Perpetuum also makes a PMG27 for
helicopters. Based on analyses of the complex
vibration patterns of vibrations during
typical helicopter missions, it’s tuned
to a 17.2-Hz resonant frequency. At the
forum, a group from the University of
Bristol presented a dedicated self-powered
helicopter system.
Some of the most interesting talks at the
NanoPower conference dealt with thermal
energy harvesting. As with vibrational harvesting,
I was struck by another reminder
from those basic mechanical engineering
classes—in this case a bit of simple thermodynamics.
A Peltier or other thermoelectric device is
a heat engine. The heat difference across the
junction depends on the head flux through
it, which implies the necessity of getting rid
of heat on the hot side. Moreover, maximum
efficiency for any ?T is never going to be
better than the efficiency of a Carnot cycle.
Within those parameters, there still appears
to be a lot of promise for patient-powered
biomedical devices.
GETTING COMPLICATED
So far, all of this may seem a little too
basic. But much greater sophistication is
certainly out there as well. According to
Ferro Solutions’ chief scientist, MIT’s Bob
O’Handley (who is one of the go-to guys
for magnetostriction), when you sandwich
piezos between magnetostrictive layers and
pre-stress them with a field, interesting
things start to happen.
Other examples of blue-sky research
were in evidence at the Darnell conference.
IMEC Nederland reviewed research on
body-powered and PV-powered patientmonitoring
medical applications. A team
from the National University of Singapore
presented a paper on powerline harvesting,
while another team from the University of
Colorado at Boulder discussed rectennas
and far-field harvesting.
Reporting from New Mexico, TPL
evaluated a number of configurations of
piezoelectric cantilevers for use with the
EnerPak. Figure 5 illustrates the I-V
performance TPL observed from a conventional
bimorph (bends in two directions)
with a metal shim and two multilayer
unimorphs with different layer thicknesses.
While the multilayer devices were susceptible
to fracture under high loads (low
frequency, high acceleration), their performance
was noticeably superior to that of
the bimorphs at low acceleration values.
On the other hand, at high amplitudes,
bimorphs delivered voltages that significantly
exceed the input voltage level of
the control electronics, although at low
current values.