Piezoelectric Energy Harvesting Nanofibers - Hierarchical Nanostructures for Energy Devices - page 156

under higher strain rate while the total accumulated charges remained
about the same under the same magnitude of applied strain as shown in
Figure 7.6(d).

d n 3 r 4 n g | 2

7.4.3.2 Multiple PVDF Fiber Nanogenerators Connected in
Serial or Parallel
In order to increase the total electrical outputs, either serial or parallel
connections of these nanofibers could result in multiplied voltage or current
outputs, respectively. Experimentally, a single PVDF fiber was electrospun
using the NFES process with a designed pattern on top of a comb-shaped
metal electrode fabricated on a flexible polymer substrate as shown in
Figure 7.7(a). 23 The organized pattern was well deposited by the near-field
electrospinning process using a computer-controlled x-y stage on the col-
lector in Figure 7.7(b). Figure 7.7(c) briefly explains the fabrication process
on top of a polymer substrate. It started with a standard photolithography
process to define the comb-shaped electrode. A room-temperature silicon
dioxide coating was conducted and followed by the deposition of the gold
electrode layer (a thin chromium layer was used as the adhesion layer). The
near-field electrospinning process was conducted to deposit PVDF

.

Figure 7.7 (a) A schematic diagram showing an arrayed PVDF fiber structure and a

comb-shaped electrode on top of a flexible substrate to increase the
electrical current outputs by parallel connection. A continuous near-field
electrospinning process is used to control the depositions of these fibers.
(b) Fabrication results showing the energy harvester unit. A total of 500
energy harvesting sections formed by 50 fibers and 10 electrodes are
found to produce 30 nA of current. (c) Fabrication process.
Reprinted with permission from ref. 72. Copyright (2012) Elsevier.