RF Exposure and Modular
Equipment Considerations
Washington Laboratories (301) 417-0220 web: www.wll.com
7560 Lindbergh Dr. Gaithersburg, MD 20879
RF Exposure Rules
SAR and MPE Estimation Summary
Based on current interpretations of US
radio law by FCC
Based upon the TCB Exclusion List and
various interpretations by FCC
Based upon experience of ATCB
RF Exposure: SAR or MPE ?
Questions to ask:
o Is device used at less than 20cm to the
body? And is the device above the “Low
Threshold” conditions in the TCB exclusion
list of July 17, 2002?
o Is the device listed in 2.1093(c)?
If the answer to either of the above is YES than
SAR evaluation is required
Definitions and Nomenclature
o Host-independent: certification for device to be
installed and expected to comply in any
applicable host – unfeasible for portable
exposure conditions
o Module: Transmitter operating (usually)
internally as part of another device or product
o Full Modular Approval: Part 15 Tx module that
meets eight criteria of DA 00-1407, e.g., EMC
tested stand-alone (stand-alone SAR is
undefined), FCC ID label on host, etc. A full
Modular approval with unlimited SAR
configurations is not allowed.
Definitions and Nomenclature
o Limited Modular Approval (LMA): LMA is used
with SAR testing on an Unlicensed module to
allow SAR tests to be applied to more than one
model.
o Licensed module: Certification for Licensed Tx
daughter-board or Tx box, installed in RF
category Mobile or Fixed conditions only.
Antenna might be specified with limit on gain.
o Dedicated host: Tx intended for OEM integration
or permanent installation into a specific host
product; also covered by 3-host method for
integral-antenna plug-in cards. Applies
specifically to Part 15 modules above 100mW
Portable Devices
o Operate less then 20cm from any user or bystander
o Usually involves body worn or ear or face held
devices
o SAR Testing required if above the low threshold limit
in July 17, 2002 TCB Exclusion List
o Some devices are specifically required by law to
have SAR testing as a condition of Certification,
regardless of RF Pout.
o Example: Cellphones; 802.11a PCMCIA card
Safety Rule References on Human Exposure
o
o
o
o
o
o
o
o
o
ANSI C95.1
IEEE 1528
OET 65
OET 65-C
FCC Part 1.1037
FCC Part 2.1091
Mobile Devices
FCC Part 2.1093
Portable Devices
FCC Part 15.247(b)(4)
FCC Part 15E
Part 15 and RF Exposure
The FCC will require a MPE study (RF estimation) for both
Mobile and Fixed devices. (i.e.15.247 and UNII devices).
Estimation should be performed with highest gain antenna of
each antenna type.
For SAR and MPE evaluation, the default limits are the
Uncontrolled Environment. It is assumed that users of Part
15 devices have no understanding of radio principals.
You cannot evaluate any Part 15 device to the
Controlled/Occupational limits.
Part 15 and RF Exposure
The vast majority of Low Power Part 15 Intentional
Radiators are categorically excluded from “Routine
Evaluation” under the FCC rules. However, the FCC will
require a SAR test for RF category “Portable” devices if the
power exceeds 60/f(GHz) if contact with antenna is allowed,
or 120mW/f(GHz) if 2.5cm is maintained to the antenna.
Example: 15.231 key fob Tx do not need SAR test
Supplement C: MPE Exposure Limits
(A)
Limits for Occupational/Controlled Exposure
Frequency
Range
(MHz)
Electric Field
Strength (E)
(V/m)
Magnetic Field
Strength (H)
(A/m)
Power Density
(S)
2
(mW/cm )
Averaging Time
2
2
|E| , |H| or S
(minutes)
0.3-3.0
3.0-30
30-300
300-1500
1500-100,000
614
1842/f
61.4
---
1.63
4.89/f
0.163
---
(100)*
2
(900/f )*
1.0
f/300
5
6
6
6
6
6
(B)
Limits for General Population/Uncontrolled Exposure
Frequency
Range
(MHz)
Electric Field
Strength (E)
(V/m)
Magnetic Field
Strength (H)
(A/m)
Power Density
(S)
2
(mW/cm )
Averaging Time
2
2
|E| , |H| or S
(minutes)
0.3-1.34
1.34-30
30-300
300-1500
1500-100,000
614
824/f
27.5
---
1.63
2.19/f
0.073
---
(100)*
2
(180/f )*
0.2
f/1500
1.0
30
30
30
30
30
f = frequency in MHz
*Plane-wave equivalent power density
NOTE 1: See Section 1 for discussion of exposure categories.
NOTE 2: The averaging time for General Population/Uncontrolled exposure to fixed transmitters is not applicable for mobile and
portable transmitters. See 47 CFR §§2.1091 and 2.1093 on source-based time-averaging requirements for mobile and
portable transmitters.
Supplement C: SAR Limits
(A) Limits for Occupational/Controlled Exposure (W/kg)
Whole-Body
Partial-Body
Hands, Wrists, Feet and Ankles
0.4
8.0
20.0
(B) Limits for General Population/Uncontrolled Exposure (W/kg)
Whole-Body
Partial-Body
Hands, Wrists, Feet and Ankles
0.08
1.6
4.0
NOTE 1: See Section 1 for discussion of exposure categories.
NOTE 2: Whole-Body SAR is averaged over the entire body, partial-body SAR is averaged over any 1 gram of
tissue defined as a tissue volume in the shape of a cube. SAR for hands, wrists, feet and ankles is
averaged over any 10 grams of tissue defined as a tissue volume in the shape of a cube.
NOTE 3: At frequencies above 6.0 GHz, SAR limits are not applicable and MPE limits for power density should
be applied at 5 cm or more from the transmitting device.
NOTE 4: The time averaging criteria for field strength and power density do not apply to general population
SAR limit of 47 CFR §2.1093.
MPE Estimation Formula
To Determine Power Density (s):
o S=P x G /4piR2
o FCC requires that RF category “Mobile”
devices calculate power density for 20cm.
o Calculation of power density at other distances
for “Mobile” products not allowed.
o Calculation of power density for “Fixed”
devices is allowed, as long as distance not
shown less than 20cm
Full Modular Approvals (Part 15)
By Definition, these transmitters must have own reference
oscillator. In addition a separate letter on Applicant
letterhead addressing all these items must accompany
the filing:
1. RF shielding.
2. Buffered data input/output ports
3. Power supply regulation
4. Permanent antenna or unique connector
5. Tested in “stand alone” condition
6. Labeled with own ID number
7. Instructions to operator / OEM integrator
8. Must meet RF Exposure requirements.
Limited Modular Approval (LMA) Part 15
If any of the 8 elements on the preceding slide
cannot be met, a limited modular approval may
be obtained in some circumstances. LMAs
define special circumstances where Certification
is valid
Example 1: Wireless mini-PCI 802.11b/g card
without voltage regulation
Example 2: Wireless mini-PCI 802.11b/g card with
SAR results which may apply to a specific
chassis or model notebook PC host.
Licensed Modules
There is officially no such thing as a
“Licensed Modular Transmitter”
The Rules of DA 00-1407 do not apply –
DO NOT ATTEMPT
Complex Example
Notebook PC with built-in Bluetooth, WiFi, and GPRS
o Are Part 15 transmitters separately Certified?
o Are Part 15 transmitters Modular Approved?
o Are any transmitters capable of co-location?
o Is BT below 5mw?
o Are any transmitters end-user installable?
o Labeling?
SAR Testing Updates.
o SAR Probes must be calibrated on a yearly basis.
The only allowed exception is when the probe
manufacturer specifically permits different calibration
intervals.
o Tolerance between RF conducted power measured at
the EMC lab and SAR lab must be within 5%.
Common spectrum analyzers are good to only 1dB
(~25%)
o TCBs now allowed to do SAR approval work from
300MHz to 6GHz.
Additional Documents
FCC has released specific guidance for SAR
testing of WiFi products.
FCC is now specifying specific combinations of
channel, power, and data rates.
FCC has released SAR review to TCBs to
frequencies of 6GHz.
Contact Information
William H. Graff
President and Director of Engineering
AmericanTCB, Inc.
6731 Whittier Ave.
McLean, VA 22101
mailto: whgraff@ATCB.com
Corporate Phone: (703)847-4700
Corporate FAX: (703)847-6888
Direct Mobile:
+886 920399260
SKYPE: whgraff