Biomedical Engineering Reference
In-Depth Information
Figure 4.28
(a) An undirected graph for the Euler-path-based structural test and (b) the corresponding
directed graph for the Euler-path-based routing test.
to a directed graph, which can be easily derived by replacing every edge in
the undirected
graph with two directed edges in opposite directions. The
Euler-path-based method is then applied to the directed graph to derive a
test plan for the routing test.
Note that in the structural test, a test droplet is routed to traverse the array,
following the Euler path derived from the undirected graph in Figure 4.28a.
As a result of this procedure, half of the directed edges in Figure 4.28b are
also traversed, with exactly one edge visited for each pair of directed edges
between two nodes. The edges that are not visited can be ordered to form a
“reverse path” corresponding to the Euler path derived earlier. Therefore, the
routing test can be carried out by applying two iterations of the structural
test in opposite directions. Recall that all the defects listed in Table 4.1 can
be detected by the structural test; therefore, they are also detected by the
preceding routing test procedure.
The preceding test procedure also tests the functionality of the capacitive
sensing circuit. If a test droplet is routed to visit the electrode connected to
the target capacitive sensing circuit, a positive pulse is expected at the output
of the sensing circuit. By examining the amplitude of the positive pulse, we
can determine whether a capacitive sensing circuit is normal, insensitive, or
oversensitive, as shown in Figure 4.29.
4.5.3 Mixing and Splitting Test
Next, we discuss the functional testing of two widely used microfluidic mod-
ules: mixers and splitters. In a digital microfluidic biochip, two droplets are
mixed within a cluster of electrodes, referred to as mixer. Even though mixer
designs and configurations vary considerably [49], the underlining mixing
mechanisms remain the same for all designs and configurations. Two drop-
lets are merged at one electrode and routed to move about some pivots in the
mixer, as shown in Figure 4.30.
Thus, a mixing functional test is equivalent to the testing of the merg-
ing and routing operations within the target cell cluster. Recall that the
droplet-routing test has been addressed in Subsection 4.5.2; therefore, a
