Figure 3: Variation of instantaneous heart dimensions with time
during a cardiac cycle.
UWB transmission in human thorax
using Debye first order
model
The transmission coefficient of a signal through a multilayer structure
depends essentially on the sum of the losses occurring when i) the wave
propagates through each layer of the material and ii) the wave gets
reflected at the interface of the layers. The amplitude of the
electromagnetic signal reduces while propagating through the successive
layers of a multilayer system. Transmission coefficient (dB) is
mathematically defined as, 27
Transmission coefficient (dB) (1)
Eqn. (1) can be rewritten as,
(2)
The EM wave propagation through the layered model shown in Figure 1 is
created using CST MWS to study the interaction of human thorax in terms
of transmission coefficient (dB). The tissue parameters associated with
permittivity, permeability, and conductivity used in this work are from
Gabriel’s data book.28 In view of the assumption of
normal incidence of a planar wave on the layered model, the CST MWS
implements a TEM mode, generated by using the waveguide ports of the
model by mimicking a plane wave with the defined wave guide ports and by
specifying the appropriate boundary conditions. The solver excites the
structure with an UWB Gaussian pulse in the time domain, by default. The
simulation of the model is performed using the time-domain solver. In
order to allow for the dispersive behavior of the tissues, the Debye 1st
order model was used in the simulation. The CST MWS software tool
requires to input the values of (i) optical dielectric constant ε∞, (ii)
dielectric constant of vacuum ε0 and (iii) relaxation time constant of
the tissue τ(s), which were obtained from the internet resource
(http://niremf.ifac.cnr.it/docs/DIELECTRCIC/AppendixC.html) for the
compilation of dielectric properties of body tissues at RF and Microwave
frequencies. The value of Mue (permeability), by default, is
taken to be one for the entire band of frequencies throughout the
simulations. The simulation results are presented in Section 3.