Chemistry Reference
In-Depth Information
•
Chemicals like ureum, present in sweat do not interfere by possible
adsorption at the electrode surface.
•
Other electrolytes like sulphates, potassium and calcium are present in
much lower concentrations than sodium chloride, and therefore their
contribution to the conductivity can be neglected.
•
Sodium chloride in sweat determines the overall conductivity of the
sweat.
For each application envisaged in this chapter, tests were performed to eval-
uate the behaviour of the sensor system in its performance for sweat and
urine detection. For this purpose, stainless-steel yarns were incorporated in
baby nappies for detection of urine. Figure 10.6 shows the results of some
of these tests. It can be seen clearly that the detection of urine is marked
by a large change in resistance between the electrodes of the sensor system.
In addition, the value of
R
after urine detection is an indication of how
much urine has been formed. However, the latter is not really of scientific
relevance, and is therefore not considered further here.
For the detection of low sugar levels in the blood, the sensor system was
less successful. Despite its possible use as an early-warning system for dia-
betes patients, it shows serious limitations owing to interference from other
3.50E
+
06
R
(ohm)
3.00E
+
06
2.50E
+
06
2.00E
+
06
1.50E
+
06
1.00E
+
06
5.00E
+
05
0.00E
+
00
-4
-2
0
2
4
6
8
Normalised
t
10.6
Resistance measured between two yarn electrodes implemented
in a baby's nappy as a function of time, with
t
=
0 the moment
that urine formation occurs.
