Piezoelectric Energy Harvesting Nanofibers - Hierarchical Nanostructures for Energy Devices - page 164

d n 3 r 4 n g | 2

.

Figure 7.12 (a) Schematic diagram showing the possible artifacts of nanogenerator

outputs due to the contact electrodes from the sources of C gap and
C overlap under small (left) and large (right) substrate actuation tests. (b)
and (c) Experimental voltage outputs from upward and downward
actuation tests, respectively, with small (left figures) and large (right
figures) substrate actuation. Under small actuation, C gap could be the
dominating factor to change the polarity of the output signals of
upward and downward actuation as shown. Under large actuation,
C overlap could be the dominating factor and no polarity change is
found due to upward or downward actuation as C overlap increases in
both actuation directions.
Reprinted with permission from ref. 72. Copyright (2012) Elsevier.

capacitance of the device due to contact pads is the sum of the capacitance of
the gap between adjacent electrodes and that of overlapping area as illus-
trated in Figure 7.12(a).

C contact pad ¼ C gap þ C overlap (7.1)

Since the magnitude of capacitance is proportional to the area and inversely
proportional to the gap distance, a small contact electrode area and large gap
distance are preferable to reduce the impact of artifacts due to the contact