Dosimetry Workshop
Chair: Professor L Barclay
In this session researchers involved
in carrying out nine dosimetry projects presented short talks about
the progress they have made with their projects in the last year.
Most of the projects are funded directly by the programme although
three are funded by the Department for Trade and Industry (DTI)
as adjuncts to the MTHR programme.
Assessment of exposures from handsets
Two of the projects are concerned with the assessment of the quantity
Specific energy absorption rate (SAR) arising from the use of either
TETRA handsets or hands-free mobile telephones. TETRA is a digital
mobile radio system used by organisations such as the Police. The
TETRA project involves producing an accurate model of a TETRA handset
and then performing calculations of the energy absorbed in the head
from this handset. The main aim of the second project was to characterize
differences in exposure between using a handheld mobile telephone
and use in conjunction with a hands-free kit. This was done by a
combination of SAR measurements using realistic physical phantoms
and numerical modelling. Both projects have been completed.
A third project is concerned with assessing exposures from emerging
technologies. This project will provide validated data on the electromagnetic
field strengths and energy deposition within the human body associated
with future mobile telecommunication use. The project is currently
on going and due for completion in early 2005. A fourth project
is measuring the dielectric properties of biological tissue in vivo
and in vitro at microwave frequencies and making an assessment of
the expected uncertainty of the data prior to studying their age-dependence.
The project also includes a study of dielectric properties of the
skin of human volunteers. During the presentation, an explanation
on how to estimate uncertainty with some examples for measured tissues
and details of trial and final measurements were presented. This
project is on course for completion on the due date (end 2004).
Assessment of exposures from Base Stations
The MTHR programme is also concerned to obtain additional data on
exposures from base stations. A project funded as an adjunct to
the programme is assessing exposures from microcell and picocell
base stations. This involved undertaking measurements to characterize
the fields in the vicinity of a random sample of base stations.
It is anticipated that the project will be complete by the end of
2003.
The assessment of personal exposure from base stations is seen as
an essential prerequisite for undertaking reliable epidemiological
investigations in relation to base station emissions. At present
such assessments are extremely problematic and one possible way
forward would be the development of an accurate and reliable personal
exposure meter. The Programme Management Committee (PMC) was therefore
delighted to welcome Dr Joe Wiart (France Telecom) as an invited
speaker to discuss his work in this area. Dr Wiart began by outlining
some of the difficulties with assessing personal exposures, which
may show complex spatial and temporal variations that result from
absorption, reflection, interference and traffic.
Any personal exposure meter should ideally be capable of logging
exposure over time and reading exposures from a variety of different
frequency bands including those used for broadcast television and
radio, and private communication systems in addition to those used
for mobile telecommunications. There were significant technical
difficulties in developing a personal exposure meter that would
have sufficient sensitivity to record the extremely weak signals
from base stations, but sufficient dynamic range to cope with the
much higher power emissions from mobile phone handsets. The effects
of interference by the wearer would have to be minimal, whilst the
personal exposure meter should not be so large or cumbersome that
it interferes with the wearer’s ability to carry out their
normal activities.
Supporting projects
These presentations related to projects supporting research in this
area.
The standard exposure
system developed specifically from the MTHR programme has been described
in detail elsewhere.
Work to refine the system is on going.
The National Physical
Laboratory (NPL) provides advice and support to both the PMC and
research teams in relation to measurements and dosimetry. The aim
is to ensure that MTHR projects follow nationally recognised measurement
practices and to ensure that all measurements are traceable to national
standards. MTHR projects should make best use of the metrological
infrastructure within the UK (The National Measurement System (NMS)).
In addition this project also included work to quantify low frequency
magnetic field emissions from mobile phones and this work has been
completed.
The third support project
aimed to update the EMF Dosimetry Handbook. This would promote and
develop high quality EMF dosimetry. It was envisaged that the resulting
Handbook would be available on line and would be a living document.
Summaries
of the closed sessions of the MTHR Research Seminar - 4th of November
2003 |
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