Biomedical Engineering Reference
In-Depth Information
using a honeycomb structure. The motion of the left ventricular wall was
measured for testing a prototype resonating at 6 Hz. This prototype was
made of stacked strips (50 layers, 20 cells per layer) of corrugated polyes-
ter
m) and
a mass (780 g) on top. An accelerometer placed on a dog ' sheartwasused
to drive a test setup with the same motion. The power output from
the generator driven with the replicated heart motion was employed to
pace the dog ' s heart at 180 bpm for over 2 h. An average of 36
film with evaporated aluminum (50 mm 3 30 mm 3 30
μ
μ
Wpower
was obtained while for the stimulation pulse 18
μ
W was required.
Mitcheson et al. (2004a) reported an electrostatic nonresonant pro-
totype employing a variable-gap parallel-plate capacitor. For a pre-
charge of 30 V producing 0.3
J per cycle, 250 V were generated. This
arrangement followed the coulomb-force parametric-generator
(CFPG) architecture (using the contact force to damp the movement)
described in Mitcheson et al. (2004b) and was reported as suitable for
large amplitudes and low frequencies. Energy is produced only when
the inertial force is larger than the damping force. A capacitor plate
(200 mm 2 ) with a proof mass made of stacked silicon plates
(10 mm 3 11 mm 3 0.4 mm) was fabricated for a maximum displace-
ment of 450
μ
m. The final discharge of 250 V was produced by a
capacitance change from 15 to 127 pF (11 pF parasitic capacitance).
Other work from this group presented a modified version of this
parallel-plate capacitor. Energy of 120 nJ and voltages up to 220 V
were reported per cycle (using 30 V of charging voltage), although up
to 2.6
μ
W
of power at 30 Hz). It is expected that if using gold as the proof mass
material, the power output could be increased up to 10 times.
μ
J per cycle could be obtained for an optimized device (80
μ
Arakawa et al. (2004) used an electret-based approach to avoid the
need of precharging. An overlapped area capacitor using amorphous
perfluoropolymer (CYTOP), as the electret, was presented. This elec-
tret material choice presented a charge density up to 0.68 mC/m 2 which
produced 6
W with a sinusoidal input oscillation of 1 mm at 10 Hz.
Later work from this group was presented by Tsutsumino et al. (2006).
They were able to reach a charge density as high as 1.37 mC/m 2 using
corona discharging on a 15
μ
μ
m film with 1,000 V of average surface
voltage. At 20 Hz and 2 mm p-p vibration amplitude (150 V sinusoidal
peak-to-peak waveform), 38
W of power output was achieved. When
compared against Teflon AF, CYTOP presents a surface charge den-
sity,
μ
σ
, about 3 3 larger. A 9 3 increase in power generation could be
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