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R. B. Pachori and V. Gupta
12.6.1 Formation Aspects
The formation aspects basically revealed the propagation light modulation in body
tissues simultaneously with dynamic physiological phenomena. This modulation
extracts the physiological information present in optic biomedical signals. The
formation aspects of the induced optic biomedical signal include an artificial
incident light source which entered the body through the skin, incident light
coupling into body, and light propagation through body tissues to a distant light
sink applied on the skin [35].
The emission of the artificial incident light depends on the accelerated charge
in which energy is released during the transition of electrons from higher to
lower energy levels resulting in light emission. The sources of light used for this
purpose are of two types, namely, broadband and narrowband. The broadband light
sources emit light in a relatively wide band of the electromagnetic spectrum such
as incandescent lamps and noble gas arc lamps whereas a narrowband is covered
by narrowband light sources such as lasers, fluorescent sources, and light-emitting
diode (LED) [35].
In these light sources, the LED is the most popular and widely used light
source in order to induce optic biomedical signals. The LED basically works on
the principle of electroluminescence. A charge migration takes place to obtain the
light photon [35].
After coupling of light source, the transmission of light through biological tissue
is a major aspect. The optical light path is started with the light source and then
it diffuses through tissue. The diffusion is subjected to changes in light intensity
because of the light absorption, diffraction, reflection, scattering, and refraction. A
large portion of light intensity has also dissipated and does not reach the skin where
a light sink is placed due to this fact [35].
The interaction between light and tissue can be determined quantitatively such
as quantitative strength and duration of the interaction and the spatial distribution
of the tissue interaction. The interaction is limited to areas of tissue where coupled
light is easily reached. This interaction depends on light and tissue characteristics in
which light characteristics represent size of incident light, while light transmission
is determined by tissue characteristics [35].
The propagation velocity (υ) of light in a biological medium which oscillates
with frequency (f ) and wavelength (λ) along its propagation path can be written as
[35]:
υ = λ × f
(12.36)
where the electric and magnetic properties of propagation medium determine the
value of υ and it can be computed as follows [35]:
υ =
c
√
μ r ε r
(12.37)
R. B. Pachori and V. Gupta
12.6.1 Formation Aspects
The formation aspects basically revealed the propagation light modulation in body
tissues simultaneously with dynamic physiological phenomena. This modulation
extracts the physiological information present in optic biomedical signals. The
formation aspects of the induced optic biomedical signal include an artificial
incident light source which entered the body through the skin, incident light
coupling into body, and light propagation through body tissues to a distant light
sink applied on the skin [35].
The emission of the artificial incident light depends on the accelerated charge
in which energy is released during the transition of electrons from higher to
lower energy levels resulting in light emission. The sources of light used for this
purpose are of two types, namely, broadband and narrowband. The broadband light
sources emit light in a relatively wide band of the electromagnetic spectrum such
as incandescent lamps and noble gas arc lamps whereas a narrowband is covered
by narrowband light sources such as lasers, fluorescent sources, and light-emitting
diode (LED) [35].
In these light sources, the LED is the most popular and widely used light
source in order to induce optic biomedical signals. The LED basically works on
the principle of electroluminescence. A charge migration takes place to obtain the
light photon [35].
After coupling of light source, the transmission of light through biological tissue
is a major aspect. The optical light path is started with the light source and then
it diffuses through tissue. The diffusion is subjected to changes in light intensity
because of the light absorption, diffraction, reflection, scattering, and refraction. A
large portion of light intensity has also dissipated and does not reach the skin where
a light sink is placed due to this fact [35].
The interaction between light and tissue can be determined quantitatively such
as quantitative strength and duration of the interaction and the spatial distribution
of the tissue interaction. The interaction is limited to areas of tissue where coupled
light is easily reached. This interaction depends on light and tissue characteristics in
which light characteristics represent size of incident light, while light transmission
is determined by tissue characteristics [35].
The propagation velocity (υ) of light in a biological medium which oscillates
with frequency (f ) and wavelength (λ) along its propagation path can be written as
[35]:
υ = λ × f
(12.36)
where the electric and magnetic properties of propagation medium determine the
value of υ and it can be computed as follows [35]:
υ =
c
√
μ r ε r
(12.37)