Biomedical Engineering Reference
In-Depth Information
The IPMNC mounting apparatus consisted of a Plexiglas cantilevered clamping
device with conductive contact points and wire leads. Again, the leads were con-
nected by BNC cable to the DSA input, without any conditioning circuitry. The
apparatus was positioned under the shaker block with an initial static displacement
such that the tip of the cantilevered IPMNC patch was deflected by the actuation of
the shaker over its entire range of motion. The block was covered with Kapton tape
at the contact point to avoid bleed-off of the current into the optical table during the
experiment. The response of the IPMNC in cantilevered mode to a sine sweep of
the shaker was measured over a frequency range of 0.015 to 50 Hz. The frequency
response spectrum was calculated in terms of voltage output versus end deflection.
7.3.4
E
XPERIMENT
R
ESULTS
Any conditioning circuitry design for an accelerometer will require an accurate
understanding of the complex impedance of the active element over the frequency
range of application. Hence, this spectrum was measured for the IPMNC. Figures
7.11 and 7.12 represent the complex impedance of the sample. This IPMNC patch
had been left to dry in the open atmosphere for approximately one month before
these data were taken. Note that the element is fairly capacitive at low frequencies,
but is almost entirely resistive above 100 Hz. Despite the simple appearance of the
curve, this impedance response cannot be modeled simply as a three-element resistor
and capacitor circuit, but rather requires a series solution.
Figures 7.13 and 7.14 depict the impedance curves for similarly sized IPMNC
samples immediately after having been removed from their water-filled storage bags.
Note that the magnitudes between wet and dry samples differ by almost three orders
of magnitude. Moreover, Shahinpoor and Kim (2001g) measured an impedance mag-
nitude spectrum (not shown) that lies between these two extremes. This surprising
variability underscores the importance of accurately knowing or controlling the moisture
state of the active element before IPMNC materials may be used effectively in practice.
10000
1000
100
0.01
0.1
1
10
Frequency, Hz
100
1000
10000
FIGURE 7.11
Dry IPMNC impedance magnitude.
