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Communication channels as far I have seen(Air and conductors) are modeled as Linear systems. Was wondering if there are mediums/materials that make the channel nonlinear? For example, if channel is through human body, how do I know if it's linear or not?

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  • \$\begingroup\$ Can you give an example? Of the linear model of a communication channel. \$\endgroup\$
    – Eugene Sh.
    Sep 11, 2018 at 20:35
  • \$\begingroup\$ @EugeneSh. any conventional passive circuit component and their combination is linear for example. \$\endgroup\$
    – doubleE
    Sep 11, 2018 at 21:17
  • \$\begingroup\$ Put a ferrite bead on a wire and overcurrent it. \$\endgroup\$
    – Janka
    Sep 11, 2018 at 22:27

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Linearity in the medium is usually limited by the variation of the dielectric constant Dk. For cables with Dk reducing somewhat above 1Ghz and for optical fibre the same is true for single and multi mode glass fibres which causes diffraction due to the Dk value. So variations in Dk cause group delay skew variable and optical diffraction variances.

I have tested my body up to 6GHz with an Anritsu VNA and and HP spectrum analyzers and found no such cutaneous or subcutaneous external harmonic distortion or peculiar resonances other than natural inductive leads with variable capacitance. However there must be some dielectric variation effects found in Nuclear Imaging but this is beyond my bandwidth to explain or professional experience although I have collected and created many such datasets in both CAT and MRI for my amusement in 3D analysis. (most diagnostics are done in 2D)

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  • \$\begingroup\$ So basically if a pacemaker(located inside the heart) for example sends a pulse train, and if I put some sort of sensor that can pick that up in palm of ones hand, then I should expect the same pulse train(plus interference of course)? \$\endgroup\$
    – doubleE
    Sep 11, 2018 at 21:15
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    \$\begingroup\$ Output waveform depends on conductance, and capacitance which depend on surface area, source and load impedance and current limit. I don’t know if they use current source or voltage source, I suspect current pulse to overcome electrode oxidation, which translates into muscle force from xx uA currents. \$\endgroup\$ Sep 11, 2018 at 21:47
  • \$\begingroup\$ You're right, that depends on the electrical model. They use voltage source. So bottom line is it's expected to be linear: If a Sin(w) is applied to one end, a.Sin(w-phi) should be observed at the other end. \$\endgroup\$
    – doubleE
    Sep 11, 2018 at 21:54

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