Development of a Oxygen Sensor for Marine ... - DTU Nanotech

Chapter 1
Introduction
Roughly 70 % of the world is covered by water[1], and have been an inspiration
for mankind over the ages, from explorers such as Columbus to works of
fiction, such as Hemingway’s ’The Old Man and the Sea’. Several time the
oceans have shown the tremendous forces that rest within in various forms
of natural disasters such as tidal waves, floods, tsunamis and many other.
However the oceans is also a source of life, in fact the original source of life,
not just for us but for the fish that lives below.
This thesis have been subpart of a larger project (Fish and Chips), where
the main goal is the development of a multi-sensor for marine environmental
studies. In that, the prototype for a Micro Electronic Mechanical System
(MEMS) have been developed, with then intended use for fish tagging. While
this thesis does not have quite as wide a scope, it does focus on one of the
more important aspects of it, namely oxygen, or rather dissolved oxygen.
There are commercially available dissolved oxygen sensors already today,
however these are more often than not macro scale sensors attached to a
buoy, and therefore only measuring in one place. They can also be attached
to ships, however they will only measure the oxygen level at the surface, and
therefore not give a full accurate picture of the oxygen level.
Why dissolved oxygen? Well there are many reasons, mainly like us the
fish needs to breathe, and the gills of a fish are not all that different form
our lungs[2]. Basically there needs to be enough dissolved oxygen in the
water to favor diffusion of oxygen from the water, through the gills of the
fish and into the blood. When the oxygen falls below a certain level this
passive diffusion fails to be able to drive, the oxygen into the blood and the
fish suffocates much like a human might at high altitudes. So by monitoring
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