Biomedical Engineering Reference
In-Depth Information
Helical
spring
Dial
indicato
Liquid in
Artificial
muscles
Liquid
out
FIGURE 4.54
Vertical self-powered pH meters equipped with PAN fibrous artificial muscles
and a resilient rotating cylinder.
FIGURE 4.55
Vertical pH meter assembly made from a parallel type PAN fiber muscle and
a specially designed container holding the fluid with unknown pH to be determined.
of the probe tip or solution can cause erroneous readings. Although they can indicate
up to several degrees of accuracy, their requirement for a power source makes it difficult
to use them in remote field applications where there are often limited resources.
As shown in figure 4.55, a simple cylindrical container made of acrylic was used
to hold a PAN muscle arranged in parallel fibers much the same as pinnate muscles
in the body. The ends of the fibers are secured to two glass rods of 1-mm diameter.
Glass was used in order to avoid interfering with the corrosive fluids inside the
container where the pH was unknown. The top and bottom caps of the container
had slots and the muscle was wrapped around a core cylinder and put in tension via
a retracting spring assembly located on the top cap assembly and secured to the
center core of the container. By varying the pH of the solution, contraction or
expansion of the muscle fiber assembly was initiated, causing the core drum to rotate.
By a simple calibration and dial marking on the top plate, it was possible to get a
crude pH reading in the range of 4-12. Although not entirely accurate readings, this
assembly was perhaps the simplest pH meter that did not require a power source
such as a battery to indicate the pH of a solution.
