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An analysis of the effective radiation efficiency of the normal mode helical antenna close to the human abdomen at 150 MHz and consideration of efficiency improvement
Abstract
In this paper, a new radiation efficiency based on the available power is defined with regard to a normal mode helical antenna at 150 MHz placed close to the human abdomen, so that the power loss caused by impedance mismatch and by the resistance of the antenna itself can be taken into consideration in the treatment. In this way, the variation of the effective radiation efficiency of the antenna in a practical situation caused by the antenna length and the distance to the human body is analytically derived. Further, by deriving the loss power in each section, the factors causing degradation of the radiation efficiency are analyzed and the mechanisms for efficiency degradation are clarified. Based on the results, the possibility of improved radiation efficiency of the antenna near the human body is discussed. It is shown that the radiation efficiency of the antenna near the body is less than −20 dB, that its main cause is impedance mismatch, and that improvement of the radiation efficiency by more than 10 dB is possible by always maintaining conjugate match near the human body. These findings are experimentally confirmed. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 23–33, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1115
... In this section, we investigate the differences of the electric field distribution caused GND electrode using the equivalent circuit models [4]. Figure 7 shows the equivalent circuit models of the transmitter attached to the arm. ...
This paper presents analytical results with respect to dynamic shadowing properties of BAN antennas due to the movement of the arms. Particular emphasis is placed on the identification of important parameters for designing BAN systems, such as radiation efficiency and dissipated power, which can not be obtained only by experimental approaches.
This paper presents analytical results of an arm-waving dynamic phantom that can simulate human walking and running motions. Firstly, shadowing characteristics caused by the movement of the arms are shown using the method of moments. Analytical results are also shown for the case where the combined outcome of shadowing and multipath fading emerge simultaneously when a human walks in a multiple radio wave propagation environment while swinging both arms.
This paper presents a newly developed arm-swinging dynamic phantom that can simulate human walking and running motions. The arm-swinging phantom has unique features, in that swinging of the right and left arms and the direction and speed of swing can be controlled independently, leading to excellent capability for replicating the variety of natural walking and running styles seen in the average human. Using the phantom, we have attempted to develop a dynamic channel characterization for BAN systems, such as shadowing properties and path loss characteristics, when the geometrical relationships between the arms and the human body change continuously due to the movement of the arms for both off-body and on-body situations. Assessments of communication quality, such as the signal bit error rate, were also conducted to gain useful knowledge of the way and the degree to which arm-swinging might impact the performance of body-attached BAN devices. Analytical results are also shown for the case where the combined outcome of shadowing and multipath fading emerge simultaneously when a human walks in a multiple radio wave propagation environment while swinging both arms.
The purpose of this paper is to analyze and measure the internal SAR (specific absorption rate) distribution in a human abdomen created by portable radio terminal antennas at 150 MHz. To this end, we have developed a unique phantom that can be split into two pieces in the longitudinal direction along its center. A thermographic technique is used for the SAR measurement in the cut plane of the phantom. An analytical approach involving thermal analysis using the finite element method was conducted in conjunction with EM analysis by FDTD to estimate the cooling effects that occur by thermal diffusion in the phantom after exposure to EM energy.
To determine the effective performance of handheld cellular radio antenna, it is essential to evaluate the electromagnetic (EM) interaction between the antenna and the human body. EM evaluation using the real human bodies has drawbacks such as poor repeatability and traceability. This is because the different ways of holding the terminal give a variety of geometric relationship between the terminal and the human head and hand. To develop antennas that are less affected by the human body, the mechanisms for the variations in the characteristics with respect to the antenna structure, caused by absorption in each region of the human body, must be considered. However, measurements made with the respective parts of real human bodies are difficult. Thus, human phantoms are widely used in the various fields of antenna engineering to solve these problems. In realizing human phantoms for the purpose of antenna design, there are two points that have to be considered; (1) What kind of antenna to be estimated? (2) What kind of characteristic to be measured? This paper presents recent status and some technological issues for the development of human phantoms used for antenna designs from the above-mentioned two perspectives. Furthermore, as a new trend of phantom applications towards future wireless radios, MIMO over-the-air testing (MIMO-OTA) using a phantom and an arm-waving dynamic phantom for the assessment of body area network (BAN) systems are briefly introduced.
A cylindroid whole body phantom is proposed to evaluate the local specific absorption rate (SAR) and radiation characteristics when a small normal-mode helical antenna (NHA) of a 150-MHz wireless terminal is in the vicinity of the abdomen of a human body. For their investigations, the distance between the NHA and phantom was set to the value in actual usage conditions. The thermography method is employed to evaluate the local SAR. It was confirmed that the local SAR of a wireless terminal with a transmission output of 5 W did not exceed 5 W/kg even in impedance-matched conditions. In addition, to check the interrelationship between the local SAR and radiation characteristics in actual usage conditions, an analysis that considered impedance mismatch loss was employed. The results show that the rise of the local SAR decreased by deterioration of the radiated power due to mismatch loss when accompanying a phantom approach. Although the local SAR for a mismatch condition did not exceed 1.2 W/kg regardless of the distance, the maximum gain deteriorated at least 10 dB compared with the matching condition. The authors show that by setting the target value of the local SAR to at most 2 W/kg and controlling the matching condition or available power of the power supply, the gain can be improved 5 dB or more. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 48–60, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10084
This paper presents a simple abdomen model of pregnant women and the evaluation of the specific absorption rate (SAR) inside the proposed model close to normal mode helical antennas (NHAs), which are replacing the portable radio terminals for business at 150 MHz. First, dielectric properties of amniotic fluid and those of fetus of rabbit, which have about the same electrical properties as human, are measured. As a result, the conductivity of ammotic fluid is 1.8 times and that of fetus is 1.3 times higher than that of adult muscle at 150 MHz. The result also suggests the modeling of pregnant women including the ammotic fluid and the fetus is necessary. Next, a simple abdomen model of pregnant women based on the measurements of magnetic resonance (MR) images of Japanese women in the late period of pregnancy is proposed. Finally, the SAR inside the proposed abdomen model close to 0.11 lambda and 0.18 lambda NHAs is calculated using the finite-difference time-domain (FDTD) method. As a result, we have confirmed that the 10-g average SAR in the fetus is sufficiently less than 2 W/kg, when the output power of NHAs is 5 W, which is the maximum power of portable radio terminals in Japan.
This paper, presents an automatic impedance matching technique for normal mode helical antenna technique for a normal mode helical antenna near a human operator in the 150 MHz band. The helical antenna incorporating varactor diodes for changing impedance maintains a good matching condition regardless of the distance between the helical antenna and the operator. This eliminates a power loss caused by the impedance mismatch due to the human body. The technique makes use of the steepest gradient algorithm that can achieve an adaptive control algorithm of the impedance condition.
Antenna fundamentals and definitions are examined, taking into account
electromagnetic fundamentals, the solution of Maxwell's equations for
radiation problems, the ideal dipole, the radiation pattern, directivity
and gain, reciprocity and antenna pattern measurements, antenna
impedance and radiation efficiency, antenna polarization, antennas in
communication links and radar, and the receiving properties of antennas.
Some simple radiating systems are considered along with arrays, line
sources, wire antennas, broadband antennas, moment methods, and aperture
antennas. High-frequency methods and aspects of antenna synthesis are
discussed, giving attention to geometrical optics, physical optics,
wedge diffraction theory, the ray-fixed coordinate system, the
cylindrical parabolic antenna, and linear array methods.
When a portable telephone is used close to a human head, the handset and the shoulder are in close proximity because the shoulder is raised. Thus, the shoulder could influence the antenna characteristics of the handset. However, there have been few reports dealing with such effects. This paper describes a basic study of the effects of the shoulder on the impedance and radiation characteristics of a half-wavelength dipole antenna located near the head at 900 MHz. Further study shows that there is a change in the mean effective gain (MEG) in a multiple radio wave environment, and the mechanism by which this change is effected in relation to antenna location and polarization is clarified. The wire-grid method is employed in modeling the human body as a cylindrical head and a trapezoidal left shoulder. Studies were also conducted using a dipole antenna close to a homogeneous human phantom and an adult man. The analysis of MEG is verified through indoor RFM measurements. The analytical and empirical results indicate that when the dipole antenna is in a horizontal position the radiation to the shoulder is suppressed and consequently a greater radiation intensity at the higher elevation angles of radio signal arrival is obtained due to the presence of the shoulder. This effect results in MEG values 0.8 to 2 dB greater than those obtained from the human model without a shoulder. These facts suggest that the presence of the shoulder should be taken into account when an adequately accurate evaluation of the radiation characteristics of portable telephone antennas is needed, since portable telephones are commonly near the horizontal orientation in the usual talk position. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(1): 21–30, 2001
The purpose of this work is to make a wire-grid analysis of a
diversity antenna comprising a whip antenna and a built-in planar
inverted F antenna (PIFA) to include the electromagnetic effects of a
human operator and to evaluate the diversity performance with regard to
the head-to-radio separation under various incident radio wave
environments. Investigations are also made on the power absorbed in the
head, hand and shoulder, on the power loss due to impedance mismatch,
and on the dissipated power in a non-excited element when the
head-to-radio separation is changed. From the results, a mechanism for
changing radiation efficiency is explained
Portable radio antenna performance on the human body was measured
for several different radio models in the 150, 450, 800, and 900 MHz.
bands. In-vehicle measurements were made at an outdoor antenna range
equipped with a vehicle turntable. All other measurements were made in
an anechoic chamber. Tests were made at the head level, at the
side-level swivel-type carry case, at the side-level belt-loop type
carry case, and at the shoulder level with a speaker microphone antenna.
A statistical analysis was made of the data for use in coverage
propagation predictions, and system designs. The results of the
statistical analysis are presented
Fifth-scale phantom models were exposed to 2450-MHz electromagnetic fields to obtain the average specific absorption rate (SAR) and SAR distribution in man exposed to 1 mW/cm2 450-MHz radiofrequency radiation for various polarizations and body positions. The average SAR was measured calorimetrically and SAR distribution was determined thermographically using an interactive computer system, The mean SAR, as averaged over the body, remained relatively constant at 0.050 W/kg, with a standard deviation of +-0.007 W/kg for all polarizations and body postures considered in the study. Peak SAR values were as high as 0.650 W/kg, occuring typicaly in the wrist.
Analysis of mutual impedance of a normal mode helical antenna
- Cho K
Theoretical study of resonant length of vertical mode helical antenna
- Inagaki N
- Tamura K
- Fujimoto K
Fundamental study of SAR measurement by thermography using a brain-equivalent solid phantom
- Okano T
- Hase A
- Ito K
A study on the human phantom model for analysis of a 150 MHz band small antenna
- Koyanagi Y
- Asahina T
- Ogawa K
- Ito K
Analysis of a dipole antenna placed near a human body
- Koyanagiy Ogawak
Theoretical study of resonant length of vertical mode helical antenna
- Inagaki N
An analysis of the performance of a handset diversity antenna influenced by head hand and shoulder effects at 900 MHz
- Monmak Ogawak Matsuyoshit
A study on the human phantom model for analysis of a 150 MHz band small antenna
- Koyanagi Y
Fundamental study of SAR measurement by thermography using a brain‐equivalent solid phantom
- Okano T
Practical usefulness of normal mode helical antenna
- Hiroiy Fujimotok