Biomedical Engineering Reference
In-Depth Information
be the center of a set of three electrodes, we have to connect a capacitive
sensing circuit to it, which results in high production cost. Moreover, the
serial-processing method requires a large number of droplet-manipulation
steps and electrode actuations. As shown in Table 4.2, excessive actuation
may result in a variety of catastrophic defects. Therefore, efficient algorithms
are needed for the droplet-merging test.
Droplet splitting is simpler compared to mixing. The fluidic operation
involves three adjacent electrodes. By applying an appropriate electrode
actuation sequence, a droplet that rests on the center electrode is split into
two smaller droplets, which rest on the two side electrodes. Thus, a split
operation can be viewed as the reverse of droplet merging. Consequently, the
splitting test can be carried out by applying the merging test methods in a
reverse manner. The only difference lies in the fact that instead of connecting
a capacitive sensing circuit to the center electrode, the splitting test attaches
two capacitive sensing circuits to the two side electrodes. The test outcome is
evaluated by comparing output amplitudes of the two sensing circuits.
We next combine these two tests into a unified test application procedure.
We start from the simple case where the mixing and splitting test is carried
out for two three-electrode groups centered at one electrode. For simplicity,
we limit our discussion to linear merging and splitting; that is, the electrodes
involved are linearly aligned in the same row/column. The test procedure is
illustrated in Figure 4.32.
In Figure 4.32, we carry out the mixing and splitting test using four steps,
that is, horizontal splitting, horizontal mixing, vertical splitting, and vertical
mixing. Note that the ordering is carefully chosen such that the four steps
can be carried out consecutively, with no additional routing steps needed in
between. However, this procedure still requires every electrode to be con-
nected to a capacitive sensing circuit. Moreover, in order to extend this test
scheme to a microfluidic array, we need 4 N 2 manipulation steps for an N × N
array of electrodes, which is very inefficient.
To achieve higher test efficiency and lower hardware cost, we apply the
single-electrode test methods in parallel for array testing. The key idea is to
carry out the mixing and splitting test for all the electrodes in a row/column
concurrently. For simplicity of analysis, we demonstrate the method using a
directed graph, where each electrode is mapped to a node in the graph, and
Figure 4.32
The mixing and splitting test for all the groups of three electrodes that are centered on a
given electrode.
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