Artificial Perceptual Sensors - Artificial Human Sensors: Science and Applications - page 136

ing to establish an improved interface between the human and artificial prosthesis,
that exhibit advanced skills in brain control and fine-tuned grip functions that cor-
respond to a normal hand function. The prosthesis development aims to make use
of a complete system approach, when mimicking human behaviours in order to
provide sensory and motor capability to make fine-tuned grip functions. When
able to be controlled by brain thoughts then we may experience a new technology
era in the field of prosthesis, Sebelius (2005).

6.3 PERCEPTUAL-BASED CHEMICAL SENSORS

A chemical sensor is a device that transforms the chemical state in the measured
sensing volume in a chamber, or area of a surface, to suitable detectable data. The
perceptual-based chemical sensors, have a direct additive effect on the human-
based principles and are useful to complement the olfaction and gustatory sensing
of humans. However, their operational principles are quite different and not quite
competitive with the biological sensing abilities.
The liquid-based sensors often utilise an electrochemical principle using the
chemically influenced response of an applied electrical signal. Electrochemical
techniques can preferably be used to measure chemicals and some biologically
related compounds that are reducible (or oxidizable). In electrochemistry, the
analytical techniques are typically based on oxidation/reduction reactions, and
normally called redox-reactions, Skoog (2004).
The use of electrochemical-based operation principles, Nanto (2003), can be
catagorised into three techniques: sensors using conductometry, potentiometry
and voltammetry principles, Wang (1994).
The measurable current arises when a potential is applied between one or
several individually designed electrodes and a reference electrode. The measure-
ment procedure is related to the surrounding liquid and the device detects the
current behaviour. When applying an initial pulsed current of both positive and
negative levels, the control of attracting or rejecting chemical molecules located at
close proximity to the electrodes can be modelled by a chemical principle of, e.g.,
Heimholtz double layers model. Different model approaches are described as the
variation in ion concentration with opposite charge of the electrode(s) distance to
the electrode surface, Holmberg (2002).
The chemical gas sensors are based on the general principle that analyte
molecules get in contact with a chemical material, which is sensitive and causes
a change in the properties of the surface material. The material can typically be a
Metal Oxide Sensor (MOS sensor) that consists of a coated surface of a sensitive
material. The surface is doped with a small amount of catalytic metal additives,
e.g., palladium or platinum. The doping of the sensor element changes its oper-
ating conditions, having an effect on the sensor selectivity to different odours and
compounds, Loutfi (2006), Lundstr om (1981).
By modifying the restricted definition on an electronic nose from, Gardner