BIOPHYSICS RESEARCH

Research in this area includes:

Mechanisms of interaction of non-ionizing radiation with biomaterials.

Engineering support for life-scientists studying the biological effects
of non-ionizing radiation. Current collaborations exist with the University
of Maryland at Baltimore (Drs. George Harrison and Elizabeth
Balcer-Kubiczek), Polytechnic University (Professor Shirley Motazkin), 
and the Food and Drug
Administration (Drs. Russell Owen and Ewa Czerska).

Dielectric measurements on biomaterials.

In a collaboration with Professor Leonard S. Taylor of this department
and Dr. Edward C. Elson of the Walter Reed Army Institute of
Research we have been making a comprehensive series of
measurments of the complex dielectric constants of tissues in the head.
This research is supported by Wireless Technology Research LLC.

In order to assess human exposure to the radiation from cellular telephones
complex numerical modelling of the energy absorbed in models of the human head
with realistic models of the cellular phone itself included are being carried
out. These numerical models generally use detailed volume pixellated
subdivisions of the head by tissue type determined from, for example,
magnetic resonance imagery. In order to make the theoretical analysis
meaningful reliable values of the complex dielectric constants of different
tissues in the head are required. We have completed a comprehensive series of
such measurements from 500 MHz to 10 GHz on 27 different tissues. The tissues
measured were taken from the heads of freshly killed pigs, and measurements
were made as soon as possible after death. Pigs were used as a model
since there is general consensus that their tissues are similar
to human tissue. We have monitored the change
in dielectric properties of various tissues over time, and as a function of
temperature, in order to determine as reliably as possible the likely value
of the dielectric constants in-vivo. We were able to make
measurement of the external tissues on human subjects.
The measurements were made by the ``open-probe" technique [1]
and the reliability
of the data checked by measurements on standard materials.

The tissues that we have measured include: cortical and cancellous bone,
human skin in various locations on the head, muscle, cartilage, white
and grey brain matter in various locations, the medulla, cornea, aqueous
humor, sclera, meningeal tissue, tongue, pons, peduncle, ventrical
lining surface, and subcutaneous fat. Measurements on soft tissue are 
relatively easy to make, and the results generally agree with the recent
data of Gabriel et al. However, the measurements on bone show great variability
and are very strongly influenced by the degree of drying of the sample that has
occurred. There is strong evidence that the real part of the dielectric
constant of bone is higher than previously thought, 
perhaps as high as 40, and that this may vary
from location to location. The conductivity of bone varies up to about 0.5S/m
at 900 MHz and about 0.8S/m at 1800 MHz. It would be very desirable for
additional measurements of the complex dielectric constant of bone
to be made by an independent technique.

REFERENCE

Jian-Zhong Bao, Mays L. Swicord, and Christopher C. Davis,
``Microwave dielectric characterization of 
binary mixtures of water, methanol, 
and ethanol"
J. Chem. Phys. 104, 4441-4450, 1995.