Human Skin as Arrays of Helical Antennas in the Millimeter and Submillimeter Wave Range
March 2008
Physical Review Letters 100(12):128102
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Abstract
Recent studies of the minute morphology of the skin by optical coherence tomography showed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. A computer simulation study of these structures in millimeter and submillimeter wave bands show that the human skin functions as an array of low-Q helical antennas. Experimental evidence is presented that the spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure.
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Human Skin as Arrays of Helical Antennas in the Millimeter and Submillimeter Wave Range
Yuri Feldman,
1,
*Alexander Puzenko,
1
Paul Ben Ishai,
1
Andreas Caduff,
1
and Aharon J. Agranat
1,2
1
Department of Applied Physics, The Hebrew University of Jerusalem,
Givat Ram, 91904, Jerusalem, Israel
2
The Interdisciplinary Center for Neural Computation, The Hebrew University of Jerusalem,
Givat Ram, 91904, Jerusalem, Israel
(Received 22 August 2007; published 27 March 2008)
Recent studies of the minute morphology of the skin by optical coherence tomography showed that the
sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. A
computer simulation study of these structures in millimeter and submillimeter wave bands show that the
human skin functions as an array of low-Qhelical antennas. Experimental evidence is presented that the
spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration
system. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood
pressure.
DOI: 10.1103/PhysRevLett.100.128102 PACS numbers: 87.50.S, 87.90.+y
Experimental evidence indicating that the electromag-
netic properties of the human skin in the sub-Terahertz
frequencies are governed by its morphology is henceforth
presented.
The human skin is the largest organ of the body, de-
signed as the primary interface, utilizing numerous of
functions and interactions between us and our environ-
ment. The complexity of the multilayered skin morphology
provides an extremely broad range of features of sensors
that utilize a number of physical phenomena. One of these
skin features is the perspiration system that traditionally is
mainly considered for body thermoregulation [1]. Its main
components are sweat glands embedded into the dermis
and connecting through the epidermis with the pores on the
surface of the stratum corneum by ducts, filled with a
conductive aqueous solution. The general illustration of
sweat glands presents a convoluted arrangement for the
sweat gland and a more or less straight tube for the duct
[1,2]. In recent investigations of the subcutaneous mor-
phology of the human skin by optical coherent tomography
[3,4], it was found that the sweat duct is in fact a remark-
ably arranged helical conductive tube (Fig. 1). This, to-
gether with the fact that the dielectric permittivity of the
dermis is higher than that of the epidermis, brings forward
the supposition that as electromagnetic entities, the sweat
ducts could be regarded as low-Qhelical antennas.
Inherent to this supposition is the requirement that the
duct possesses an electrical conductance mechanism that
is effective at the extremely high frequency (EHF) range.
Even though the ducts are filled with conducting electro-
lytes, the ions mobility rates associated with sweat are slow
compared to the characteristic frequencies under consid-
eration. A mechanism that qualifies for such a requirement
is fast proton hopping through distributed H-bond net-
works along the duct surface. It is well established that
these networks exist in biological structures [5] and it was
found that the characteristic time for such proton transport
is about 1013 sec [6].
When the potential drop caused by the difference in pH
values between the skin surface and the dermis is taken into
consideration [2], such hopping can account for the ac
conductivity that is necessary for the sweat ducts to yield
an electromagnetic response in the EHF range. Moreover,
it is known that the human skin contains approximately 2 to
5106eccrine sweat glands distributed over most of the
body, with higher density in several areas such as on the
palms of the hand, the forehead, and on the soles of the feet
[7,8]. As each gland is connected to the skin surface by a
helical sweat duct, the skin organ in its entirety can be
regarded as an array of helical antennas that operate in the
EHF range. It has been ascertained that the level of sweat-
ing has a dominant effect on the conductance parameters of
the various components of the skin tissue. As pointed out
above, these parameters strongly affect the spectral re-
sponse of the skin organ. Hence, it is predicted that the
physiological and psychological parameters that are known
to be expressed in the activity of the perspiration system [9]
FIG. 1. 3D optical coherence tomography image (reproduced
with permission from ISIS GmbH) of a single human eccrine
sweat gland embedded in the human skin and a schematic
presentation of the duct as a helical antenna [20] embedded in
the skin, where the dermis-epidermis interface acts as a dielectric
reflector. The respective permittivities of the skin layers are
marked. They were estimated for the specific frequency range
based on the water content of the layers [10].
PRL 100, 128102 (2008) PHYSICAL REVIEW LETTERS week ending
28 MARCH 2008
0031-9007=08=100(12)=128102(4) 128102-1 ©2008 The American Physical Society
Citations (62)
References (36)
... We may assure him that he would have had full access had he done so. In addition, Foster et al. appear to be unaware of our previous publications on this subject (Betzalel et al., 2017;Feldman et al., 2009Feldman et al., , 2008Hayut et al., 2014Hayut et al., , 2013Safrai et al., 2014Safrai et al., , 2012. ...
... The latter would coincide with the authors own model (Alekseev et al., 2008) of 2008. Intriguingly their model also produces our result of heighted absorption due to a standing wave linked to skin layer thickness at 60 GHz ( Fig. 2 of (Alekseev et al., 2008)), confirming the findings of our other papers in this vein (Feldman et al., 2008;Hayut et al., 2013;Safrai et al., 2014Safrai et al., , 2012. It is the existence of the sweat duct and its ac conductivity that proves to be significant in heighted absorption above that expected from a simple layer model. ...
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... We may assure him that he would have had full access had he done so. In addition, Foster et al. appear to be unaware of our previous publications on this subject (Betzalel et al., 2017;Feldman et al., 2009Feldman et al., , 2008Hayut et al., 2014Hayut et al., , 2013Safrai et al., 2014Safrai et al., , 2012. ...
... The latter would coincide with the authors own model (Alekseev et al., 2008) of 2008. Intriguingly their model also produces our result of heighted absorption due to a standing wave linked to skin layer thickness at 60 GHz ( Fig. 2 of (Alekseev et al., 2008)), confirming the findings of our other papers in this vein (Feldman et al., 2008;Hayut et al., 2013;Safrai et al., 2014Safrai et al., , 2012. It is the existence of the sweat duct and its ac conductivity that proves to be significant in heighted absorption above that expected from a simple layer model. ...
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... If yes, then one may ask where in the skin layer would it originate? In 2008, we demonstrated that the Human sweat gland ducts, coiled in the epidermis, could be regarded as electromagnetic entities [2] and in 2014 that they could behave as an array of helical antennas [3]. The results of our previous studies clearly indicate that the reflection coefficient of the human hand is correlated to universally accepted indicators of mental stress [4,5]. ...
... The inference is that the Sympathetic Nerve System [8] is engaged. Based on our previous work [2][3][4][5] on the reflection coefficient of human skin in the Sub-THz frequency range we suggest that the helical sweat ducts may play a significant role in this phenomenon. ...
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... MMWs may have effects on nerve endings and capillaries in the skin and through these, they may influence deeper structures and functions in the body (20,21). Sweat ducts in the skin may act as helical antennas and respond to MMWs for penetration (22,23); however, this would only display a small exposure enhancement. MMWs can also exert effects on bacterial growth and can augment antibiotic resistance (24), which can lead to difficulties in the treatment of severe infections. ...
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... It was suggested that the coiled portion of the sweat duct in upper skin layer can regard as a helical antenna in the sub-THz band [130][131][132][133] . Experimentally it was shown that the reflectance of the human skin in the sub-THz region depends on the intensity of perspiration, i.e. sweat duct's conductivity, and correlates with levels of human stress. ...
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