the coaxial feed and the lower part of the coil-shaped conductor is connected to the outer conductor of the coaxial conductor. In this paper, a method of shorting the upper part of the coil-shaped conductor with the inner conductor and of opening this part are proposed as feed methods. The antenna height of the former is about 1/26 wavelength and that of the latter is 1/80 wavelength. Both structures can be matched to a 50-Ω feed line without any matching circuit. The present antenna attached to a small metallic case has a vertically polarized omnidirectional pattern in the horizontal plane and a figure-8 shape in the vertical plane, similar to those of a usual monopole antenna. The measured gain is about –15 dBd relative to the dipole. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 11–22, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20170

Small helical antenna for the applications of the dual ISM bands

AbstractA new design of a miniaturized multilayer ceramic (MLC) antenna is proposed and presented for the applications of the dual ISM bands (hyper LAN and WLN). The antenna‐size reduction is achieved by folding the simple microstrip monopole around a low‐temperature co‐fired ceramic (LTCC) substrate. This paper presents measured data to show that the 10‐dB bandwidths achieved were 180 MHz and 750 MHz at 2.4 GHz and 5.2 GHz, respectively. The co‐polarization far‐field radiation patterns of the chip antenna are quasi‐omnidirectional at 2.4 GHz and 5.2 GHz. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 140–142, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10848

Small helical antenna made of high-temperature superconducting thick film

To realize a highly efficient small antenna, high-T c superconducting thick films with zirconia cores are adopted in order to fabricate both a self-resonating small helical radiator and a quarter-wave matching circuit. The actual gain of a superconducting antenna measured at 478 MHz using a 1/70-wavelength radiator was 4.9 dB higher than that of a copper antenna.

Wave impedance in the near field around the fundamental electromagnetic radiating elements

AbstractStandards for electromagnetic protection taking into account human health have been established in a number of countries. Most of the present standards are expressed in terms of the intensities of electric and magnetic fields or the power density of the irradiating electromagnetic field. Usually, for conversion among these quantities, the relationship in the electromagnetic field at a distance far away (far field, plane wave) is used. However, near the electromagnetic source where the electromagnetic wave is the strongest, the relationship among the forementioned quantities varies depending on the location of the observation point or the type of the source. Therefore, there are recommendations to reconsider the standard values.The purpose of this paper is to provide fundamental references for modeling the electromagnetic sources in various electromagnetic equipment to reconsider the protection standard of the near field, and to develop the electromagnetic shielding theory in the near field. In this paper, the distance characteristics and the spatial distribution of the electromagnetic wave impedance characterizing the nature of the electromagnetic wave are studied near the elementary radiating elements such as the electric dipole, magnetic dipole, half‐wave dipole antenna, small current loop and small helical antenna.

Small helical antennas

A distinction is drawn between open and closed small helical antennas. The polarization of the former may be made circular only in the plane; orthogonal to is axis. Elsewhere it is in general elliptical, but becomes linear for one direction in spoeo determined by its circumferential longth in wavelengths. Comparative expressions for the pattern and radiation resistance of the small closed helical antenna are also given.