II
Abstract
In academic or industrial research usually need frequent measurement about pH
and oxygen partial pressure. In medicine, pH or oxygen partial pressure plays an
important role to evaluate critically ill patient's life characteristics. They commonly
used in patients with clinical diagnosis of blood, body fluids and respiratory activity,
etc. In the food processing industry, the amount of H+ and O
2
is directly related to the
quality of drinking water, food freshness and bacterial content of food or drink. For
heavy industry, the value of pH is an important indicator in wastewater treatment and
environmental monitoring acid rain. In ocean analysis and research, also need to pay
close attention to these two parameters.
At present, multi-parameter optical fiber sensors still have many problems. In the
aspect of production, to turn multiple unrelated sensor into a integrated probe not only
makes production more difficult, but also makes the sensing probe bulky. Therefore,
the spatial resolution gets worse because each sensor unit in the space is not consistent.
In terms of sensing mechanism, each individual sensor need different measurement
methods and measurement conditions, thus different design of optical paths or circuits
which will result in complicated structure and difficult versatility for every sensor
become more necessary.
In view of the fact that reliability of measurement in multi-parameter optical fiber
sensing technology remains few problems, it is excited to design a new sensing
system, which arranges all sensing unit in a probe using different optical modulation
to measure two kinds of concentration. Research shows that the symmetric molecules
such as oxygen molecules, their structure determines they have only stretching
vibration but no vibration produced by change of dipole moment, so that we cannot
use optical absorption principle for direct measurement. Fluorescence measurement
technology emerges as the times require and become the object of study in many
fields because of its high sensitivity and high selectivity.
In this paper, firstly, we measure phase information instead of light intensity
information which simplifies the design structure. According to the traditional double
fluorescence lifetime reference technology, we need to find two different fluorescent
substances which have the similar emission wavelength and the similar absorption
wavelength. When these two fluorescent substances are excited by the frequency
modulated light, they can emit the same frequency but larger wavelength light called
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