59
Coupling of Electromagnetic Fields into Biological Systems
• There is very little difference in induced current irrespective of whether the model
is grounded or not. This is due to the fact that most of the energy in the pulse is
at frequencies in excess of 300 MHz, where the effect of the ground plane on the
induced current or SAR is minimal.
1.13 Coupling of Millimeter and Terahertz Waves
Recent advances in mmW and terahertz technologies have motivated a wide range of
telecommunication, industrial, medical, and scientific applications including security
screening in the form of whole-body image scanning for concealed objects. Some of
the specific applications involve manufacturing inspection, biomarker and trace chemical detection, automated vehicular guidance for cars on highways, advanced radars to
obtain better forecasts of localized and intense rainfall, and high-capacity short-range
wireless data communications.
In general, mmW occupies the frequencies from 30 to 300 GHz with corresponding
wavelengths of 1–10 mm, whereas terahertz waves span the frequencies of 100–1000
GHz (or 1 THz) with wavelengths of 0.3–3.0 mm. Clearly, there is an overlap between
mmW and terahertz waves. Studies on mmW interactions aimed toward biomedical
applications began about 30 years ago (Gandhi 1983; Pakhomov et al. 1998). However,
recent advances in device technology at terahertz frequencies have spearheaded considerable interest in terahertz applications in biology and medicine among others, as mentioned earlier. A comprehensive review of the research conducted on biological effects of
mmW, especially from the former Soviet Union, showed that at intensities of 100 W/m 2
or less mmW can affect cell growth and proliferation, enzyme activity, genetic status,
functions of excitable membranes, peripheral receptors, and other biological systems
(Pakhomov et al. 1998). Nevertheless, there is a paucity of investigations on transmitted fields and induced energy deposition in biological tissues at these frequency bands.
The discussions of this section (1.13) focus specifically on the coupling of mmWs into
biological tissues. For a complete discussion on the biological interactions of terahertz
radiation, readers are referred to Chapter 7 of this book.
1.13.1 Transmitted and Reflected Millimeter Waves
and Terahertz Fields, and Energy Deposition
In principle, at the frequencies of millimeter and terahertz waves the induced fields and
energy deposition in biological medium can be determined in much the same manner
as for RF if the permittivities of relevant tissues at these frequencies is known. Although
some earlier extrapolations were conducted based on Debye formulas and using complex dielectric permittivity of the skin at low frequencies, some measurements for skin
within the mmW range have recently become available for humans (Alekseev and
Ziskin 2007) and rodents (Alekseev et al. 2008). Data for human skin in the frequency
range of 37–74 GHz are shown in Figure 1.34, in which the measured results are compared to earlier extrapolations. It can be seen that the recent data tend to be lower. More
importantly, at mmW frequencies the permittivity of skin is governed by cutaneous free
water contents.
Coupling of Electromagnetic Fields into Biological Systems
• There is very little difference in induced current irrespective of whether the model
is grounded or not. This is due to the fact that most of the energy in the pulse is
at frequencies in excess of 300 MHz, where the effect of the ground plane on the
induced current or SAR is minimal.
1.13 Coupling of Millimeter and Terahertz Waves
Recent advances in mmW and terahertz technologies have motivated a wide range of
telecommunication, industrial, medical, and scientific applications including security
screening in the form of whole-body image scanning for concealed objects. Some of
the specific applications involve manufacturing inspection, biomarker and trace chemical detection, automated vehicular guidance for cars on highways, advanced radars to
obtain better forecasts of localized and intense rainfall, and high-capacity short-range
wireless data communications.
In general, mmW occupies the frequencies from 30 to 300 GHz with corresponding
wavelengths of 1–10 mm, whereas terahertz waves span the frequencies of 100–1000
GHz (or 1 THz) with wavelengths of 0.3–3.0 mm. Clearly, there is an overlap between
mmW and terahertz waves. Studies on mmW interactions aimed toward biomedical
applications began about 30 years ago (Gandhi 1983; Pakhomov et al. 1998). However,
recent advances in device technology at terahertz frequencies have spearheaded considerable interest in terahertz applications in biology and medicine among others, as mentioned earlier. A comprehensive review of the research conducted on biological effects of
mmW, especially from the former Soviet Union, showed that at intensities of 100 W/m 2
or less mmW can affect cell growth and proliferation, enzyme activity, genetic status,
functions of excitable membranes, peripheral receptors, and other biological systems
(Pakhomov et al. 1998). Nevertheless, there is a paucity of investigations on transmitted fields and induced energy deposition in biological tissues at these frequency bands.
The discussions of this section (1.13) focus specifically on the coupling of mmWs into
biological tissues. For a complete discussion on the biological interactions of terahertz
radiation, readers are referred to Chapter 7 of this book.
1.13.1 Transmitted and Reflected Millimeter Waves
and Terahertz Fields, and Energy Deposition
In principle, at the frequencies of millimeter and terahertz waves the induced fields and
energy deposition in biological medium can be determined in much the same manner
as for RF if the permittivities of relevant tissues at these frequencies is known. Although
some earlier extrapolations were conducted based on Debye formulas and using complex dielectric permittivity of the skin at low frequencies, some measurements for skin
within the mmW range have recently become available for humans (Alekseev and
Ziskin 2007) and rodents (Alekseev et al. 2008). Data for human skin in the frequency
range of 37–74 GHz are shown in Figure 1.34, in which the measured results are compared to earlier extrapolations. It can be seen that the recent data tend to be lower. More
importantly, at mmW frequencies the permittivity of skin is governed by cutaneous free
water contents.