The signal transmission
mechanism for human body channel has been described by the
propagation of electric field on the surface of human body from an
electrical dipole source [1].
The electric field
received from an infinitesimal dipole in free space is given by the
following equation, [1]
Where, I is the current in
amps, dl is the length of dipole in meters, k is the wave number, ω is
the angular frequency in radians per second and ε0 is the permittivity of
free space. The term 1/r refers to far-field, 1/r2 refers
to induction field and 1/r3 refers to near-field of the
dipole.
If we assume that the
electromagnetic wave propagation theory as depicted by the above
equation correctly explains the phenmenon of signal transmission on
the surface of human body then how the following contradictions could
be explained?
- The relative permittivity for human body is aproximately 50 times more than in free space. If εr term comes in the denominator then the above electric field equation suggests 50 times weaker electric field propagation inside human body than free space. This is contradictory to the fact where conductive property of human body is described as a more suitable medium than free space for electric field propagation over a larger distance.
- The above equation also suggests that the length of the electrical dipole decreases with increasing frequency. For a frequency of few MHz, the theoretical length or dimension of the dipole suggested by this equation is much greater than the practical electrical dipole which is actually used in the human body channel experiments in different research papers, which is again a contradiction.
References
[1] J.Bae, H. Cho, K.
Song, H. Lee, and H.-J.Yoo, “The Signal Transmission Mechanism
on the Surface of Human Body for Body Channel Communication,”
IEEE Trans. Microw. Theory Tech., vol. 60, No. 3, pp. 582-593, March
2012
