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PROBLEMS
As in every experiment there are problems, some in the experimental system and
some in the algorithm. During the experiment problems arise and problems are
solved. Here following are the crucial problems:
Noise:
One of the main problems, if not the major problem, with the system is the noise
problem. In each one of the chapters there is a specific reference to the noise problem.
As was mentioned in the simulation chapter, the estimation algorithm is quite
sensitive to noise. During simulation the system we found that for signal noise ratio
(SNR) higher than 10[dB] the results exceed a reasonable mistake. Spikes especially
close to the signal frequency can influence the estimation. In the simulation we
assumed white noise at a maximum SNR of 10[dB]. Rising the estimation accuracy
can minimize their effect. The accuracy can be accomplished by a high-density lattice
of starting points as shown in the optimization chapter. Hardware improvements could
reduce sensitivity to noise. At the given stage there is no way to overcome this
problem. Filtering some of the noise is possible only outside the frequency band
relevant to the experiment. The noise disturbance from the electricity net (around
50[Hz]) and its harmonies are quite close to the frequency band (starting around
160[Hz]) which enforces us to filter near the signal which is likely to corrupt the
signal. The superposition of the sinusoidal signals causes the noises inside the
frequency band to accumulate, and some of the noises even exceed the signal
magnitude. The random noises vary from one experiment to another and therefor have
to be handled manually per experiment.
Time:
Dealing with biological tissue requires compelling conditions to imitate the natural
biological surroundings. However much we try to emulate these surroundings we are
unable to supply conditions that will prevent the tissue’s denaturation. As the time
passes the influence on the conductivity could be greater. We tried to carry out the
experiments as close as possible to the tissue removal from the biological body, while
keeping the temperature and the salinity of the natural surrounding. Due to the bad
results from the system we didn’t analyze the data from a tissue, we referred only to
short condition, and therefor we are unable to determine the influence of the time on
the tissue conditions.
Heat:
One of the side effects caused as a result of a current flowing through a resistor, is the
heating of the resistor. The higher the current is the resistor temperature rises. The
biological tissue is not different from a simple resistor, only that the heating affect is
accompanied by tissue denaturation. To avoid this effect the measurement time was
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set to 10[msec]. We checked the influence of the heat by running two sequences one
after the other. Again due to the results we got we were unable to refer to the tissue
data and therefor analyze the influence of heating on a biological tissue. However we
could smell the meat cooking throughout the experiment.
Hardware:
The system is imbalanced and noisy. Even measurements in short conditions gave a
different output for the different channels, and different outputs under the same
conditions at different times.
Possible solutions:
Software:
1.
Filtering the signals.
2.
A higher-density lattice of starting points.
As was explained this solution is good only as additional solution to improving the
hardware it can not stand by itself.
Hardware improvement - which is inevitable.