Biomedical Engineering Reference
In-Depth Information
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
10
-2
10
-1
10
0
10
1
10
2
Frequency, kHz
FIGURE 7.16
IPMNC frequency response magnitude.
without any conditioning electronics. However, the IPMNC response begins to roll off
above 40 Hz. This high-frequency limit, which depends on the geometry of the patch,
must be taken into consideration when designing IPMNC accelerometers for specific
applications.
7.3.5
D
ISCUSSION
AND
C
ONCLUSIONS
Based on the frequency response spectrum of an IPMNC patch under cantilever
excitation, it seems likely that this material would be useful in low-frequency accel-
erometer applications. Unlike piezoelectric elements, the IPMNC specimen tested
produced a useful output in the subhertz frequency range without any conditioning
electronics. Care must be taken when designing circuits utilizing the material as an
active element due to their extreme sensitivity to moisture. In response to this
concern, Shahinpoor has developed a polymer-coated IPMNC patch that severely
retards moisture evaporation, allowing for consistently performing devices. However,
the moisture-retaining performance of such specimens must be quantified in detail
before device shelf-life estimations may be made.
The nature of the material requires that accelerometers utilizing IPMNC active
elements must include a mechanism to induce bending in the material under accel-
eration. This mechanism may take the form of a cantilever in the manner of the
experiments described here, a drumhead type membrane with a mass in the center
such as that discussed by Sadeghipour et al. (1992) or even a low-profile flat spring.
Overall, IPMNC active elements enable near-DC acceleration measurement devices
with modest power, volume, mass, and complexity requirements, provided their unique
properties are accounted for in the design. The advantages of IPMNC over conventional
piezoelectric approaches open up the possibility of thin-film or extremely lightweight
accelerometers or, if integrated, devices with rough position-sensing capability.
