1. Assessment of Exposure of People to Non-ionising Radiation
STSM COST Action BM0704
Silvia de Miguel Bilbao
Lisbon, 19/04/2012

2. 01 Introduction
02 Objetives
03 Description of the work and results
05 Conclusion: benefit of the placement

3. 01 Introduction
Training and familiarisation with different aspects of assessment of exposure of people to non-ionising radiation.
(27/06/2011 to 08/07/2011)
The STSM stay has been in the centre of radiation, chemical and environmental hazards, Health Protection Agency (HPA)
This centre is in Didcot, Oxfordshire, (England)
Centre for Radiation,
Chemical and
Environmental Hazards.
Health Protection Agency (HPA)
Centre for Radiation, Chemical and
Didcot, Oxfordshire (England, UK)
Centre for Radiation, Chemical and
Environmental Hazards.
Health Protection Agency (HPA)

4. 02 Objetives Activities At HPA ElectroMagnetic Fields (EMF) Group
Measurements of duty factor for Wi-Fi devices: 3 techniques
Methodology of electromagnetic field measurements around selected telecommunication devices:
Wi-Fi
DECT phones
Mobile phone masts
Familiarisation with computational modelling techniques that calculate the exposure of different parts of the human body to electromagnetic fields.
Two further technology centres have been visited:
Vodafone HQ
National Physical Laboratory (NPL)
to become familiarised with some aspects of the assessment
of people’s exposure to non-ionising radiation and the measuring equipment

5. Calculation of the duty factor for Wi-Fi devices
03 Description of the work
Calculation of the duty factor for Wi-Fi devices
The exposure levels from Wi-Fi sources depends on the time during which the devices are transmitting data.
The duty factor is defined as the ratio of the pulse duration to the pulse repetition period.
Duty factor !!
A way to quantify the exposure to electromagnetic fields
Three methods to determine the duty factor were investigated:
The measurement of the channel power with a spectrum analyzer
Using a Transmit Time Accumulator (TTA) device
AirPcap wireless adapter and Wireshark software
The exposure levels from Wi-Fi sources depend on the time during which devices are transmitting information.
The duty factor is defined as the ratio of the pulse duration to the pulse repetition period.
Determining the duty factor is a way to quantify the exposure to electromagnetic fields
Three methods to determine the duty factor:
The measurements of the channel power with the spectrum analyzer
Transmit Time Accumulator (TTA)
TTA + WIRESHARK

6. Duty factor for Wi-Fi devices: spectrum analyzer
03 Description of the work
Duty factor for Wi-Fi devices: spectrum analyzer
Spectrum analyzer: measures the channel power
LanTraffic software: sets and maintains the data rate
The mean of the power is called set point: dBm.
Duty factor is obtained with the following formula:
Duty factor =

7. Duty factor for Wi-Fi devices: counter devices
03 Description of the work
Duty factor for Wi-Fi devices: counter devices
The Transmit Time Accumulator (TTA) is a device designed by HPA to measure the total time that any RF device is actually TRANSMITTING INFORMATION over a given period of time.

8. Wireless interface and Wireshark
03 Description of the work
Wireless interface and Wireshark
The Wireshark shareware software, installed on a laptop, captures the Wi-Fi traffic in the local environment.
Used with Wireshark, an AirPcap wireless adapter connected to the laptop, allows analysis of the captured data packets, and provides the value of the duty factor.
Another method to calculate the transmission time of the laptop is by using a wireless adapter
(AirPcap) connected to the USB port of a laptop that detects the Wi-Fi traffic in the local
environment.
The Wireshark shareware software, installed in the laptop, measures the traffic of the
environment, and provides (before previous calculations) the value of the duty factor.

9. Other measurements with Wi-Fi devices
03 Description of the work
Other measurements with Wi-Fi devices
Investigate the variations of the electric field created by an access point when wires of /2 and /4 length are located at a distance of /2 and /4 from the access point, respectively.
To measure the change in the electric field generated by a Wi-Fi signal that is being attenuated, using two devices inside the GTEM cell: an electric field probe, a dosimeter
Procedure for calculating the Equivalent Isotropically-Radiated Power (EIRP) of a Wi-Fi access point.
Analyze the variations of the electric field created by an access point when wires of /2 and /4 are located at a distance of /2 and /4 from the access point, respectively.
To measure the change in the electric field generated by a Wi-Fi signal that is being attenuated, with two devices inside the GTEM cell:an electric field probe, a dosimeter
Procedure for calculating the Equivalent Isotropically-Radiated Power (EIRP) of a WiFi acces

10. DECT Phone measurements
03 Description of the work
DECT Phone measurements
A basic DECT system consists of two components:
Base station
Handset
The handsets in the coverage area of a base station scan for the best channel available for call setup and the base station continuously scans its idle receive channels in order to detect the set up attempts by the handsets. This procedure involves emissions that can be detected and analyzed.
A basic DECT system consists of two components:
the base station and
the handset.
The handsets in the coverage area of a base station scan for the best channel available for call setup and the base station continuously scans its idle receive channels in order to detect the set up attempts by the handsets. This procedure involves emissions that can be detected and analyzed.

11. DECT measurements: results
03 Description of the work
DECT measurements: results
Beacon pulses from the base station in the frequency domain
The beacon pulses from the fixed part in the frequency domain

12. DECT measurements: results
03 Description of the work
DECT measurements: results
Beacon pulses in the time domain (span = 0 Hz).
The beacon pulses in the time domain (span = 0 Hz).
The period between two consecutives beacons is 10 ms, so the sweep must be at least 15 ms to visualize two beacons. If the sweep was 5 ms, only one beacon would be visualized.

13. DECT measurements: results
03 Description of the work
DECT measurements: results
DECT telephone is receiving a call  the incoming call is detected in another carrier in the frequency domain.
When the DECT telephone is receiving a call, the incoming call is detected in another carrier in the frequency domain.
When the call is established the peak of the incoming call disappears and appears in another carrier, because it changes between one channel and another looking for the best channel available.

14. Outdoor Environmental RF survey
03 Description of the work
Outdoor Environmental RF survey
Evaluate the exposure in the surroundings of two mobile phone base stations
Measurement equipment:
Biconical antenna
Spectrum analyzer
Dosimeter
The frequencies of these base stations are the following:
- Vodafone: 900 MHz (GSM), 2100 MHz (UMTS)
- Orange: 1800 MHz (DCS), 2100 MHz (UMTS)
The frequencies of the mobile phone base stations have been detected with a Biconical antenna and a spectrum analyser:
The measuremets wre taken with the following instruments:
Hewlett Packard E4407B spectrum analyzer
Antenessa EME SPY 120
Narda SRM spectrum analyzer: with this instruments the results are quite similar than the rest
The measurements have been obtained in the proximity of the Vodafone base station, so the major contribution is at the GSM frequency. The measurement devices have been: Hewlett Packard (E4407B) spectrum analyzer, an Antenessa SPY 120 dosimeter, and a Narda (SRM- 300) spectrum analyzer

15. 03 Description of the work
Outdoor Environmental RF survey: result from the spectrum analyzer measurement
The higher values of the electric fields are at the GSM frequency.

16. Outdoor Environmental RF survey: result from the Personal dosimeter
03 Description of the work
Outdoor Environmental RF survey: result from the Personal dosimeter
The results of the dosimeter show that the higher values of the electric fields are at the GSM frequency.
Grx: GSM900 BaseStation, Drx: GSM1800 BaseStation, DCT:DECT, Urx: UMTS BaseStation

17. Other activities during the stay
03 Description of the work
Other activities during the stay
Some short training was provided on computational modelling procedures that calculates the exposure levels to electromagnetic fields of different parts of the human body.
Specific Absorption Rate (SAR) is a measure of the rate at which energy is absorbed by the body when exposed to a radio frequency (RF) signal.
The results of such calculations generally show that the SAR depends on several parameters:
The position of the human body, specially the sitting posture.
The location of the antennas in the device (for example a laptop).
The duty factor of the transmitted signal from the device.
During this STSM visit, a short training has been provided on computational modelling procedures that calculates the exposure levels to electromagnetic fields of the different parts of the human body.
This software has been used to calculate SAR values at different scenarios of exposure to Wi-Fi sources in particular laptops.
The results of such calculations generally show that the SAR depends on several parameters:
The position of the human body, in this particular case, the sitting posture.
The location of the antennas in the laptop.
The duty factor of the transmitted signal from the laptop

18. Other activities during the stay: visit to NPL
03 Description of the work
Other activities during the stay: visit to NPL
The National Physical Laboratory (NPL) is the UK's National Measurement Institute (NMI).
One of the missions of NPL is the calibration of scientific instruments and devices.
In the EMC field, many devices such as dosimeters, antennas, devices, probes, etc…, are calibrated. For this purpose there are large infrastructures available, such us, anechoic chambers and other facilities.
The National Physical Laboratory (NPL) is the UK's National Measurement Institute (NMI). NPL's core mission is to provide the measurement capability, and it is a world-leading centre of excellence in developing and applying the most accurate measurement standards, science and technology available.
One of the missions of the NPL is the calibration of scientific instruments and devices. In the area EMC dosimeters, antennas, devices, probes, etc…, are calibrated. For this purpose there is available a large infrastructure, such us, anechoic chambers and other facilities. Other objective of the visit is the familiarization with the measurements of the tissue parameters, in particular, dielectric metrology with coaxial sensors that are used to measure complex permittivity.

19. Other activities during the stay: visit to NPL
03 Description of the work
Other activities during the stay: visit to NPL
NPL
Anechoic chamber
Anhecoic Chamber of the NPL

20. Other activities during the stay: visit to Vodafone HQ
03 Description of the work
Other activities during the stay: visit to Vodafone HQ
Purpose of the visit: familiarization with the procedure of SAR measurements using iSAR technique
Specific Absorption Rate (SAR) is a measure of the rate at which energy is absorbed by the body when exposed to a radio frequency
The purpose of this visit was familiarization with the procedure of immediate SAR measurements using iSAR Flat from SPEAG, a device which is an ultra-fast scanner that can evaluate the overall RF performance of a wireless device, SAR pattern and peak spatial SAR for one gram and ten gram averaging volumes, in less than one second.
iSAR Flat with a mobile phone that is being testing
iSAR Flat consists of an active measurement area of 240 mm x 120 mm that is covered by a sensor array of 256 dipoles. The sensors are conformal to the top surface and embedded in an absorbing material that simulates body tissue specifications in the 500 MHz to 6 GHz range.
iSAR Flat evaluates wireless devices operated on the body. Specifically it has been used to measure the SAR produced by the use of mobile phones. During the visit, several types of mobile phones operating at 900 MHz and 1800 MHz have been evaluated:
The steps to measure the SAR are indicated as follows
The call is made from the mobile phone that is been evaluated
The call is received by radio transmitter to control the tests.
While the mobile phone is transmitted the SAR is measured by iSAR Flat.
The result of the measurements is the absorption pattern (or hotspot), a graphical representation which shows the SAR as a function of the position. Different absorption patterns are obtained depending on the shape of the mobile phone and the location of the antenna.
Figure 21 shows the components involved in the tests to calculate the SAR produced by a mobile phone
Block diagram to calculate SAR

21. Other activities during the stay
03 Description of the work
Other activities during the stay
iSAR Flat consists of an active measurement area of 240 mm x 120 mm that is covered by a sensor array of 256 dipoles.
The sensors embedded in an absorbing material that simulates body tissue specifications in the 500 MHz to 6 GHz range.
Diagram of the components to measure the SAR.
The steps to measure the SAR are indicated as follows
1.- The call is made from the mobile phone that is been evaluated
2.- The call is received by radio transmitter to control the tests.
3.- While the mobile phone is transmitted the SAR is measured by iSAR Flat.
The result of the measurements is the absorption pattern (or hotspot), a graphical representation which shows the SAR as a function of the position. Different absorption patterns are obtained depending on the shape of the mobile phone and the location of the antenna.

22. 04 Conclusion: benefit of the mission
My main interest is to study the exposure of people to non-ionising radiation, specially in hospitals and care environments.
Presently I am finalising my PhD thesis, which is focused on the shadow effect of the human body in indoor environments.
The following aspects of my visit were very important for my scientific development :
How to quantify the exposure of people to electromagnetic fields.
The factors than can influence the levels of exposure to electromagnetic fields.
Familiarisation with procedures for different measurements and the indicative parameters.
Your mission’s objectives and its importance to your scientific development and to your ongoing work
A summary of the work carried out
The results achieved
A comment on your experience of the mission- how you feel you benefitted from the mission

23. Silvia de Miguel Bilbao sdemiguel@isciii.es Tlf: +34 918 222 567