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Ultrasonic wave
Silicon zigzag electrode
coated with Pt
ZnO nanowires
Bottom conductive electrode
Figure 16.10
A ZnO nanowire array-based direct current generator [200].
and piezoelectric semiconducting coupling process converts mechanical
energy into electricity [200].
Piezoelectric properties-based nanogenerator can be use to convert
mechanical, vibrational, and/or hydraulic energy into electrical energy.
Lateral nanowire i lm-based l exible device can open up the large-scale
production and encourage practical applications of nanowire-based piezo-
electric nanogenerators for self-powered nanosystems [201]. Recently,
Kim and his collaborators have shown that simple muscle stretching can
produce electrical current using l exible thin-i lm piezoelectric nanogen-
erator fabricated by solution process [199]. h ough piezoelectric-based
nanogenerators have shown a lot of promise, low output voltage, design of
charge storage device, loss of free packaging and durability are a few of the
existing challenges that currently need to be addressed [14].
16.6.4 h
ermoelectric Energy Convertor
A h ermoelectric device can convert heat into electricity based on the
Seebeck ef ect. h e ability of a material to generate electrical power is
quantii ed by power factor (σS
2
), where S is the Seebeck coei cient, and σ is
the electrical conductivity [202, 203]. However, the ei ciency of a material
for thermoelectric power generation is demonstrated by a dimensionless
quantity, know as
i gure of merit (ZT);
ZT = σS
2
T/λ, where
T is temperature
and λ is thermal conductivity. h us ei cient material needs high value of
Seebeck coei cient and electrical conductivity, while least value of thermal
conductivity [202, 203, 17]. In order to design a new material for ther-
moelectric application, we should have a short phonon mean free path
compared with grain boundaries, which can enhance phonon-phonon
scattering. Small-sized grains for enhancing phonon scattering should
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