SAR Report

FCC ID: LDK102044

RF Exposure Info

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FCCID_247556

SAR COMPLIANCE TESTING OF CISCO MODEL AIR-CB20A-A-K9 (FCC ID# LDK102044)

PC CARD INSERTED INTO A LAPTOP COMPUTER

May 29, 2002

Submitted to: Mr. Jim Nicholson
EMC Compliance Engineer
EAG WNBU Engineering
Cisco Systems, Inc.
320 Springside Drive, Suite 350
Akron, Ohio 44333

Submitted by: Om P. Gandhi
Professor of Electrical and Computer Engineering
University of Utah
50 S Central Campus Dr., Rm. 3280
Salt Lake City, UT 84112-9206

SAR COMPLIANCE TESTING OF CISCO MODEL AIR-CB20A-A-K9 (FCC ID# LDK102044)

PC CARD INSERTED INTO A LAPTOP COMPUTER

I. Introduction

The U.S. Federal Communications Commission (FCC) has adopted limits of human

exposure to RF emissions from mobile and portable devices that are regulated by the FCC [1].

The FCC has also issued Supplement C (Edition 97-01) to OET Bulletin 65 [2] and a more recent

version of the same [3] defining both the measurement and the computational procedures that

should be followed for evaluating compliance of mobile and portable devices with FCC limits for

human exposure to radiofrequency emissions.

We have used both the measurement and computational procedures for SAR compliance

testing of the Cisco Model PC Card (FCC ID# LDK102044) inserted into a Laptop computer. A

photograph of the unit with the Cisco Model AIR-CB20A-A-K9 PC Card inserted into a laptop

computer is given in Fig. 1. A picture of the Model AIR-CB20A-A-K9 PC Card placed on the

laptop is given in Fig. 2. The Cisco Model AIR-CB20A-A-K9 PC Card operates over the

frequency band 5150 to 5350 MHz with a nominal transmit power of 13.2 dBm (20.9 mW).

An engineering drawing of the Model AIR-CB20A-A-K9 PC Card is given in Fig. 3. For

spatial diversity, the Model AIR-CB20A-A-K9 PC Card uses two rectangular patch antennas each
of dimension 0.67" × 0.61". Also used for each of the antennas is a parallel rectangular parasitic

patch of identical dimensions 0.67" × 0.61" with a separation of 0.79" above the driven elements.

At any given time, one of the two antennas is used as a transmitting antenna while the other is used

as a receiving antenna.

For SAR measurements, two configurations of the wireless PC relative to the experimental

phantom have been used:

a. Since the wireless PC may possibly be placed on a user's lap where the RF antennas would
be the closest to the body, a planar phantom model with inside dimensions 12" × 16.5"

(30.5 × 41.9 cm) and a base thickness of 2.0 ± 0.2 mm (recommended in [3]) was used

for SAR measurements and the wireless PC cards mounted in a portable computer (as in

Fig. 1) pressed against the bottom of this phantom (see Fig. 4).
b. For a bystander, the "end-on" SAR value is obtained for the PC and the card edge at 90° to

the flat phantom with a spacing of 2.5 cm (see Fig. 5).

II. Computation of SAR Distributions

The Finite Difference Time-Domain Method

One of the most successful and versatile methods for SAR calculations is the finite-

difference time-domain (FDTD) method. This method was first proposed by Yee [4] and later

developed by Taflove and colleagues [5-7], Holland [8], and Kunz and Lee [9]. This method has

been extensively used for calculations of the distributions of electromagnetic (EM) fields and SARs

in anatomically-based models of the human body for whole-body or partial-body exposures due to

far-field or near-field irradiation conditions [10, 11]. In this method, the time-dependent

Maxwell's curl equations

∂H ∂E
∇× E = -µ , ∇ × H =σ E +ε (1)
∂t ∂t

are implemented for a lattice of subvolumes or "cells" that may be cubical or parallelepiped with
different dimensions δx, δy, and δz in x-, y-, or z-directions, respectively. The components of E

and H are positioned about each of the cells as shown in Fig. 6 and calculated alternately with half-
time steps where the time step δt = δ/2c where δ is the smallest of the dimensions used for each of

the cells and c is the maximum phase velocity of the fields in the modeled space. Since some of the

modeled volume is air, c corresponds to the velocity of EM waves in air. The details of the method

are given in several of the above referenced publications [4-9] and will, therefore, not be repeated

here.

In the FDTD method, it is necessary to represent not only the absorber/scatterer such as the

human body or a part thereof, but also any near-field source/s such as the two antenna and the rest

2

VI. The Measured SAR Distributions

The SAR distributions were determined using the automated SAR measurement system

developed at the University of Utah [15]. As described in [15], this SAR measurement system has

been validated using a number of wireless telephones at 835 and 1900 MHz, respectively.

The highest SAR region for each of the measurement frequencies (5.18, 5.26, and 5.32

GHz) was identified in the first instance by using a coarser sampling with a step size of 8.0 mm
over three overlapping areas for a total scan area of 8.0 × 9.6 cm. After identifying the region of

the highest SAR, the SAR distribution was measured with a resolution of 2 mm in order to obtain

the peak 1 cm3 or 1-g SAR. As given in [15], the SAR measurements are performed at 4, 6, 8,

10, 12 mm height from the bottom surface of the body-simulant fluid. The SARs thus measured

were extrapolated to obtain values at 1, 3, 5, 7 and 9 mm height and used to obtain 1-g SARs. The

uncertainty analysis of the University of Utah SAR measurement system is given in Appendix A.

The combined standard uncertainty is ± 8.3%.

The SAR distributions were measured for transmit frequencies of 5.18, 5.26, and 5.32

GHz and are given in Tables 1-3 for the "above-lap" position and in Tables 4-6 for the "end-on"

position, respectively. The peak 1-g SARs are summarized in Table 7. For the measurements in

Table 1, 2, and 3, the separation between the Cisco Model AIR-CB20A-A-K9 PC Card and the

bottom of the experimental phantom is on the order of 1 cm. For the "end-on" position, the
separation between the card edge at 90° to the bottom of the flat phantom is 2.5 cm and the SAR

distributions at 5.18, 5.26, and 5.32 GHz are given in Tables 4, 5, and 6, respectively.

The experimentally-determined peak 1-g SARs for the "above-lap" position in Tables 1-3

are somewhat lower but of the same order of magnitude as the calculated peak 1-g SAR of 0.146

W/kg in Section II. The slightly lower SARs may well be due to the conducted RF power for this

particular laptop being somewhat less than the nominal power of 13.2 dBm assumed for the SAR

calculations. In any case, it may be noted that both the calculated and measured 1-g SARs (given

in Table 7) are significantly less than the FCC 96-326 guideline of 1.6 W/kg.

6

VII. Comparison of the Data With FCC 96-326 Guidelines

According to the FCC 96-326 Guideline [1], the peak SAR for any 1-g of tissue should not

exceed 1.6 W/kg. For the maximum radiated power condition of 13.2 dBm (20.9 mW), the Cisco

AIR-CB20A-A-K9 PC Card has been measured to give peak 1-g SARs of 0.064 to 0.127 W/kg

which are considerably smaller than 1.6 W/kg.

7

REFERENCES

1. Federal Communications Commission, "Guidelines for Evaluating the Environmental Effects
of Radiofrequency Radiation," FCC 96-326, August 1, 1996.

2. K. Chan, R. F. Cleveland, Jr., and D. L. Means, "Evaluating Compliance With FCC
Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields," Supplement C
(Edition 97-01) to OET Bulletin 65, December, 1997. Available from Office of Engineering
and Technology, Federal Communications Commission, Washington D.C., 20554.

3. Federal Communications Commission "Supplement C Edition 01-01 to OET Bulletin 65
Edition 97-01" June 2001.

4. K. S. Yee, "Numerical Solution of Initial Boundary Value Problems Involving Maxwell's
Equations in Isotropic Media," IEEE Transactions on Antennas and Propagation, Vol. AP-
14, pp. 302-307, 1966.

5. A. Taflove and M. E. Brodwin, "Computation of the Electromagnetic Fields and Induced
Temperature Within a Model of the Microwave Irradiated Human Eye," IEEE Transactions
on Microwave Theory and Techniques, Vol. MTT-23, pp. 888-896, 1975.

6. A. Taflove, "Application of the Finite-Difference Time-Domain Method to Sinusoidal Steady-
State Electromagnetic-Penetration Problems," IEEE Transactions on Electromagnetic
Compatibility, Vol. EMC-22, pp. 191-202, 1980.

7. K. Umashankar and A. Taflove, "A Novel Method to Analyze Electromagnetic Scattering of
Complex Objects," IEEE Transactions on Electromagnetic Compatibility, Vol. EMC-24, pp.
397-405, 1982.

8. R. Holland, "THREDE: A Free-Field EMP Coupling and Scattering Code," IEEE
Transactions on Nuclear Science, Vol. NS-24, pp. 2416-2421, 1977.

9. K. S. Kunz and K. M. Lee, "A Three-Dimensional Finite-Difference Solution of the External
Response of an Aircraft to a Complex Transient EM Environment. The Method and Its
Implementation," IEEE Transactions on Electromagnetic Compatibility, Vol. 20, pp. 328-
3342, 1978.

10. O. P. Gandhi, "Some Numerical Methods for EM Dosimetry: ELF to Microwave
Frequencies," Radio Science, Vol. 30, pp. 161-177, January/February, 1995.

11. O. P. Gandhi, G. Lazzi, and C. M. Furse, "Electromagnetic Absorption in the Human Head
and Neck for Mobile Telephones at 835 and 1900 MHz," IEEE Transactions on Microwave
Theory and Techniques, Vol. 44(10), pp. 1884-1897, 1996.

12. G. Lazzi and O. P. Gandhi, "On the Optimal Design of the PML Absorbing Boundary
Condition for the FDTD Code," IEEE Transactions on Antennas and Propagation, Vol. 45,
pp. 914-916, 1997.

13. ITT Handbook, Reference Data for Radio Engineers, Fifth Edition, Howard W. Sams & Co.
Inc, p. 4-19, 1968.

8

14. O. P. Gandhi and J-Y. Chen, "Electromagnetic Absorption in the Human Head from
Experimental 6-GHz Handheld Transceivers," IEEE Transactions on Electromagnetic
Compatibility, Vol. 39(4), pp. 547-558, 1995.

15. Q. Yu, O. P. Gandhi, M. Aronsson, and D. Wu, "An Automated SAR Measurement System
for Compliance Testing of Personal Wireless Devices," IEEE Transactions on
Electromagnetic Compatibility, Vol. 41(3), pp. 234-245, August 1999.

16. IEEE Std. 1528 - Draft "Recommended Practice for Determining the Peak Spatial-Average
Specific Absorption Rate (SAR) in the Human Body Due to Wireless Communication
Devices: Experimental Techniques," IEEE SCC34.

9

Table 1. Above-lap position. The SARs measured for the Cisco Model AIR-
CB20A-A-K9 PC Card (nominal power of 13.2 dBm) inserted into a
laptop computer at 5.18 GHz.

1-g SAR = 0.127 W/kg

a. At depth of 1 mm

0.171 0.184 0.181 0.172 0.164
0.179 0.194 0.189 0.193 0.189
0.188 0.199 0.192 0.187 0.179
0.186 0.187 0.194 0.199 0.193
0.176 0.180 0.202 0.190 0.171

b. At depth of 3 mm

0.140 0.147 0.146 0.139 0.133
0.145 0.156 0.154 0.152 0.149
0.149 0.157 0.153 0.150 0.147
0.149 0.151 0.157 0.159 0.152
0.144 0.148 0.159 0.148 0.135

c. At depth of 5 mm

0.116 0.118 0.119 0.113 0.109
0.119 0.125 0.126 0.121 0.118
0.117 0.124 0.123 0.121 0.121
0.120 0.123 0.127 0.128 0.121
0.117 0.123 0.125 0.116 0.106

d. At depth of 7 mm

0.097 0.097 0.098 0.093 0.090
0.100 0.102 0.104 0.098 0.096
0.096 0.099 0.101 0.099 0.101
0.098 0.102 0.105 0.104 0.096
0.098 0.103 0.100 0.092 0.083

e. At depth of 9 mm

0.084 0.085 0.084 0.080 0.078
0.088 0.086 0.089 0.083 0.082
0.082 0.083 0.086 0.085 0.088
0.085 0.087 0.091 0.088 0.082
0.085 0.090 0.084 0.077 0.068

10

Table 2. Above-lap position. The SARs measured for the Cisco Model AIR-
CB20A-A-K9 PC Card (nominal power of 13.2 dBm) inserted into a
laptop computer at 5.26 GHz.

1-g SAR = 0.108 W/kg

a. At depth of 1 mm

0.138 0.144 0.154 0.151 0.141
0.141 0.155 0.155 0.150 0.152
0.149 0.161 0.170 0.166 0.156
0.152 0.157 0.164 0.157 0.163
0.142 0.152 0.154 0.155 0.144

b. At depth of 3 mm

0.117 0.120 0.126 0.125 0.117
0.116 0.126 0.126 0.124 0.123
0.124 0.131 0.137 0.135 0.126
0.123 0.128 0.132 0.125 0.127
0.118 0.122 0.124 0.125 0.119

c. At depth of 5 mm

0.101 0.101 0.104 0.104 0.097
0.097 0.104 0.104 0.103 0.100
0.104 0.109 0.112 0.110 0.103
0.102 0.106 0.107 0.100 0.099
0.100 0.100 0.100 0.102 0.098

d. At depth of 7 mm

0.088 0.087 0.088 0.089 0.083
0.083 0.087 0.087 0.088 0.083
0.090 0.091 0.094 0.092 0.086
0.086 0.088 0.088 0.082 0.080
0.085 0.083 0.083 0.085 0.082

e. At depth of 9 mm

0.078 0.078 0.078 0.078 0.073
0.074 0.075 0.077 0.077 0.073
0.080 0.079 0.082 0.079 0.076
0.075 0.076 0.075 0.070 0.069
0.075 0.072 0.072 0.074 0.071

11

Table 3. Above-lap position. The SARs measured for the Cisco Model AIR-
CB20A-A-K9 PC Card (nominal power of 13.2 dBm) inserted into a
laptop computer at 5.32 GHz.

1-g SAR = 0.096 W/kg

a. At depth of 1 mm

0.122 0.127 0.131 0.129 0.129
0.125 0.131 0.139 0.131 0.125
0.134 0.138 0.129 0.132 0.115
0.114 0.118 0.134 0.123 0.125
0.114 0.116 0.112 0.123 0.119

b. At depth of 3 mm

0.110 0.112 0.112 0.111 0.109
0.108 0.111 0.114 0.113 0.108
0.112 0.113 0.109 0.110 0.100
0.098 0.104 0.110 0.105 0.108
0.101 0.100 0.099 0.104 0.099

c. At depth of 5 mm

0.100 0.099 0.097 0.097 0.094
0.094 0.095 0.095 0.098 0.094
0.095 0.094 0.093 0.093 0.087
0.085 0.091 0.092 0.091 0.094
0.090 0.087 0.088 0.090 0.084

d. At depth of 7 mm

0.091 0.089 0.087 0.087 0.083
0.085 0.083 0.082 0.086 0.085
0.083 0.080 0.082 0.080 0.076
0.076 0.081 0.079 0.081 0.083
0.081 0.077 0.079 0.079 0.074

e. At depth of 9 mm

0.083 0.081 0.080 0.080 0.076
0.079 0.075 0.075 0.078 0.079
0.075 0.071 0.074 0.072 0.068
0.071 0.074 0.072 0.075 0.075
0.075 0.071 0.073 0.072 0.067

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Table 4. End-on position. The SARs measured for the Cisco Model AIR-
CB20A-A-K9 PC Card (nominal power of 13.2 dBm) inserted into a
laptop computer at 5.18 GHz. Distance to the bottom of the flat phantom
= 2.5 cm.

1-g SAR = 0.089 W/kg

a. At depth of 1 mm

0.137 0.121 0.136 0.140 0.139
0.144 0.141 0.141 0.136 0.137
0.153 0.135 0.132 0.131 0.110
0.130 0.116 0.123 0.115 0.116
0.121 0.115 0.112 0.126 0.086

b. At depth of 3 mm

0.109 0.109 0.110 0.113 0.113
0.120 0.116 0.115 0.114 0.112
0.117 0.110 0.111 0.103 0.091
0.101 0.094 0.097 0.090 0.089
0.093 0.094 0.093 0.097 0.076

c. At depth of 5 mm

0.088 0.097 0.090 0.092 0.093
0.100 0.097 0.095 0.096 0.092
0.091 0.089 0.093 0.080 0.076
0.079 0.076 0.076 0.071 0.068
0.072 0.076 0.078 0.075 0.067

d. At depth of 7 mm

0.072 0.086 0.075 0.077 0.079
0.085 0.082 0.080 0.082 0.078
0.072 0.074 0.078 0.063 0.064
0.062 0.062 0.061 0.057 0.055
0.056 0.063 0.065 0.058 0.058

e. At depth of 9 mm

0.064 0.076 0.066 0.069 0.070
0.074 0.073 0.071 0.072 0.070
0.062 0.063 0.067 0.052 0.055
0.051 0.051 0.050 0.049 0.048
0.047 0.054 0.057 0.047 0.048

13

Table 5. End-on position. The SARs measured for the Cisco Model AIR-
CB20A-A-K9 PC Card (nominal power of 13.2 dBm) inserted into a
laptop computer at 5.26 GHz. Distance to the bottom of the flat phantom
= 2.5 cm.

1-g SAR = 0.082 W/kg

a. At depth of 1 mm

0.113 0.112 0.109 0.122 0.106
0.109 0.107 0.110 0.104 0.108
0.116 0.107 0.113 0.116 0.114
0.119 0.114 0.107 0.120 0.108
0.112 0.125 0.117 0.116 0.108

b. At depth of 3 mm

0.095 0.094 0.093 0.101 0.090
0.091 0.090 0.092 0.088 0.087
0.095 0.090 0.095 0.096 0.094
0.095 0.095 0.092 0.098 0.089
0.093 0.099 0.099 0.096 0.089

c. At depth of 5 mm

0.080 0.080 0.080 0.084 0.077
0.077 0.077 0.077 0.075 0.072
0.078 0.077 0.080 0.079 0.078
0.077 0.079 0.079 0.081 0.073
0.078 0.078 0.082 0.080 0.075

d. At depth of 7 mm

0.069 0.070 0.070 0.071 0.067
0.066 0.067 0.067 0.064 0.061
0.065 0.067 0.069 0.068 0.067
0.064 0.067 0.069 0.069 0.062
0.067 0.064 0.070 0.068 0.063

e. At depth of 9 mm

0.062 0.063 0.064 0.063 0.060
0.057 0.060 0.059 0.056 0.056
0.057 0.060 0.062 0.060 0.061
0.056 0.059 0.062 0.061 0.054
0.060 0.056 0.062 0.060 0.055

14

Table 6. End-on position. The SARs measured for the Cisco Model AIR-
CB20A-A-K9 PC Card (nominal power of 13.2 dBm) inserted into a
laptop computer at 5.32 GHz. Distance to the bottom of the flat phantom
= 2.5 cm.

1-g SAR = 0.064 W/kg

a. At depth of 1 mm

0.072 0.073 0.077 0.064 0.072
0.073 0.075 0.078 0.076 0.074
0.072 0.081 0.077 0.085 0.081
0.079 0.076 0.068 0.0831 0.076
0.081 0.084 0.079 0.062 0.073

b. At depth of 3 mm

0.067 0.068 0.069 0.064 0.067
0.066 0.067 0.069 0.070 0.069
0.066 0.072 0.069 0.073 0.072
0.073 0.069 0.064 0.074 0.071
0.072 0.072 0.070 0.060 0.063

c. At depth of 5 mm

0.062 0.064 0.063 0.063 0.062
0.061 0.061 0.062 0.065 0.064
0.062 0.064 0.063 0.064 0.064
0.067 0.063 0.060 0.066 0.066
0.064 0.063 0.062 0.057 0.055

d. At depth of 7 mm

0.059 0.060 0.058 0.061 0.058
0.057 0.057 0.057 0.062 0.060
0.059 0.059 0.059 0.058 0.059
0.063 0.059 0.058 0.061 0.062
0.059 0.058 0.056 0.054 0.049

e. At depth of 9 mm

0.056 0.057 0.054 0.058 0.055
0.054 0.054 0.054 0.059 0.057
0.057 0.057 0.055 0.055 0.056
0.059 0.056 0.055 0.058 0.059
0.056 0.055 0.051 0.050 0.045

15

Table 7. The peak 1-g SARs measured for the Cisco Model AIR-CB20A-A-K9 PC
Card (nominal power of 13.2 dBm) inserted into a laptop computer.

1-g SAR in W/kg

Spacing to
PC position relative the bottom of 5.18 GHz 5.26 GHz 5.32 GHz
to the flat phantom the phantom

“Above-lap”: bottom of PC
pressed against bottom of 1 cm 0.127 0.108 0.096
the flat phantom

“End-on”: card edge at 90 °
relative to the bottom of the 2.5 cm 0.089 0.082 0.064
flat phantom

16

z

Ey
Hz
Ex Ex

Ez
Ey

Ez Ez
Hy

Hx

Ex

(i,j,k) Ey
y

x

Fig. 6. A unit cell of Yee lattice indicating positions for the various field
components.

24

APPENDIX A

Uncertainty Analysis
The uncertainty analysis of the University of Utah SAR Measurement System is given in

Table A.1. Several of the numbers on tolerances are obtained by following procedures similar to

those detailed in [15], while others have been obtained using methods suggested in [16].

25

Document Created: 2002-05-30 15:30:13
Document Modified: 2002-05-30 15:30:13

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