Signal Pick-Up

FELICE, CARMELO JOSÉ.; MADRID, ROSSANA ELENA; VALENTINUZZI, MÁXIMO EUGENIO

Understanding the Human Machine. A primer for Bioengineering

World Scientific Publishers Co. Pte. Ltd

Año: 2004; p. 271 - 298

Once the signal is identified, the task is to pick it up in order to study it at leisure, to characterize it and sometimes to better determine its true source. It may not be an easy enterprise. History of science has taught us several sweat-and-blood examples, as the nerve action potential and arterial pressure, to mention only two. Obviously, a gadget is required, something equivalent to the fishpole-fishhook-bait assembly. This is exactly what electrodes, sensors, transducers and biosensors are for. The latter three words are often used interchangeably, however, they have slightly different meanings. Strictly speaking, a sensor just detects the signal under the original type of energy (electrical, mechanical, thermic, magnetic, chemical, luminic) while the transducer only transforms the small amount of energy (whatever the type) contained in a signal into another type of energy, the second usually being electrical. Thus, it literally “translates”; but it needs a sensor. However, the sensor proper is often so well immersed in the transducer as to make it essentially impossible to dissect them out. Electrodes are specific electrical sensors; in a way, they might be considered as electric-electric transducers because their input signal is in the form of electrical energy and the output is also of the same kind. A biosensor, as its prefix indicates, includes in it some kind of biological material, as for example an enzyme, which reacts with an external substrate to catalyze the production of a given substance that, in turn, generates a transducible signal. The whole may turn into a semiconductor chip. The final output will be always electrical. Many textbooks on bioinstrumentation have dealt with this relatively new and still developing subject. Herein, the objective is to introduce the student to another section of the biomedical engineering world recalling, from the very starting line, that no recording system can be better than its picking up gage, for sensorstransducers, in general, are the bottleneck of the system. Tremendous advances have been made in the XXth century and they are still subject of research and development with new ideas being incorporated almost every day to scientific and technical knowledge. Most of this material belongs to the area of bioinstrumentation, one of the traditional and early specialties of bioengineering/biomedical engineering.