Electrodes are devices that convert ionic potentials into electronic potentials.
Electrodes in which, no net transfer of charge is possible across the metal – electrolyte interface is called perfectly polarized electrodes.
Microelectrodes are the electrodes are used to measure bioelectric potentials near or within a single cell.
Skin surface electrodes are the electrodes are used to measure ECG, EEG, EMG etc from the surface of the skin.
The micropipette type of microelectrode is a glass micropipette with its tip drawn out to the desired size.
Immersion electrodes were separated from subject’s skin by cotton pads socked in a strong saline solution.
Floating electrodes can eliminate the movement errors (called artifacts) which is a main problem with plate electrodes.
We can use disposable electrodes which can be used only once and be disposed after the use.
Suction electrodes are well suited for the attachment to flat surfaces of body and to regions where the underlying tissue is soft , due to the presence of contact surface.
Scalp electrodes can provide EEG easily by placing it over bare head.
One of the main advantages of needle electrodes are that they are less susceptible to movement errors than surface electrodes.
Normally in biomedical applications the transducer input is in non electrical form and the output will be in electrical form.
Major difference between transducers and electrodes is that transducers make use of some transducible element for the measurement. But the electrodes directly measure the signals.
An active transducer is one which gives its output without the use of excitation voltage or modulation of a carrier signal.
In a magnetic induction type transducer when an electrical conductor is moved in a magnetic field in such a way that flux through the conductor is changed, a voltage is induced.
A piezoelectric crystal (such as Quartz) can produce a voltage under deformation by compression or tension called piezoelectric effect. This effect is the basic working principle of piezoelectric type transducers.
Passive transducers convert the physiological parameter (such as blood pressure, temperature etc) into an electrical output using a DC or AC excitation voltage.
The principle behind strain gauge is that when an electrical conductor is stretched within the limits of elasticity such that it does not break or permanently deform, it will become narrower and longer which increases the resistance.
Capacitive transducer is a measurement device in which variations in pressure upon a capacitive element proportionally change the element’s capacitive rating and thus the strength of the measured electric signal from the device.
In an LVDT, when the core is displaced in one direction, the voltage in one coin increase as the other decreases causing the output voltage to increase from zero to maximum.