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.