Akira Itou

Ally Y Simba

Lira Hamada

Soichi Watanabe

Takuji Arima

Toru Uno

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TABLE I: ELECTRICAL PROPERTIES OF THE NaCl SOLUTION USED IN EQUIVALENT ANTENNAS WITH CONCENTRATION OF 
2.7 % 
f [MHz] 30 40 45 60 80 100
εr 86.4 85.2 84.7 83.5 81.7 80.7
σ[S/m] 4.04 4.05 4.06 4.07 4.09 4.09
Comparison of Induced Ankle Currents of the Human-Body Equivalent Antennas 
and Anatomically Human Models Exposed to Nearby Monopole Antennas 
 
Ally Y. Simba1, Akira Itou1, 2, Lira Hamada1, Soichi Watanabe1, Takuji Arima1, 2, and Toru Uno2  
 
1National Institute of Information and Communications Technology, Tokyo, Japan 
 
2Tokyo University of Agriculture and Technology, Tokyo, Japan 
Email: simba@nict.go.jp 
 
Abstract 
 
 In this paper, the induced ankle currents of the liquid-type human-body equivalent antennas are compared to 
those of their corresponding Japanese adult male and female models when exposed to monopole antennas placed at a 
distance of 3 m away. The purpose is to determining if they will be in good agreement like the case of plane wave 
exposure from which they were designed. The investigation of the monopole antennas exposure is important, because 
they have been used to provide experimental validation of the performance of the equivalent antennas. Our results 
indicate that good agreement in induced ankle current is obtained for the frequencies above 45 MHz. This may be 
explained by the fact that at the frequencies above 45 MHz, at 3 m distance away, the equivalent antennas appear to be 
at far fields of the monopole antennas, at which the fields becomes almost like those of the plane wave.  
 
1. Introduction 
 
 At Very High Frequency (VHF) bands (30-300 MHz) the power absorption by the human body due to RF 
exposure reaches maximum values. This is because the whole-body resonant absorption frequencies lie within this 
region [1]. It is known that large current flows at the ankle if the human body stands on the ground at the whole-body 
resonant condition. The local SAR around the ankle (SAR ankle) can be estimated from the induced ankle current 
(I_ankle) and the equivalent section area of the ankle (A_ankle), i.e., SAR_ankle = (I_ankle/A_ankle)2/sigma. As a 
result, the induced ankle current is used as an additional exposure limit in the VHF bands in the ICNIRP and IEEE 
guidelines. The liquid-type human-body equivalent antenna that can be used for measuring these currents has been 
previously proposed [2]. The antennas consist of acrylic rectangular blocks and metal plate, which are filled with NaCl 
solution and connected together using conducting pins. While we have conducted detail investigation of the induced 
currents of the equivalent antennas using plane wave exposure, and validated our numerical calculations using 
experimental results obtained when the antennas are irradiated with nearby monopole antennas, there have been no 
investigations to compare the induced ankle currents of the equivalent antennas and their corresponding human model 
so far. This is important because, we have been using monopole exposures to validate our numerical assumptions. In 
this paper we consider equivalent antennas for adult Japanese male and female models [3]. The induced ankle currents 
are calculated using non-uniform mesh FDTD analysis to minimize computer resources [4].  
 
2. Equivalent Antennas and Method of Calculation 
 
2.1 Equivalent Antennas 
 
 Fig.1 shows the structures of the liquid-type human-body equivalent antennas for the adult male and female 
Japanese models [3]. The equivalent antenna for the adult male model is made up acrylic blocks placed on top of metal 
plate; they are connected together using conducting pins. Antenna for female model is made up of 5 blocks. The 
antennas are filled with NaCl whose electrical properties are obtained by measurements. The electrical properties of the 
liquid used are listed in Table I. It should be noted here that, the electrical properties of the human models were derived 
from Gabriel reports [5]. 
978-1-4244-6051-9/11/$26.00 ©2011 IEEE
1600 mm
1900 mm
 
Fig. 1 Liquid-type human-body equivalent antennas. From left to
right: Antenna for adult male, and female 
20 40 60 80 10
0
10
20
30
40
50
In
d
uc
e
d 
an
kl
e 
cu
rr
e
nt
 [
m
A
]
Frequency [MHz]
 Human model
 Equivalent antena
Adult male model
          
20 40 60 80 10
0
10
20
30
40
In
du
ce
d 
an
kl
e 
cu
rr
en
t 
[m
A
]
Frequency [MHz]
 Human model
 Equivalent antena
Female model
   
(a) Adult male                                                                                           (b)  Female 
Fig. 3. Frequency characteristics of the induced ankle currents of the human models and their equivalent antennas when exposed to nearby monopole
antennas. (a) Adult male, and (b) Female 
20 40 60 80 10 120
10
20
30
40
50
60
In
d
u
c
e
d
 a
n
kl
e
 c
u
rr
e
n
t 
[m
A
]
Frequency [MHz]
 Human model
 Equivalent antena
Adult male model
       
20 40 60 80 10 120
10
20
30
40
50
60
In
d
uc
e
d 
an
kl
e 
c
ur
re
nt
 [
m
A
]
Frequency [MHz]
 Human model
 Equivalent antena
Female model
    
(b) Adult male                                                                                           (b)  Female 
Fig. 2. Frequency characteristics of the induced ankle currents of the human models and their equivalent antennas when exposed to plane wave
exposure. (a) Adult male, and (b) Female 
2.2 Method of Calculation 
 
The non-uniform mesh FDTD technique was used in this 
investigation to minimize computer resources. This technique, 
which is based on Maxwell’s curl equations represented by 
midpoint method and Yee-cell notation, utilizes either a linear 
or quadratic interpolation at the coarse-fine cell boundary to 
reduce reflection errors [4]. 
Throughout this work, a fine-size cells of Δx = Δy = Δz = 2 
mm were used to model the regions around the monopole 
antennas and human model. Other areas of the FDTD 
problem space were modeled with coarse-size cells of 20 mm 
in all directions. During equivalent antenna calculations, a 
fine-size cells of Δx = Δy = Δz = 5 mm were used. The 
coarse-size cell must be ≤ λ/15, where λ is the free space 
wavelength. 
Beranger’s perfect matched layer (PML) [6] having 8 layers 
and M = 4 are placed at all boundaries of the FDTD problem 
space to absorb the radiated outgoing waves. Metallic structures such as ground plane, equivalent antenna metallic plate 
and connecting pins, were modeled as a perfect electric conductor (PEC) by setting all of their E-fields to be equal to 
zero. 
TABLE II: FAR FIELD DISTANCE OF MONOPOLE ANTENNAS AT A GIVEN FREQUENCY 
f [MHz] 28.6 35.740 45.0 56.5 70.9 88.8
d [m] 5.3 4.2 3.3 2.7 2.1 1.7
 
3. Results and Discussions 
 
 Fig. 2 compares the induced ankle currents of the equivalent antennas and their corresponding human model 
when exposed to E-polarized plane wave exposure. We observed good agreement between the results with maximum 
difference of less than 10-% [2]. 
 Comparison of the induced ankle currents for monopole antennas exposure is given in Fig.3. They were exposed 
by monopole antennas operating at 28.6, 35.7, 45.0, 56.5, 70.9, and 88.8 MHz. We observed large differences at lower 
frequencies, for example the difference of 12.5, 14.4 and 10.3% were recorded at the frequencies of 28.6, 35.7 and 45.0 
MHz, respectively, for the female model. These large differences, at these frequencies, may be explained by the fact 
that for the distance of 3 m from monopole antennas, the equivalent antennas are in fact in the near field region of the 
monopole antennas. This can be argument may be support by calculating the far field distance of the antennas as 
indicated in Table. For the far field condition of the of the monopole antenna to be satisfied the distance d must satisfy 
the equation: λ/2 2Dd ⋅≥ . 
We can clearly see in Table II that for the frequency below 45 MHz, the equivalent antennas are in the near field.  
 
5. Conclusion 
 
 In this paper, we have compared the induced ankle currents of the liquid-type human-body equivalent antennas 
and their corresponding Japanese adult male and female models. We have found that good agreement is obtained when 
the equivalent antennas are placed at a distance such that they are in the far field of the monopole antennas. At the far 
field of the monopole antennas the exposure field may be similar to the plane wave exposure, which was used in the 
design of the equivalent antennas. 
 
6. Acknowledgments 
 
 Calculations in this work have been conducted using the supercomputer (NEC/SX-8R) at the National Institute 
of Information and communications Technology. 
 
7. References 
 
1. P. J.  Dimbylow, “Fine resolution calculations of SAR in the human body for frequencies up to 3 GHz.,” Physics in 
Medicine and Biology, vol. 47, pp. 2835-2846, July, 2002  
 
2. A. Y. Simba, A. Itou, T. Arima, S. Watanabe, and T. Uno, “Improving the performance of a Liquid-Type Human-
Body Equivalent antenna,” European Bioelectromagnetics Association, EBEA 2011, Abstract Collection, 5207, Feb, 
2011.  
 
3. T. Nagaoka, S. Watanabe, K. Sakurai, E. Kunieda,  S. Watanabe, M. Taki, and Y. Yamanaka, “Development of 
realistic high-resolution whole-body voxel models of Japanese adult males and females of average height and weight, 
and application of the models to radio-frequency electromagnetic-field dosimetry,” Physics in  Medicine and Biology, 
vol.4, pp. 2319-2329, Dec. 2003 
 
4. H. Jiang and H. Arai, “Analysis of computational error in antenna’s simulation by using Non-Uniform Mesh FDTD,” 
IEICE Trans. Communication, Vol. E83-B, no. 7, pp. 1544-1553,  July 2000. 2005.  
 
5. R C. Gabriel, “Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies”, 
Technical reports, Brooks Air Force, AL/OE-TR-1996-0037 
 
6. J. P. Berenger, “A Perfectly Matched Layer for the Absorptions of Electromagnetic Waves,” Journal of 
Computational Physics, Vol. 114, No. 2, pp. 185-200, Oct. 1994. 


COMPARISON OF INDUCED ANKLE CURRENTS OF THE HUMAN-BODY EQUIVALENT ANTENNAS AND ANATOMICALLY HUMAN MODELS EXPOSED TO NEARBY MONOPOLE ANTENNAS

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=E01D39847A0761FAD3C045DDACABC3EB?doi=10.1.1.1050.7935&rep=rep1&type=pdf

COMPARISON OF INDUCED ANKLE CURRENTS OF THE HUMAN-BODY EQUIVALENT ANTENNAS AND ANATOMICALLY HUMAN MODELS EXPOSED TO NEARBY MONOPOLE ANTENNAS

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