A broadband plate antenna with slits

Recently, UHF RFID tags are planned to commercialize in many countries. Requests for smaller size antennas are becoming strong. Promising candidates for these requests are meander line antennas (MLA) and normal mode helical antennas (NMHA). In this paper, extremely small MLA and NMHA are developed. As for MLA, design data for 0.02 to 0.05 wavelength antennas are shown. By loading high r materials, possibilities of achieving antenna efficiencies greater than -5 dB are shown. Moreover, a convenient feed structure to achieve excellent impedance matching is proposed. As for NMHA, design data for 0.025 to 0.1 wavelength antennas are shown. And achievements of antenna efficiencies greater than -5 dB are shown. Moreover, a convenient feed structure to achieve excellent impedance matching is proposed. Finally, very important measurement method to measure radiation resistance and ohmic resistance are shown. Through this measurement, extremely small antenna behaviors become very clear

Recently RFID tags of 900 MHz band are interested in many commercial fields. Tags are requested to be used on liquid bottles, medicine bottles and metallic plates. So, antennas are requested to be made very small and to have properties capable of use in metal proximity. In this paper, important design subjects to achieve very small antennas are summarized and technical solutions are explained first of all. Following this summary, the normal mode helical antenna (NMHA) is selected as a promising antenna that is suitable for achieving high gain in very small size and metal proximity use. Next, useful design data of NMHA to achieve high gain and metal proximity are shown. And an example of achieving a low profile NMHA is shown. In order to ensure realization, measured results of a fabricated antenna is shown. Moreover, the fabricated antenna is applied to the commercial IC chip. Communication distances are compared with that of the commercial tags.

Recently, very small radio wave sensors (RWS) are tried to be put in to a human body for human health case purpose. As for a very small antenna in a sensor, normal-mode helical antenna (NMHA) is suitable due to its high efficiency with very small sizes. In this paper, antenna design method and electrical characteristics are clarified for very small NMHA which size is from 0.03 to 0.06 wavelengths in a human body conditions. Firstly, antenna self-resonant structures are clarified through electromagnetic simulations. Next, antenna input resistance changes for human body conductivity changes are clarified. Moreover, radiated power changes are also examined.

Normal-mode helical antennas (NMHA) are well known for achieving high antenna efficiencies in very small sizes when antenna structures are tuned to self-resonant situations. The design equation determining self-resonant structures were developed in free space conditions. However, in practically, NMHA mostly used dielectric or magnetic materials as cores. The design equation for these cases is not studied yet. In this paper, fundamental self-resonant structures are studied for NMHA placed in dielectric or magnetic material. In order to obtain correct calculation results, calculation models of an commercial electromagnetic simulator (FEKO) is studied. Many data for structural change from free space condition to inside materials are achieved. Moreover, input resistance and antenna efficiency changes are also obtained.

The resonant frequency of the normal mode helical antenna (NMHA) varies with its number of turns. Several experiments were conducted to investigate their relationship. This paper presents linear regression analysis on these experimental results and tries to find a simple equation relating the resonant frequency and number of turns of the NMHA. An empirical equation giving relationship between them is suggested.

A simple technique is proposed for modeling short normal-mode helical antennas using a commercial finite-difference time-domain (FDTD) code with a rectangular grid and a nominal extension of the wire. The approach allows affects on the input impedance and radiation performance of the helix to be examined and importantly does not require modification of the excitation subroutines. Normal-mode helical antennas for mobile communications use at 900 and 1800 MHz were designed using the proposed method and good agreement with measurements of impedance and near-magnetic field strength was found. The radiating performance of the helix was compared to that of a /spl lambda//4 monopole and generally found to be inferior at 900 MHz due to only 19.2 % efficiency in the presence of the head. At 1.8 GHz the two antenna types showed similar characteristics except in regard to bandwidth, 36.1 % for the monopole and 7.8 % for the helix, in the presence of the head. The modeled helix antennas produce spatial peak specific absorption rate (SAR) figures that are up to 27 % greater at 900 MHz and up to 49 % greater at 1.8 GHz than the corresponding monopole values due to the shorter antenna.

This paper presents the Specific Absorption Rate (SAR) analysis of a Normal-Mode Helical Antenna (NMHA) implanted in human stomach tissue at 402 MHz (MICS) and 2.45 GHz (ISM). While NMHAs are widely studied for in-body communication, their SAR performance remains underexplored. Using identical antenna geometry, SAR1g and SAR10g are simulated and compared. Results show that to comply with the IEEE SAR1g limit of 1.6 W/kg, the maximum input power is 15.5dBm at 402 MHz and 7.3 dBm at 2.45 GHz. For SAR10g, the input power must remain below 19 dBm and 10.5 dBm, respectively, to meet the ICNIRP 2 W/kg guideline. These findings offer practical input power thresholds and emphasize the frequency-dependent safety considerations for ingestible medical antennas.

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 dipole antennas are widely used for RF communication applications and usually provide a potential front-door path of coupling electromagnetic pulse (EMP). In this paper, the transient current response of dipoles exposed to EMP is calculated with an equivalent circuit based model, which consists of an equivalent pulse voltage source and an antenna equivalent circuit. A center-driven wire dipole and a normal mode helical antenna are utilized for validate the circuit models. The results from the circuit based models agree well with data obtained from full numerical solution of the actual antennas. They takes only a few seconds to calculate the transient response with circuit models, which could also be directly connected to RF front-end circuits of communication system for electromagnetic susceptibility assessment.

Relationship between the reflection coefficient bandwidth and quality factor (Q) of a small antenna is revisited using a simple frequency independent model. A tuned small antenna is considered in this case, which is modeled as either a series or a shunt RLC network. When the antenna resistance is matched with the characteristic impedance of the feed-line, both configurations lead to an identical relation, which is also interestingly identical to the well-known inverse bandwidth-Q formula for small antennas. However, this well-known formula is only applicable when the antenna is perfectly matched to its feed line. In this paper, a more general and yet simple form of this expression is derived, which can encompass the effect of mismatch between the antenna and its feed-line. Furthermore, we derive separate relations for the bandwidth-Q product, for both the loaded and unloaded cases. As an illustrative example, a microstrip patch antenna is considered to validate the results.

This paper presents a wireless, miniaturized, bi-directional telemetric artificial anal sphincter system that can be used for controlling patients' anal incontinence. The artificial anal sphincter system is mainly composed of an executive mechanism, a wireless power supply system and a wireless communication system. The wireless communication system consists of an internal RF transceiver, an internal RF antenna, a data transmission pathway, an external RF antenna and an external RF control transceiver. A micro NMHA (Normal Mode Helical Antenna) has been used for the transceiver of the internal wireless communication system and a quarter wave-length whip antenna of 7.75 cm has been used for the external wireless communication system. The RF carrier frequency of wireless communication is located in a license-free 433.1 MHz ISM (Industry, Science, and Medical) band. The radiation characteristics and SAR (Specific Absorption Rate) are evaluated using the finite difference time-domain method and 3D human body model. Results show that the SAR values of the antenna satisfy the ICNIRP (International Commission on Nonionizing Radiation Protection) limitations.

The normal mode helical antenna (NMHA) is widely used for RF communication applications and usually provides a potential front door path of coupling electromagnetic pulse (EMP). Many numerical methods are employed to analyze the transient response of antennas under EMP, such as time-domain finite difference (FDTD) and time domain integral equation (TDIF) methods. While the numerical methods give accurate results, they can be time-consuming and only provide snapshots of EMP response in very specific circumstances. In addition, the transient data obtained from numerical tools is often required to be handled for the subsequent EMP vulnerability assessment in the RF front end circuits of communication system. The analysis of transient response for communication systems in the presence of EMP was usually complicated in the traditional field-circuit method.

In order to measure the junction temperature of power equipment, a novel strategy of temperature measurement based on surface acoustic wave (SAW) passive wireless temperature sensor was designed. The antennas and the matching methods of antennas and sensors were also discussed. In this design, the reader antenna was designed as the planar inverted-F antenna (PIFA), and the sensor antenna was designed as the normal mode helical antenna. The simulation results showed that the center frequency of the antennas both are 915MHz and the voltage standing wave ratio (VSWR) are less than 1.5. The matching method of the planar inverted-F antenna was obtained through the location change of the feed point. The Smith v2.0 was utilized to match the normal mode helical antenna. Finally, both antenna designs met the requirements with the impedances of about 50Ω.

An equivalent circuit consisting of eight frequency independent lumped elements is derived for center-driven normal mode helical antennas. The equivalent circuit is composed of two parts; a five-element circuit representing the wire antenna and a three-element circuit for the helical turns. Comparison of the calculated input impedance of the equivalent circuit with full-wave simulations demonstrates reasonable agreement over a broad frequency range that includes the first resonant frequency, where the antenna usually operates. Application of the equivalent circuit does not require an EM solver and it is readily implemented in circuit simulators.

The complete analysis for the complex vector effective length and the polarization mismatch factor for one turn helix is given and new analytical closed form expressions are deduced. A triangular current distribution is assumed along the wire to verify the boundary condition at its ends. The same parameters are calculated for multiturn normal mode helical receiving antenna using the method of moments.