Toward Sensor to Reproduce Human Sense - The Electronic Nose Artificial Olfaction Technology - page 134

of 50 kHz-1 MHz, and low current range in between 20 lA and 2 mA. This
impedance of signal contains information regarding blood volume, blood
distribution, automatic nervous system activity, and more. There is a defined
frequency range (50 kHz-1 MHz) chosen to minimize electrode polarization
problems, and the low current range (20 lA-2 mA) are preferred to avoid
tissue damage due to heating property. e.g., impedance plethysmography or
measurement of galvanic skin resistance and measurement of respiratory rate
based on bio-impedance.
3. Biomagnetic signals: Biomagnetic signals have very low signal to noise ratio.
Various organs, such as the brain, heart and lungs, produce extremely weak
magnetic fields (10 -9 -10 -6 T). These magnetic fields produce signals which
provide information as it is useful for diagnosis and not included in bioelec-
trical signals. In designing this type of measuring system great caution must be
taken of these signals. e.g. EEG.
4. Bioacoustics signals: Human body generates some noise or as defined in
biological terms generates typical acoustic noise. i.e., the blood flow in heart
through blood vessels and valve generates acoustic noise or sounds which are
used to measure the pressure of the blood. Bioacoustics signal generate sounds
like coughs, snores, chest sound and lung sounds which is used as primary
diagnosis in medicine. The transducers used for measurement of this sound are
microphones or accelerometers.
5. Biochemical signals: The cell contains concentration of ions and this ion of
living tissue is measured in the clinical laboratory. So this concentration
measurement is example of such biochemical signals. Measurement of blood
pH, ion analysis in blood or respiratory systems are examples of biochemical
signals.
6. Biomechanical signals: All signals which are the outputs of mechanical fuc-
tion occurring in the biologic system. Motion and displacement signals,
pressure and tension and flow signals are example of biomehanical signals.
Blood pressure, non-directly- phonocardiography, and motion of the chest
wall are a good example for this type of signals.
7. Biooptical signals: The result of optical functions in biological system taking
place due to the induced measurement is origin of these signals. The trans-
mitted and backscattered light from a tissue in defined wavelengths is used for
measuring blood oxygenation. Dye dilution method used for monitoring heath
output is outcome of fiber optic technology.
8. Thermal biosignals: The physical and biochemical processes which occur/
proceed in organism is measured by variety of thermometers. They carry
information about temperature circulation on the body surface.
9. Radiological biosignals: Interaction of ionizing with biological structures
formed this type of signals. Information about inner anatomical structures of
human being is known by Radiological biosignals which is most useful in
diagnostics and therapy.
10. Ultrasonic biosignals: Ultrasonic biosignals are produced by interaction with
organ tissues. Information about acoustic impedances of biological structures