Download What is Signal ?

Presented byMd. Bashir Uddin
Roll: 1215502
Dept. of BME
KUET, Khulna-9203
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A signal is defined as a fluctuating quantity or
impulse whose variations represent information.
The amplitude or frequency of voltage, current,
electric field strength, light, and sound can be
varied as signals representing information.
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A signal can be simply defined as a function that
conveys information.
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Signals are
represented
mathematically
as
functions of one or more independent variables.
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Examples: voltage, current, electric field strength,
light, sound, etc.
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Biomedical signals means the bio-signals which are
generated in biological systems only.
Biomedical signals are observations of physiological
activities of organisms, ranging from gene and
protein sequences, to neural and cardiac rhythms,
to tissue and organ images.
Examples of biomedical signals:
ECG (Electrocardiogram) signal,
EEG (Electroencephalogram) signal, etc.
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Biomedical signals are electrical or magnetic
signals generated by some biological activity in the
human body.
Human body is composed of living tissues that can
be considered as a power station.
Action of living tissues in terms of bioelectric
potentials generate multiple electric signals from
two internal sources-muscles and nerves system.
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Bioelectric Signal
Bioacoustics Signal
Biomechanical Signal
Biochemical Signal
Bio-magnetic Signal
Bio- optical signal
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The electrical signals which we can measure
mainly on the surface of the body is known as
bioelectric signal.
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It is generated by muscle cells and nerve cells.
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Basic source is the cell membrane potential.
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Examples: ECG, EEG, EMG, EOG
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The Electrocardiogram (ECG) represents the electrical activity
of the heart.
It is characterized by a number of waves P, QRS, T related to
the heart activity.
Another wave, called U wave is also present but its
importance is not yet identified.
Fig.: A simple model of ECG.
Fig.: EEG signal originating from the brain
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The Electroencephalogram (EEG) is a recording of
electrical activity originating from the brain.
It is recorded on the surface of the scalp using
electrodes, thus the signal is retrievable non-invasively.
Signal varies in terms of amplitude and frequency
Normal frequency range: 0.5Hz to50 Hz.
Electromyography (EMG) is a
technique for evaluating and
recording the electrical activity
produced by skeletal muscles.
EMG is performed using an
instrument
called
an
electromyograph, to produce a
record called an electromyogram.
An electromyograph detects the
electrical potential generated by
muscle cells when these cells are
electrically
or
neurologically
activated.
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Generated by biomedical phenomenon in the
body;
e.g. – flow of blood in the heart through
valves,
Flow of air through the airways in lungs etc
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Generated by all types of motion,
displacement signals,
Pressures and flow signals; e.g. –
movement of chest wall in accordance
with respiratory.
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Extremely weak magnetic fields are
produced by various organs such as the
brain, heart, lungs.
The measurement of these signals provides
information which is not available in other
types of bio signals such bioelectric signals.
Example: Magnetoencephalograh signal
from the brain.
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These signals are generated as result of
optical functions of the biological system.
For example blood oxygenation may be
estimated by measuring the transmitted
/back scattered light from a tissue at
different wavelengths .
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ENG: Electroneurogram - Signals from nerves
EMG: Electromyogram- Signals from muscles
ECG: Electrocardiogram- Signals from Heart
ERG: Electroretinogram- Signals from retina of an eye
EOG: Electrooculogram- Signals from cornea and
retina of an eye
EEG: Electroencephalogram- Signals from brain
MEG: Magneto encephalogram- Signals from brain
using magnetic field
USG: Ultra sonogram- Imaging from ultra sound
reflection from the internal organs of the body
Diagnosis of diseases
 Patient monitoring
 Biomedical research
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