Physical nature of different biosignals

Definition:
Biological signal is a summarizing term for all kinds of signals that can be (continually) measured and monitored from biological beings. The term biosignal is often used to mean bio-electrical signal but in fact, biosignal refers to both electrical* and non-electrical signals.Biosignal can be defined as a description of a physiological phenomenon.

*The term electrical Biosignals refers to changes in electric currents produced by the sum of electrical potential differences across a specialized tissue, organ or cell system.

Classification
Since there are many Biosignals it is very hard to find a unique way of classifying them.

By Existence: * Permanent Biosignals
 * They can exist without an artificial trigger and are available at any time. The source for those Biosignals is 	already inside the body.

Induced Biosignals
 * are artifically triggered or induced and last only during the time of excitation.

Another option for Classification is by their Dynamic Nature: A static biosignal carries information in its steadystate level which may exhibit relatively slow changes over time. Dynamic biosignals yield extensive changes in the time domain, with dynamic processes conveying the physiological information of interest.

The third method of Classification is by their origin. The most common origins are - Magnetic biosignals These signals include motion and displacement signals, pressure and tension and flow signals, and others. - Optic biosignals are the result of optical functions of the biologic system, occurring naturally or induced by the 				measurement (Blood oxigination) - Acoustic biosignals Many physiological phenomina create noise like the flow of blood in the heart or throuhg blood vessels. also the flow or air through the airways creates acoustic sounds. - Chemical biosignals reflect chemical composition and its temporal changes in body solids, liquids, and gases. Examples are 				measuring the concentration of various ions and vicinity of a cell by means of specific ion electrodes - Thermal Biosignals Temperature measurement shows physical and biochemical processes proceeded in organism.(Heat loss, heat 			absorption)